The Non-Destructive Testing Spotwelds in Alclad Aluminum Alloy Sheets Citation McMaster, Robert Charles (1944) The Non-Destructive Testing Spotwelds in Alclad Aluminum Alloy Sheets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/yqs7-mv19. https://resolver.caltech.edu/CaltechTHESIS:08252025-221021251 Abstract No abstract. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: (Electrical Engineering) Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Electrical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Lindvall, Frederick C. (advisor) Sorensen, Royal Wasson (advisor) Clark, Donald S. (advisor) Thesis Committee: Unknown, Unknown Defense Date: 1 January 1944 Record Number: CaltechTHESIS:08252025-221021251 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:08252025-221021251 DOI: 10.7907/yqs7-mv19 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 17646 Collection: CaltechTHESIS Deposited By: Benjamin Perez Deposited On: 28 Aug 2025 09:35 Last Modified: 28 Aug 2025 09:35 Thesis Files PDF - Final Version See Usage Policy. 109MB Repository Staff Only: item control page

THE NON• ·DESTRUCTIVE TESTING OF SPO'l'WELDS I N ALCh!:..D ALUMINCJM ALLOY SHEB;'l'S Thesis By Robert G,. MeMaster In Partial Ful fillment of t he Requirements for tb.e Degree of Docto1• of Philosophy California Institute of Technology Pa sadena , Califor nia 1944 SUMrt.ARY This thesis presents the results of an investigation of non .. destrueti ve t es t methods f'o r sheets. spotwelds in alumi.nui:n a lloy The purposes of' the research we,re: (a) to intras tiga.te proposed non..-destruotive test method s for spotwelds i n aluminum alloys , (b) to determine the feasibility of such tests, (c) to develop suitable methods .for practical appli• cation and (d) to te s t each useful method. for reliabil i ty and accuracy on a large number of indust.r ially made spotwelds-. Investigation was made of approxima tely t hirty proposed non-destructive methods of testing spotwelds, - including electric current conduc t ion tests, eddy current tests, thermal tests, s onic and vibra tion tests., ma t erial p1•operty tests,, penetrator tests; x...r ay tests, and mechanical proof tests-. Preliminary tests a,nd analysis of the requiremen ts of a s.u:t table non-des- tructive test indi cated th~t penetrator,; electrical:,. and x.. ray methods showe d t he mo st pr om1se. Extensive developments of e a eh of these me thod s were carried out, anr:: each test method wa s tried on groups of several hundreds of industrially ·ma de s potweld$., The r eliability and a ccuracy with which weld size, streng t h ;. and quality were predi cted by e a ch test were determir.ro, , It wa s found t ha t, in terms of reliability and accu1~acy, the, most promising non•destructive test met.hod is t .h e radiographic inspection of spotwelds ,~ From spotweld :ra diog:raphs made vu-1th the prope,r technique, it is r.,ossi,ble to interpr•et weld struetmre, size, geometry, and streng th, as we ll a s to detect def.a c t s such as cva oki ng, porosity, inclusions,. expulsion of metal a t the faying pl ane, exten sive segrega tion of eutectic, i,nadequate or exeessive nugget pe:Qetration, excessively large hea.t• a.ffeeted zo ne s, excess.ive tip s kid, and rnis•shapen nuggets. The most promi sing non... radiographie tests wer e found to be t he ring pe netra tor (mechanical) 1H;ist and the ring electrode (electrical ) test . Tb.e ring penetrnto:r test is sen sitive to s potweld nugget size and shape. '.I.he ring electx•ode test 1 s sensitive to t he total bonded area at the f'ay1ng pl ane of the apotweld. Both tests ar e subjeet to wi de err ot' if t he test p;robes are not centered a ccura tely ove;r t h e we ld • • On production spotwelds, t he penetra tor, electri cal.,, ani radiogr aph ic rlon -.destructive tests oae,h me a sure spotweld static shear strength with reliability iantll a ccura cy well above the requirements of pr a ctical industrial s pot weld inspection . :t. Page Introduction 1 II. The Problem of Non ... Dest.r uctive Testing of Spotwalda In Alolad Alumi num Alloy Sheets. 3 .ih Requir eme nt s of Test. 3 B. Weld Properties and Nomenclature. 0 c . Fa ctors Contributing to \~eld She ar Strength and Q.u ality ._ D. Weld Types To Be Disor1minated . 11 15 III . Proposed Methods For t h.e Non... Destructi ve Testing of Spotw~lds in Alolad Aluminum Alloy Sheets. 26 A. Visual Inspection of Spotwelds. 27 B. Electric ~rent Conduction Tests. 2.8 c. Eddy Curren t 42 n. Thermal (Indu eti,on ) Tests. 1 .Pest Methods., 52 K. Sonic a.n d Vibration Tes t s,+ 61 l;jl • Sheet .Surface and M~te:i;-;la.:t. Property 'l'e.ats • 71 G. Ilnpressor of Penet:rator rrests, '73 H • .x- Ray T~ ats. 80 I •. Mechanica l Proof Testa, 89 IV. Selection of .Suitable Test Meth ods., 95 i\.. Correlation of Weld Prop erties With St a tio Sheal'.' Strength .. 95 B. E,ffeot of Sheet Preparation and Conditions of Welding Upon Weld Properties. c. Destructive Tests of Spotwelds. 103 108 D,. Measurements Required of Non .. Destructive Tests . 111 E •. Suitable Components of Non-Destructive Spot ... weld Testers. v. Development of Penetrator and Ring Electrode Tests it 112 114 A• Design and Construction o:f Spotweld Te st1ng Maehine #l. • 114 B. Prine-iple of' Operation of Machine. lltl. C, Procedure I n Opel'ation of Machine. 118 D. Results o:f' Tests . 120 E. Conelusions Based on Results of 'l'ests . 123 F. Proposals for P:r/i;\ctical Forms of 8potweld Tester. 125 VI. Development of Radiographic Inspection Methods, 127 A, Technique of' Sp ❖tweld Radiography. 128 B, interpretation -o f Spotweld Radiograplls. 133 c. I n spection Procedure . 141 VII, Results of Tests On Industrial Spotwelds, 149 A, '11ests On 166 Federal Sp otwelds Made by the Vega Ai:rcr~ft Corporat1on of Burbank, California. 150 B. Tests On 100 'l1aylor"'W1n.fie ld Spotwelds Made By the No:rthrop Aircraft Corpo~s.tion cf Hawth or•ne, Calif).51 o. 11eat s of 138 1I1aylor ... 1din.field Spotwelds Made By the Consolidated~Vultee Aircraft Corporation of San Diego. 152 n. 'lies ts of 326 •Taylor ...: irµ:'.ield Spotwelds Made At The Univer·si ty of Sc;ru the:rn. Galifor•nia. E:'• Summar•y o:r Re sults of Tests On I ndustrial v1 elds. 153 154 VIII.Coneluai ons . 155 I X. 157 Acknowledgements . 1 'l'his thesis presents the results of' an investigation of non•destructi.v.e teat methods tor spotwelds 1n aluminum alloy sheets, T'.ae pu:ri:;oe_e$. Qf the re ~ear eh wer~ i To investiga t e propoeed non•destruotive test methods for spotwelds in aluminum a,lloy sheets, to determine the • I feasibility of :;iuch te..sts., to recommend and deve.lop those methods found suitable £Qr reduction to practieal appli• cation and to test each useful method for reliability and a.c.cu:racy orl thQusands of industl"lally made welds. The ll~e4 f'or practical non... des.truotive tests .for spot.. welds in aluminum alloy sheet is recogni zed in the airl"I> craft indu,s try.,.. Prese nt industrial proc~ss cont:t>ol and visual inspection procedures a.re '.ina dequate to guar-iantee that all spotweld.s made in aluminum a.11.Qy sheets .for a ir•• craft will meet minimum strength , requirements.. Consequently i spotwelding of aluminum alloys in aircraft appl.ications ha s bean limited.., for the most part, to secondary or un.,.. stressed structures. The f a.bri ca.t;ton a..d vantage s of spot ... w~lding are yet to be realized for a la~ge part of aix•• c1"ai't const.r uction involving primary or stres.sed strueture.s which are critical in the operation of' the aircraft, Until 2 adequate process control ; moni toring of t he \Velding pre• cess, or rel:if.l ble non.destructive tests a.re previded to gua.rantEle weld quality,. the spotwelding of primary ai:t>• craft structures tends to be delayed_. When destgne:rs and inspeeto:r a are shown undeni~ble proo.t that weld qua ... lity is adequate, the spotweldling of' primar y aircraft structure .s may be exp€)crtedit A rel.i able non•destruetive te$t for spotwelds would provide this proof' of adequate weld quality. The aRplic a tion.~ visualized fo1"' practical non-.destruct• ive tests for spotwelds include routine production te sts on some or all welds of certain vita.l aircraft structures, and occasional cheek tests on we ld quality at any point in the aircraft fabrication proee ss.. Fo;r, t he routine production tests, the equipment must be capable of rapid testing; for the incidental check tel$tSt portable equip• ment is desired.,- For all applica tion$, absolute :relia.• b1l1ty is required. II .. THE PROBLEr, OP NON- DESTRUCTIVE TESTI NG OF , SP0'111~ritLPS l N ALC4~ ALUMJ:NUM t\I.,,LQX _SHlilE TS To ind1cat-e the nature and ecope of the problem in... trolved 1.n developing neu•destruotive tests tor spotwelds, thel!e a.1.~e now listed: (a) the requirements 0£ an acaeptable test, (b) spotwelGl ,- propertie$ and nom<:n1clature, ( c) faator•s contributing to weld shear strength and quality, (d) weld types to be diserimirie.ted; and ( e) quanti ta ti ve raeasn1:rements needed to measure wel d quality.A. Re9;1,1~:rem~pt~. _ o,1f -~P. Acoe;p~a.ble N9p• D~s,tr-µe,t1 v~ Spotwe.ld. 1 11es:t The non.destructive spotw:e ld test mu.st be. reliable and s houl d be praeti.o.a l, fast, e fficient;., and economieal bo th in labor and equipment . It shoul-d be suitable for production t~sting and for occasional j.nspeeti,on cheeks on questione.bl~ welds at any point in the fabrication process . It should detect bad vtelds regardless of their To be more apec,i fie, the test must be; 1~ Reliable•- It should dis,eriminate mormal welds, (static shear strengths 2,~tf to ~~5% above 4 the minimum acceptable strength) from welds \Vi th less than the minimum' acceptable strength• with oom~ plate reliability,. To obtain this reliability, the method should predict spotweld static shear strengt.h within plus or minus 20% of actual weld strength, and. more aecurate.ly 1!' po$sibleif throughout; the range of strengths f'rom one-half tb.e minimum a cceptable strengths to the highest strength ob t a:tned under norma.l pr-oduetion conditions in aoeeptable welds • * 2. Pra.Qtic~l ... ,,,., It must be su.cl:1 that it can be used reliably by aemi•,$k111ed personnel under normal production conditions . •:t- A ~eeasonable m\lX,iUn,WJl accuracy to be expected from a n.o.n•destruetive · spotweld test :ts t hat te~t indications . ' should measua."'e we::!.1 oiiit,ee, ..1gth ~s Jlo.s ely ~s nugget diameter • (whieh could be Qbserved by destructively sectioning the weld) correlates v1:tth weld strength. P.n:y non-.destructive test which approaehea this standat>d sho'Uld be oon.- sidered suece1s.sful, for the relation between nugg.e t diamete:r a11-d weld strength is ge.nera.lly recognized as the most signif • ieant relation betwe.e n a single weld parameter and the static she ar strength of the weld+ 5 3, llaat ...... Because of the large number of ~ weld$ to be- tested, a production testing device should pre.ferably o~era te in s. .f'e\:V ~e conds and be eapable of b~ing quickly transfewr,e f and po$1tioned For this reason, its loca tion with for testing, r espeet to the weld nugget should pref"er-ably 11:ot be 4. Im1ne~i~te ~P. Refpons~ .,.,;lt In produ,ction tea,t• . . . . • I . 1ng 1 it would be desirable to have an immediate in• dication of ueld st:reng-th1. to a.void delay and un• neoesary i dentification of SJle eifie wel ds under test, 5.. I~~e.12enqe~t ,9~ W~ld &,(!,)Ga,ti,on ;;..,. ~rest results should not be invalidated by t he proximity of other welds, er of' cotiner.s., slot~ ot· edgeS, in the 5Jheet, or of large masses. of metal. 6,. In<ie;ea nde p.t or 4n!P+®.n t po~?¾t'-?ns t;i,nd fi! 31.u"faoe Oondi tions o.f W,elded ~ ee.ts .-... Si nce ' ' weld ttH~ting may be done on p~oduct :ton lines w.i t hin ouildings or out-of•doors, test results mu st not he af.fe.cted by tempera ture, noise, vibration, dirt_, hum"' 1d1 ty or other te ·$ 't conditions dependent upon loot,; cation. Sheet surfaces rnuat not require exceS-sive 6 prepa.1'"ation., nor should sur.face conditions resulting. from normal productien processes invalidate the test. 7. Non-qes.t~ucJ;j.ye •• The. w.e ld must .not be damaged by the test, nor sh<>uld the Al.clad layer be broken nor the Sheet or pa.rt be disto:rted by the test. In addition, it would be highly desirable (but not necessary) tbat the test equ:t.p:ment be wortable and that it require a.ecess to only one side of the welded sheets . lf used on fabricated pieees., it would be advanta.ge¢>us 1f the portion of the tester to be brought to the weld wa:re small., weighing only a few pounds at most; and were easy to move and set accurately in position. (For production testing of small parts before t'ul"ther assembly, the work might be brought to a fixed testing machine). Although 95% of the spotwelds in aircraft are a.cce.s$.; lble trom both sides of the vmrk at some point in the fabrication process,; a testing unit operating from only o:n.e $ide of the sheet would be very advantageous, provided reliability of measure• ment were not sacrificed to obtain this advantage . Figure l shows photomaerographs of both cross-section CROSS SECTION AND FAYING PLANE OF A TYPICAL SPOTWELD IN 24 ST ALUMINUM ALLOY, SHOWING SIGNIFICANT REGIONS OF WELD; (A) PARENT MATERIAL, (e) ALCLAO LAYER, (c) CAST ALLOY NUGGET, INCLUDING (c 1 ) DENDRITIC ZONE ANO (c 11 ) EQUIAXEO ZONE, (o) CORONA, (E) ALCLAD INCLUSION, (F) PENETRATION, (G) HEAT AFFECTED ZONE ANO (H) FAYING PLANE. 2ox. FIG. 1 A). PARENT MATERIAL, 2ijST ALUMINUM ,LLOY. 500X. (c 1 ). DENORITIC ZONE OF NUGGET. 500X. :II). EQUIAXEO ZONE OF NUGGET. !5QQX. (E). ALCLAD INCLUSION INTO NUGGET. 500X. • HEAT AFFECTED ZONE SHOWING INIENT MELTING AT THE GRAIN BOUNDARIES. x. (G 1 ). HEAT AFFECTED ZONE SHOWING EUTECTIC "STRINGER" OR "INTRUSION INTO THE GRAIN BOUNDARIES". 50QX. 7 and fayi ng surf'ace a.nd photoraiorographs of' signi.fieant regions, of a typical spotwel d in Alclad 24 ST aluminum alloy sheet. Tb,e follow'ing nomenclature, whi4 will be used th...roughout this the s ,i a,. refers to this fi gure . l. 'l"he ;e~r~nt sh?et ( A) is the 243T e. l umin:wn alloy sheet '., in the region outside the weld proper which hs.s not been affected i n any manner by the welding process, This alloy is composed of 4.5% coppert 0.6~{ mangane se, and 1.5% magnesium, with aluminum and normal i mpwities making up the bale.nee . (Ref. #1) Ingots ar·e rolled into sheets which a?"e subsequently tempered by heating to 920°Ii in a.n 1 air furnace or in a molten nitrate bath and then quenched with minimum time delay into cold water. Aging at romn temperature follows, 11he 24ST (temp- ered) alloy develops a.beut 41,000 ps:t. sheal;'ing strength, while 24SO (annealed) alloy develops only 18 1 000 psi. 'rhe incipient melting tempera ture of this 24S alloy is only 956°F, (Ref, # 2) 2~ The A,lolad lay;~r (B) is a thin layer {approxi ... mate ly 5% of t h e parent sheet thickness) of' comrner- cially p't!tre aluminu..-n bonded to each surface of the parent sheet. Its prime purpQse is to protect the parent sheet against col"rosion, I t is important that 8 the we.l ding opeJ:>ation should not impair the protect""' ion provided b y this eoa.tlng. This conunereia.lly pure aluminum develops about 9500 psi. in shear and . 0 . . bas a -melting po.int of about 1200 F. (Ref. #1 and 1/3) I 3. The \Yeld . ~':1SS~t ( 0) is .an ellipsod;d.al volume of' me tal which has be$n, melted by the weld:J.ng current; possibly being stirred so as to effect a redist:r i• bution of it-s chemtcal constituents 1 and ·which, h~s then sol;i.di.fied into t .wo distinQt zones as .a ciast structure. (Ref. # 4) The dendri tic zone {C,) shews evidence of ve~y rapid s.olidific.a t1onJI while the equiaxed zone ( C") shows evidence of 'r elatively slower c.o oling. The nugget is softe:r than the parent sheet and develops only about 18,000 to 22,000 p$1 . shear strength~ ( Ref. //3 ) 4. l'he corona. res1.on. (D) .sux-:r-ou.nds the weld nugget at the .faying plane, and is that area of the Alclad coating which has been aubjeot to p:ress1U'e and heat during the welding process, The natur•e of the corona ma.y depend -q,pon the surfa ce preparat;lon of' the sheet before weld;tngt ~nd in the co:eona region thePe may be no bonding, partia.l bonding, or e.omplete areal bonding depending -upon the sheet eondi t i Qn and t he condi t1ons of we-lding. It is not t'lf~ to ,u.urume the bo~ed are,~ ot t\~·ona to bt pJ:-10• p:o t>t1onal to i,.ugget l1.t'$~., ft"Jr th$ purpQte$. of 't!.Qn• de-ttr11etttve t,e$t dev~lopmi.uiti ~ . C;OYJJ.p lete oQrl).n&a bonting ,m$_y. de:vialop 'i,tl nmch nt 9500 Ql'J 10600 p e1-.. ah~ar!ng a ~ensth• (11et •. #5) i• The' &\~f).ad ~~l?a:1:!!l'.6t!t (l,O 1lcltQ the 'f1eld tl~~g$tl 1,n~=-.-111~: • t1.t ' .. • ,.. .J, _, 0 :4 Jt' .'. J the fa:r· :n g ].:)lane ooxM;!hrt, 0.1.· t:ilw.d .nuul or t • P.J.• •elad l$..; f$t' wh&oll lUHJ tl:Q;t b~e-tl allQ~d into th~ nug ~t. • Th~ ele!:t$nt ot Aloliad 1nclu.si<1n. i~ q\Qitfl vat it;tblei 1 and t ~nd~ tQ bQ gr<fat11H?· witk1 th!ek J\l~l,Qd ls10Ft!1, ~nd !.n l.ow $tt~rgy :el<le w1~b thtn nlilggetm.,. Exoe$sive .t~~lad :i.1 ie,lUS.ion wealt·<Ul$ a. Wl))ld in th.~?' lo&ding, s1no-e at d~c,~f)asea tbe etf e,~ti ve mii~t '-1r-~• at tlt~ t~ring plan$<il I t ifl po.aeible t~ <:l\'ifVflop a nusiet in both sntets,, Jet hivve lOO;i AlOltld ltlQlUsittn, u,~f, I $) In t,,b.i;S ¢~$ft tr1<a V'l~ld ~~gget e.<:uat1~tbtttllll$ nothi~g whatever to the wel.d et:ren~.t h.- s. iJ.'.'h~ i~f;~~:~Al,n, {I-") c,t the. w:eld nug£,~et i.nt,o th~ pu,,ent sho~t meiurtu-·~$ the pQrt$t'.>cr~ oi' the ~beet tbic'W..nfH:1s •Q~t1u,piad by th~ Wflld n~~t. P~nttr~t1().ne flt tao~ to oori o.t the $h~e·t tbiUkttlfJ,$ ,$ U"$ U$Uf.tllf e~l'l•· a1de~~d aC~J:ltabl~ ., (R$',t* #5) E~ee~s:itte panetr.a tton (80% t .Q 100,· ) u~uallJ i:miieatetl tt bti tt.lii'-, O)l'aokad1 or po~~a wel.d. 1 ::ind lt 1,s 1.1i1des:t1•able 'botl1 be~,a.ust C!'t 10 laek o.f ductility in the weld,. s.nd because the ct-ei.oks .ma.y spread to the suI'face . breaking 'the Alelad layer and permitting corrosion. Inadequate penetration. (below 2010 is. frequently aeeo.mpalllied by excessive Ale.lad 1nelus·ion and ine-o nsistency in mtrength. In the normal ra:nge ( 20;1& to 80%), penetra. tion seem a to have little or no e:f.t'ect on W$1d strength, 'l .. FJ.'IJ:le heat affected zone ( G) is that ,region of the parent metal surr•ounding the weld li'1lgget whose properties l:ual,fe been changed as a result 0f e~posur(!) to elevated temperatures,. The shea!' and tens.ile strengths of the 24S'r alloy are reduced in this r .e • gi.on~. Struetur-al changes,- such as :incipient melting of the material and intrusion of e·u teotie along grain boundaries, occu;r in this zoneec (Ref . //-6 ) Ver,y la:t>ge wel.d s tend to "pull a button'1 \When t .h ey fail undeJ? shear loadi ng, the failure possibly oocur:r..:t.n,g in part through t his heat affected zone•· (Ref • .f/7) Weaker welds., which tail by shearing the nugget through the faying plane are n0t g71eatly aff'ected by thi.s zone insofar as t he shear load required :t'o:r failure is concerned .• 8+ The :f~yir+g plape(H) is the plane of join""' . . . . ( . ing betwe$n the welded sheets. Bonding between the 11 two sheets in this plane gives the weld its strength .•. c. Fact01"$ Contr.}hµt1Ji5 to Welti, J>he~p Stl?~P,sth and g;ua:i.itz Sportwelds a.re seldom desi gned to be loaded in ten• sion .. The spotweld is much stronger under shear loading and is normally des.igned to carry (supposedly) static shear 'J.1he most oommonly use.d. measurement of we ld strength loads• is the static shear strength of' a -$ ingle s pot lap joint. {Ret. #5) It is this static shear stre.ngth which must be predicte.d reliably by non ... des·truct:tv•e tests, to obtain their general acceptance, If static shear str-e ngth cannot be predioted reliably~ the n<.m•destructive tefilt me thod must be consider ed a failuret regardless of how well it measur(Hl other v.e].d properties. Unfortunately~ st~tip she.i:ir st+:"?nStll, alone is not a good measure of spotweld gua.lity, Weak we.lds without any nug513t bonding whatever at the faying su:rta.ce may pass minimum accept.able static shear atrength requirements by Vil."tue of Alcla.d bonding; yet these welds might fail in $e.rv1ce. Very large welds with ove:csized,: cracked, brittle nuge;;ets and insuffieient ductil i t .y may snow very high static s hear strengths,. yet cont:r-ibute to ea):)ly i'at;tgue failure. and :rapid cor rosion. An ideal non .. de$tructive test ought to distinguish between these defeats, but to do so without excessive eomplieation i n test equipment or inter• 12 pretation usually X'E)sulta in less reliable prediction 0f ste.tie ahear strength. Likewise, welds with nugget pe.ne ... trations of 50 to 80}& of the ·thickness of the parent sheet are much more reliably dete cted by ee1:tain non• destruetive tests t han welds with 20 to 50% penet~a.t.ion. However, t o increase OIi further. restri ·c t the etandards of a. ccepta'.ble apotwelding, merely to m~ke possible. the use of a non-destructive te-st method, is out of the question _in pr a ctical industrial spotwelding applications. The single spotweld parame::te:r which by itself correlates most reliably with static shear strength is the \',f~lc\ nuse;e~ diamet~r at the faying plane • . More p.r•eeisely, it is the net area of east alloy (total nugget area lees the area of t he Alelad inclusion) at the t'aying plane which deter~ mines weld strength,. With excessive Alelad inclusions,, measurem$nt o.f the ove:ra.ll. nugget die.meter can be mis-. leading to the extent of 100% erro1· in predicti.n g weld strengths,. With normal Alelad inclusions, the nugget dis,mete:r measures weld $ta.tic shear strength with an e:rrQ:r of p.l us or minus 10% to plus or minus 20% of actual weld strength (See Fig., 41) Por welds without excess:1.ve AJ.clad inclusions or corona bonding, whieh fa.ll by shearing the nugget through the .faying plane" the correlation is quite . For stronger welds ivhi ch fail by· ttpu11ing a,, , reliable ;c • ' ' 1 .3 buttontf, the oerrela.tion is· leas reliable, but in all such oases the W(;lld strength is less t han would be expected mtf'a.iluve by shearing tn.rough the nugget at the faying plane. The -s:eeo.nd pa.rrunet~r~ in addition to the net a1•ea of cast alloy at the f'aying p lane., which contributes sig~ -~ nificantly to spotweld she~:r st~ength, is the e~ftrqtive, ~J;~a of Al,ela:¢1 or corona bonding a.t the .faying pla,ne. In cases where the cladding is fully bonded. between the s,h eets , near the weld; t here occurs a stt-e ngth contribution per unit area of bonded cladding,. equal to e;pproximately '.b.alf the unit strength ot the ea.st s.l,loy. In weak weld$; the a~ea of' bonded cladding may ea.aily exeeed th67 east all0y m:-ea in the rat.i o ◊f 3 ov 4 to l-. In thes·e caaes tne bonc:Led olad.., --- dil1g oontribute.s a major port ion of th$ eta.tic shear stFength of the weld. T't1is a.dde<i s.trength would b~ 1,. evld.ent in -the static shear pull te$t, ir.~t _coul!SJ not be P~.lied • upon J?Q:r the. lif~ ot a welde.d str.-u cture_. as th~ Al.cl.a d bohd i ,e ot questionable natut>e. It is difficult' to rn:ea.su:t>e the net area of Ale.lad bond;tng, not ~nc.ludi.ng .tlle area of nugget bonding , in a 110:r1-.destr-uctive test. However, 1...f reliable i.nd.-0.pendent. measurements can be mad~ of t b.e total bo:nde;¼d 61.l"ea and or the net nugget area at the fayipg plane, their d:lfferenee 14 measure s the area of bonded cladding. Adding the strength contributions of both ·n ugget a.nd Aicl~td bonding mak~s pos,11> isible the predio.ti.on of spotweld strength with a n error of le$•S than plus or minus 5%' to plus or m'inus 15% of' actual weld strength, ( See Section IV D) Ot~e~. ,~om.e.i>ric pa,:rameters of t he ,Spotweld. have little intluenoe upon weld st:re:ng·ch, undeP normal co:ndi tio.ns . Penetration, in t he f.l e ceptable ~ange- o:r 20% to 80% of te.e sheet thickness, has no significant ip:flue.nce., although welds of low pene•t~ation seem to show inc11 ·e ased unit. strength in the nugget because of t h@ strength eont~ ibutions o:r pro• port1onate1y la.Pget> ar eas of Alclad bending. con clusions of Reference 8) (Compa:re with Nugget volume and s'.b..a.pe are significant only a s they affect t he cast alloy area at t he faying plane. C~a_c¥;i:t;l6, a ~d ;porc;>f,3~t:x; \"Ii t h in the wecld nugget have negligible ef:t'ect upon st~tio shear strength, ex cept insofat> a s they affect t h e bonded area at the faying plane, to the sheet; surfa ce greatly inerease eo;r,;roaion . Craeka Cracks also probably contribute to fatigue failur.es in 1;p otwelded struot- * The extent of this effect probably depends critically upon the geometry .o f the . cra ck., &:nall spherical cav!.t:tea and similar porous. a.ond.iif:ions mi ght have negligible ef'feot upon fatigue strength. 15 'l1he influence of the different typea of l,Uet,a;Lluz,e;1·e al. structure on the characterist1ea of spotw~lds is not known at pre s ent but it 1s probably of mu.c h less importa.nc$ than factor$ such as s:tze;. shape., soundness, and fFeedom .from eraeking t! (Ref"-// 6) Our mea surements have shown no rf1111a"" ble direct cot-r•elation be.twe~.n any metallurgieal property and ·weld strength, except insofar a.a nugget geometry has been measured by structural properties -• • rflle task of developing non'!tdest.ruetive tests .for sp.a ,t• welds is frequently given by production welding groups to research groups or outside organizations whose famili:e.rity tv-i th production vrelding condi tiona is lim1 tad . All t oo fre~uently, these r~sear eh workers have a falsely simpli• fied eoncept .o f the nature., geometry, and $.t ructure of spot- welds, 011 opme1~ts~ which to base their non"'" destructive test devel• It must therefore be :recognized that the size;, sha.p~, and bonding., particularly of weak weld$_, are ex... eeedingly variable . Static shear tests alone tell very little about weld g~ometry, . si ze, and quality ♦ Many anomolous conditions exist, which tend to invalidate p.ondestructive test methods, To aid in evaluating d~:rvelopment$ of non-..destructive 16 spotweld tests;;, a classi.r ieation chart is· now given show~ ing the .faying surfac.e and a section through the nugget for several typical s potwelds made u:ndeP indust:rial wtfld• 1ng conditions . Th.ese welds were made on energy sto.rage welders 0 f both the 1.na..gnetie and condenser typesJ which tend to produce simila r weld structures_. No a.ill,.. weld s a'.i:'e 1neluded; but similav results can be o'bta:tned with a.o . welders un-der certain conditions. For aimpl1eity 6 t he classi.fication chart begins with ve'!!'y low energy v1elds,. · and progresses to lar-ger and stronget> welds made with increasing energy-.. In this manner the signi.ficanee ot' the various weld x•e gions in oontributing to weld strength ea.n be easily determine.a., These welds were made on .industrial spotwe.lding machines with all pvepara.tion and welding eonditions normal, except e,n ergy setting orf in a. few oases., fo.r· ge pressure delay time. Thus, the net heat developed in the weld was used as the chief variable 1n producing these weld t -ype's ,. The ba d welds were purposefully made weak ·ror.• use in developing non-1odes .. t;ructive spotweld test$• ( See Table I) '.£3:;pe A Wel~s ,• _Ale_ l ad Bonqin.f1 Only W:Ltl:l ~~o Nug5e~ Fo1"1nati on. Weld A•l* ...•repre.sents t he lowest e nevgy setting sheets. All a.re shown a t lOX .magni.fioa.tion, TYPE A WELDS - - ALCLAD BONDING WITHOUT NUGGET FORMATION A - 1 STRENGTH BELOW 5() POUNDS A- 2 STRENGTH 100 POUNDS A- 3 STRENGTH POUNDS FIG. 2 215 of the welding machine producing obse:rvable bonding at the faying surface. A small region of the Alclad layers has be-en heated and subjected t;o pressure;. producing a weak bond .possibly due t ·o plastic deformatton and keying at the faying su1.. f a ce. weld fell apart upon handling. This The bonded points are good conductors of heat and eleotricity across the faying surface between the sheets; the surrQund• ing faying surface is a very PQ:tlr conductor as a result of the presenc~ of a thin layer of aluminum oxide,. which acts as an ins-ula.tor. No significant changes have oecu:rred in t he parent. metal, and no nugget formation he.s occurred. Weld A-2 ........ was made under the condition s :o f Weld A•l, but more ext~nsive bo11.ding has occurred at the faying plane. 111 .i. he .A le.l ad layer has bonded over a slightly larger area ♦. was 100 pounds -, '.the sta tic shear strength This bond,. because of inore as-ed area, shows less overall resistance t o t h e f' low of heat and electric current aoross t h ~ faying plane than the bond of' weld A• ·l ♦. Weld A•3 ..,•..,. made with increased energy she-ws a still larger area of Ale.lad bonding , and developed a static shear atrangth of 215 pounds . The resis;,. tance of this bond to the flo.w of electtie current 18 and heat is still less than that of Weld A~2, because of the increa s ed bonding area. All the vreJ.ds of · 'lype A~ f:riequently ca lled 11 stuck 0 welds; involve only Alclad o~ corona bond• ing without any nugget development whatever, and should be classi:t'ied as worthl ess . 11his type of bonding results only under a locally 1detll condition ,of sur.face preps.ration., such as wire brushing or car eful etehing. A fingerprint or the use of other methods of surface preparation may result in ab .. solu.etely no 'bonding under the same conditions of welding. Welds of this type have been frequently obsex-ved with much larger areas of Alclad bonding, which develop more than the Army rnin;i.mum acceptable static she ar strengths.. T'.ae we ld shear stre ngt h is diree:tly proportional to the net area of true bQnding ? and the unit shear strength is near 10, 000 psi .• r:y;;p~ ,,13 W~*ds •~, E;lementary, !-fugg~p, forra~t,iOIJ: Weld B•l. •- shows the eff e .c t o:f a diffe.rent method of surface cleaning upon the bond at the faying surface~- Suffio.ient. welding energy to pro- vide an elementary migge t in both sheets has been sup1lied., yet almost no bonding whatever has occurred TYPE B WELDS - - ELEMENTARY NUGGET FORMATION WITH OR WITHOUT ALCLAD BONDING B- 1 STRENGTH BELOW 50 POUNDS B- 2 STRENGTH POUNDS 360 B- 3 STRENGTH .580 POUNDS FIG. ~ B- 4 STRENGTH POUNDS 480 B - 5 STRENGTH POUNDS FIG. 3 340 19 •ija.ve on the peI•iphery -o f t h e heated area .- This nweldn :fell apart upon handling , 'l ~-l d B-2 ..... rep'.resen ts t1 slightly h i ghe:r> weld energy than t he welds of' Type A~ with very element• ary tendencies toward nugget for>me.tion i! Nearly 100% of' the bonded area consi s t$ of Alclad bonding with an almost negligible area of east alloy o:r nugget bonding" This weld f'a.1 led at a s h e Hl" load of ~60 pounds, t he increase in strength ove;r> weld - A•3 Fesulting chiefly .f:r-om the increased area of bonding . Weld B""3 ..... repl"esen ts a further increase in weld energy, producing a Ftcre:;rnent 0 or t1doughnut 0 s h aped nugget development . Some of' the Al elad layer has been melted and a lloyed wi t h the nugget ma. terial, permit ting t he cast alloy o.f the nugget it$elf ·t;:o f0-rm a dir•ect bond otrel" a sma.1 1 ring shaped area<t This weld dev~loped 580 pounds in static shear test, most of t he gain in strength over weld ~2 resulting not ft>om a change i n the area of bond• ing, but rather i'l"◊m a change. i n the .t tpe of bond• i.ng~--rrom Alel~d _p_on,dins to ce. s:t,_,allP:Y. bondiry~ in the nugget area. The ca st al.loy bond usually de• veleps about 20 .. 000 psi . unit shear strength, approx• i mately twice t lw t ch aracteristic of the Alela.d bond . Thms t his weld would not be discriminated from weld 20 B~2 by non-destructive tests involving only th$ mee.eurteme:nt of the total a:r~a of bonding at thfD faying surface. \llJefl.d B:.io.~ ·• • made with still greater energy, developed a. flat nugget of .la I'ger $1,ze, but s~ ems te lack Al~lad bonding e.ntirt"tly. Its $tr·angth of 480 pounds is consecpient.ly lower than might be ex• pected+ This failur e of corona bonding may have resulte-d fro m local surface contamination of' the faying plane, as by a i'ingerprint ,. Thus neither t h e :ir>e lative size o-f nugget rwr the rela.tive bonded area. of this weld can measure its strena;th reli.aoly in comparison ·with pre -c eding welds . Non""'destruet:tve tests bas.a d only on mea su:rement Q;f the conducting a:rea at the :raying plane would classify this weld as near to weld A"'2., which has about 50%' of its arest; yet or.J.y 21,; of its streng t h, and so the tests would be 100% in $rro:r. l'ests ba se,d on nugget size alone 1 would ela.s.sif'y it s.s stronger tha:n weld E~3., and would probably be 40 to 60% in errox-. Weld B-5 .,..,.. developed a flat nugget. comparable to that of weld B..-4, but the total bonded a.re a oove.r;;. ed only half the usual circular area., and contained only a small area of ca.st alloy bonding, Consequently, 21 this weld is weaker strength ( 340 pound) · than welds B-i-2 and B~a~ All the \~elds of 'rype B., frE!)quently called 0 doughrmt 0 or 11 crescentn welds, involve small re ., gi.011.s of cast alloy or nugge t development with or without extensive Alele.d bonding depending upop condi tions ;of surface preparation. ':Phe east alloy bond develops about twice the unit shear strength of t he complete Alclad bond~ Hence weld strength is not me a su;red reliably by the to-t al area of bond.., ing at the faying surface, Usually th.e streng th var•ies widely between successive welds made under these welding conditions, so hhat all these welds are undesi:t"able because of laok of consistency,. even t h ough a group of these welds. ma y pass the minimum acceptable shear strength require.ment . Incidentally, the changes in weld energy in this group of \11 elds we,:>e obt;a:i.ned with constant energy (current relay) setting of th~ Sciaky welder by advancing by varying amounts of time the appli.,. cation of forging pressure. 'l)12e C . ';J'el.d.$ • . &naJ._l Dia.met~r... ~us~et~ With Nol'mal AJ,.cJ,.ad . . Incluslons and Low Penet:ra't;1on. Weld G.,.;,l - • has a small nugget of normal shape TYPE C WELDS - - SMALL DIAME TER NU GGE TS WI TH NORMAL ALCLAD I NCLUS IONS AND LOW PENETRAT ION C- 1 S TR E NG TH 200 POUNDS C- 2 STRENGTH POU NDS FIG. 4 380 and a reasonable amount o:f' P.lelad inclusion, typical •of welds ma.de with h i ghel" energy t h an the type B welds, but with i n sufficient energy to produce full s;i.ze nuggets. Little .Alclad bonding oocu:rred on this The weld strength is only 200 pounds.. !T old.. l1he 1 pen:etna.tion is low,, amounting to about 30J6 of the shE;let thiok.ness., Weld C•2 •.- was made wi th greater energy than weld G•l and has somewhat larger dia:n1ete:r and a.bout 55% penet J?ation. The strengt h is 380 pounds,. The nature of the corona bond on t his wel d is question• able -. Type C welds result under otherwise normal welding eondlti ons when weld energy is sli.ghtly low for the production of normal s;i.ze welds , If the corona bond happens t o be extens i ve t he ~elds develop n ormal Sta.tie s hear stl?ength. However, if' eo1"'ona bonding is absent• the weld s t reng th is low, In!lt oon sist~n oy of streng ths r~sul ts, p$..rt;i.cularly if sur:t"ace preparation and cleaning of the sheet were ina dequate. ~rype D, Welds _~ ;N9:r•mal Di ameter__Nug~C;lts with Normal , . i-7 . , . _ l . . . . ( - - .. , Penetrat,ion VJeld D,o,l .,...,.. is a 1,veld of no rmal d iameter, pene• tration;; and shape. Its strength waa 725 pounds, TYPED WELDS - - NORMAL DIAMETER NUGGETS WITH NORMAL PENETRATION D- 1 STRENGTH POUNDS 72!5 D- 2 STRENGTH 580 . POUNDS FIG. !5 23 It has an adequ~te area of cast alloy bonding at t he faying surface, to which coron.s. bonding .adds f'ur-ther strength. cessive. The 1U olad i n elusi<:m is not e~- The we ld is ttsound'' iije. it is free o:f' craeks and pQros ity ~ The penetration is not ex~ ee.s sive, since t he heat aff'eoted zone does no t extend to the surtaee of' the .2 4ST .a lloy-. pi:eferred typ.e of weld. ifu1s is the I ts maximum ·st:r.ength ha.$ been xiea.lized beeause it failed by sne aring through the nugget at the f aying plan$. Weld D~2-•is a weld of normal penetration and shape, with slightly l ar ger diametez,than weld D-1. It :failed by "pulling a. button"* w;lth partial shearing .o f the nugget; a nd· so developed only 580 pounds shear s trength. The welds of Type D consistei4tly develop ac• oeptable static shear strengt h, and are characterized by normal diamet.er; well sl'Ull..ped nuggets of reason- ab le penetration,. The welds a re usually sound and free from defects ( cracks, porosity i and l a ck of' fusion). '.l1y;pe E _fi(?l.ds _.._ Ov~rstzed Nugs~ts with E;xc~~rniv~ P@netr~ti,c,mi _,Gpac.ks 1 Porosity 1 or SJ2it;tir1s; , VJe1d E-1~ ...has a nugget of normal diameter with excessive penet:Pation into one sheet; and a tendency TYPE E WELDS - - OVERS"IZE NUGGETS WITH EXCESSIVE PENETRATION, CRACKS, POROSITY OR SPITTING E- 1 STRENGTH 700 POUNDS E- 2 STRENGTH 590 POUNDS FIG. 6 E - 3 STRENGTH POUNDS E - 4 STRENGTH 1385 POUNDS 680 E- 5 STRENGTH FIG. 6 640 POUNDS 84 u<>ward cracking in the nugge t, Sheet ~f.ficieney ma,y be impaired by the excessive penetration, and tatigue strength might be lowered through furthe:r grq,wth of the craeks ~ Should the craeks extend. th~m• sel ve.e to the sheet surface, eerrosion lnrould further impair t-h e weld quality. Strength was. o/00 pounde,. no greata:r the.n that of a normal penetration we ld. with the same nugget diametex-. We14 E•2••$hOW$ exoessive era.eking in a weld of .nearly normal nugget diameter and penetration. This results i'rom inadequate electrode pressure dur·ing welding""'•in this particular case the appli- cation of forging pl:'e$S.ure was purposefully delayed to obtain this reault. :i'he t'at;i;gl;le and corrosion t.>esiste.nt properties of the weld ~ay be impail?ed .• Strength was 590 pounds. Nugget cracks usually lie in planes normal to the sheet sur~aee, and radiate spoke•like fr.om the eenter of the n~gget . Current and he.at flew through the bonded area normal to the .faying surface are not appreciably affected by such cracks, x~rays, or eddy current flow parallel to t he plane of the sheet will detect this type of cracking. W~l~, E•~... •has a large diameter nugget with ex• cessive penetration into one sheet. Crack ing is f'r·e • quently prese.nt in such oversize welds; pa:rticula:rly 25 where ;tnad.eq-uat© tip pressure has been used,,- i'urthe:r inot-ease in nugget size of'i'e:t>S· little advantage, tor possible :i,ncreaset in statie sheat\ strength is offs0t ' ' by reduotions in fatigu.e strength, sheet eff'icie:no,y_,. duettlity and corrosion rE)siatano.e ., \.,hen e:x:cessi V'e penf!1t~ation and c:re.eking result. W~J,ti E.• .4; .......ha.$ a.:n abnormally •large nugget with exee$sive penetration and ora.cks extending to the 41heet $U:r>faee,, .I t developed a ,etatic shear stl"ength of liiB5 pound!$, but the eraok wluld serve as a foeal point fQr ~orro$ion er fatigue tatlu:1:·e + W$ld E~:&.;;~~.xhibi ts n spitting" at the faying aurtaee,; a eondition wh:teh is usually accompanied by poroai ty and, re.dueed atrength ( e40 pounds) • Welds .of' fype· E may occasionally dev~lop g:reatet:- static shear stre·n gth than normal welds, but this gain i e o!'fset by a deei~ease in stl:'ength eonsistenoy; and a probab.1lity of exeess1ve penetration and cracking. 26 II J; ... PROPOSED METHODS FOR TI!E NON-.DESTRUCTI V.rn TESTIMG 0}!., $?0T\!f.E;LDS I:N AIJJ 1Af.) ALUM.INlP..l ALLOY SHEETS At the ti. me this :r e seaz:oh was begun, several methods :f'o:t the non-des t ructive testing of epot we ld e in alumi num alloys had been propos ed. .Eao~ of these methods invalv~d an attemp t to· ine a1;1 ure the total axea of bond i ng at the faying plane. tb.?ouih the flo w of d ireot c:urren t, alternating or eddy curxent, heat, v:ibration or sound waves ae-ros.a the faying plane a t the bond. tlo r e li ab l e test of this t y pe had be e n develo pe d by previous resea rch •. Als o, xadio gr aphic me t hods of i nspect ing spotvrn ld s had been developed t o show g:r ea t pro mise. ( Ref . 114, 6, 8, 9. & 10) The ~adiogr aphing of epo t vHe lde , howeve:i:, seemed una t t ratot ive to ab :~ ,. ~:raft ma.n ufaoture;rs becau.e e of the cost, time delay and skill re qu ire d in t esting , as well as t he poss i bi li ty of mi sinter p:reta. ti on of t he radiog raphe or mi s use of the method. 'fhe practicability of the method kl.ad riot been p:roven fox i ndustri a l production ine peo-• ti on. It had not be.en shown that weld $trength could be determined fro m -rad i ographs_. ·rest rnet hods invest igated in this r esearoh are now l :iated and :ieaoribed., Methods proposed and developed inde pend ently a t Ja. lifo r n i a Ins tit u t e of Tec hno logy are i nd icated wi th a. (¢) sign. t eth0.ds propos ed elsewhere are ind icated by a su pe reori pt letter. Je n eral info:r m.ation on t he me t ho d ie include d wnere it may prove :ie etu l ., 1'heee method s inolude • (a) Vis-ual Ins ,p e <1ti on of Spotwelds {b) Elestiio Cur ;cent (Conauetion) Tests (c) Ed dy Our:rent ( Induction} Test.s (d) Thermal (Heat Flow) 'l'ests (e) Sonic and Vibration ·reete (f) Sheet surface Condition Teats ( g ) Impteeaot ox Penet;ra.toi Tes t ,s (h) Meohanieal Proof Teets ( i) Radiog raphic 'feete A. Vi~u~l l,nspe¢ti()n .of S.;ilQtweJ..d.q Qualit.y eontrol of e-potwe lea in the aircraft industry i s obtained a t present by; (Ber. #~) l. C.:a.;.:e:f:ul proeeas .o ontr Ql 2~ Q,uaJ.ifio at ion test:tn~ of maehines 3. Percentage destructive testing '• St :ength consistency teets 5. Weld metal stiuoture 6. Visual inspection of weld~d pa.rte and struct ures teete, and Visual ins pection iB the only non+deetru¢tive t es t wl-iioh has xe9eive a gene:r al aeceptanoe in tbe induetr.y. A skilled inspect or, :t'arailiBlt with the oond 1 tions of p-. repara.tio:n and we l ct lng , and tb.e oha.raeterieti¢.s of paxtioula; ma.chinee, in a given plant, ean obtain a g re:a t a.moun t of • :l.nf():,:rna... tion c oncerning ,w e ld quality by vieual in~pection of the fini.ahed pa.rte. Pa.r ts showing: excessive indentations of the sheets by the wel<;ie:t electrodes are, of ooutse, xejeeted for i;urfa.ees expoeed to the a.it st;ream~ 28 The pxeeence of s pite or fla ~h ee .,. o.:t evidence of e,xcees ive ti p p ie k-up , o f ten i nd ica tes bad we l d ing cona i tions " Welds with orao t-: .s extending t o t he :ahe e t s urface are eas :ily o bserve d , a nd canno t be El.C0'!3 pted becau.se t h.e s e cxac ks serve a \tl fo cal p ointe for c orrosi on. Svide noe:a of ex.ces e ive s h eet ee par a tion ir1<U aat e bad we l ding c ond i t io ns , wi th pos s ib l e e.xpula io n of metal !xon1 t.he we ld zo ne a nd res ul tant era.e ke OJ? porosity.. Certain eUJ1fac e oondlt:ions can be c orr elat ed witµ ductility or; conve rsely, with br i ttleness i t >. the weld • . Under co n t.rolled c on(l it ions of we l d ing , nugget s iz.e , , r1eld e ne:r gy, a nd timing o;f fot ge pr e s s ur e ea n be o or;i: e la.ted with , utfa.ce inden tat io n of t h e s heet. Good j udgment on the pa.t t of the ins p ector i e :required as s u:r f aoe cond iti ons d :) n ot p:r 0V. i 9e H>mp l e te i nf' ox ma•tio n as to weld qua lity. , ., Eleotitc Ou.r ren t Oonduet i on Tes t1:, !.nd iea t i one obtain ed i n e l eotl'iQ ou:o:en t conduot i on tes ts le pe n d · upon the mea1u.rement of' resistance in the weld t .eg io.n,. ~hey de pend i n partiaula1 ~pon the ieometry of the 00ndu•t1n1 ,a.th, a nd upon the e pecif+,o .t es i~tivi t y of v olume$ and s ur f ace e gi ons i n t hat pa th~. Due to the very low resis tance of alwid,nwn .lloye, even with a c urren t pa,th l imit.e d to the weld regi on {t9 bt a in s ensit i vity t o weld oo nd ittone), lar ge au:rrente . (10 tp .00 a mperes } a r e us ually xequ i ;eed. Qw Sene i ttve pickup units with internal resistance, d esi gned t o ree p ond to 5 to 1) 0 micro• olts, ar e ne eded . Only a s ma ll :portion of the to t al energy input o the we le re g ion i s a vailable to actua te the indic a ting inst1ument 29 1n the p ic kup system~ The relatively lax~e effects of contact resistances and ther mal electr omotive forces rnust be reduced in the measuring circuits. It is diffio ult to deteot vari a tions in the specific..r .e sis-. tiv:iJ;;2: in the various metallur gical xegions ot the s:p'.o tweld, fr om the outer s u:rface of the s heet . Des pite the f a ct that 24ST hae appro xi mutely twice the resistivity of 2SO t and about 167% of the re.sisti•v ity of 24S 0, the usua l we ld nugget has little r esistivity eff'eot upon electrical measurements from the out er suifaoe of the s he et. Thel'e are no boundary re gions of very hi gh resistance between the nugge t a nd th e paren~ me ta l" For welds of nor mal or low penetr a tio n , the ovexly i r+g laye:r of parent meta l tends t o:. mas k small o hanges in resistivity •w ithin the nugget... AS an e.xarnple of this con-di t ion, a rectan gular p l' ie i;n c '"'n- taining half a we ld nug et was cut fro m an .064" 24ST Al.olacl s heet containing ty pical spotweld s • ·rhe sides of the pris m were machined s moo th and par a llel, ;resulting in a blocl{ .06 4 11 x .020 11 x l'' eontaining half the weld nugget, ae ehovm in Fig. ...,. 7. Direct current was pa.esed through the strip f;r:om end to end . 1'he paten• tial di s tribution was measured by means of a potentiom.ete;r easily adjusted t o 1/2% of the total voltage dro p in the piece, through t he use of a sharpened aluminum al.loy ;pr obe and a d t viding eng ine. ;f il e potential distribution was found to b e that shown in Fig. 1 for measurements on the side of the bl oo k whioh had be en the faying plane .. No significant discontinuities exiet. Measurements on the opposite side of the block ehowed a l ineai- potential diet:ribut,ion. Simila:r piofiles in which the difference in voltage between t wo probes •.04tt apart was measured as the probe aesemhly wae moved ~! .• ,/ "4~- i! ff ~ 1......i1n i. vo . 0.1 _ 0.2 _ 0,3 o,~ o.s os ••. LOCATION Of' MOVIHG ·PR<a ClllcH£$ --t-+--t----1 ++++++-t---'i I I ::;QJC APil ,I 5~ ·our 'our· OF AN AL CLAD SHEET .CoNTAt NI NG ·,, '.:\F1 G.> '7. ::. f!o-itN.TI AL · OtsT~j BUTI ON ALONG T~e SURFACE _ --~ _,. ,- ]·t '4-+-!-',-iH--y-ct- -~-~ ~~ STR•-1' ·: • '. - AL CLAD, ' • I ·r.. ••;/ ~#2zz•. ~,--!If _ , _.,.-----·· .--·.,,---) --,--;,·-i,:~.. • j - - --. >'·- c ::~-~:-'!~;;~ i~_:;_,~~~: -(- r·€i'~(~ ~-.;:.•.it?- -~ . ·· .• .• ;:;~·•• · 0 ~· i T • ., • \ . .... -l ' f ~ I ·. r J . • -· 1-<( ab=.,, • - ~ • r ~ re;,:1; -z.~ a \ - , . - I " ·<· , ---.."&. oi 1 · ·. • !~ - J_, ,_ ' -- ..., . ."" , JJ., f RE SULT S OF A Two-S10E D IRECT CURRE NT ,; ,. "-'i 'ii' ' ~ 8 , LOCATION 0, EL!CTROOE ASSEMBLY CONUCT WITW. TOP ANO. BQTTOM SHEET SURFACES AT I . ' _. ?OTENTIA.L ls .MEASURED BETWEEN ?Rob es (Pl. • C1i"RRE,NT FLOWS BETWE[.N ' C,YLINORl·CAL'·','ELECTROOES IN ' F1G: T14E Two-S1oe - 0 1.RECT CURRENT TEST OF THE •• Bo,No~o -'AUA AT THE FAY .I NG PLAN{ THE' SPOTWELO. 9. • - ... ~ .. :'..";-..-~:::: - ·• .. 47 -.... -;::;.:-.- -..!~.- ::,;{\:~1.rJ.;: :•.r:Jj:q,:::;. ---1;-~ ~- ,.-•=-·,- ·PRQ.FH.E h s T Oe A L•RGE Sl'OTWELo· IN .064" 24S T AU!LAD, FIG~ - 11. d r,te' ,. ' "' .j .. . LOCATION 0, (L!~TIIOO[ .USCMel.Y • ;; I :, u ~- . L-'= ! ~ • Does t.lEASURE T11e ARu OF 80~_~ ·1i/G. 0 A. ' CURRein: -FLow PARAt, LEL To e FAYING PLANE " Doe S NOT t,IE ASU RE T14f'. AR.EA OF BONO I NG• B. CURRE-NT FL·ow' NoRi.iAL 'To THE FAYING PLANE FIG. B, ·'- t.lE.ASUREMENT OF BOIIOEO AREA ; OF A SPOTWELD THE Fiacfw OF. Eucnn.c CuRR e'i._r . - • •• • Bv (· .•·. i ~~- Fl G. 10. ~ESULTS OF A Two- '; I DE :)l RE rT CuRQE .~ T PROF ILE TEST 'OF A S'-'U l SP J T\HL 0·: N , (' 64" 21ST • '"'· ._'-;,} ·.,f!'-Sf!.6'Tw·t L0" N,UGGET, WIT14 DIRECT CURRENT FLOWING -· ?-: · ; ,. 1-.· °;! , ~.: _;:_ \t~ ;~;.;ii_;~..{~~?-;'f,-,, : r-,rT ~~~~wl~~·1±,l. . f 1!~;:"·f·~=~~:::1=~=~=:~:~;~~;-:~:~!!11!: \:'£ •::~ • ., ,_:,_· along the pieoe also showe~ no resietanoe dieeontinuitiee~ In the absence o:f: poxes and c:rac ks, therefore, it ie obviously very diff icult to uee epecif'io VQlume resistivity mea.sureme:nts ftom the outer surface of the welded sheets to measure weld eize o:r quality. It ie feasible to detect va:r iation in the total opndu¢tini ate§ of the bond between the eheete at . the faying ple!.ne, of a ;,, e·potwel<h '!'hie rnay be done by using direct current t' lowing ac.ross the faying plane (no:rmal to the eheet eurfaoe) at tne ' bona. several d ireet our rent tee ts of this type have been ptopoaed. Di:tect ourxent flowing in the plane of the sheet doe$ not mea.eure the area. of bonding, unleee a si~eable noxrnal component of flew through the bond can be establj.ehed,. (Bee- Fig, 8) Advantages of direct current methods lie in theix simplicity and theit immedi a te response.• DiBadva.nt,ae;es of dixeQt cu:rent teet methods lie in the oiffieultiea of establishing satie:facto:ry pxobe ey&tems without exoeaeive oontaat resistance or thermal eleo~xomotive foxoes, as well as in the em.all enersy available in the pickup system• 1. Two Side Di;r:eot Cut:r~nt 1'eet.a t .I n this teat, a laxge di.r eot eurxent is paeeed ftom a ou:u:ent electrode (.l ) in oontaol with the sheet aurfaoe above the spotweld through, the weld normal to the :faying plane to a similar cur.rent el¢Qtrode in oontaat with the sheet surfaoe below the epotweld, (See Fig,. 9) Potential probes (l?) in contact wi.tn the outer eheet surfaces and connected to a low resistance galvanometer, meaeuie the 31 potential dl'op through the weld. 'fhis test rn.e e.sux ee the total bonded area. at the faying plane of the weld. For welds with small are as of bonding , the lines of ourrent flow are orowaed to gether a.t the faying p lane and n:oduoe a ;eelatively hi ghe :r potential di' op than fo:r welde with a. large a.t'ea of bondin,n { Figs• 10 & ll) Higher potential read inge tnua tend to i~d ioate s mallet ., and presumably weaker, we lds. !)~ec;a.u~~<!PI.. to be obae,~ved in rnaki,~ft this teet a.re: l~ 'l'he CU:l: .r ~nt el.eet.:r:odes must be fixed relative to one another and be very caieful ly aente).'ed a bove the aetuaJ. "I; eld,,. ( Ineiden tal.ly * the weld may not be cen te:re(l U.."ld er t he. irn:piession of the tip of the welde.r elect:r:od(a.,) A displacement of the current electrode l/16° trom the 1..:.ptimum point with respect to the weld may introduce a 100% change in potential ind:1.eation* (Se~ Fig. 10) Each al'ea. of the current eleot~ode must make the .same degree of' oontaot, and oa.r:ry the same proportion of the total ourxent, on ~uece$eive measurements, in e~ite of variations in the geometry of t.h.e indentation of th.e sheet ~u:rfao.e by the welding tipaf 2.. 1.,ne UQtenU,al. :12robe:fi must be vexy oa1;efully and per manent ly located with l e speot ta the ouirsnt ele Qtrodes. A displacement of l/64" prodUQ(iS a large e:rtor in potential indic;iation. Centering the potential probe eymr:net;rieally with respeot to the · current el.eot:rocles, so as to measure only the voltage diop due to ouxrent flow nor mal to the ahe e t surface, 32 hai5 been shown to g ive optimum eensi tivi ty._ 'i'he potential probe should ~ave a e hal'P tip of a hardened alloy, capable of puneturing the o~ide film on the surface of the aluminum sheet without requiring the a ppli<:ation of exoesaive preeaute or penetrating a variable distance 1:nto the sheet. resistance m.ue t be obtained.. Lowt constant contact Futthermo:re, the potential p:robee must be ma.de of an a lloy whieh aevelope only a very small thermal emf._ when in eonta.ot with aluminum.. This ie necessary oeoauee the potential drop aotoss the weld amounts to only a. few mierovolte (0 to 50) in o,:dina:ry welde, for ~ot a l o u:rrente la:r ge e nough t o . heat the weld r egion a ppreciably.,_ 4.'. 'fhe apRlied pre1un ~:t:El and total te l$ t o ur;r ent should no t h~ lar ge e~ough to; <;:aue e fu:rth e r fuein g of A lolad a t the fay i n g s u); face, as thi e na turally in ·tr.od uoes eitoneoue t eet indic a tions~ 5.. Clea.nine; the . sheet s urfacee a:bove the weld wi, th s tee 1 wool and acetone tends to i mp:rove t est oons is tency •· _Inl;le,rent_.e ~ioxe in .this test method , preee-nt even when tee t equipment is oox:r;·eff;¼Y ~ ea i gne~, aQ<.rn.ra t~ly built, •' and p:rope:,;ly used, are: l~. An e1.:to~ in p;i:ecl;ioting weld \ ll·.t ;r e-1;1Gth amounting to ae muo n aa l 'JO% of actua l weld s treng th, resulting 33 fto m the inability of this t est to d isc;.riminat@ the :relative a:reas of Alclad and nugget bonding at the Both types of bonding have low ;reais tanoe faying p l anell in compa.ris on wi t h the unbonded oxide oo.ated a;reaa of the fay ing plane., and both types of bonding serve equally well as electrically o onduoting a reas in this test. 2., An e:cror. of as much as 100% i n potential ind ica .. tion, resulting ftom displace ments of the electrode assembly by l/3 2 11 O:t' more from ooncent:rictty with th.e bonded area at ·the f aying planEh S inae the:i;e is no lndioatio:n on t.he outer ~h eet surface of the exact loe atior1 of the bond at the f aying plane, s av~ the indentation ca.used by the welder tipe t t hi s err or oaunot be iemedie d exeept by profiling the weld iegion to obtain a minimum indic ation. Besulte of typioal profile eleetxiaal teafu on welds ar e gi ven in Figlh lO & ll • .• z. An erroJ; of · var ia.ble rnagni tude ·r esul~ing from. varia:t ions i n the e~a.E~ of the oonduoting are a at the faying pl ane .. • A long narrow. bonded area mi ijht develQp the same shear a t.ren.gth a.e • a c iroul ar bonded area. of equal magnitude, but test indic a tions would va:r.y. 4.. An exxer of variable magnitude re·aulting frern the pxeeenee of adjacent welds or :rivets near the weld under test, A poxtion of the testing current is shunted ·thiough t heee a.dJaoent bonded areas, lowering the test 34 ind iGatio n-, -S i mi lar la:rge e.r rsre in indi cation m1;1.y result when " e p its 1• or e,x.pu lsion of metal oceux and bond the fayin g surfa ce near the weld under teet'II l mprov em ents. in 'this tes ·t me thod we:;:e obtained by follo wing the listed precautions, and, in addition; 1 ♦. By modifying the ori ginally proposed 3 p().int cur ret1t e lect:r ode as sembli~s to ue e 4 to 6 points (,¢) or areas of contact arranged in a airc l e, or a oylin,drioal a u:rface. , This elimina ted et?ore oceuring on welda o:f type B:..:3 or B--4, when c:,ha.nce a.lone detexmined whether only one, or t wo of the cuxxent electrode$ in t he 3 elect:rode asaembly l ay over the bonded half of the i eld~ 2. By selecting t he • iamete:r of the oiroula.t c urr e nt e lectro d e s lig htly la:r ge:r than ·the bonded area of the nor mal weld, optimum senai tivi ty to W3 ld axe a we.a Qbtain ed ; wi th minimum shunt.ing of oux:rent t hrou gh adj a.eent welds., 3. By applying a measured p:re se u,x.e (¢ } to the eurrent eleetrodee which we re aouuJa.tely ali.g ned in the for m of a. e i:role of sphe:r ica.l contaot e or a cylindri cal contact~ varia tion in depth of penetration of the current electrodes into the sheet, and ex-xors in a lignment; we ;r:e g ;i::_e at ly :r{~du oed,. ~dvan_~~g~s.. of the two s ide direct current test inelude: ;,35 (a.) its eimplieity, {b) its g:r:ea t se.neitivity to we ld p:reaenoe (ind .:. cations i ncrease by a factor of 80;.l as t he electr od e aese mbly ie moved off a we ld to e. po int half ,vay between t wo we lds one inoh apart), (o) its effectivenes s in measuring the e,rea of c ontaot iegardless of t y ~e of bonding pr esent (t he extent ·of Alclad bonding ie very diffioYlt to meas u1re by othe.r methods): Disa.dvantages of the t we -s id e direct ourrent test inc lu.d e: ( a ) it.s inability to measu re et:renith due to th.e weld n ugget sepa,:ately from the effect of Alclad ~orona bonding _., (b) its inherent errois, (o) the 'fact that it requires access to both s i des of the weld , ( d) tile large tee ting currents 1eq uir ecl , ( e) the am.all em~rgy available in the pot ent iul circuit • .Dea ~ri ption of test equi pment and <leta.ileo results of two- side di r e ct current teats on a large number of in• dust.rially made epotwelds are g iven in Sections V and VII,. :r-espe-o ti ve l y . 2~ Qne .. Si de Direct . Our~ent .Tes,t b In this, test, a direct cur rent .d$ passed between t wo Qur:rent electrodes (I) both of wilioh are in eonta.ot with the s ame outer sheet eurtaoe a.bove the .spotweld• The potential drop between t wo probes (b) pl aced on the center li n~ o:f the ouxtent electrodes, aleo in contact with the same oute:r surface of the sheet is measure d by a pG1tent i o- 36 meter ox J.ow resistance gla.vanometer (See Fig,. l.2). ln the weld r egion, some of the current tends to flow down below the faying plane t.hl'ough the bonded axea., ~educing the cu:n:e nt density in tb.e upper sheet a.hove the we ld, 'i'hus the potential g;r:adient i e lower.ea above a. epotwe l d with a large area of bonding , and lower potential indi~ eat.i ons. ;reeult ♦ Pregautiona identical with those lie ted for the t wo-sd,.de te s t must be observed with thi.s method. +sherent error,a identical with those list ed for the t wo ... side test exist with this test method. In addition, the one-side tes t ia very much less sensitive to the preeene e ,of' a weld (let alone its size) than t he twoside teat. Whereas the t wo ... s ide test indi cat ion changes by a fa.etor of 80: l a.a the test · assembly is moved from a loca tion 1/2'1 :from the weld to a point over the weld 1 the one-.e ide t est chan ges its incii!Jation le ss than 20% with a. s i mila:r movement of the assembly" Since only a s mall fra ction of the total c urrent flows below the faying plane a t the weld• the pe:ro entage ah~nge ;i.n indioaticm be tween small welds and large welds is l ee :a; th&n 101;. unde:r: op timum t es t conditions involving only one weld in a ~ 11 wi~ shear t est atl'i'P • 0£ See Fig ♦ 13 for typical :reaults of tests mad e on 29 spotwelde in one inch one spot lap joint 1600 l400 iii ~ I 31200 1 lJf ~ -rooo ~ ~ 3 800 ~ ~=t i .:. ~ 200~., ..,........ 0 ~··· 93 ~o ..J FIG. 12. THE ONE-SIDE DIRECT CURRENT TEST OF THE BONDED A~EA AT THE FAYING PLANE OF THE SPOTWELD. DIRECT CURRENT FLOWS 9ETWEEN '11 ANO } 2 THROUGH SHEET POTENTl~L Is MEASURED BETWEEN P 1 AND P • 2 ~ - ~, -4- 3~6 - -3~8- -40-~ 4-2- ~ 44 ELECTRICAL INDICATION MICROVOL TS/AMPEREANCH BETWEEN PROBES 0. 13!1' A""RT FIG. 13. RESULTS OF 0NE-SIDf J IRECT :::uRR ENT TE STS O• Sl~GLE SPOTWELO SPECIMEN S IN ONE INCH S HOR Te s , ST~IPS. NO DIFFERENCES IN INDICATION ARE 0 BTAINf C BETWEEN LAR GE ANO SM ALL ~ELD S I• [ xTEN DEC SHEET S 3 v THIS Tes,. _.------ .. ~I FIG. H. EFFECT OF SHE ET INOEMHTION IN MASKING INDICATIONS OF BONDED AREA AT TH E FAYING PLANE 8Y THE ONE- S IDE DIRECT CURRENT Te s,. ----~~--- I ,r FIG. 15. WHEATSTONE BRI CGE Fo•~ OF THE O• e- S 1oe DIRECT CURRENT TE ST OF TH E 90 NDED AREA AT THE FAYING PLANE OF THE SP OTWEL D, ': uARENT FLOWo 'l ETWEEN CONTA<:T POINTS (1). POTENTIA L ls ·MeA s u•e :; ACROSS EQUIDISTANT POTENTIAL PROBE S (P ) . l•E ELECTRODES _FOR~ A WHEATST ONE 8RI O~l C IR CUIT, W•IC~ Is UN9ALANCED SY THE PRESENC E CF A I ELJ . test str i ps of .G64u 24ST Alclad she e t., In laxge aheets containing i;na.ny welds; the change in indicat i on becomes exceeoing.l y small and v·ery difficult to deteot ....e:xve~iments cm ir:tdull!ltr ially made wel.de showed thie change to be entirely masked by- the inverse effect of the indentation of the e.heet by tn0 we l der e l ectrode . { Se e F i g . 14).. The limits of eenaitivtty of thi s method , determine.d by oa.leulatiano, a nd c hecked by potential rneaeurements in a l axge eoale sa lt-water mod el of the oonduotox in the weld iegion, are very low, In p:ra.o tioe, it ie di!f ieult to xealize even~ fract i on of the theor et ical limit of sensitivi ty, lm9.r,0vem.E1nte in this teat method were ob tained by f ollowing the li st ed p:reoautiens, and in additi on 13y mod ifying the eleotrooe a ssembly to fo r m a Wheatstone bridge o ir cui t with the weld und er one leg of the bridge. {See F._g ,. 15) • 'l'he d ir eet current -pass es thr0ugh the sheet fxo m electr ode I1 to eleot;rode r 2 -. 'l'he. weld, i .f adequately bGnd ed, lowe r e the :reeistan oe of one l eg of the brid e, A potential appea rs be -twe en Pl and P2 due only to the eff e.ot of the weld in unbala ncing the current distributicm~ A fax great er pe rcentage change in indi cation with ahange in weld s ize is obtained than wi th the unmod.i.fied one-side teat. Thie test also discriminated we l ds with Jai:ge bonded area fro m welds -w it h sma ll bond ed aiea in eingle epotweld l" t est st ripe, but suffered g re a t loss o:f sensitivity when applied to large sheet$ with many welae. 38 'J:b.e aavant.ase, of the one ... side test l.ies in the :!'aet that aoo ee.s ie required to only one side of the we lded structure~ Although 90% to 95% .o f all s potwelds i~ ai.rc:ra.ft etruoture e are aQ·oesaible :from both s ide$ at $ome point in the fabrication p:roo ess, this test would make possible the tee ting of welds even on closed et.ruetures. The d 5.~adv,arrtaeee of the one-side tee t lie in its • inherent erro:re a.nd in i te ver y low sensitivity. On ly s mall deflections oan o.e obtained, even with l~ng ],'SI iod, ,.,.~ high aenei tivitY galve..u::netPIS in the p·o t.ent'ial ciro•ui t. ·r.eet ihdieatians ·a re affeoted. as muoh by s heet inde.n/tation a:s by the p :r:esenee of' weld b onding. No pra.ctiaal :reliable fo:rm of 'tl"1is test ba.s been de,velo ped as yet~ 3.. ~p Jqi.nt Ili:reo~. 9,ur1,'ent 'I'e,st (ft) In this test a d ix ect cu:rrent is passed through tl;le weld betwe e n two ourient eleet:rodes, one. of which ie in conta.ot with the top eurfaee of the u ppe :r sheet d ir e ctly above the we l d , While the ot her i s in co.ntaot with the top s u,rfaoe of the low-et sheet adJae ent to · the weld~ (See Fig , 16). 'l":h.e major pa:rt of the cu.:rr en.t thus passee normally t h:rough the faying au.r f ace of the weld under investigation. 'l'he pot,ential p:robea axe located at the centers of the oylindiiaal ourx ent electrodes, in one f orm of the t eat ass e mb.1,y~· Var i ations in the area of bonding at the weld int.roduce variations i n the potentia•1 d:rop near the fayin g J __ ~-CJ~---==-· = ·c____ ; ~~ ~~~~-----~ - _) ~-~::_ ~;.,:_;-.~ ~ L I II L - -·- · J . T HE LA P JOINT Q 1R ECT C u qRENT AR EA THE 4T TES T O F FAYING P LANE CF IHE Ro~GED Fis . lP. , -~ c~E ~LE : T~ OQE CI RE: T cu~QEN T TEST J F T~ E 90 N:E : ~T T~ E SPO TWEL D . THE ~.Y IN G P L ANE OF 6 ;::. ~ u - - ~- -- + - --i- - + - - ~ ; ! ! ··r--i- i3 ~ I ;J 2 0 ii: u I !.·····}--i-··! j __ - t- .., .., f' .J S f.s, I T I VITY G F 'SE L"AP Tc UF ~'1E PiH.S E~CE JO I N T J I RECT S POTW ( LOS, 4s :u, ,:: ,-:- r , ,:.· Sv 0 RCF IL E ')11ow-.. "'."E~TS . THE . SPOTWf. L J . ~- 0 ~~ surface which tend to introduce vat iat.i ons in the total drop between t.he potenti a l pro bes.. Highex p otential drops should o.oour wi t h weak we lds of small bonded a.tea. Ptec•Utione to be observed in making this test include th.Ge e listed for the t wo side ct.09 test, exoept that t he cur:rent eleotro d e in eonta.ot with the lower sheet mast be in a .f t xed poeit:i.on with respect to the weld, as cl()ae aa poseible to the weld• 'This elect.rode should o<Jnta.ot only the lowei sheet, :tnheient errora, eimil$.? to those listed fo.r the two ~ide d o<h test, exi5t :fo:.r thi.e method., In addition, muQh larger errorat due to extended path of current flow along the lower sreet, result from va.r1atione in geometry of st:ruoture, edge eff eots, adjacent weld$? and amount of ov e:rlap in : the la p Joint. The ~Ll.::Hidva.nta.B;e of this tee t, which m.akes it wor tl:l- lee s, is its vexy low sensitivity. Tb.e maxi mum possible variations in the total potential whi oh could reaul t from va.;ying the geomet.r y o:f bonding at. the fayin g surfaee of the vveld axe only 5 C> to 10% of the total poteniiai drop. This is no t nea rly a suf:f'icient deg:ree of sensitivity. Uneon~ tl'olla'P lf: ":'aria•~ione due to othe r faotois ate of tne same orcle:r o:f magnitude ♦ In general, the variations at the faying ~ur f aoe are compl e tely m.~ked, and the tes t is of no value. J,"ig. 17 shOVH:I the · ~enei tiv ity ~f _the a.ssemblz t o 40 t_he preeence r:if a, welp. The aseembJ,y was .moved length-,. wise over the surfac e of tb..e weld, and readin gs taken e veiy l/16°. Compax is on of' this out ve with Fi gs . lO & J.l ;for the two side test s~owe clea,rly how much less sensitive this ass embly i s to the presenoe of a weld. In t he t wo- s i ded teat, the r atio of poten tial meaauxement halfway between we lds to pot e ntie,l measure ment direotly ove r the weld i s a b out 80 to l .; · hereae in t h i s case the ratio i s only a bout l. 5 to l., 4<i One . ,Electrode Di:r; eqt Curt.en t _ Test (¢) ;tn t his test, current paseee into the weld ;region fro m one electrode (f::requently a ;ring contaot), and ia. o.olleat ed from the spotwe lded str uctute & t remote points,., 'Tw o potent i al pr obes (P ) are radially dieplaoed within t he current electrode ( I }. (Sea j i g . 13 ). Ov er the cente:r of a unif orrn s heet.,, ve~y l:,ii~ ~.e potential diftexence appeats ae:roe s the potential ptobes when cu.:r,:e nt flows $,Way from t he cutrent el~etrode symmet:rioally through the sheet. If ou:rten.t ;flows into the lowe:t sheet of a joint thxough a weld µilqe;t the ele ctrode assembly,.. a larger a iffe:reua.:~ ·q~ i,' 1):<1l;t,~~¾ial a ppe ar s between the radially ' ' dis placed potential p ro bee.. 'lhe potential die t1 i blil.ti'on in the weld xegion is simila r to that abtained with heat flow fro m a. e oufoe i.n contact wi th the sheet surface, The variabi 1.i t,y of the r e turn cui::rent pa t h makes this .. ,.·,,, .... _ 41 tes"t lese :reliable than even the lap joint di:r e ct current tea t. 5.- Al terna£ing Cur;rent Cop,gu~.t ~on . 'f\:1atsa, (¢) Eaah of the types of t est deeo1;ibed fo;r direct cur:rent mi ght conceivably be used with alternating cux:i:ent, pxov ided 1nduqtive p iak:up eould be eliminated fJ:om the f)Ot en t ia l probe s and leads, and p:rovide.d a eui table detector for .5 t ·o 50 lll;iorovolts a. c •. can be use as pQtential. indicat or s ; so vaouum tube a mplifiers wit h stabl.e oalibratio.m a re usua lly indic a ted. A. d ,dh galvanometer ue ed with a suitable ooppe:r oxide rectifier of very lQw resistanoe can als o be applied, for lar ger p<rt e~t i~~ ~+.'OPS ~ ~ :· ~ <' . . . .!1•, :.,, _: . In addition to the precautions listed ~for direct current teat'a , es peoial oa.:re must be use d to avoid , inductive pickup in t-he potential prG.bes and l e,a ds. The z esietanoe drop of poten tial aoxoes the weld is eo small tha.t the induc t ive pickup in unshielded potential leads would be several hundted times la.rger. Ev en though this induced voltage be 99% oanoelled by a reverse• induetive ·voltage purp.o sely int:rod uced in the po.tential circuit• a l a.r ge ·~rro~ in indioaticm would re main.. Tllie diff iculty nullifies othe~ apparent a dvantages in the use of alternat i ng cur:r ent. 42 l.nb.eient errori.;;, identical wi th those listed fo:r Qortes pond ing a .,o .o t e ats, exist with alternating current e ond uotion tests Advant.a gee, of alt e:rna~ing ou:r:tent over d irect ouxr ent in conduction teete lie in ti1e eimplicity of hi gl1 cur:r eni~ei supply t::ranafo:r mere and the possibility of inst~nt~neo-ue indi cations. ' J)is.ad11antages due t o inductive pieku-p and lac k o:f eenei tive a.o-.. potential in<li oat o:rs have been ci te<h C!>e Eddz Our;r(;nt -. (Indµqti on) Tests Se ve:ral types of eddy curx-ent tests have been pr opos ea • In theae tests, alternating ma g-n etio fields are ea ta bliehecl i n the r e gi on of the we l d , resulting in a flow of alternat i ng electric aurrent through alosed paths within the we lded she e t s ._ . Since the resistivity diff erences of the vaiious :regions of sound welds ar e too small to serve effectively for diec:rimina.tJ.on ot· weld quaJ;.ity , eddy eur.rent te st s• like co~duation teats• muat m~a.eure t .h,e a1:ea of bonding at the fayin e pla.n e to predict we ld st1eng t h,.. Thie oa n b~ achieved ohly by a :f low of cu:rfent normal to the fayin g eur- faee at the bond. Bu t in thin conducting eh$ets it ie ve;ry difficult to establish a ej,.gnif ica.nt component of current flow norrt,1al to the sheet sutface.. have been tried, A va :riety of induction assemblies aorne even using massive blocks of go od conductor to f orce the magnetic field down into the e heet, wi t h no e ucoes s whatev er i n establis hing a s i gnificant amount of cur rent f low normal t o t he f aying sur.faoe at the bond .• :De teotion devices produoin.g eddy cun:en ts :flowing predomin• ately in planes pa1 a llel to the sheet surfa.cee have not be en able to dif fe:rentia.te betwe en good and bad epotwe lds. (Hee Fig. 19). Eddy ourrent tee.t deviaee :r es pon d sene i tively to s heet su:rfa oe geometiy, weld oxac king , and porosity.. ( Ref . # ll). 'l'hey are applicable i n dete c. t ing the s e oondi t ions whioh may c orrelat e wi th the fat ig ue stre n g th of the we l d ; btit whi oh do n o t measu:r;e sta tic s hear strength. lifo eddy current oeVice pro pos ed and kn own to the autho:r measur~s static shear if trength . .9!:f'f eoti v:ely., A.d vantas;ee. of eo dy cu:rr ent t ee t me th ode a:re: is re qu ired to on ly 011.e sid e 01' {l) access the welded s he et, (2) n J eleqtx i oal con t a ct wi th the eheet eurtaaes is zequ ir a d , (3) inetantaneous indic a tions are ~os eibl.e, (4) de pth s ensitivity may be adjusted by choice of fre q ueney. Disadva,ntag~~ of eddy current test methode al'e • ; ( l) oi:ff' io ulty is enc ountered in establiehing current flQw n or mal t o t he bonded area at the f a y ing surface, (2) probe assemblies pio k up very little energy~1. (3 ) c:raa ks, poro s ity and she et indentation tend to aff ect indica t.ions i ·"· ~... ~ ,' {!~ ·:Y )0 1~ ;->:J L O A ! J I N (, LO[, V C U ~..l( NT '-- ► rF/9-Ft+H-I- ; t . J ~ F LOWING IN PA TH ? NORMAL ... " , ~ : i \l ;t ·. : -~-. , .J, ., ·• . f- R! L .. ::.'f. ';;) i.fl •. • ti, ;·... J, ~ u . · ,L_, _., ; ",Jift .; •,.11 . .. .' 'i' ,~cum; '!'U Bil YO.i.T~illi C I Q C U I ':'" ~ ... - W I TH AU1;12 . . -~ 1 :'! , TO THE y:d::., FAYING SURFACE 0 0 MEA S URE AREA OF BONDIN G, Eoov ~URRENT S I ' ;;. A,•.; ::, r O HM £ ;./ r. 1G . 19. t FFE CT OF PLANE OF FLOW OF EDDY CURR ENT UPON MEASUR EMENT OF BONDED AREA AT THE FAYIN G PLANE 0F THE SPOJWELD, A. EDDY CuARENT S FLOWING IN PA TH l PARA LLEL TO THE FAYING S URFACE DO NOT- ~EASU~E AREA OF 80NO I NG, 8. T E. ".) T . O F S t1t:E l llO .lL .. l O ;;_. ~1~ TV:i IND U C TI O N -- - --◄------,1 INOE NTAT I CN. ! RAN S F O ~MFR ,,-- - ANO S HEET r 1 r•• 20 A. ?0 c. I I I I I 1 I ·~· '© I ,\ t' . UH10.:; r ,:1 H CU ! 1'" MW\,.\~ R E. SO N A. N T l ... lJ~C T I S N Ti. :.> T. f°I G . •C• .:... t ~ ' I I I I u :) f. 0 w iT ~ . .. : . ~ ,, , .. 1, , \ 1 ~ ~1, : J.. . . :' l ~ A. "i'-, t~· :..-•1. 1µ i•' ~ : . ?l ' l!:X'.'. ! T l Nc; ~,; ;L oJ T H ': uN:;":;r;,,; ~ i'O Li.S . £ xC ITIN G CO IL AN~ C J ijC UL ~R EDD Y CURRENT .\ i ...~·! T I I I 1 ~ ~ f'C; R O S IT Y , PA.TH ESTA.HLl~HEO, ~ I G. ~Oll,_. 11:J ili,;;,o'w/ t',.\T!i ES '!'/\ .)~l. i:.~L ~:)l>Y YI.EL D C H.\ ~ K S, .; .ii1 ,: L .i./ \4\ THI C l< NES S , - _,. ,; t'1 I ., 44 .• far mo:re···,tnan ---........ ...._ d oes the a r ea. of bonding at the faying . p l ane , ( 4 ) e d-ge effects anti adjacent welds a f f ect ind ioat i ons, and (5) even if eddy c ui-r ent flow c ould be es tab.,. lis hed n 0 n o.al to the faying p l ane at the weld bond , no cUecrimination between oas t alloy bonding and Ale lad bonding (with on ly h al f ·the streng th of the fo:rme:r) oould be obtaine~. l. Tranefox- me r Load ir;tg ,Induct ion Tea t (¢) The eimplest eddy ou:rr ent ind uction test unit. OQn• sists of a co i l oariying alternating ourrent placed above the cond ucting sheet so aa t o produce eddy currents whi c h act as a se oond a.ry t:ranefor mex l oad on the coil. Using oores of powd exed iron in wax moulded a bout em.a ll coils, a highly eensitive system of mea.su.ring s he e t thiokneset surface indentation, and resistance t o the flow o:f eddy ew: re n t s f lowing in planes pa;t a lle l. to the sheet e urfaoe has been obtained .. No pic kup coils ox amplif iers a;re used ; instead the CQ l l and a s uitable cond ense? are made part& of a se rie s res onan t a :rm of an a. o. bridge, the :f low of eddy curx ent s in t he s heet be ing reflected in the coil by in ... oxeaa e.d pr i ma:ry co i l current. ( See F i g - 20) • The change in imiuctanee due to t he s eoond a.ry currents detunes the. res onant circuit, and for a coil Q,• as low ae 20, a 300% • -- Q, ie the r atio of s tored enexgy to· d i ss i pat ed energy in the o oi l " and i s given by Q, : wL/R, where W ;; 2 rr times the freq uency, L is t•he inductance, and R i s t h e effec tive ;res is ... tanoe of the oo il. eha.nge in voltage across the condeneer ocouxs when tlae unit ie li .f teci f tom the surfaoe of the conducting shee t. A 2% ohange in the tl'lio kness of an .oao u she et can be r ea cH:l Y d eteo t e,a, wl th out the brid ge cirou.i t,,. by measuring chang es in voltage a ot ose the condenser with a V'aouum tube vol tme te:r ( l % changes are obse rvable with the brid ge circuit assembly). The looation of the ed dy curr ent pa.t h in th.e eon- duot ing a h ee t aan be contr o lled by the use of a. co noentrio pole aese·mbly wh ioh aan be eas ily :fo:i:rued tp ahw desired shape (us ing the ·powd ered i -r 0n in wax). A few n;: the more - use f ul oonfigura.tione a.Xtl shown in Fi g. 21. The depth of p~netx a tion of the eddy currente may be decreased by :i.ncreae ing the ap plied frequency. A qu.i e k aheck on eddy current penetration may be obtained by biinging a mae e ive bl oo K of conductor into oantaet with the sheet surface opposite the coi.l; and o b$erving th e hig hest fxequenoy at whi c h it affects t h e ind icatiOR• No arrangement of po le pieoes · ha.s yet been devised to foxce sizeable components of the eddy curxen·t s to flo w no:rma.l t o the s heet surface at the welch The f low of ed dy cuxrent e in s mall airoular paths in the plane of the s heets has proven very eff ective in detecting weld crac king and po:ro$;ity. s uoh weld cracks a:re usually r ad i a l crac ks , nor mal to the sheet surface , extending out .. wa;rd t'rorn the oent ex of' the we l d nugge t, and so 11e . " -- -- - --~- ~- -- ~ :,-; : :, ---- ,I\ I I :, ,, :, " . :1 :-_. •- '- :,_ - - - 0 () •,:,iJl ~I!1:!1~;m~!:~11E' Fl<;, . 23, T_H E --UP JOINT TRANSFOR"'ER INDUCTION,, TE,ST OF T11E__.. BONDEO 'AREA ,; _, .- AT . THE FAYING PLA'NE OF. - _,;,:. , :," ·._-._ ;. SE"'BLY/,USED ·_.TO RES TRI.CT EDDY CUR- -.,,,_'. _·.-, ;:;· .. ~:-- d:Nts ' 'r,o .A:---c.111cuLAR"• PA.TH .- - - • - ,_ ·<.·,. '/t'c·. .Re c-r~i.GuLi.R. _PoLE Asse .. eLY usEo ;'}".{<¼,{'';?':'r~~;~~,:~~;·;:::~:. ,._·t -~;;•, ·~. < 0 cu'RRENTS TO A }<: ., •- I • '--.: .. .\,-,· INDUCTANCE ~·f l _G, 22, R~-S-ONANT CI RCU 1-T -- RESPONSE OF ~ALL CIIA~_~ti li' I'll j TRANSFORMER £DOT CURRENT l!IOiJCTAIIC£ PRODUCE LARGE Cll·A.IIGES IN I NOUCT I ON UNIT, I NOtCATION , TH { ' SPOT.l !ELD , directly a oross the pa th of the oirou.lar our;rentia . Figs. 6 &; 20) (S ee 1~11e im.U,ea:tion mea.e tt:1ee tl:le ovexall e~ten.t of era.eking and porosity,. without mea~uring the geometl'y of individua l crao ke~ This device ie alsQ $eneitive to the ai:r gap between th.e pole pieces and the eheet f¼Ut:faQe.. Thus it responds "to inde.nta;t ion of . tn.e sheet by the eleotiod es of the welde.r, and actually has ap 1J~:Hlred t.o dia o:riminate between good and bad wel'1a th:£'ough the measuremen t of the increased indentation whi oh tends to accompany larger weld nugget.a. l?:i:~c a ution,$ to be ob served in using the transformer eddy out;rent assembly a:tet • (l) f:requ.enQy muet be selected t,J obta in eddy aux.r ent ;penet :ra:tion adequate f0t seneitivity to weld pr ope rt ies, {2) the air gap be t we en pole pieces and eheet surface must be maintained constant, (3) oor• :reQtions must be made fo:r change~ in sheet thioknes.e, materiaJ. 11 and tem per ., and {4) i t muzt be reco gnized that ourx l., nt f low ie predominately in the plane of the sheet and that the t est does not mea sure atat io shear stxength o:r spotwe lde, sine¢ its indioatione axe 1nd.epe:ndent of the bond betwee n the sbeete .. l +nnere,nt e:rx9i,s in thia teet method a:re (.l) its 1.n... . • ' ability to disorimiriate among poxo.sity or small oraoka, oextai n large:-,: c;:raok defects, and loa~l changes in the re~istivity of the material. .• and opexating at the higheet ftequenoy consistent with a.diiquate penetrat ion of eddy cu:rxents into trie s heet in a straxp, high .re,sonant pe a l! i n the law retiatanoe o1:rouit,. By operating on the 5teep elope ef the :reeonan!l e curve (aee Fig. 22) maximum. sensitivity to sheet r e sistivity eond i t ions is ob tained. By including the aoil OlZ oa.:pa.o ity in one '.l.eg of an a .. c. bxid ge., the indicator may be set to zexo when, the coil is in poa it ion above noxm.al eound sheet. material; and vaxy it s ind ioation only when the coil ie over cn:aeke and une-ound sheet material. P;y using oonoenttic pol'3 s, the eddy c urrent path may be confined to a naxrow ting. eliminating effects of adjacent edge s , holes, and welds not und et test. Advan.taie~ o.t· thie t est method are; .req ui;i: 0d to on l y one s ide o:f (l) Aooees i .s t ·1e eheet, {2} no ijheet prepa1ation or cle aning is required , and no eleotiiaal oontaots - are mad e with the aheetJ ( 3 ) measurements ID!!kY be mad e t hr ough paint or i nsulating coatings wit h.out * ... Fiequenoies of 3,000 to 30,000 cycl es wer,e found useful with sheet thicknesses varying ftom .1e1 11 to ,016°.. Example: fo r .. 064n sheet, I# 34 millihenriee, c•-G025 ,µ f, f•l?, 000 gave a change f rom 24 to 100 volte ao;ros s conoeneer when coil assembly was li f ted off sheet. ,damage_ or :i;n.u~_o_ture,., . (4) n o pro bee q:r lcyw ene1:gy fndi·"'· cat,ing ci:rouite a.:re uaed ...... hence no diff iculties due to contact rea-ista,nce, thermal emf1a., inductiv e piok:up , high gai n am.plif ie;rs ot sensitive me ters are encoun teted • ( 5 ) wide :flexibility-., due t o c ho ice of fl'eq uenoy, geome try of pol:e aeeem.bly, anc! sharprViH~S of tuning, c an be o btained in a p plioationa ~ ( 6) t.he 8ddy our :rent pattern is ideal for the detec tion of xadial ex:ao ks in e potwelde, and {7} the device s erves effectively a s a. t hi olm ee.e or alloy detector f or cond uoting sheets• J;?isa4;v@ta.se!, ot t l'.li a test method are: (1) onl y ed dy GH.ur e nt s f' .lowing in planes pa r a llel to the she e t e utfa.oe can be established readily, so bonding a t the faying eµ rface is not meaeur ed, (thus apotweld e tatic ahea.:;: s trength oanno t be m.eaeure d ) J (2) va xiatione in the a ir gap between pole pieees and sheet euxfaoe have a large $fi' eot up.on inaica..ti ons ; ( 3 ) indentations and va riatio ne i n ehe et thickness atf ec.t indications; {4) the exact geometr y of otac k e a nd porous defec ts cann ot be de t er mined. 2. 'rr an§fgrmer Loading Inch igtiou Test ;Mod.1.fieg ;fqr • IAill .;to~rtt,a -, d • •• A modif ic a tion of the simple trans.former load ing teEt makae possi ble the induotion of ed dy ouxx ents whi ch flow no:rma. l ly thr ough th e \v eld bond at t he fayin g s ux:t'ace, if a return path can be provided.- An exoi.ting <mil with oanoentric ooxes ie designed to i'i t over the lap joint, as s.llown in Fig . 2~h Frequency is a.d.jueted so that eddy cua:-r en ts are not indmrn·d in signi:fioant ~mount e at a depth greatei than one sheet thioknees. I:f' the exoi ting coil i s placed on the lap j oint betwe e n two s potwe lds ; the edcly aurrente fl.owing .' beneath the t urns of tne ·exciting coil ( Qetw e en the inner and outer magnetic po les) tend to follow a path through the upper sheet, dawn through one we ld to the lower sheet, and r et urn through t he second we ld~ Small bonded areas at the· we .l as t end to int:rodu.oe resistance into the eddy cur.ient path, while w:i;. th no oond uc:ting bQnd at the we lde, a 'Hn:y high resistance is int:i;oduced-, 'fhese cond itions a.re reflecte d in the res onant p rimary oil'Ct;tit and indioated by a , VaQuum tube voltm.eter. Inhexent e:r:iors in this test method make it practically worthles s fo:r spotweld ins pe ctions. These errors include (1) all the inhexent erroe listed for the t wo s ide di:reot curr ent test; (2) lar ge exro:re due to ed ge eff ects, hole s , riveta, and the irregular spacing between a.d,jaeent spotwe l ds; (3) an ettor due to varia tions in ovet lap and in the d i 5 tanoc of the weld fro m the lap edge of t he she e t; (4) exrois reaulting fro• effects of I \~ welcls in the ;return path (at · lEiae t indic ati on). t\~O welds affect each The location of the spetwelde ·with xeepect to t he lap j oint has a gtea tex effect upon indications than do es we ld size or quality. 5. Pi ckup Coil Eody Cur;rent Tes t[d In these tests, eddy au~zents are induced in the s heets una et tee t by curr ents in exoi ting coile , and variations in the eddy curre nt pat t ern a.re det ected by sensitive piakup ooile connected th.rough high gain amplifiers to euitable ibdioatore. (Ref. # 12) In • many desi gns, the pickup ooils measure only the d eparture , ot' the eddy curr ent pattern i'rom the pattern in a. unifoxm sheet. s everal typi¢a.1 pickup units are shown in Fig. 24. ~ Pioku);! Unit Ad has an exciting coil and ooncent rio poles similar to thoee deeorib.ed f or the tra11sforme;r induction tes.t. In addition, h9wevei, a sensitive mag ... netic pia kup system. is eymm.etrioally looate<a within the cent e :r leg of' the c ore. The two poles of the pickup are elightly dis placed f:rom each othe r.. The pickup coil i e shielde d .from the magnetic field of the eXQi ting coil. With the normal G:iroular flow of eddy cur rent:: es tab liehed in eound cQntinuous eonduoting sheet by the e:xoiting coil., no magnetic flux va.riatione ocout in the core of the pick up 0oil. .when the coil is placed over a or a ok or cl:i.saont:tnui ty., however, the mod i f ied eddy ou:crent pattern produce~ an alter- na ting magntHio field through tbe pickup aoil11 (See Fi€h 25) F1 okup U.ni t :a.e was s pe c;ific al ly designed in the Nava l Heaearoh I.abo:ratory fox us e i n testing apotwelde, with the hope that a $izeable component of eddy curr ent flow mi gh.t be - - - - - - - - - -- -- - - - - -- - - - --- - - . . ··- -- ----- ·- - · - j ~~ j t. --__j i\l~~~. ~ FIG, _i A 2'1, CURRENT \\I/ TYPICAL TEST A. PICKUP COILS UNIT PICK-UP COIL EDDY UNITS, FOR HOMOGENEOuS FLAW DETECTION PLATES IN DEVELOPED 6Y Ross Gu••• N. R. L. (REF . II 12.) r-·1 -i=.:::-t 8. UNIT AND POROSITY VELOPED ~--:l I r - - -- -·- __ I . .. J _ _ _ _ _J - - ----7 i _. _ _ _ _ _ ,__ _ _ J 8 A FIG. 25, EDDY A. FIELD IN HOMOGENEOUS 8. FIELD IN PLATE CURRENT FIELD WITH INDUCED PLATE, FLAW, BY PICKUP UNIT A. FOR DETECTION IN OF .CRAC(S SPOTWELDS BY N. R. L. DE- (REF." 11,) 51 eatabliehed aeI·ose the fayin g aux-face into the lower eheet a.t t he weld , producing an unbalanqe cw:iren·t in the pickup. The fiarne on i hioh the coils a.re wound ts made of ttans--for me:r l am inatione . The magnetic field of the e.J.Cc:tting coils ie addi tive so that the outer pole faoes at e of' opposite ma.gnetic polarity. used. An e~oit;i.ng frequency of 1000 cycles was Analysi s of eddy cu:rrel1t p~tterns shows that if the weld i e e:rac ' ed or porous,. or 1:f eddy ourrent1.t1 do flow below the faying pla11e through the weld bond a pickup due to unbalance should r es ult if the ·w eld ie ~symmetr:toally lo• ca.te a with reepeet to the cent.er pole o,n which the pioktq:> <Nil is located. Sc.a nnin g :i._s required to obtain rn.aximum ln:fo:m~tion concerning a weld-. Nava.l. aee,ea.roh Labotatory teat~ of this unit indicated: ( l) Thie e<idy ot.u:r ent metnod is not r,aatisfa.ototy f ot the dete.-;;tiam of the quality of fusion between tn~ two welded sheets. ( 2) The eff'eot of poros ity or oxaeks on the 4 eteetor wa-s $Uoh as to overshadow all othex effects, This makes possible the d etection of ,u:-aoks ot po:r ... oaity with littl e difficulty. Tests at the California Inet.itute of 1.'eohno l Qgy on similar imite $Onfifm these :eeults-. A,., t2 i ckup_ un:i;tf .: des ignea. e.t the Lockheed Aire.ta.ft Cor poration for use in testing s potwelda em.ployed large 52 bloctis ot copper conductor tQ force the magnet1.o field of the exoi ting ooi le into t,he welded ehaet. .Deepi te f!everal modifications, the di.ffieul ty in establishing a sufficient eddy current flew normal to the faying plane at the weld prevent~d 6uoceseful mea.su:i:ement of th.e area of fusion at ·,. the weld, In general, resea.l'ch has sh·own tbe pickup Ct;) :l.l eddy our.r ent te s ts to be e ubj.ect t.o the limitations and .i nhexent eJ;;i:i o~s pxeviouely listed for eddy ou;rrent. teats. No suocese• :f'ul method baa been d evieed f or m.ea.aur ing the bonded area. at the faying plane through the uee of eddy cu:rtente., D. Ther1Ual . T~a t M~tl'lod.a Thermal test methods in•r1olve tbe flow of heat _tl'4rough the 1eld region and the measurement of resultant tempe;r-a.tures or ;empera. tur e g radie nts ., 1'he p-:reaence ©f the weld modifies the tea·~ flow J>a:t tetn in an unwelded ehee t :. J.. geomettieally, since heat tends to flow normally across the faying plane th:rough the weld to the oppoeite sheet and$() possiblymeaauree weld nugget diameter; and 2" t-htough it.s variable heat oonduotivity (if di:ffe,t<ences in conductivity do exist in va:ious regions of the weld) and the pr es ence of cracl'C~ and porosity~ Heat capaoity of the region um er test atfeots the transient teraperatuie :res pom1e only,. 53 .Adv~ntasErs .... .-..Heat f l ow methods are read ily adap table to one-ai de testing , as we l l as to t.wo ... sid e testing ll paths ar e nec es aary. llo retl.ll'n Heat fl ow may measure total weld diameter at f aying s u:rfac-e, Disadvant~s;ea . .. Due to heat capacity ef!eots, b.et f J.aw rne t hode cannot be inatanta.ne0us and usually axe slow teet~h Ambient tem.perature , , au.rfae e the.:rrnal oontaet reste tano e, s ize of paxts we l ded , or i gi nal temper.a t ure of work , ·p res en oe of :,rac ks , natuxe of h eat ing and metho-d o.f t empera.:tur e measu.r ement e•- 111 change reeultant tempe.r atw: ew and tend to inval.idate tea.dings. rhexmo couples to measute t -emper.atwi'e have emall ene·:r:gy· outpt1t, ~~ve slow xeadinga and :i:equire a ensi t11:e ind icators. Although ieat flow indieat :i.one r e spond to weld cxaci<:ing and poioa;Lty, they lo not d iffer ent iate au.ffioiently between tb.e oaet alloy nugge t ind the pa.rent metal ,t o rneas u.re nugget geome tr y♦, Also,. hea t flow ;e,s te fa il to differentiate be•tv1een caet alloy bonding and Alolad ionding at _the :fayin_g s urface, so the static ehear etrength ot ·e ld s is not accut a 'tely mea.euterl. l. :Eie?,;t . ~.ee .e rvair .Tu:erma,l, .Tes,~ ; e A c opper heat teeervoir (simi lar to a: massive so l dering iron) with t wo contact lugs aairying 1rn bed~ed tnermoooupl.el, ( See Fi g .. 26) i s heated to a ternpei·ature oone1d .e :rably a bove that of tne wel(} to b.e t ested. One lug is placed i n contact wi t h the sheet surfa.c~ above \ LUG MICROMETER FIG. 26. HEAT RESERVOIR THERMAL TEST OF THE BONOEO AREA AT THE FAYING PLANE OF THE SPOTWELD, E A A +--~- - - ....-:"..,..°'T"!~,.......,~....__~ _ _ _ _ __,~=---=-....::-=--..- ::- == t= =~ -//_,,. ,_ - - I \ G ..., ..._ - - - - • _,..-'-=----......._ _ _ _--! = =:: _-_---:.."'f A. POWER SUPPLY B.INDUCTION COIL C.HEATED ZONE D,F. THERMOCOUPLE E,G. GALVANOMETER W. WELD FIG. 27. INDUCTION HEATING THERMAL TEST OF THE BONDED AREA AT THE FAYING PLANE OF THE SPOTWELO. A. HEAT FLOWS ACROSS FAYING PLANE AT WELO. 8. LITTLE HEAT FLOWS ACROSS FAYING PLANE WHERE NO BONO EXIXTS. 54 the weld• a nd he a t .flows into the we ld :region by con... I ' a weld is p:reaent; hea t flows thx ou gh t h e duot i on" bonded a.te a of the f aying p lane t o the lower sheet, and the to tal r a te of he a t f l.ow from the reaexvoir. is gre ate r t ha n when t he weld i s abeent, f o; in the latter ea.ee only the uppei she e t o:onduots heat away from the reee;vair* 'l'he dro p in, tenrpe;ra.ture recorded by the ther 1nocouple i mbedded in the lug in contact with the sheet is a measure of the :rat.e of hea t f'lo J fro m the :reservoir to the sheet. The therm.ecouple imbedded in t h6 @econd lug through whioh n o heat flowe meaeu;res the tempera t ure of the reeeiv oir, A sensitive galvanome,tei i e e mp loyed to meaauxe the differential output of the thermoco uples. :Precautions t o be observed in ma.k ing this test are:- 1. The heat source lug must be accur a tely located a bo ve th e weld, and must make conta ct with the eame sheet are a on each we ld tested . ( Variation i n the sha pe of the electrode indentation makes this ve ry dif.t'icult in p:ra.ctice )., 2. The sheets to be tested should not var y widely in te mpera t ure, and should pre.fetably be at ambient tem.-: pe r at UZf$. 3 -, The ambient ai;r mus t be at:l.11~-.a alight draft ' 55 changes indio.ations -far more than the p:tesenee of a we l d . Innerent .Erro~1e in this test method, identical with thoee listed t ot the t wo wide d ixeot current test, exist. l.. In addition, a vexy la:rfe error results f:tom var i ations in t he t he rmal contact reaiistanoe at• the e heet surfaoe where hea t is being 1nt:rod uced•, due both to C-h[u'lge e in oonta~t area a nd to e urfaae fillll6 of var i able na. t u:re. 2~ Changes in a mbient te.m _perature o:r air velocity, and i n material temperature, affeo.t im ioa.tions· gteatly ,f 3. Progressive heating of the woxk as euooea 5iVe welde a.r e tested changes indications, even on. identical welds. 4. The presence of adjacent welde, l,'ivets, edges, mas s es of metal,, holee in the sns et , nspit" or expulsion of metal f r om the weld x:egion- .... a.ll :result in errcmeOU$ indi cati one•· ~m1~.ro'V~me,n ts on this teat method were obtained by follovJ i ng the lh,ted 1ne oa.utiona, by insulating the heat reservoir and lugs fro m the ambient a i:c, by clean• ing the sheet ei and luge and removing oxioe before _eaoh test, by hold ing t he unit on the sheet sur:f'a.oe under eont:rolled -pxesauxe a fixed period of time, and 'PY wo.r ldng in a s mall closed room with wo;rk at room tem- perature. Thie lattei item required a delay between weld measu:reme·n ts, the tirm being ueed for oooling and cleaning the sheet. : over the next weld with acetone., 56 Advant:a;ges of the heat res ervoir ther ma:i test are: ( a) acoees i s required to only one side of the wo.rk ('b) t he heater an0 temperature indicator may be in· a single· unit re quiring only one a pplication ( c) no mar king of or darnage to we lds ieeult$,. Piaadvan:ta.5ee ot this teet include; (a) 1t.s in-. lleren.t e:riore (p) its sens;itivit.y to ambient air conditions (c) the difficulty of obtaining uniform thermal oon ta.et . wi th the sheet eurfa.o e and (d) its inability to measure we ld static a hear s trengtb.~ 2. Induct ion Rea.t in~ 1'est~vCa) In these tests he at i s supplied rapidly to a small area of th e Alo lad sheet d irectly above the we l d, at a. measured rate or in :fixed amount, by ·modified industrial induction surface hardening equipment. The frequeno.y is ohoeen suffioi ently high to limit the penetration of the neat""p:rooucing eddy currents to a thin layer at the sheet surt'aoe.. Thus the:tmal contact reslstanoe between heat eow:ce and eheet a;re eliminated as va.riablea ., and the rate and a.mount of he at production are oont;ollea. ~!hen a large area of weld bonding ie p:t eeent a la:rge f;raction ef the genera.te-d he at f lq:v s nor mally a.c:ros s th e faying plane into the lower sheet. With no vireld bonding, all the heat must :flow away in the upper sheet. (Se e Fig. 27 ). rrtius the heat flow ia e ensitive to the area of bonding. 57 .F·o r one .s ide testing, the temperature indioato; must lie under tlte inducti on heater on the same eurfaoeof the wor k... -henoe must not be affected by the high fre ... quenoy field, Only a carefully e hielded the:rmoc.o u.ple woul d be euitable. However, 'by clos ing the thermocouple a i :rauit to it e indioa,ting galvanometer only after ·the hi gh frequency field is turned off, the eooling tl'ansieEt of the sheet surface may be rec.oxdea, provided the gal..;. vanometet responds with e u:fficient rst;pidi_ty. SQme success h.a. s been attained by the use o:f a thin layer of wax* Ot thermoplastic in the sheet s ur;faae, bf obee:rv ing the t'I i ame t e r o:f' t -he softened mel led area whi ch :reeul ts when the oontr olled quantity of heat 1s generated above the weld. For t wo side tee tin g , the ind icator is placed on the a ide of the wox k opposite the weld, where it is- not a.f'fected by the hi gh :frequenoy field. Ir1 thi e case,, t he b,ea t wh ich reaches the temperature indicator must flow tb;r.o,ug:h the weld at the faying plane, Tlle en tire he a ting and ceoling t;tansient tor the controlled hea t generation oyele oan be obee:rved, with great sensitivity to the size of the bonded area.. :Both ther mooouple and ·wa.x film indic a.texe have proven t0 be eft'eotive. * --.Suita ble ca librated wax tem.pe:co.ture ind icato rs are OGH.utnetcially av ailable from the Tempil Oo:r: p Qxation in the for m o-f 1'empiletiks, 'femp;i.l l?ellet e and Te.mpilaq .. The ffi(ffl t <1H:U'l11 fHlieiit toim ,o,f tb@)HaOO(llli;>l.-e imi J.oatf:lt- eve loped tor till~ ptttJH>tH~ _o<H.1s iete of $. low thtxmal capa@ity the.rmo.eeup l~ u.uppo:rrtftd ~a.inst t .be ~heet iUJface by a *mal l rubb,e:,: s uotJ.Qti oui., Tri~ inner. au:rfaee ot 'the cup 1~ ooattHJ w1th & beat l'-efle.et.tni tn11faQe ti1eir~u-1llf in,:nilt'+iteo from tbe rub'tJer ,, ~~d- the• 11n,iot.1Qn r.ntp ~l.t~lu<iet t tvJ t.lflibient a.il'••ht1,'.u'-$• <Ulapit~ &,h eet ri;u:1tta.ce Q,onoit:1~u1, tb0 th®:!'HUiHJtH.1plli fo,:Llowe tbe tn~et tft'i~fiil!'~t\ut~ $lostU.yi 1· n($l tH~lihand jun~tt,;,n ie e-im,U..ti t ly at~eh.ed 1Hi t ne· ilaEt~t at a xernote point. 1lHll tb~t otitly ttmpiutatu~e 41tfeten0e$ du.@ to ttie h.,,~\inB of tbEi weJ.a t'ti1o.n ~,~ meaf.HA,re.f ·• J otl'l J~otion";- a.1u: q,ui<Ht-ly and e.aei.ly attaohffd ti;l -~ n7 Iltl)J.rAt ~:r th~ 1~be~t ~utfaet by meaJ'i$ of the &u~·U.on cu~-. and may be pull~l t>ft t\nd f!J.ott~d flt wa.l.l• The lath'.>l'at~ty wa:x t.ilm !t$dioat.01 c· nt&i&te of a tni11 QD ls.yG;r of' pa,r~wex 01; tr.eimoplae:ttio ~teri.&l pl.ao,ed th.e ebeet e:-i.u::t~c-e~ ·~b&n ()0111 and. ha.tdt a (hty 1 u.o.lored pol der ot dy,e i& apt1n1'led tvtu;- tll~ -au. linttf b.ea t Cftiuie~a.'ted 1n the opposite ~ne 0t a-t the -rnl.<l fl.tma th~u~n ttr !fel.o ;.n •uffiu1e:.nt qu~11:t.tt;y. tb wax t\bo'te tne bQnded a;i:ea. IQ,elti, ~Utt in t hit :egion th$ Ji(llV<iet beCO!:fiGS 1r.nbaddea. A o'Qm:plete Jo:i:~t •Y oe t ofated at, on:a ti.in~, a.nd a pe.1-. man~nt rec:01:0 obt.t)i,n~o by e ub~~qu~n tl:, pa.o:intt a. !$'t:tip at s ootc.h. tap~ ov~r t,be line of W(tld.fh 1'l'i~ ·a.p$ pick$ ~P th~ ~ow .er -ove:ir all. axee.e exo~;pt wb~re the 'W(ls;'& flai;; , .~~lted antt imbedded 't . ~ }>(J'm!de;r,. Fb r ·p raotloal ae• 59 welda, small weld s , and no bond whatev er are re &dily discriminated from one anoth@r by the extent of melting of the wax, llrec~ut~ons to be ob;:ie.rved in using the induction te:st , a.1·e: l. The induction he a ting unit must be aocurately located abo ve the we ld• The temperature i.ndio a.tor must be equa lly aceura:tely lo oa ted, a e the temperature gxad·ient i n the plane ot the sheet is quite large,~ 2. the rate and amount of heat gener at,ion must be p:eo:i.i5ely o(>ntrolled by eynch:t'onoue en: eleotronio timing. units, if bonded axea is to be determined ae~Uiately from tempel'atuie indioa.tione:h 3+· .Ambient a.ir ~nould be qu.-iesoent. No o-ondensed moi~tu:re should be present on the etruotuJ?e. Al.l pai ts of the joint ehould be app:ioxima tely a.t room temperature. Inherent errors in this test method a~e similar to those listed fo;r the heat :resex,ve,ir t e st, save that erxore due to oontaot resia.ta.noe a:re eliminat ed. 4c1v.anta.gee, of the induati(m heating method aJ:'ei. (a) the test may 'be made with a.qoes$ to either. one or bot h su~ f aoes of the wotk (b) the method rneasuies total bond~4 axea .r.e l:La.bly, and permanent reoo:,;ds c·a n be eaeily produced (o) oon tao-t thermal resiatanoee t.=q:~ eliminated as val'iables . I.),i~~aa:v~n_t~ges ar.e (a) Finite heating times (a few eeeon4•) are requir ed (b} Careful positioning and oontrol of ari1bient conditions is necessary (o) Spot:weld sheax strength :is not mea.eured ~e U.a.bly. (d) J\djaeent weld~, ~dgea-, holea, and m.aa- ses of metal introduce la.:rge e:u:o:rer. In these tbei:mal tests, .h eat is eupp11ed to. the ~u:r:faoe of the weld ed sheet by · :radiation., as from a con~: oen trated ne a t lamp and focuseing syater°'* The ahee\ surfa.oe ·must be oleaned or painted to obtain uniform heat abl'?orbti on 0vet the te-st atea. Thermocouples may he us ed on the one side teat if shielded fi:om direct radiation• without internal heating effeots pre s ent with ind uoti.on heating methods •. 'fb.e method is , slow, and is subject to the pr e viously liated erroie 0£ t ·h ermal tests. 'femp.e rature indications a.re obta.ined ae in the induction heat inrg test, when the indicat-o r is on the opposite side of the weld fi om tbe radiant he at eouroe. 4,. Canta.et D:ro 2 ,Iteati,ne- _T.e~ t( .¢) One condition hae been found in whioh eleot:ric our rent f lowing f ·t om po inted ~ le~tlio d e·s into Ale lad acheet p:roduoe:s a oontaot dro p of' potent ial a_ppro.ximately constant at about 0.2 volts for currents fl!om 20 to 90 amperes d. c _., releasing oonside xable h eat at the point of contact. This is equ.iv-alent ,t o a po int sou:oe ,:rt 6l heat. and the rate ef temperature rise pet watt o.t' energy inp ut would be af'!ec ted by we ld presence. This method is especially .e u.i table :for use with wax t,empeia.t u:r:e i.nd i -o a• · tGre, either in one or t wo side test, a ltb.ough theJ:nio .. couples may be used• 5. Di_f~t3r~atia.l .Hft;,t:f;:i;ne,, .'l'.~s,te.(¢) In methods 2, :3 and 4, ~ffeote of weld pxesen.o e could be inereaeed, and the effe0,ts of va riable ambient oonditio!le te~uaed by the h eating o;f t wo $i.teas. one over the welo and one not over the weld , unuex identieal oonditi one, and measuring the differential temperat~e of the two :regions by a therm ooo up l,e s)'item. Because of the au p lioaticm of he a ting equipment required; t h is mod i f ic-a tion has not been investi ga ted in this :research.. :,. Sonic and Vibra.ti.on Tes.ts: Son;i.o and vibration tests a.re usually of th.tee basic orms ; measu:i;ement s of v i bration damping ; measurements o.f ave ;tefleotiona; xne a euieruente of the na.tu~al f:requen.oies of acilla tions., Each ·ty pe has been pr o posed for the non•deatxuctive eating of spotweld s in aluminum a.lli:ty eheet:a,. Sonio and vibration teat c , by their very nature, are more I aeily applied to pieces of fixe ', oize and shape, to detect aterial pro pertiee and defecta , than to .s truotutee of irregular. :1d v a ria ble shape. Spotwelded ~truoturee offe; a less promi s ing 62 field of ap plicat i on beoauee of their c ompl e x sha pes, Whiell :a:enoe, oare m. ue t be ta. ken affe ct tee t inc ica ti ons considerably. to avoid the development Qf test procedures which cannot be reduced t o piao t ical for ms a pplicable to epo twelae . V'ibration Dam12ins Teets t i ' One fo r m of Vi bration or damping test pt~posed f or e potweld tes ting employe a d river to establish oe cil• l a.tions of adjust a ble f :req u e noy in the we ld r egion and a detector to me asure the resultant amplitude• For s onic and lower frequencies,, a ooupled eJ,.eotromagnetic•meclla.nioal ' t:r:ansd.ucex {similar to the driving unit s o;f loud speake;rs) :j.s employed as driver, while fot eupere onio fre q uencies, mag neto-et:r:uction or qua.rtz horystal gene:ratore a re us ed-* Powe r i s s upplied f rom varia ble frequenay os oilla tot s to these oriving unite" Deteotore for meaeuring the res ult a nt vi brat io n a.m.pl i tude usually c one .tit of a piezo ... e lee trio pic kup ar other mior ophonio device• conne cted t hro ugh aui table vae uum tube amplif i e r s to incH oa.tiug i ns.tr ume nts ( See Fi g , 28 h The dampi ng c an be d ete r mi n ed f or a syst em of any s ha pe 1 provid ed i t can vibrate., In one me thod of meaeure• rnent , constant energy is supplied the driver a t v a ~ying fre q uency, to op tain in the d eteoto:r a :ce s onanoe curve (See Fi g. 29) showi ng the amplitude af vibration as frequency * ..... Ma gnetostriotion genera.t ors are useful f ro m. about 8, 000 to 50,000 cyole~, and quartz crystal generators are ueQful at h i gher frequencies. VAR I AB~~/ RE OU E_:_C_Y_ _ __ _ POWER SUPPLY• I DR Ill ER _ MICROPHONIC Pl CK UP ......,...____,::_ _---, AMPLIFIER INDICATING INSTRUMENT FIG. 28. VI BRATIO N DA MPING TE ST ARRA NG EMENT. ). - - ---- - - -- - MAXIMUM AMPLITUDE .707 MAXIMUM - - - - - - --AMPLITUDE w C ::, 1...J a.. ~ I· I I I I I FREQUENCY F I G. :29 . VI BRATI ON ~ESONANCE AND DA~ PI NG CUR VES . THE OECREMEN T FA CTOR 6 I S .:; I VEN BY /H 6f • 0 = 1 • 81 4 - f= n f RES RES 63 f is va:t>ied t~ou.gh one/ ~f the natural fX'equeneie$ of the sys:tera. '11.heory ind.ioat~s· that the .me.ehani·o al <aamp;ing ot re.a,onanoe cur-v.'es can be readily d.~termined from theizbrea..a.th., If t l?ep$>esents the breadth <>f the resonance curve at half tht maxim:u.m a.mpl:t tude,, then th~ d$1r1ping ~ :ts given by where the :reeonant t'requene¥ f:i;~ea- and the ft-equency dif' te:rence of the half amplitude points, r½ , are mea.s ured. in eyolea or v1b'l?at1on!!l per second. A seoond method o.f measuring damping requires that ose..i llations be . established, thE9n be- allowed t -o die out by disc.onnectj,ng the driver. lt the amplitude of suce.es;. ~1va vi bra t1ons a.:re observe;d. by the use of a cathode ray oscillograph o~ equivalent; the damping may be dete~.ni:1ned wheve An and An ..,. l are two ccmsecutive amp:.U,tudes of the free v-ibratiou. . WhE)re the fre.queney ia too high or too small ·tG make pQS$ible this measu.r$mentt the damping may be _d~te:rtn1ned from the time required. for the amplitude of' the resonant oseillation tQ fall to one half its original value; by the relation 64 B.693 = t7·f -2 this ti me res t½, or even the product t½ f res, may be de ter mi ned di:reotly by tbt, use af e l eotzon tube ind i .... oat o:rs , even wi th very high £:requenoy ose:il1at ione, ( Ref' . In bax 1;., cf f ixed geome,tty, f aul t a o:t' a ny kind in the mat.~r :'1,~.}. qombin~ 't o r a:j.se th.e dam.ping , eo that oavi ..: . . ,· ~J-~·: ~-':•· t ies.,. oiaalts a nd poros ity are easily derte:min.eeil. In s pot·~te lde; lar ge d i ff er encas of' geometry may exi st, in addit io n to possible craoka or poraaity , and cas t and wrought a .l loy, as we ll ae pute aluminum cladding, ate pr e s ent s i muJ.taneously. Th-e eef t, nugget rnat.e1ial tende to increase da mping , and a. c hange in nugge t volume could n ot ae d i f fe:rentiat eo in tests .f to m the in troduotionoof or a o.king. Preliminary tests ahowed dampi ng indica.t ionis to de,pend u pon too many weld. properties to serve as a re,. liab l e ind ic a t o:r of spot.weld p:ro pertiea.. Fur thei devel,op- me nt of the method \1as p,o e tpon:ed while s impler tett methods we:re exploited. 2. W~ve Refleotion Teete(i) lt ha.a been proposed that the a rea of bonding of epotvte l d !:: mi ght be me asured by supe r sonic wa·tres • which wou ld reflect fa: orn the .faying euxfa oe of un bonded :re gions, but wou l d pas e through t he fs.ying s ur face at the we ld bond• Fo r one e i d e tee t me tho ds, t he pr esence of bond i ng mi ght 65 be dete cted through ( a) the f requenQy at which standing waves ( half wave :ree onanoe) co ul d be established bet\'ween t e oeci lla to:r and r ef lee t ing eurfaoe, Ql' ( b) the t im.e requi:red :for a wave t;rain to :paes from the s end~:t to r ef lecting surface a nd return. the (Se e Fig . 30).11 A :f ine development of supersonic testing eq ui pment ha$ bee n ca.rt1e d out by ? :rof'ee eot Jr. A. Fires tone of the Univer$ity of Michigan. Ii:i.s eq ui pmen t !)l'oduoes th:ree wav e ty pee•,-longi tudinal, shear, and su:rfae,e ...... and pxovipee sui ·tahle de t ection and reoo :rd ing equi pme nt. • Us ing his Su ?e:t ~onic Re.flecto:;pc ope t l?:r .ofee :s o:r: Fires tone hae di s ting uished a e :pot whi c h i s \~ elded fto m one whi c h i e not bonded a.a follows (q uoted f rom a le tt el' fro. m Professor Fiteet one); ''A wa,re t;rain of lo ng i tudinal waves i e sent in a t the u pp er face of the we la. ~~ he weld as-.. s ernb l;y is ao thin that the f irst :tefleoti.on !rom. t he ot he r e i de of i t c annot be distinguishe d bJD.t the waves reverbexa.te back and forth through the thio~..n eeli; of the weld a.saembly while t he tot a l d i s tance of th.eir travel k>a.ck and forth may be eeveial i nohest Thei:,; suo oer:, sive i mpingement Qn t he e:rye tal ganera.tes a voltage whioh can be observe d on the r efleotosoo pe sor een several inches after the sending out of the wave train.. 66 0 lf, now• one ho lo e his, o- i ly f inge:r a gainst the bot t om face of the weld, these sue·ceeai ve ref'lect..i ons ~vill be damped out, thereby prov i'ng that the waves a.re rally ·passing th:r o ugh to the bottom .f'aae and tQ.a t t here i~, the;re:fore, a we ld .• If the re ie no weld, a s imilar se iiea of eucee$&ive xefleotione is o beetveo, but upon touching Uie oily :f ingeI to the bot tom face of the weld th~re ie no change in the appear• ano e of thE? :refleotogram, thereby prov ing that the waves a.r e not eQ.tering the lqw:er plate~ Thus f .a .r, the method is not quantitative, 'but merely all or none. One can imagine i mprovements in the method as the %eeu.lt o:t' reaea.reb. which would imp:rove i ts u.s efulneee. The a.bove•mentioned tea te we,:e made with p... megaoyel.e 10.niitudin,al waves; but we have ptoduc ed aa high as 20 megacycles and we have a ls o .pro d uced sheal' wa:vee which travel he.lf as fast as longitudinal waves eo that tb.:ie rep:reeents a fa.eto:r o:f 8 re duct ion in wa-v:e lengt h. V 71th theee sho,rter wav e leniths. it mtgh'tl be pos "'" sible to aQtually explore ove:r the surface of the weld and theieby de termine the aotual 'W elded areas . 'l'hie would be partioularly feasible on the heavier gagee. wher.e the weld ie oom.paratively la:r ge. One oa n i magin e sending c.o mpara,ti ve J.y power .. ful QQntimaoue waves t hroughtb.e we ld a nd have the bac t{ Gi d e coated with something like· paraffin whic h would be melted in those areas where the wave ene:rgy was being xeceived and would thexeby outline the welded area~; We ha,ve used lonij;ltudina.l or. shea;r wa~es for the a.oQu:r a te roea.aurement of the thic knee s ot • a ~heet when. one side is inaeoeu; s i ble usi.ng the general me thod of eatab l if-?bing a half.,.wave . reaon,,. a.nee th.tough the thic knesij of the plate and then d eter rnin.:j.ng the f:c equenoy. 'fhis meth(,d mitht b~ applied to weld testing since, i f ther e is n o weld und er the ar.ea bein g tes.ted t the thi ckness thus indioated would be a pproximately that of one a 1eet, while if the weld exists the tlliolcnees is -approxi- mately that of t wo sheets~ we oan a.ls(:) produce aurf'ae e waves whioh xun over the su:rfaoe of a metal part in muoh the same way tha t water wavee tr avel-, s u:r:face wav ee could , be eent a. long the lo.we:r face of the upper plate a.rl<i .refleqtion obtained fro m the closeet poin t in the weld , even thou.g h that mi ght be in the cladding ." Pr eaent indications a re that detection of the a rea. of b4>.~1'ns ~, -@; S!,!O't\ltl4 at. th~ te.yins s~t-;i~~ ml.g ht thu.t b$} t~~td,hle by S'Q:.p ert"$'~lli(! ~~:S t~i~, but t h~ t.bilt:• ~t Sl1lW~.$liltll.~ ·t •trt$ to di $.Jijt~inrln.~it~ b~tw1&,e:n @$8:t ~ll~' b-~ni.U.ns &.M Ale:l~lit t)~":td1tat ~ $ n.o t JO,f; b$'$;l1 Q~~onst~-t-:tt$<;4t ~M~~, 'W<>\'!ld. -~~bl.f LUttwite,, l}e. so~ t1tfi.(fuJ,tr in <tettleti,n i Wl$1d ~~~g~,1i ~1 \"14V~ v~fl:e$ti,Qn ~•tb~da. .. ". )llir,-11 ,TI ., 1• ·~~~fJ'1 , , !i$tt•, tQJ\' t.u 1lt$p,e\tl~ et fflll'J~lmi&.'14.I J $~Wal?t·e nlt "ttltf)tl.C\Jl t -t ~t iJt~ dlt•ti ~nia; •~tm t"'- be 11mttu t~ 1,f(lt~tt1~(¼m~nt1 ot tt,1~, t~t:a1 boiid:ed a~ea ~'o t;b • ta.71~. ~Wf.f:lQ~ ')h~- tw'i:'A•·tide ~ltctr!o,a l fJt$t 1u3,ke.a tb.1$ mea:1ul?~!t~nt w!tb aimiple ttB-t t.n s ~q,ntpment,, /!.\nd; &ifl@.;fj th1t filt}~$~,em$Uf(l} $..lQ'O i~ not ti);- ~~11-t ibl~ 1~108• t1an- ot t -p,o.t w~ln $'b.~(ln;t!\\1- nt: ~l$b.Q1~Stt-ct d$'v~lQ~nt ot au~t"'$@r4e t:eBt ~qu1pnwnt !\(a~ be.~n :1-.n,~ luded iii t b1s w~.. $f Jali'-et'.t !,l"~~·t A.$$:tltijll\ij $.il itt~l h$.ijH~i•~t~u:s w~J.r1 rt,l$S$:t tt flat$ te.n~d. $ph$1jQ>1dal. itn~p&,; (J.n(}l~-, ~d w1t1'1!.1~ ~ ll.~f!ittUO'i;l$ -.:se o.t h&;v:ftf, t••t~~,f¼'i p~QPfftt_,, dltf-<a1.l'l.0 nt tv·~ !)$.~~nu mtt~l wt t h ])h;t$l .o a;i t11~$~ ot .tb~ ~l.4 nupt:1',, the ftte~>utn.ey ,t 11tttura.1 os:e11J..~t1ottt Gf tb~· wiirld nu:~fat ~taf b$ ltt1tr'Ulfit$.'1.♦ l ·t haa b~~n p~0Jf;.l$.6d t• ·~$1 le- wen ntagfge~ G:li!<.\.ille. ti.On$ by Xl'ie~us qt qu~~,~ ~,r-t t~l e~;1pl~t ~e the eiheet ,~~f~t oe, at by .a n ui.1 -•P.t· e.nd at·te~ €.l. 69 f i:xed e.:x,a i ta.ti on pe;r iod , to us e the s ame c xys tal ae a detector t o obsettv a the damp i ng o.f the free osoil l ;,a,tion1r Oox-rel1;;t,ti (ms between natu.r-a.1 frequenoy and nugge t e ize , ' and be-t ween dampin g and duc tility, o!a.oldng and porosity have be en pxeo icted, This teat haa not se ~ro.ed suffi cient ly feas ible to jus tify development. Weld nuggets a.:re of very irregula r sha pe a nd have internal inhomogeneities and detects~ - Weld nugget V'Olume does not meaeure we ld st:reng t h pr eoisely. The difference between nugge t and pa.rent me ta l p:ro pertiee ie not euftioient t o :provide an ef'feo ~iv e dit,Jaontinuity to the f low of vib;ratitjm t:inergy. The natural frequency of nugget oscillations would be extiemely high. Effeete o! adj a cent mat erial and sheet geGm~try mi ght affect t eat indicat;i.ona exoeesively• ' Si mpler tes t methods offe r roo:e pr omis e •. 4. Ul,t,X{z; So.:1;10 Wa,v e _Pfl, t t~:rn ·rest 1 (¢') Thie test differs tr,om t h os e previously outlined i n the method of application of the energy source and in the method of pic kup; A moderately high ultrasonic frequency has been used (a bout 1,000,00 0 vibrations p er e eoond) to obtain hi gh resolving p,n11er by the sount waves. •rhe sound is tr anemi t ted fxorn an u ltras onic gene:ratol' to the sheet surface below a epot-we ld by an 70 anvil and the ·v ibta.tions t;ravel through the weld to the uppe r ehe et suitaoe. If oil or other l iquid ■ are plaoed there-ont rad ial circles centered over the weld will be obsarved. These axe standing wave patterns th·e con- figurations of whio.h may ind iaa te the bonded area. of the . weld .. By the subetitutian of a material such ae 001 ... lodion for t he ind icating oil, a pe;rmanent record o.f the we ld has been obtained. The results so far obtained on thie test are not oo nelusiv~ but the method shows pro.m iee and should reeeive :fur.th.er consideration and investigation. • Ad v.a ntages - The weld geometry oan probably be determined f;ro m this te e t, through the analysis of the wave ... patte:rns px od uced. Obvioue ly if lit-tle or no me chani cal coupling exists between the upper and the lower sheets at the we ld, bonding at the faying plane ia lao King and resulting patterns differ from. those denoting satiefaetoxy bonding condi tions~ J:?:i.sadvan.t~g;e,a o.f this test method are; ( l) The equi pment neeei,sijary for the teet ia rather ela.bor .. ate , and i .ncludee an oaoilla.tor capable of suppl ying about l K. W. a:f :radio ... frequenoy power to the ul'ttasonic generator, which in turn hae auxilla.:ry equipment neCe$..,. 71 sa.:ry f o:r continu~us operation. Thi io auxilla.ry equi pment is eo mewhat compeneated i'ox by the stable and :reliable ope rat i on eeeu:ed* ( 2) T:r:aining 1$ :requi:r ed f o:r one unskilled in th is method of t esting to :r e liably interpret patterns in terme or· weld quality. ( 3 ) Eriors ·may resu:i.t i'xo m poes.ible dispere ion effeots a nd va t ia.tion in tfeatment and/or ao mpositbn of material to be e:xa.mined, (4) The c·ou pling anvil should be pr operly oentered on the bottom indentation to eec-u:re unifor m. meona.nical eoupling, an.a anvi l oontouis shou l d fit' those of' the weld indentat,ion 11 ' ?. Sheet $1,1:rface a;nd, Mater i8;l P;r o pe~_tz Tee ti,; It ha.a been eugge·s ted that spotweld pto pex-tiee mi ght )e c or1:-elated , ith conditions measured at or nea:r the Sheet rnxface abov e the weld . PtC3pert ies ineluded a.rei sheet sur:t'aoe indentation by welder elect:r: odes,meaew:ement of ~urfaoe marks oi oonaition, thioknees of Alolad layer, t ough1esa, ductility, e lastto1ty, impa.ot- :reaieta.nce, eo:,:atch or ~e ar resistance, and rnetal l ul'gical. st:ruoture at vari ous d epths 7rom the sheet s urface at the i" eld . 1. W~llile;r Eleott o(3e Ind e.n. t~~.1.on Te~ t$ (Ji) Indentation of the $Urfaoe of the Ale.lad sheet ~y the welder electrode ie a :t'unotion Ci>f eleotrode eiie and shape, weld current and tempexature t.raneienta. preeaure progxam; and sheet pr ope rties. Vii th :r:easonable eont;rol of current wave shape and electrode tip oontouir, a.nd precise co:nt;rol of timing and ampl;itude of tb.e tip p:cesaux e , the $he~t ind en tat io.n wi l l correlate we l l 1d. th weld nu i-et ~ize.- The l a r i er the volume of melted alloy, the grea ter the in.denta tio:n cauaed by the tips,. provided the pres sure progfam ie p r e oieely contl;olled a nd sufficient hold down p:r e seure ie exe:rted to pievent expulsion of metal at the faying plane,. The s b,e,e t indentation may moet easily be mea$ ured. through the uae of' a sensitive dial gauge graduated in ..,0001 11 unite, 1~rovid cd with a suitable collar to rest tbn the s r1eet sur.f ace jus t outside the indentation. Edd y cu:r- rent or eleetri.cal oa.pa.oitance gauges may be employed, a nd p:rovided with permanent :c e ooid dev-ioee if desired. - Inh~J$nt _exxoxs in t h1e t est method xes ult tr om nor, ... m.al p:r octuoti0n conditions , to an e:xtent sufficient t o invalidate the tes t . Lar ge changes in electrode shap ~ and con t our pr od uce oor.reapo nctingly large changes in indentation, although the eff@ot of :repeated ti p oleaning in a few houre rlil1 on the a e l of tips ie not extensive. Changes in ' ti p pressur e , or in f o.rf$e p~e s eure time d elay , change in• den t a tion gre a tly. Tb.e eas e wit h wh ioh tip -pressure and cont our may be changed in prod uction welding would prevent t h i s t est f rom attaiting reliability. As control of weldin g conditions ,imp~ovee, tip s hape and presa u:re p:r og:ram ,vi 11 be more preoieely controlled, in. (A) W~VES PASS TH~OJGH WELDS AT FAYING PLANE ■ I~ t+ : • • + t ,,,,,,,I + 3.5 • • 4.0 4.5 5.0 5~'5 1 6.0 6.5 - - - 7.0 _______ - -· -·--·-·-· ..... ----- · • : FIG, 31 ■ ELECTRODE AND STRENGTH, ' INDENTATION OF WELDED SHEET TEST OF SPOTWELD SIZE 7.5 . - - - -· -·-- - --- - ---1 ·- - - - ·- • - ·· · .... _ --- ·- 1-- - • • 7 ~ • - -· -i-- • _j ,,,,. : - ---- •/ , •" INf'ENTATION BY UPPFR ELECTRODE COOi") 3.0 i • ),,"/ • ~• ~. I_ t ____ •,• : • Y:- - - + - -...L------t-_______; __ __ __ _ , ,.,,+/ ' 1: ,, . . .• . ; 7,,, ■ t: . • + .d, /t-:: + t ;. . o (B) WAVES REFLECT FROM FAY~NG · PLANE WHERE NO I ,.;-•~ I+ .. 1 8 v~ ,, WAVE REFLECTION TEST OF BOUNDED AREA OF ;: :1 i/I I I 1 400 I * u. er <l 5001 w er 100 :::> ~ <( 600 I ~ 30 ■ 80ND EXISTS. 900 :::> 800 0 z v, ,I'\ rooo FIG. SPOTSEL0S ■ A •.,....--s ouR CE /\ NO f>ICK Uf> UN I-TS - ~ ~ '-r ✓ ,?- ---- --- _ INDENTATION OVER LARGE WELD SCIAKY WELDS IN ~040 " 24 ST ALC LAD. 0. RESULTS OF INDENTATION TE STS ON 1 41 C. LARGE 6. SMALL LUDENTATION OVER SMALL WELD A, DIAL GUAGE WITH COLLAR C· r-- ~ B ~ . " " ·- · . .0001 OIVISlON S 11 SENSITIVE DIAL GAUGE PR OB E-\l-= ~ .J., A 73 whicb, oa~e the v~lidi ty of the . ti p iadent~tion teat wi.11 i mpiove. (See :ti1 i gure 31 !Gt .reeults of indentation measu:t<EHuente en i:eiduetiia.lly mad(l} welds) •. 2~ gg.~e.t .,S'.'4-~f,a.ce P:r~ p~;i:tz Tea~ rJ-i 1 No m<aasu:r;ement e of ph.ys ioal pJopettiEH;, of the e~ee;tt sul'fa.oe layeie have $hown any corl'elation w.ith w·eld size or q ualt ty ♦. Mar king or thi G kne~ s of the A lo laid la.yet have no signifioance wbateveti, The sttuctuxe and metal.• l ~:rgical pro.petties et the 24ST allgy are very li·ttle af;;. fe oted except in the ·weld nUijget and naxrow adjacent :r e .... g i ons where ineip:Lent meltinf;;', along g rain bound.ariee a.no Only mea.e u.remente 01.· pro... int:r:u~ ion of et;iteet io oq,QUl:• pett ies i n and a.dja,Qent te the weld nugge.t. cortela.te with weld ~tre111:rth and quality. Superficial surface teets, meaeare nothin f l!itnif'ioant e:xe .e pt when the weld nuggets penet1:a.te to the she.et s urfaoe ( e.xoesei ve penet:r at ion) ., G. lJnt>,r~~a:O,;I\', ():t J?enet:~tQ ;c \t~~.t 2 ; In these tes ts a loa.d~a pen,~ t;r ator ox gtou.p of penettatoxs is. forced in to the welded sheet above and/or below the el)otweld t o euch a <li~tanee that :12r<:>per~ie13 a.n.d .e,ten,t ,ofv tne ao._t't,ene~ Oa¥3t ~llox of ~.h,e ,v.r<r,ld n~('l~e~, :rather than of the terap$l'.'ed pa:r ent lliletal, de:t.exm;in,e 'the deAJth o.f. .p~rietra.;tion. I . . . .. .. ,. .. . .. . , . Any other type of penetrator or ba;rdness teat ha.e little e!gni:f icanoe. It has been 74 round that the tempe:red pa.rent .metal ia :reasonably homogeneoue e:xce pt in a na:x;row zone e.djaeent tne weld nugget where i .n<Jip.\e. nt nelting and intrusion 6-f eutectic ooour aleng g:rain bounda.rieei, CYhile on the othe r hand the enti.ie volume at the weld nugBl®t ha.a be~n very appreciably softenGH:il • weld nugget geomet~y . Me.nee penet2;atox teste meaeµre By profiling the weld region with euitable p-enetrat ors, the shape of the ·w eld nugget, can be mapped quit er 9.0curately •. rt e ld nugget geomet11y :reliably, it must be noted th.at meaeu:re~ nent s f rom the 01ater surface o:f the welded eheet meaeua;-e onl,X the ge ometry of the outer bounda.ry of the nug~·e t in t!.1e sheet under t est . The natu:re of the ~ond at the faying @u.rfa.ae, pa:r - tiaularly vlheJ:~e eiQJa'ss·tve ilclad inclusions exist, i s riot 1 :~ one aide of the weld~ Inherent eu:oria in penetratoi tee te re~ ult T x om , (+) ill• tiom.ogenieties in the oompoa it ion and hea..t treat ment ef the ar ... ent eheet {2) varia't ione in the thiGkne·~ s of the cladding layer of pure aluminum. (5) inseneitivenese with we ld nuggets of low penetration beoaus,e of the tbiok layer of parent metal througn ivhieh the penetxation test must measure nugget geometry. 75 {l.) .'.11he method is feasible for either one er two aidt1 testing. (2) the test a.e.tually measures nugget geometJ?y (nugget diametel" is the single weld parameter whieh eorr-elat~s re .. liably with the static she 1rtr st:r-e.ngth of spot welds); ( 3) indications are ne arly instantaneous.~is!l;.dya:.n t~s~.s, of penetr a tor tests a.re: (l) tfue test be"- comes insensitive with thin nuggets (2) oQnditions at the faying plane are not measured.,, l. One•Side,, One P9i_n~ ftH).~t.~a..tor _Test _. t In t h :ls test, a. single penetrator is fore.ad into the sheet sur.f'aee above the center of a spotweld, in a manner similar to o:rdinary hardness testing., but applied in this case to & non•homogeneou.s st:ruc·tur-e . The change in pane .. tration between t he application or a preload (sufficient to force the penetra tor t hrough. local surface regions) and applica. t.ion o.f full load ( sufficient to force the penetrator into a region where the weld nugget aff ects penetrce..tion) 1s measured by a sensitive dial gauge " The one point me a surement te-nds to mea su1"e nugget penet:ration at the cente:i"' of the weld . ( See Fig . 32) . Nugget pene+ t.ration is 1nd1;rectly correlated with nugget volum~ and diametert for welds made with similar elect;rodes under similar welding c011_di tions" He nce t h e one point penetra- tor test predi,cts weld strength only through a. chain of F ~ ! ~- 0\'< ·•.••.•.·>-d,L ' K•§f§,•' - '-~~ ;• .A -=1 ,· ., . 8 • ~;- APPLIED.· ·" ! • -~· • .- FORCE: .'. ~'. • • . •'.~. -. ,.• ' . / •. • .~~.:.-:. I . ...; _;'..- • I .• ' • , r • :_ :,, ·, ' • " · FIG. 32• ONE POIN;TONE ..: Sl ,OE -:ff ENt'TRATOR ,lESTi>F SPOT w.EL o NuG .GET PE,N e T~A r 1.oN ; -· •Geeii'ER •INoe'N"i-AtioN s • Re...su.L r qvrn LARGE . •' '• ,'. NuGGE Ts .. (A) THEN< ov.eR sMAl:-L ~LJ:c,;Gef s {B). . ~r. . ., .·. • ~ .• ,,. .:45 · . so 55 ·so ONE POt'NT PENETRATOR TEST, INOICATION . ,• 4. ' . 33, RESULTS O,F ONE .PC I NT ONE S I OE ? ENE TR ATOR 9F. llll SC I AKY ,rt:,ElDS IN : 040" 24ST AL CLAD·, ,F I G • TEST 65 76 eot-relations. with weld nugget diamet.e r. '.?rec~utions to be observed in applying t b.e one point pene• trato:r test are; (1) The penetrator must be very carefully located ovell the eente:r- of the w~ld nugget (2) The- shape and size of the pen~tra tor mu.st be .fixed and. constant (3) The conditions of loading must be controlled accur&.tely ( 4} Tests must be made on welds all of which have been made with id.en~ t1oal 1elder tip size and oontouir,. attd on the side of the shee t which wa s in contact with a pal"tieula.r electrode tip. ;Inhe~~nt Ex-ro~s ~f t his 1w:>'thod :tncludet . . .. , (l) Errol:'$ due to the la.ck of a reliable CO!'l?elation between nugge t dia;;. meter and nugget thickn~ss (2) .E;r;ror$ due to unsymmetl~ically shaped nuggets or nuggets whose ·cente1:'s are displa.eed f'rom the .faying plane (3) E;r,r ors due to inaccurate po sitioning •. ~dvapta.ge s of this method have b€)en listed under pel!'letra:• tor tests. 1f d~sir$d • . ~· Standard hardness t~sting .ma chines may be used This test nequ1~es access to only one side of the work. p:t,,sa.<1vanta.5 ~e of this test are (1) i .ts relative unrelia• bility, due to !ts i ndirect aorrelatl.o.n with weld nugget diameter, and (2) its i nherent errors. '.tU~!.~~l ~~sults ef on,e .. side:t one point penetrator te-sts made on industrially made spotwelds with a Rockwell Standard Hardness Te sting machine as penetrator a.re shown in Fig, 53. 77 2., G;µu~t,tetP..tlPtts Ty.1,0.,.310.e,, O:n_e Pfit1.;t _P~n~tr..a~of ~Pe.st!• :I.tbi s test method differ$ frora the1 omi.,,,aioA1l 1 one point test only in th.at simultaneous penetration t~sts .from both shee,t surfaces are mad:e on the weld., This test ha s t he .iJlight a.dvant.age of cheeking symmetry wi t h r 'e spect to the faying plane and of detecting we lds with ne arly all the weld nugget on one sicle only of the faying plane, However, it requi.:res a .c cess to both sides of t he workt 3t :J?~net~1;;ttor ¢' .. Pl'Qfll~ T~$:l;Jh . , T.he penet1?ator px,ofile t;es-t ia the most :reliable method of determining weld !ll\lgget diametet,, ·s hape i!lnd penetration .• In th.is test a su,5. tably l .o aded penetrator ear-ries out a sueeess:ton of measul"ernen ts o.ver t he sh e.et ~mrface above and/w below the spotweld~ 'I'b.e shape of' the nugget alG>ng an_y see-.. tion can be determ:tned by penetra tol? ,profile ma,asur .e ments along a line over that section.: (. Se-e Fig• 34: for• oharacoi!o . te:ristic. penetrator prQ.files of' spet\Velds i n .oe4 tt 24-ST Aiel~d. She-et),_ ;tnereHl$~d s{?n$.1. tivt ty to weld nugget geome try is <ibte.in<:l,€1 w1 th penetrato;r p!!?of1le tests as sheet. th+ckness is deereas,ed . F1rom _penetr-ator profile maasurements 1 nugge·h size,- sh ape I and thio.kne.s s oan be cletemninedt instead. of a succe-ssion of' point penetra tie.>n measurements, a con~ t:inuous profile by a rolling sphere e:r wheel following a. · linear or spiral pa.th nw.y be used~- Si :mul taneous two.... s:1.de penetration pr.G.f'ile t;-e .s ting is .feasible under some coi1ditioni __ D 35 r-3~B _ C 30 r - - - 25 - - - E B A F _§___ Ii__ __I_ - C D E F G H g 351---- - ~=~ ~ - - - - - - ----,, ::::::-_ ~ 20 ;---- - 15~ - - 15 10 5 0 ______,,.._____-../_____ll!l._ 35 A ~ ~ A~ _B__C__D _~E ~_F_~G ~_H_ _ :~! '~ _ 15 - - -- - - - I I ,o~ I - - -- - - - - - ~ - -- ~ ,. • ~ ~,;_____J I A B C 35 30 25 20 15 10 5 0 B C D E F C _p E F G C D E G H - - D E 35~-- - - - - -- F G H 35, 301----- -- - 3Q L 251---- 25 :201 1510 1 ~ 20 1---- -15 1--- -- - ~-.:c--- - -./ -- - - ; 10 1---- - - - 5 5 0 -------.._,--~ 0 B A - - D E F G H A B C 35~...:...:....--='---=----''-----=--- -- -- , 301---"<-- - - - - - - - - - - - :r-----1 251---- ~ - -- - 20 1---- --"""=----==,-.~_,_ 151---- - - -\0 1---- - - - 35 A 30 25 20 15 10 5 5 0 0 FIG. 34 B CHARACTERISTIC PENETRATOR PROFILES OF SPOTWELDS F G H_ I ~ 78 Pre~aut_iQns. (1) '.i'he eingle point penetrations nrust be spaced sufficiently far a.put to be independent of effect$ of precedeing penetrat.i ons (2) Roll1.n g profile units must be very rigidly n1ounted to .avoid de.fleetion due to the large f'orees ~equ,ired t.o move t h em OV$r the work . (5) Rea,ul tant grooves must not cause tt "noteh effect'' to weaken t he welded joint ( 4) Sensinive measu;r,ernents with ~espect to the sheet surface, a ccurate to nearly 1/io, 000 inch,. a.re req'Uir@d• AdVAA't:;ages of penetrator profile measurements lie in their . ; . complete mapping of weld nugget geometry. P1aa_dv~:u~t~gf4s of penetl?ator pro.file measure-menta. l:te in (1) t h e complexity and accura.-c y req;ui~ed in suitable testing apparatus; (2) the time required tor testing, (3) possible weakening of the joint by grooves . 4. !t'lult~.~O:i.I,1,t O;r' £: .~re P~pv,tra.~;O~; ?,1~-~~S, • ¢ These tests are designed to obta!i;n the significant in• formation of the profile tests, with simpler equipment,. A direct me a surement of nugget diameter is made by a s:uita.ble ring impresser o:r ei1;"'cle of point pe:n et.r ators ea..pable of de.te;r,m1n1ng whe-ther or not t he nugget lie$ under the cirele of' penet.J?a toris-. (See Figs. 52 .. ec, ;ln9i • .,. als'O Section ;V) ~, If t he nugget is smaller t han the penetl"•a tor circle, or has excessively low penetra tion (0"'20%' ), the penetva tors indicate only par~n t me~ .l to be present,, If t h~ nugget diam<;,te~ _, . , 79 app1~oaehes and pisses that of the ring., penetrator in• dleaticms detect -this change sensitjvely . Al l nuggets of diameter mu rih greater t han t he ring d.iamete.r, are. recorded a s la!lge nugge ts. For any sheet thiolrne s s, the range of very high test sen.si ti vi ty can be ma tehed to ai."ly chosen weld nugget dia.'lleter by sele ction of the appropriate pane• trator :t'ing di ameter+ One ... s ide o:r s.i mul taneous t wo•side t e sting is f e asible. The accura.ey o.f measurement 0£ weld nu gget diamet~r and of -vveld strength is nearly identieal w:t. th the aecu;r acy with which weld st:i:·ength and diameter can be corr elated "to the diameter obse.rved by destru.ot;I.vely see• tioning the weld nugge t. 1'' -, ( See · ig . 41 and :t'1 g . 59),. l Precautions to be obse:rved 1n applying ring pene tra tor tests include; (1) 'l he pene tra tor a .s:seibbly must be accurately centered over the weld nugget. ( Wl-2.e faet t hat the nugget does not always lie directly under tne indentation ° dimp1e 0 on the sheet surface int:roduces t h e l argest e:r:ror in this measurement). (2) 'lhe size, shape, and a rrangement of pene - t~ato-:rs must re.main eons -t;ant (3} E;t'fE;Jcts of v :.,,riations in shee t s.emper must be compensated... :[pli~r ent er~~o~s are (l) an error of incl:eas1ng magnitude with decreasing nugget penetrati on t• due to decreasing test sensitivity,. '"iith l ess t han 20% nuggot penetrati on, test indicates no nugget. I Rowevex-, Alclad i ncl u sions a.re usually excessive, and weld q~al i ty is very u:nreliable with such r I , I I I I I . .,.. ....,.~. .. LEAD SHEET INE GRAIN XRAY FILM WEL OED SHEET F IG. FINE GRAIN XRAY FILM ELDED SHEET F I G. 35. RAO I OGRAPHY OF SPOT WE~D.S. +-IONIZATION GAUGE 36 . AR RA NGEM E NT O F E QU IPMENT F C R ION IZATI O N GAUGE TESTS OF SPOTWELDS. 81 Tests of equipment built by th~ General Electrie X.. Ra.y Corporation and tried at t he Glenn L-. 1'i'iavt1n Oompany in Bal t ... imore, Md• as well as research at the Taylor Winfield Company (Ref. # 4) of VJarren, Ohio and the Alu.rn1num Company of amerioa {Ref. # 6) at New Kensi ngton ,, P-enn. indicated that the radio• gr aphi c ins pection of spot welds on fine grain film wa s p1r-ob• ably feas i ble., riios-t radiographer•s- do not believe fluo:rose.o pic inspection of spotwelds to bo feasible because fluoroseoplO so:reens in use today have a grain si~e some l0,000 times l arget> than fine gl"ain x _,.ray film and because i mage intensity differen ces are t:;ma.11 . Ionization gauge inspection is like• wise con sidered very difficult because of the complexity of spotweld images ♦. 1. 1/e.l d OU'bl.ine Test ( Ref• 1114) In t his test, a fluid cont aining radiogr aphica.lly opaque ,materials :ts caused to penetrate between the we lded sheets at the faying plane . 'lhe penetra ting qualities of the .fluid cause i.t uo cover the faying plane up to the very boundaries of t he bonded zone at each weld-. I.f t he joint i s now: exposed to x.... rays 1 while the i.mage i s rec0rned on X"!',r ay film or viewed on a fluoros ·c opic screen., the welds appe ar as re gions re- la t:tvely transparent to X"!'rays surrounded by mare opaque 82 are:as. The outline of t he actual tota l bonded at-ea of ea.ch weld . is thus detected readily . Pre~au.t1ons to be obser ved in a p:;<tying t h is test are (l) The flui d carrying t he ra diographical ly opaque . materials rtiust not damage or e()rrode t h~ a luminum sheet, • nor should the joint be spread in or de:e to i n troduce the fluid, (2) Reasonably constant radiographic density should be obtained outsid.e the we ld region,. (3) '11he fluid must penetrate to the bou.ndary of t he bonded area of the weld; and into any inte:-rstices between bonded Inherent errors may result if the fluid .fails to penetrate to the boundary of t b.e bonded area e.t all points .. The contribution o:f' t he corona bonding to weld strength is not ne ceesarll;y measured. f~dyant$lg~s of the me th,od a:re : (l) the total area ·o f bonding oan be measured :relif::lbly (2) exposure conditions need no'!; be precisely oontroll~d ( 3) special fine grain .films are not neca" sar-, ( 4) x. .•:r,ays from stan dard indits• trial equipment (30 Kvp to 150 Kvp) may be applied, Disadvap.yase~,l_ of the method a:re: .The inhere.nt e,:-rolJ listed , (2) the add1t1on a,l p,pePations of' flowing in the fluid befor e exposure and of cleaning the sheet after exp osur-e'- ( 3) the added cost of film and delay of develop.- 83 ing film, requiring ident:tfieation. of welds ( 4) Sl possib le hazard to inspeeto:re if fluoroscopic visual i nspe ction is employed, without adequate precautions (5) relatively elaborate equipment and skilled operators. are requ.ired,.-:: ;o Careful tf;lsts o:f this, me t b,od during this resear ch have s hown ths.t the ext ent of penetr 1:1 tion of the solvent through the corona. region of spotwelds is very variable. Trials of all available solvents 1 with suitable dye indioa:bors:!! with many methods of flowing the fluids into t he fayins plane (vacuum and pressure techni que s , supersonic p:umping 6 he&,ting; etc~) hav~ shown th,11t some w.e l de permit the .fluid to flow through the corona re• gion ( even whan appreeiabl~ eorl,lns. bonding is present) while otn.er welds of ident ica1 strengt h s top the fluid a.t the corona boundary . Te sts on several hundreds of welds indicat ed the fluid outline to be a. poo:l? measure of' weld 'bondtng and a misleading -indication of weld strength. In some cases., t l1e flu i d and dy0 pewr: tra t~d to the inner extremity of the 1 lclad :inclusion i nt o the weld nugget, Haa. this been universally the case, the me t hod woul d have been exceedingly useful, as it was the only non♦. destructive test whi ch ever showed promi se of indicating the extent of t he Alclad inclus ion into the weld nugge t. 84 2. ~~dj.os,r§.phie } 1es~~B ( Ref. //4., #·6, #8, -#9, #10)¢ In the .s e tests,. the welds are subj e ct.ed to irradiation by oar•efully controlled low volt.age x .... ra,ys and t h e ·ield i mage. is recorded on fine gra i n photogra.phi¢ film placed b ehind the welded joint. The X-ray· voltage s hould be: stabilized t0 plus or minus ¼ KV .• , and should be selected to obtain maximum F-ad iogr ap.h io eontr a S1:h ( Twelve Kv. x..rays pr oduce a.pp:reeiably greater con trast t han 40 KV . x...rays ( Ref. #9),) The ef'teetive f'oce.l area of the t ube should be small i.11 comparison with the target fi l m distance. An effeotiv0 foea1 area one mi~limeteJ? square vfi th a 36 inch ta.1•g0t to film distance has given -a cceptable defin1 tion with standa.rd i ndustrial X,;;.ray equipment ( Ref. #6L. '. b e f ilm sh ould have fine. grain {Eas tman 1fype M and Ag;f.'a Superay B have been used suecess- .fully), be wrapped only in pho-to.gl?aphic pape1., wi t h 1/16 inch lead backing behind the fi.lm,. a.nd be placed re a.son• ably close to t he \'IJ eld. 1:wo Ol' three l ayers of x.....;ray 1 film can be used vli thout; appve-0ie.ble loss in definition . Exposure concU tons must be precisely contr olled to obtain optimum oon t vast and o.ef'ini tion ., v I ):., ( f>e e Sectio,n rh1s x·esearch has shown tba. t unde1° opt i mum exposUl? e 1 conditlbone, i ma ges of' the quality shown in F'igs . 66 to 67 may be obtained con sistently on produc tion X..-ray equipment; rated as high as J.50 KVP . 85 mu.at be ,~rapped. only in thin pape;r opaqu~ to light but transparent to X•rays of le.w veltage, (2) Expos~e cen• d:tt1ons and film proeess;tnig should b.~ preeisely control.-. lect~· {:$) Personnel .;ihould be p1:1oteeted f'rom X➔ rays .. Ip.h~r~n:b: e:¥."l?'();r>S. include (1) e.~ro:J;-.s resulting from inability of method to discr;tminat~ extent of Alolad. 111.elusion into the w~ld augget, Such inclusion occurs frequently with thin, sniall weld nuggets, and lowers weld str-ength appreciably, (2) E'l"~Ol'.'S :resulttng :rrom lack of def1nit.i on in ;radiographic. images of s,potwelds with thin weld nuggete, (3) E:r-ro~s in interpretation of spotweld ra.diogr~ph1c images,. {idv-~nte.g;~~ of' the test ;tnclud,e (l) 'Very eomplete 1:n:f"ormati.on as to weld straetur(:),. geomet.r>y, size and stt)ength is obtaine•d (Se.e SeetiQrt.:VI) . (2) t .h e weld is not damaged by the test., ( 3) tbe weld n<wed not be located precisely" (4:) permanent. records ara obtained. D~~~Q.V~Jlt.~ge~ include .(l) the teat requi.ree aecess to both sides of the weld,. ( 2) long e~posures ( 4 to 30 minutes) are required. with standard radiographic equip- (4} rttel~~,· o.t ' da v-e.l optne; t~ke~ tim~,,, l;lequirea id~iltlt'iL~ q'!.d ..~ n t 0ation oct"' llt:}ldel? ( 5 ) r~l.Jttively elab~."~ ·t ~ aud ~1dJ,.led opa~.ia·t o~~ ~,i~e itequ:b7 ~H.\1 ( 6) ~:r~ful 1n:til.t~.,. ·, ;i,:,~,,~tf/.Qr.1. .c,f ;~t:idioa ~phe :f'-&t;JJUl~s ot 1w ~-Q.1J.ilF-w tl •, ti 0J:tiitne. 'fie. tnvoatigt1t1 on ' •&iil.t~~~pl:iy iil?$ i.1V~n !n ~Qt.A-Ol"J --..1: . . v of epG)tw:old V!L . ,i,and VIL ~11 n,,,-».•;,o •• C ~""'J.0 ! ~"' $-'O"'• ... ,~:lo..q r:, ,~'+'•! ~p,Atf ~fri-.J~ti:')Y-,F, . '-o/eclfc aiu .. f"f •..i~.;¥'r:'•V:,~ ,~-~ i'r ~tr~r':~~~~~~ll t/, ls:~ ·th-e$e te .~ ts,. t b.1.-"I •$lds ar·~ tJ'Ubjeotod tc eJll:r~hlly c~n .l't>ll~d z,.r+~ys ,,u1e t . a :r:ew:vt~ t ~iD e a~e tr::l.f>.<t~d t~ tha w,~l,ct~d sbett., . Und.$~ opt1in.wA e ~.ncUti ot~s ; i!.'1'lg$$ ~1mil&~ 'tOI those \il.:lt~ir ~d wi. :b.. fioo @ia:tn !'iltll r?11ght ba 4 e~p~.t ,t itttl:. Mt1w~vev» t1v~il&ble fluo,r0'$€illop1e s~:r.~en'J.a aN t ~i .. t~ ~\)'~~ "• -~ ~ine-d to obta11.1 def:ln1 id.on ~1daqua t$ t"ot' :a pot • vn~l:d it1$p1;;1<11ti()n . l J.s.o t h(t ('jf,>11tr.· t:1 st betw~c;n :l;'w§l~tl $ ~t 'tb1, $pOttt~ld. ie tQO lo ~ t't)t~ $- ~ ,$1.J f't-u.011 t).s (}opi e i n $p~t1t1c~,. t~DUttin$ th1& :t.~f;ttiea~oil 1 &o ~oiani~u$s nav~ b.aen. devt?Jl.op~d ~ t ,adtH.1ius1·te .so~tw&ld rad1ogt•a·phs a.~@ obt$i1ti$d 'lt,·1 t li $."Z;,I)0(5UY'·e t ime.s &s low -~ill :e1v.~ et:H~-o nds Pl$e sia,e!I!,\ tion XIl)'f 81 P:r-ecautions arei (l) the inspector mus t be pro~ tected from excessive X-ray e:.iq>OlSUX'e, (2} to obtain r~ .. liable results careful "'da:t:'k adapta tion" of the eyes. (30 winutes in a completely darkened room) is required before inspection begins, (3) laok of sens1.M:vlty or i'ail1..1r·e to indiaate .fualts should not be taken as pr0of of weld qua.li t yi i~d,r~P:t,ae;e:3. of the method include : (1) no film is required, so inspection cost is low., (2) results of inspection are availe:bl e immediately, so no mar king or identifica tion of' v,e lds :is needed., ( 3) welds 1eed not be located a ccurately for testi ng!i J?~sadvant;ages include: {l) a darkened :room i s needed :for> view;ing the fluoroscopic screen (2) inspeetors have time delays because of fatigue. and time nee ded for "da.;rk adaptat:ton" 1 (3) access is required to both ~ides of ~he we ld, ( 4) special equipment may be required for the pr,o tection of personnel .• 4, Ioni~ation Gauge Mistpod: ~t. . ; $ . • ( . i ' In t h is t€3st, . . ' . .! x... rays pass fr,om the source through the welded sheets into a suitable ionization gauge, whi ch measm:)Gs the quantity of x...:rays p&tssing -through the sheets at the 1:1eld. ( See Fi g .. 36).. ~t- 'l~e gauge .mt-1y make l"his m~ thod is now under inves tigation by other re• search investigators. 88 eithe1"' an overall measurement, ◊l' p:r.•ofile the we ld region to obta in fln.e detail of the x ... "t:a.y i.ma.ge o:t" the weld,. 1110 ~1void lengthy exposures exceedingly senaita.ve :toniza.tion gauges a.re required:, particularly for p .! t'G• .filing the w,eld., Inhea?ent err Oi?S include {l) er:rors due t o f'ailure · ' ' .··' .,;,,-...-. , . 1,..,· .., ·· ·f • to observe :fine detail of weld in the ove1"a.ll test,- (2) possible effe cts of cra ck s a nd poPesity.t (3} error$ due to mi salignment ef the actual weld nugget and the ionization gau ge P ( 4) eI•rors due to exoessi ve eheet indentation and other ge-ome't;rie f'actors .• Adv:ar~.tages include (l) :res1)onse .i s i ramediate, mak.o , ►~ _.... , el'" .....ti ing marking or identifieatiol'i of welds uri.neeessary, (2) iridication s are ir1dependent of operator and cou1d be &.u toma tic in oper:;1tion. Pts.~$tvap:paf,es i11,clude (l) 41ccess j_s require d to both sides of' the weldt (2) ca:r.~eful locating of' the weld is requi;i."ed, (3) cracking or excessive sheet indentation may introduce er;roneous indi ce.t:i..011. t of ~@nization gauge testing equipment No ~-P'V~;lql?~~n.. has been included in t h is l"esearch. 1 since t he penetrator and electi' ical test;s provid.e e~ui val ent inf ormation with simpler equipment. 89 Io Me chan;ical P;r,oof Tests: In mechanica l proof tests, t h e a:potwe.ld is loaded to a. predetermined fra ction of accept a ble etr e ng t h i n shear or tension by a suitable mechanical test:tng tool. W J'ith welds in e.:i:ctended sheets.- it is very diff icult to load individual $pots in she a r with out exces s ive sheet distortion .. As a re-• sult; most mechanical proof tests are designed to loa d the spotweld in tension. However, it must be recognized that ten• sion strength is not neoassa.rily px-oporuional to t he sl:1 0ar st:t.?ength of' the weld o Hence t hese test"Er a:r:•e indica tive of; but d o n ot me asure shea r streng t h .. 'r he y do di scriminate between 1• stuokn welds a nd we lds of a ccept able stx•e ngth. The ereate s t dis a.dvantag~ of me oha,n i cal proof tests is t h e possibi1 ity t h at the proof load mi gb.t damage t he weld. This need not neces sarily oc cur- ... in f a c t it is pr'obable t h a t s p otwelds whi ch wer0 dama ged by p1"oof' loa di ng to a f ract ... i on of minimum a cceptabl e s trength would n ot be suitable for use i n a ircraf t a nyhow. Experience with s tat ic she ar pull. ·tes i; s on thousands of spot we lds f'ails t o show e.ny damage l''e""' sul ti ng · f rom parti a l loe.di ng , in w lds of a cce ptable strength a..ttd qua li t y o '1:he a dv:3-,r.1t a &,tt, of p_.,:oo f t e st s l ie s in t heir corapl .e te re .. liability, wh en the loa d can be properly applied to a.n in.i dividual spot .• 1. P,r¥, Tes~ M-etpods; Following t he method of the inspector who pries the 90 sheets apart nefi.r t :he spotwe l ds t o detect weak welds 1 ca librated prying tools designed to e.xert 1.mmm loads have been developed. Regardles s of t he force exerted by the operat or~ clutch or s pring devices preve.:rrt the f or ce applied t o t he we ld from e];:ce,ed:i.ng a. certe.in max:lmu..)l'.l , Hence l-:nown proof' lo · .ds may be appl i e d wi t hout damag~ to good welds. The meth od has a dire ct appeal 0 to the ins1:Je c tor be cau se it follovJS pr oven inspe ction procedure •ri t h addl ti onal a ccur a ey., A P.f9Qa ut~·P!1 to be observed i n apply :ng pry tools is that t he t ool mu s t be .t roper l y applied, and applied onl y to join ts un d sheet thic1u1a sses for which :it ha.s been designed and adjusted_,, to a.void damage to the welds, ox~ structure , I nher.e nt . erro:r--s include (1) errors resulting from the p1"' e senc$ of o ther welds very cJ.ose to the weld under t est, i f' t he load is dis tributed to theso other weld:ii, (2) erl'o:r·s due to variabl e sheet stiffness , · P.dva~t~ge,s of pry t e sting tools are: {1) mea~urements are simple t1nd direct, (2) t he load is ap ,. lied to weld at faying plan.e 1 rather t han tb.:l:'oggh sheet .. Disadvantages of p~y testing tools are: (1) the she ets a.i"'e separated and may be dist:orted hy the test, 91 (2) welds a.re difficult to reach t hro}lgb. large over .. lap, ( 3) sheet surface is aeratched at faying surfa ce, ( 4) damage to the we ld may result from carelE,ss US!:h w1; ver·y p~actt~al . tor.qi$ ot pry testing tools h~ve b.a,en developed in this research ; al though preliminary designs i,'or such tools have be~n proposedl! 2,. . dh~·RJiva Bo:q.d Test:¢' In th5.s test, suitable small ;pl ates are b onded to the outer sheet su.r-.faoe a·bove t h e weld, and/or- to the opposite sheet surface, using recently developed metal to me t al adhesives applied under heat and pressure. A typical adhesive * applied in these tests consistently develo.p ed more than 2500 P• s • i~ -s he ar str1ength and 2000 p .• s.i. tensile strength in bonds between A1cls.d sheets. It is appJ.j.ed with a . brush and all(:)wed to dry in air for an h ouri !fuen heat and pre·ssur-e al?e applied 5 to 10 Suitable minutes to cure the bond• loading toola then lift the bonded pl a tes from t he sheeti loading the individua l spot i:n tension. ( See F'ig . 37 B) . Wea.k welds f'a.il under the chosen p11 oof loa d. Acceptable we l ds a.re riot o.amaged and the s.h eet is not distorted by this test. i.-~ Furnished by .B• B Che.miee.l Company, Carnbt-idgo" Mass . aehusetts, HOLD DOWN PRESSURE @] ----------------- , SPOTWELD ALCLADSHEE -0 : _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ .J LUMINUM PLATE UM PLATE CARTRIDGE __,........,_,......,__ HEATER · HOLD DOWN PRESSURE A. BONDI NG L OADIN G DI SC T O SHEET l TE ST LO.AD ) ' , . ------, ------ I TE ST LOAD l PljJON CONNECTION .9r HAND PUMP ;PRESSURE =· GAUGE W LO , ·~ l WELD ADHESIVE BOND B. T ENS I ON TES TIN G OF WE ~D F I G. 37 , C. HY DRAULI C LOADIN G DEVI CE ADHESIVE BONO PROOF TES T OF SP OT WELD DOWN RING Pregaut1on~ to be observed i n app lying thes e t e5ts include: (1) the sheet su.:c face must be pro pe:rly eleaned and the adhesive bond must be made caxefully, ( 2 ) the load must be applied n o:rmal to tho s heet surface so ae to a.void pro g re:::L:1 ive f a ilure of the adheeive bond, (3) tbe ap plie d load should not exceed the chosen pr oof load~ Limitatione in the applic ation of the method a:re: (l) it i e n ot a r,pitca.ble to we.lda between t wo ri gid see-... · tions, as the load woul d be dis t:r i buted to eeve:al welde, ( 2 ) it may be applied to thin sheet s welded to etiffane1e, by loading fro m only one s ide, or t.o sheet to ehe e t welds with lo ading fro m a bove and below the we ld. Advantagee, of the method are; (1) the sheet is not distorted and good welds axe not da.maged by the test, (2) ditect, reliable meaeurements a-re obtained ._, Dist:itdvantagee of the method are i ( 1) teste on indi- Vidu~l welds involve exoeeeive time delay, although large number & o:f we ld e may rJe teeted relG.1:.tively qui ckly, (2) b,eating and pressure equipme:n t mu s t be uaed to make the bond, and he a t is needed t o weaken tne a.cdlhesive bond at:• t ez teeting J to remov e the te s t plate . Fig~ 37-0 ahovre a de1;3:ign for a loading tool tor use with the adhesive bond proof test. 3. J?xoo:f Te,stintx at Welde,t' lt h.a e been proposed that proof testing be oar:ried out at th@ weloe:r directly af.t er eaoh we ld is made, so 93 that d efe ctive welds can be detected i rn.me d i ately and r e.,., placed.. Suc h tes t ing mi ght be ma d e an inte gr a l part of the we l ding operation, aut-ornatica.lly a pplie d as the head of the we l d er :rises so a s to ., entail ne glig ible loes ot time.- Spe-eia.l clamp tools, poe s i bly operated by the welder ail( Gupply ; wo ul d be ne.oesra ary to hol d the sheet and load the V'J<a).ch On i :ong continuous j oint s , these ola.u1p~ mi ght al~o se rve to move and position the eheet £or welding f T~.. ~ device would load thte we ld only to a f ixed proof load , a nd release the sheet whe n thi s load waa attained, t o a.vo i d exc.e se'iv-e s heet dieto?tion~ Ho l d down ti evioes m:i,ght :be needed to av oi d lG>ading adjacent welde-. Care would be exercised to a.void exaeeeive slle et separation bec 3.us e of the clamps inserted at t'he fayin g pl ane. Ca l d Iolling subsequent t o weld i ng mi ght be necessary to teduoe, sheet eeparation to a minimum. l?te-Qautions include ( l) ca.;re to avoid damag e t o the weld through excessive proof loading. Ad'llantagea axQ: (l ) p:roo-f teeting can be carried - out on all we ld a • (2 ) dsfeot1ve welds oan be deteoted and rewe l d ed wi t h negligtble lo s t time, ('3) the test woul d be ' reliable and co nclusive. Disadvantages are; ( 1) pro of· LP:ad_s mi ght damage 94 t he we lds, (2) sheet separat i on and distortion might re•· sult , ( Z> ) tbe t i me requir ed for we l ding mi gh·t he inoiea.se d, .. (4) the flexibility of the welder mi ght be reduce d. (5) new f1xtuzee mi ght be required for special shapes of structure t.o be welded•. No d eve l .o pment of this ty pe of equi pment has been in ... eluded in this r esearch, A aketoh • of a possi ble method of a p~lying load by means of etrape a ppe ax s in Fig .. 6S . 96 To select from the proposed test methods those showing the greatest promise,. i t wae µ,eoesaa:ry to d etermine ·: A. Th~ oox-re lation .o f we l d propert ies with etat ic shear s tr'e ngth., B. Ef:fe ot of' sheet p;r:epara.t ion and <\lonai ti one of welding upon weld pro perties. a. The d estr uotive tests of spotwelds equivalent to load ing conditions in aircraft eweturea in use. D.. 'fhe raeasur·emeuts :required of non-destructive tests. E. Sui table components of n:on--,des t.ructi ve eapotweld testere. The reaults of mea.eul;'emer1te on more than a thoueana indu$·• t:rially mad¢ e-potwelds f;rom several aouicee were used to es~• tablish the following fac'te, on which the selection of suitab le te $ t methods was based. A. co:r:i:e lati 9n of W~ ld :P:ropel't i,es with ~t.a. tic. She¥ Strength l-.- 1l'yee.e of Fai lU,:re The fa~l ute a£ apotwe ldi;; unde.r at!;!.t.ic shea:r loading is usually of ohe of three basic types i (a) Shear through the nugget at the faying plane (See l!, ig. 38}. !n t h ie type of fa ilur e the maximum. strength of the weld is develo ped, .Arly eontxiwtiona t o weld strength by co-rona bonding will be :realized in addition to the strength of the c ast a l loy nugget a rea, ( b) ♦i:l? ulling a buttonn in which cas e failure usually 38, SPOT WELD FAILURE BY SHEAR THROUGH THE NUGGET AT THE FAYING PLANE, F IG. oooure at the pe xi phe xy of the nugget along the wa lls of a o ircular cylind e r through one o:f' the sheets ais shown in Figure 39. In this oase the full strengtn of the epotv eld will not be developed a.nd the streng th <hlpende only upon the effe ct ive diameter of the nugget and the qualities of the heat ... a,ff ected zone at the nugget bounda.J:y:e. The pres enc;e of corona bonding and the ahea.r st;rength of the east a).l oy at the faying plane do not contribute t o the ultimate strength of the we ld. They do :r.epresent, however, a me asure of t he maximum a trength wh ich could p os$ibl.y be developed even -w hen fail~ie ia by 0 pulling a button"• by Failuxe pulli ng a button whose size oorreepond& to the inner extremity of the Alcla.tl intil usio11 ( e uoh as ocou:u:ed in weld F-90, Fi g . \7,4! :results in reduced strength pxopo;rtional to the diameter of the actual button p ulled~ (c) Pulling a partial button with shea:r t hr ough nuggetl> {Se e Fig. 40). In this case; f'ailure eta.rte most frequently at the inner e.xt;remity of the Alclad inclue ion into the weld nugget aml p:rogresees through the oaet alJ.oy of the nugget to the eheet surfac es, usually pulling ab o ut one.-h.alf of the normal button. 'fhe strengt.h developed in th is type of failure is quite vaxiable and depends almoet entirely upon the geometry of the surfac es of cleavage. FIG. 39 ■ SPOTWELD FAILURE BY "PULLING A BUTTON". I I- z 0 I- 1::, (Il ..J <( l- o:: <( 0.. t!) z ..J ..J ::, n. >-- (l'.l w 0:: ::, ..J <( LL I- 0 ..J t!) t!) w ::, w ~ z I- 0 I 0.. t!) (f) ::, 0 0:: I 0 I- :::t 0:: <( t!) w :!:. LL (/) 97 'The sing le weld parameter which correlates most reli• ably wit h etatio shear at.r.enfth is the area of oaet all<>y bond i ng at the faying pl ane, which is meaeuxed approximately by the diameter of the nugget at the faying plane i f Alclad inolusiona. ar e not exoeasive. In no,xma.l w-e lds . the ~a.st alloy of the nugget at the fay• ing plane develops from 18,.000 to 22, 000 p._e .t .• statio shear strength with the ave:ra.ge value f or, typical welds olose to 20,.000 p . s '!i .• . Hence , most of the we ld strength i ~ deve lo ped in the nugget in norma l we lds and, in ease t he failure j.e by she ar at the faying plane, the ax:ea of oast alloy d ete:rmines the weld strength :rel iably. Hovrnvez, in many cases , an addi,. tiona.l bonded axe a of Al clad mater ial -exists outside the we l d nugget and oontzibutes to we ld strength. Figute 41 shows typio.al correlat i ona between static sheax ist:i-ength and oaet a.lli;ay area at the faying plane for several hunoxed weld s. In general, mo~t .of the welds wi th a given cast a.lloy area will have at~engths within plus ot minus 10% of the med ian strength in that area. These results have oeen confir med by, r research i l'.l other laboratoriee (Ref .. #3 & #B ). The shape of the nug get, provided it be xeasonably symme trical, i$ not cr1 tica.l to the we ld st:1?engtl'10 Miesha.pen nug ... gete , nowevex, are often an indication of poo,r surface prepa~ tion or bad welding cond itions ano usually go a long with welds - ,~-- ...J 0 L_ • A. .. aoo·I u.. .O;>O " 24 S-T ALCLAD "ADE ON + ·-· - - , - l - - ~ L· ,. ·: ,. r--...:-+-...,...+-··.·:i·:. .·+__,_-+--_ _j_ __J • • - ;-,t;-'"-'-"-'-.. I a'o I ' ·:· 0 _J 40 5.0 108 WELDS IN .064 ' 21l S-T ALCLAD MAOE ON 1300 . - - -- -- - -- -- -• •···•· ·. ' . I - 7 -- - --+---· -- -- ,- - - I J: ,__ _ ......._ _ _.......,_ . _ ___ . t--- - -- + ----i J--- -· ----+- ·- - · · I . . . : . -~ ... • ,· • . • • •.• I +--- T: ~ 1._1! 2 - • 1 ~8 WELDS ' • •f-=-~-~1 ___ -- IN .081" ,'4 S-T ALCLAD MADE ON IN TAYLOR-WINFIELD WELOtR AT THE UNJVE ~SITY OF SOUTHERN CALIFORNIA. D. - 80 ~ _lj -· ·· _ ,lu0GGET4.i1AM{fER 6/b 1·i 7: 0 - - - x ' , ~ ~ r : - - - + .~ 0 ~iuAR~ oF 3 '~~-. . . . o ~ : : - - - + - - - + - - - - + - - - 4-----+-------, - - - --~ 7 en 501.1 J -- - ·-· ··- ·1I _;; r-· ' i i •• J_-: ' i.J 1. e.o j - +-,- _ .. ~ 6001----+---+---+------i---+----+---- ~ 700 LL O\.N r.o 1 :.r,•. : • . • CALIFORNIA. -t------+- •' . . . ·r ;: c -+--- ~ !vv .. • --+-- ,. • ·• ::, . _ AIRCA.A:fT CORPORATION, SAN DIEGO, a:: IOv,.. 'I.I • 110 ..., ~ 1 IN .040 " 24 S-T AlCLAD MADE ON TAYLOR-W.INFIELD WELDER AT CONSOLIDATEO-VULTEE. 8 . . 138 WE .LOS I I ;v·r' I IO 2.0:0 4.0 5.0 •• 6.0 SQUARE OF NUGGET DIAMETER (0 I ")t ~4001-----+--+-- 51300 il201.1 01 g 100, !~ t]. ; :f I · I I I I J f. I ! l&I IOOO ~S::d I 0 - e n ~-. THESE WELDS WERE PUHPOSEL ; MADE VARIA8t. E IN STR ENGTH FOR USE . OEVELOPIN~ NO~-OESTRUCTIVE TESTS. Nore; S CIAKY WELDER AT LOCKHEED AIRCRAFT COPORATION C. 0.1") - -+=- - -.:- - - I 7.0 • • 8.0 SQUARE OF NUGGEr OIAMETE;R 3.0 ~=:=~-:~- ::L~~ _ ,00 ~.=-_--t_-~~~: 0 1.0 20 3 ~ - - i -- - i - ~ r ·--t--- 2a,-----L._ -·--· -- LL 0 <( ·-f -- ·--- -- ---- ---, 1 - 7 --+--+---+--+--L-__j 500!~ . ----t---t-'-,---~--+---4---1----L-_j ~4001'.,- - (f) ~ 6~ <( a::7oot; --:t- - t--:-+~~--+-----+-_JL__J ~ I • --1 a::I~ 3 9\A!oq'--:-:-r ~- I IN I ~ - ---to-~ fo ·- •V ··OF NUGGET OIAM.ETER • - 138 WELDS :J l ol2C(), a. I I II oor , - - + - - -- W - -- .; ;- SCIAKY WELDER AT LOCKHEED AIRCRA~T CORPOR4TION, z13oof-.---~ - ' cnl400'- 0 I -01 "l -+.. . . cl,.: -.?--:••J-·wr q f O L_ I 00 <t 200, 00 ~; , •I -;.c.--~ --t--J.~-1--t---r---i----~-7 i : -- ~~ ct .... ~ 800 I ' er 70(t:-- - 3 900~ ; - ~10001 . ~ II00[ - ~:=~-=-=r-=- ~r-~- cn1400J - ' :~ ~. 9S ~,ug~e t...)?enf:3t~a.t ~. i o n an~..· V o , l , ~ , 1 The tltictmesa of the weld nugget roea.auted by i te pene• t:ration into the parent aheet ifi.. not critieal in determining statia shear at);'en(ifth, pxovided that the penetration li~.e between 2010 and 80% of the sheet thiQkness. r, n th p e n e t r a t i o n b~low 20% nu{lget f o r m a t . i o n (Ref•: t/5). ii v e r y 1 : r 1 : e g u. . .. lax and extem, iv-e Alolm.d inolueions may result 1n gxeat weakening of tb.e bo11d at the · faying eur:tace. Thes e low penet .x a.ti'on· weld s ~11o·u1d be olaaeified as not acceptable be cause tJH~Y could not pass strength co.ne ietenoy tequire ... me,~1,t~ ~ Weld~ wi:!;ose nugget·s penetiat.e to mo;re th.an 801t und el' which or-a.eked welds :f'X.e(luenily oeeur and aX'e undesitable because the e~cese ive nugget thiokn,es.a w e a k e n e the p a r e n t sheet at the bond and usually :results 1:n a. laxge heat• aff ected iesion $U;rrou.nd ing the nugg:~t. in whteh the s t,:en.g tb of the · 24 ST alloy may be eonsideta.bly red.uoed., s uoh welde may fa i l by p'l.ill l ing buttons wheie the su:rfaoe o:f failux.e may lie in this weakened zone'll They do not develop a:a mueb. shear e_ t ;rengt,h as e<:>uld have been develo ped ha(i the nugget; enea:J,Teo through the fay ing pla.nta. our experience does not shaw that. wi tb.in the acceptable range of 20% to 80% pene't;r a tion the unit shear $trength of the weld depends a .i gnifi cant l y upon penetration,. Instead we find that wi tb welds of lovi1er penetiation there ia fre ... quently present a relatively largei area of Alalad bond ing, wboee strength aontxibution is ~eeponsible for the apparent fi oti tio~s irH:u:ease in the unit shear e trength of the 4. Total, J3ond~.Q 4\tea at. the }&h'1s; ~la.n:t 11 The •total bonch::d axea at the fayi ng pl ane cons i s t s of {a) the east alloy ;r:egion of the nugget and (b) the region of c ,.n ;ona bondlng. ln the usual oa.s e the ca.et alloy area. i o unifo rm and compl e tely bonded. However, the corona bonding is variable !'t:mn r10 bondi.n g what ev er to a c om,p l ete area l bonding,. With oo mpl.ete bonding the corona te g ion devel ope a.bout 9500 p-.e ., i• unit shear a trength. With ii n• comp lete bonding {small poin te bond ed with surrounding in• te~etiee·a} the appatent unit shear ettength of the cotor.ia for a group of welds may be a.e low a.e 6600'# GI even 4JJOO#/:. The quality of the c orona bond depends oritiaal ly upon the m.etbqd of eheet pieparation and cleaning, in addit i on to the conditions of weldinti'•· Under some oonditiona no oo:rona. bonding whatever will develop., The weld s ttength oox:rela.tes mo.re close ly wi th (A x. s ) n n - - + (A x: S ) 0 C lOO whete '\1 ; Net Cast Alloy (Nugget ) Area at Faying P lane 5 n : Unit Shear St rength of Cast Alloy (Nugget) A0 ~ Ef feotively Bonded A:tea of Alolad Co:rona $0 = Uni.t Shear Strength of Corona Bonding t han with any othei c ombination . of meaeure:a.ble spot"e-ve ld pa.ramet@r e , de.s pite the fact that in so me caees failure oo ou:u by mechanisms other than failure by e hear at the faying p lan e. 5. Coron~ a_n d NugGet Unit 8h,,ear Str engthe f he aotual unit shea:r: s treng ths of the cas t alloy bond. ,.. 1 ing and the corona bonding can be determined for a group of we lds by plotting (a) the ratio of the shear strength to the square of the oorcm.a d ia.me ter again5 t ( b) the r a tio of the s•quare of the nugge t d i amet er to the square of the cor ona d i ameter . Suc h curves are shown in Fi gure 42 fo r we ld s in .04on 24 ST Al clad sheet. 1'he i n texoept of th e median line of the cu;rve with the vertical a.xis g ives the unit shear str ength. of the oorona bonding., '!'he slope of the medi an line g ive s the unit ehe ar st rength of the cast alloy~ For the group of w·elds ehown t he meas urement shows the unit shear etreng th of the corona bonding to be about 9,600 p.s.i, wh ile that of the nugge t is 20,,500 t>.i$.i• Similar :results ha,ve been obtained in ot he r gauges w1 th all eizes of welds. Us ing th ese unit s hear streng ths in the :relation given in Section I1i( ,D), the actual streng th of. any nor mal weld ca n be piediet-ed wi thi n plus or minus 10% in the usual oa.ee :f'xom 7 A ~ i10~-~-----.-----,--------.--'------,-----r----,-----, ~ ~ ~ 60 I - -- I - - - - - - - -- -- -- ----r·-- b I :J 501---- -- -- - -- - + -- -+--- - - t - - ---+-- - --+------f c:x: T- ~40 I - - - --'------~ - ~ - - - - .------+- - --+1- - - - + -----+- z UJ a:::301--- - r -- - + - - - - - ~ ~ tcn i . J • • • 520 i --·-·-- --- i ··-- -I Q. a::: ~ i 101--'--- + - - - + - - -+ - -- + - - - - - -~~'-'-,--;,--r-----! uJ .:c CJ) 0 ' - - - - - 1 - - - - - ' - ' - - - - - - ' - - - ~ - - "'-- - . , . L - - - - - - ' - ' - - - - - - " - - ' 1.0 1.5 2.0 2.5 3..0 . 3.5 4.0 4.5 5.0 RATl,.JALLOY + _CORONA_AREA) . VX . ALLOY AREA . -. : ~ B ,;r, i90,--~-----,r----r---r---,----,---,--'---,-:--~ ~ i cj.... 80 1---__;__ __.__ _l-----+---+---'----ir--- ~ + --'-- -- - ; . - -~ c'--- • i I 0 1 0 1 - - - - - + - - - < - - - + - - - + ~ - - - - + -'---+.~ ► I 3 s o l - -- - + -- - - + - -4 - - - - 1 - -- ~ -..,..;;_.c._4 ____--+___,'-+-- ' _J ~ +50 .:c tc,40 1--- ; l -: , i ··- l : --+----"-?i4-'>,..._........i---'-----+...,,,.C..--+-----+--..;_..-~....:..---'-- -f- ---- z i i . t i ~ 301-----+-,llli+~-.:,-<:..+--+-----!..- -.+ -· . .. -+--· - -- f- -- - - -: i :n 20 ,, , - -- - ! i i ~----- -1- - ----+ ----- ---, -- - _J _J • => a 10 -- - ·--- --+~ a::: • I ! - : • - -----l--- --- + - - -- 1· . - -~i_ _ l ! 1 I , ; : : . • : ~ 0--~--~--~------~~------------~ z I 2 3 4 5 . 6 7 • 8 9 10 11 en RATI ALLOY+CORONA AREA) ALLOY AREA 1 FIG. 42. GRAPH USED FOR CALCULATION OF UNIT SHEAR STRENGTHS~ _ __ . . OF CAST ALLOY ANO CORONA BOUNDED REGIONS AT FAYING PLANE OF SPOTWELOS. A. 141 SCIAKY WELDS IN .040" 24ST ALCLAD. B. 108 SCIAKY WELDS IN ,064" 24ST ALCLAO. ,Ui 1trG1·.i oQ1l1 1ndi¢ated iu. n~ction l i l B i -f;be difteieno@& in Jt;,ij,il.it.ivi ty ot' are t Q ~m.al,: $)$Qifio ·t1olume,a ~f muta.l in th-Ei W(tl • r~ • i.Qll t-v et -llrfie efLQ-ot v,ely d a. me~:.Hare of w,~\J..g &i~~ 1u.xtae-e t .tt.Jt:HJ&h a ·t bi~lt l$ye.r of 11$,fent m~tttl . t1f OIN:t¢tte -~c.1 ?tie p,:fe$®;n,(ae pototJ ity a.nd of e~t~nf ive l:'l-btHit 1nde:nt$tit.11 tu.xtht1:r ;r;-eo-u-e e the tel1a.b 1ii ty rJf auou t!i•ea~uiem,u11tt, J?-enetr.~tione .i e~ ult1ne when ~ lo-iuh:d p,:,obe 1$ ti> ~eed 1nto thie 4'Ut<u • urf'e.o& o:t the ~htH'l't & bove the ip t ~~ e1.d nu{;r · e·t at a in@l~ p .... ;Lnt tend to me~tn -r-e. tlie- thiokne~s o:f tsmpe~e pa.rent metal lying above th$ trnld nugie, a't that p, int. lit,, atue~e.srii ~n c,t • euon .a0-at1ru1emtnit1.1 i.s o~pable o:t· det~iminini Utt it'H'H!OJt't ,Jy o.f the, ni:aggt t b OUUd$,l.'.Y in Ul~ thtf.)t under teet. Fi• g111e 34, th~ws ty pi oQl penetrator inde:nt~tiora p:tof il~:e obta.ine.d 24 ST Alol~ ehe, t + 'fl;etti e -6bow the metl:l.-o4l to be ee.p~o1all;v ~,1Hni.ait,,:tv~ wll:$:'1 tn~ -w~ld nu, 1et lie& ~l.®tH, to t he at:ui'®t s:u;,taoe ~no bl loe_.e, $EH'~itivtt1 r a.p,itlly wh.en the weld nui«~t p~netrat~$· only 20;'t t o 30;f, into il.b.~ .&he.&t '( See l'ig_ ~ch t'Um1l ~:t mea.sure!!!►• ment i cian be t%ad e wi:th. Jrni.a l l hand tat tint l§ev i e.ee •. I.m '·e$\l$ Ol' 1e:rve1 ( 'fbe ~,~~ l ' it.ably fo~ 'thin •·; aug\$--1s of aluminum li:-heet ,, .032 n a.rid thinner) . See. Fi1- -64) . s. . Metal]. tu;:gipal St.x uct\;lr e :Me t,all.urgica.1 structure is o:f lese impo;rtance than nugget size, shape, soundnese, freedom from cracking, and extent of c orona 'bond in determining weld stiength and qua lity. no metallu:r gical characte:i:is tic ha.El yet been ie l iable correlated with weld strength. "The d uctility of the weld me tal is, however, Qf grea t i mportan ce ,, as one of th@ chief deteote met in ep0twelde is la.Gk of suff'ieient auetility to pe :rmit even distribution of applied load~ ac:r oss the bonded area. :Biittlenesa seems to reduce weld ettength es pecia lly unde:r impact and fatigue lo~ing, yet i te eftects upon static eheal' strength are very small, }(enoe , duetility a.lone cannot be used to measv..l'e etatio shear strength., However, spotweld s to be aooe ptable mu~t show a ppz-eci able d uctility. lOS E;fteet o.f Sheet P~~paration ~nd Csn~ti0n of. 1 vieiu1,ns, Uii?P. ,'W~r?r fS:rWi,<i~ti~~ "' If The- size, shape and struetuJ• e . of the spotweld nu gg~t and the e..1ttent and nature o;r Al el.ad ba11ding at the f a7ing plane ave eri tiQally dependent. up.o n tb.e methods of elea.riing and preparing sheet for weldi~g and upon the conditions :or welding, l. ~~~t I?re20.r•§ltio1'l One of the most variable parameters controlling spot .. weld quality is the rneth8d. ef ahe,e t p~epara tion and cleaning. 1ber.e is little agre~mel'lt a.s yet on the precise proceduPe of e~ching and eleaning among the va.rious manufaetu:rer:rs of a;t;rera..ft • Ae a t-e .a ul t, t he surface eomii tion of the sheets,. although ueually eonsistent in any ©ne factory, varies widely from one ·compa ny to anothet>.. Uniform surface eon.. di tions .' ave requir•ed fo1~ consistent weld strength . 'l'he s.ur:t'aee co:ndi tiona., if irregular, result tn misshapen wel.d nugget s ,; spitting,, and. _oth.e-;r weld defects, a s well as in variable strength ( See Fig. 43,j. ·Tl1e si ze of the nugget devEJl oped is a !'unction of the resistance at the faying plane during the per:i.od of welding, so that a change in cleaning oond.li.tio11s may result in a change in weld size al .. though all contx-ollable conditions of welding are kept constant . lhe na.tu1~e of t he corona bond ve.;i:•ies g:J?eatly with $,heet Slll',i 'ace condition.. Sheets cleaned a de qua tely fo2" good welding 43 MISSHAPEN AND DEFECTIVE WELDS TYPICALLY RESULTING FROM NON UNIFORM SHEET SURFACE CONDITIONS. FIG. FAYING PLANES. SECTION BELOW ALCLAD. 10.4 me+y , if tint~r• »ti.n.t~<:i , $auiie ·the (foin.~:mi ¼r:)Qnd t4l ttUiil tiv d ev ~lop. e.xt. *.(jn :t:v.e '11te:r.e Alol~<.$ in-oluei O·l'.l~ intQ tn~ lll.lf,€£G~ ~,e th~ fa.ll~xe, to evelop a~a:ena t>{rncUn ~ intxodUQ~~ a iH ;&oontinu.ity int,Q tu~ ~vt:ee.&e-d te '.io.n of ~n~ tho w~l. 1oati.toutert ·to f.'ia.ily t~1lQl& undt;J oerta.in ··ype 1o,~dini. . Thui a .· e .a nitlf oo.n it!tone m.r1;y be· ttl·e pori ru:: _get {Jf ittl.e fo t a ChS.-li{{~ l)f l <>O;t tn ~fdi l o 5-'ti~tV"th r ·,:rx W$ld.$ ,1th iden.tioel 11\il iOt ~i~~ta, ei:Un1.1lJr as a i,e1ir1.ilt of the fa1ltUJe to obt1:11t1 oo:tont\t bQndi.J'Jl.4f g Ste Ji'3.gu;ee 4-4 fo:r tr·p iQa.l vat1atie)tUt in co:rone. h6»11« ~ - wh:te-n m~ f(J .tilt ftom no .. u.nit'o:tm $h:tet tH~x t·e.oe ~htidi t ijonih the iefltn-etl.'y ant.i i1littl'fao~ otmdi t.ion of' t e eld1.ng elee- tz d ,je ba~ a ~-t i t 1ea1 @£f ~ot upon tha fl nape ~r.,a e-Jttirmt nu "tet cltlrv·& lo~nt in tn i·pQtwe 1.o and up<ua t:h~ natu..Je ~no e~tant or ttte be.i-1t ...i\iteQtt·d ~one of tbe l?atent to tb~ r.m.gget.. Qf i:. etll\l r.1.~ j ~Qent 6htaJ p 1 2:r ii!.ll el.J:.H~troue tiplii tcno to t:n11u$e nuit:t~ t o~veiGpir;?tHit net!AXE<X' t c) Q0tlt,t:u•.f ti ~~ i tb. ttm tama.11 ti.Pi • di,:iy th~ nuge·t?';te tend the out e;v iht1~t eu:rfatHJ 1n .Fu.xt neJ.tllOte-, alt!> the :tipi fft tUJ to. dev~lQ;, i lea.tor ,, p enet~a.tion. ,and e-.;r.,r.n re$ctl t'!H~ outex 1s' eet t1,,utfa,c it b&oa.ui:ire o.f the 1,no1ea1id h~~.t ct .ev~~l.01;&0 at t.bie ti p co11t"ut . 0:1:1 th£~ ot.h6t ban.a • fla.t uleettOd$ ·t ip!f t':r,a quentl.y eaue0 tb.~ lltl$jf..lt t.o ,ieve.lop l(l:.llH>j FIG. 44. VARIATIONS IN CORONA BONDING WHICH MAY RESULT FROM NON-UNIFORM SHEET SURFACE CONDITIONS. . ~ia pl..aQeq · ,;)~ 9.!l'.\ t 4e f ay ing p lane t owa;rd the :r o und ed tip• ' :;: ~.'. ' :, • ... .: ; ,::.t. :~ (.;· :., .:' • ,AF;.· t he' ·t i ps ,' . g~ow di:rt1er or are hea ted up during the p~_o oes s of welding , extens i ve pi okuy f r .om the sheet sur• f ac e ooeu:r i •. To a void t h i s p io kup, t ips axe pe:ri,Qd ioa l ly c l eaned d uxi ng we l di ng ._ . Pi gu:re. 45 show-a t &pioal variations i n nugget position :tesulting f;r om cha ngee in eleot:rode ·, s hape and . $ ize. !fon;;.destiuctive teet method s mm,t not gi ve eltxoneo ue in dic a t i ons as a r esult Qf var iations in t i p otmo iti one whi ch. ha ve not c hanged weld quality. :f~lo j,n.t:z Curren,t, ~owe;r _and Iiln~rw; 'f he energy delivered to the weld det er mines the size of the we l d nugget and t he bon ded a:re a o 'l'he net ene:r gy- develdpe d i n the s he et e d uting we ld ing wi l l be g iven by t he integral., 1'hi .s ener gy obvious l y de pend s u pon the we l d ing eu.t:r ent, t he ;reetstanoe at the t'ay ing plane of t h e vrn l d , and the t i me du;ring whic h the cu:r:ren t f laws. Beca use of t he very hi gh hr~at conduoti vit.y of a lumi n um, t h e r a t e at ·whi ch ene r gy i s supp li ed t o t he weld :region is ox i tical. In gene r a l, t he hea t mus t he d evelo ped ver y rapidly i n order tha t the t emper a t ure ma.y be z; aised above t he mel t ing po i n t o:f the ca.s t a lloy a t the weld ,. Hence, the i.vave a hape o:f the c urr en t i s ve ry i mportant. S.teep-,fronted, e ho;rt ... d uration cw:rent au:rge.s tend to :pr oduce mcu: e extensive melting per watt s econd of ene;rgy delivered to the weld r e g ion than do long ... durati on wa v e-e wit h elow·l y chang ing A. 3" RADIUS DOME 5/8" DIAMETER UPPER ELECTRODE FLAT 5/8" DIAMETER LOWER ELECTRODE. B. 5" RADIUS DOME 5/8" DIAMETER UPPER ELECTRODE FLAT 5/8" DIAMETER LOWER ELECTRODE. C. 395 CO~E UPPER ELECTRODE FLAT 5/8" DIAMETER LOWER ELECTRODE. 0. 790 CO~E UPPER ELECTRODE FLAT 5/8" DIAMETER LOWER ELECTRODE. FIG. 45. VARIATIONS IN SPOT WELD NUGGET SHAPE AND POSITION RESULTING FROM CHANGES IN ELECTRODE SHAPE AND SIZE. Furthe:rmo.re, the ·wav e sha pe of the our l'ent 1111 have an important effeet upon the actual timing be t ween t he tne l ting of tb.e a lloy and the appJ.i.ca. tion ,of :forging pies,s ur.e. ·rypical variations i n weld nugget s ize as welding enetgy · i ncreae es are shown in _;Fi g .. 46. 1~on- destruetive teat methods ahould meaeure weld quality I and streng·th i i1dependently of the ourrent conditions du:r ing vrnldin.g + 'l'i p pressu;re oonditions during we lding have a lar ge ef.r ect upon the €.. leotrical resiste..nce at the faying plane and upon the energy d evelo ped in the weld._ High pres &u re a t the be g inning of tb.e welding oyale lower :s the effective resistance arid o eorea.s ee the we l _d ene:rg·y., lnsuf'fioient pressu:te duting the period that th,e alloy is melting r eeu lt i:: in ex puls i on of metal at the '.:.f ·~ y1ng plane and ' . • . ·w exces sive expansion in the heat ed region. During the perio d of subsequent cooling f':liem the per i phery of' the . . .. \1~: nugget tovua:rd i ta ~enter, cra'1fking and po:r os i ty dev e lop. "\ :. \ ,>l Excessive for g ing p.reesur·e afte:r the nu£get ha.s been formed· :r-e eulte in excessive sbeet indentation. Inat¼quate f~! fox.- ging p:r esa uz·e p ro d uoes ina~equate bonding a.t th e f ay ing s u:rfaoe. Exoes s.ively advanced f orging pres sure has the same effe c t as exoeae i ve pxee s u:re d·u.ring the welding per :iotl;, namely, 1200 MFD. 2400 VOLTS. 960 MFD. 2200 VOLTS. 960 MFD. 2600 VOLTS. 1200 MFD. 2800 VOLTS. 1200 MFD. 2600 VOLTS. 1200 MFD. 2200 VOLTS. 960 MFD. 2000 VOLTS. 960 MFD. 2400 VOLTS. 960 MFD. 2800 VOLTS. 960 MFD . 1800 VOLTS. FIG. 46. EFFECT OF INCREASED WELDING ENERGY ON WE~D NUGGET SIZE. TAYL OR WI NFIELD WELDER. it reduces the resistance at the faying plane and hence re..duoe s the weld energy. Ejtoe ssi V-Ei>'ly delayed forging time 1.s un• de$ira.ble bees.use t he we ld nugget will have solidified before for ging pres.sure ls applied, nullifying its eff ects. of advancing and delaying t he a.pplioation of for ge pressurE;) . ' upon vrelds made at) constan t energy sett;i.:ng of the welder is shown in F1igure ·47. To meet Army and I~avy spec.ifiQa.tions :fol? mininrum weld strength and strength consi.steney, aircraft manufacturers now use exteneiv·e p;t>oaeas control in the spotwelding departments . As a r esult, in any one plant ~ var iables in cleaning and con• di tions of we lding a re h eld J.')easonably' oonstant. son,. it is not necess ar•y for non .. destruotive test meth ods to be sensiitive te> e x ceedingly abnormal a¢ndit ions, but i~ather to b e e.ble to detect weld quality and st::c'~ng th rel iably under nor•mal va riations of industrial welding conditions. FIG. 47. EFFECT OF CHANGING THE TIME OF APPLICATION OF FORGING PRESSURE UPON WELDS MADE AT CONSTANT CURRENT RELAY SETTINGS OF SCIAKY WELDER. A. FORGE TIME SETTING ADVANCED FORGE 165 - - VERY 8. FORGE TIME SETTING ADVANCED FORGE 175 - - LESS C. FORGE TIME SETTING ADVANCED FORGE 200 - - LESS 0. FORGE TIME SETTING ADVANCED FORGE 210 - - LESS E. FORGE TIME SETTING ADVANCED FORGE - - 215 - - LESS FIG, 47, CONT 1 D, F. FORGE TIME SETTING FORGE. 220 - - NORMAL G. 225 - - NORMAL H. FORGE TIME SETTING FORGE. 230 - - DELAYED I. FORGE TIME SETTING FORGE. 235 - - DELAYED FORGE TIME SETTJNG FORGE, J. FORGE TIME SETTING 240 DELAYED FORGE. K. FORGE TIME SETTING DELAYED FORGE. - MORE 245- - EXCESSIVELY c. DE$TRUOTJ'. VE 'rESTS OP SPO TfffELDS Non.. destructive tests ml!tst prediet the strength of' spot.. welds as shown by d_e stru9tiv~ pull tests of apotvrnl.d speoi• . ~ . mens . !J:'ne strength o:f the spotweld depends ori tically upon the nature of the load applied to ca.use its failure... Hence, non+1>destructive tests :must be specifically designed to predict t he st1•ength of the weld under the type of loading met in air• craft structures in use . Spotwelds us e d in air craft structures are usually con.. stituents of xrJult;.iple spot l ap joints-, in which several we lds share the applied load., As a res1..1l t of this t ype of use mo st of t;h0 welds 0 .1:• 0 loaded in shear , desp$.te t he J:1a.ture of the total appli ed . load-. Furthermore, s potwe l ds are weak in tension and normal de sign calls for loading of spotwelds only in shear . 'The presenee ot adjacent we lds holding the sheets together tends to prevent the application of tension loads under normal con• d;ttions. i:he loads applied include static, impact, and fatigue - but calculations are u sua lly based on design stati c shear strength, which is less than t he minimum a ec~ptuble test streng th by a suitable factor• of safe·ty • 2. St ~t ic Shear Load.$ Normal design calls for specified static shear strengths in spotwelded joints. Specimen we lds and coupons welded during ~ $ ());l ~i¼"~iatt $t.!"tt-tlt"Ur~8 al~~ 'tHEf•~te:(!l in t.blfi- eb0p by !!Ji.mpl~ ttatie t~tulilon lo$ldS. ori si~tl.e la,- s:1n1l• ~p~t j~inta M"1"tlll.t£t<i; tQ l0t.1d. the, W'e;ld :tt,t £i0lt in $1'1$$,tl,"·• A t7z,1~t1.tl. .&h$·a:t ilP<i!f,d.flllfil!l ie, depttl:d Ul)Qn l.:H)t lllnly th~ Wiild q'1~l1t1~~ '.b-ut ilt-l~'H) _tbe £/J~thod cf t~$tlnij :.uid th~ ~:.,t:tiod ot tl.tp_ply1n($ tk\$! 1-~ d., 0!:)mp~nQ1'rts et tOt'$1o.tt lllfiHl i,U>- ot' ten~ion iltl the ;$,J)Ot $b(l'.ll(i be -eJJ.~imt:t~d it r,in;,l.'loduc.-e ~bl,e i.th0t!l1~ ~w:•e.rJg·tl.ltl tll.re to ~ -obtabt€td., J\ aimple me.clt11w d~v.11;1,loped f~~ the ah:~ av t~•ating of ~:t.1otwewld@ in tJllt reNJU\l~:r:eh 11 sh()?ffi 11l i'.1gtU?~ ii~h- i~hlll 1~e.i-thod of 1Qa.d:1n§.,. by nieat1'~ ot pin$ throogb hole$ di"i.l l~d tn liM i1r'1 ·t h the- $p&tw@'ld., p:r7~v~nts ti~ e.p.pl.ieati()n ~t tttd,~t or t~naion lO.e¼ding,. ~~let.a. mai b.e te-sted ~$ ~fllp1dl:r as t~o ~ mlw~t-~ v.11 th ;plua or minus 5Jl aeem~aoy en 1m1u miat'itb:in~. 'b.$ ClllU11l) ~1p,$ ~JNJt tpeeyu~nt;11 t"o1.u'¥1 tQ (i)bja.~t.1t1r1aPl$ 'betl$U£1¼@ it 1tt1ntG1ne!li w'l'd.l" elightly cnit o.t l .i'Ae ~Pf'~$C lttb le me1aent~ art d~v~lop&d tit. t, the WG;tld. '.lb~ a t .a .tie $hfJ~t--- t0 st is l►y f'~-~ tl1$ •$~pl$$t ~~t to be mppl.1$4 f(f~ ~o-utine w~c.ka on $pot~ld $-t:Ptif,jBtb..f In tli;bt,, ~;tnd partit'fU.l~l"'li' tUldEJ~ balltl€} eonditiCl.n.tt and vdien lMldius. ;so.J.t•,.O-¥'~tt- ,s tv'll~t,~e$ 5!/.?'e .$ubje(~t'Ele. to tatig:u$ ~nd L,~1;>a.et lo~d.L"1g,. ®1.f' 8Ja)·t w ,J.ds l~t~~- be@n f@,UJ:ld to be '\/"i/$:1:'tf v.1enk ®• el!ltrtain ty;p$M of impaet lt>w..dii15-. l,1k$:Wis~., t·tiltigu~ l.O'(.IJ;f~- INCH SINGLE SPOT FIG. 51• SINGLE SPOT TORSION TEST SPECIMEN. FIG. 50. SINGLE SPOT TENSION TEST SPECIMEN. FIG. 48 . TEST PANEL AND SHEARED ONE STATIC SHEAR TEST STRIP. \_ FIG. 49. MACHINE. IZONTAL) SPOTWELD STATIC SHEAR STRENGTH TESTING (IN USE, CROSS ARM IS MAINTAINED HOR- 1110 ing which is known to be present in joints in aircraft st~uctur€)s may lead to early failure of spot'l'relded joints, particu"" l.e.rly if cracking is present.; or .if the weld is not suffici~ntly ductile.. At present extensive rese arch on the f a tigu e proper• ttes of spotwelded joint s i s under way (Ref. //15),. The com• plate results of t his :research have not yet be en presented" rfuus it is not known whether f a tigue strengt h is a bette:t> measure of spotweld qu ality th& -i n the s tat:ie shear $trenght, Hence, the simpler of the two te s ts, namely, static shea4" loading 1s most widely used at present to determine weld quality, 4. Te.nsion Lo~c;ls It has been felt by several res.e a r ch or•ganiza. tions that the true quality of' spotwelds is more adequately measured by loading the spotw·eld in tension as indicat~d in Figure 50. In this caa.e t he proper ties o.f t he weld nugget and of t he heat- af- fect ed zones surrounding the nugget have a significant effect upon the measured strength o.f the weld. Also, t here has been a tenc;J.eney to correlate the ductility of the weld with the ratio of the tension to t he shear strep.ghh . However, for develop-. ment; of significant non-destructive tests it i s more :important to predict accurately the s t atic s h ear str ength which is t he assumed a ctual loading of the welds in use . 5. Torsion She(il.r Loads Spotwel ds are exceedingly weak in torsion because of the small nioment of area of the bonded zone about its center, so lg)j: that applied moments of force result in very high shear stress in tbe weld nugget,. The ductility of the weld is frequently measured by applying a twisting moment to a single spot speei• men p:repared a s shown in J:i'igure 51, As yet the significanee of the torsion tests has not yet been proven and t herefore it is not neeessary that no:n-.destructive tests predict t his weld quality.•. As a re.s u.lt of the conditions listed, static shear load• ing has been used for t he destructive testing of spotwelds in t h is rese arch. Non""destructive tests have be-en designed to predict the static shear strength of spotwelds. with only coin• cidental correlation with these other strengths. D, 11IBASUREMEN'l1S RE9,UIRJ~D 01•' NON•DESTRUCTIVE, 'fi5STS To measure weld quality and static shear strength reliably the non- destruetiv.e test 1'111lst measure certain spotweld para- meters and conditions pre cisely. 'f ue simplest me a surements of eaoh of these parame-ters is t h e pre.fet1re.d one. The minl.ll'ltµll, re9-ui;r-ement is that t he non .. destructlve test measure nugget di• a.meter reliably. Ii'or more accurate mea. su:rement ~of vi1e ld st;rength it is necessary to measure the total b onded area at the faying surface and to determine which portion .of' t h i s a rea is ca.st alloy bonding and which porti on is corona or Alclad bonding. su,vplementary measurements which would be desirable are; a measur•ement of the :penetre.tion of t h e nugge t int o the parent 119 sheet, a measurement of. the extent of the heat- affected zone,, a measurement of the spotweld's ductility, and a measurement of the extent of cra cking and porosity. None of these last named measurements is neeese.ary, howeve:v, to predict the static shear strength of' the welds . It is recogillized t h e.t &. visual inspection will be necessary to check sheet surface condi tions at the weld and so nondestructive tests a.re not intended to measut-e any weld condition which can be observed reliably from the sheet surface. E. 3UI '1'AB1'E. COM.rONEN'rS OF N01{.,DEST~UCTI VE BP01l.1WELD TESTE'RS, Selecticm of t he most pr·o mising test methods i n a ccord• ance with the x•equ1rements of an acceptable test listed in Sectl:on II and t he facts presented in this section has · resulted in the choice o:f (a) t he radiographic test method, and (b) the penetrator and ring electrode tests, for further develop ... ment, '1'.he radiographic tes-t provides a.n indication of weld nugget shape, diameter, and penetration, as well as evidence <i>;f defeets, It is definitely non-destructive., and by develop- ment could be made to ss.tis.fy the requ1re:ments of an acceptable test. The simplest non•~ad!:ographic test would consist Of t (a) a penetra.tol'' me a. eurement of' nugget diameter, (b) an eleatri• 11:Z ca.J. measurement of the total bonded area, and (c) if' desired• an eddy current measurement of' the .e xtent of cracking and porosity in the weld nugget. The remaining sections of this thesis present details of the development of equipment, tecbni(lue, and procedure s .for interpreting the mea surement s obtained, tor the radiographic, penetr·ator, an-d electrical non-destructive tests. test mea surements on several hundre s potwelds are included, Results of. tnctustrially p1°epared 114 V,. DEVEI,.OPMEWJ..1 OF . PEliJETR1\TOR . AND RI NG ~ L ECTRODE TESTS. For laboratory trials with the pe-n etrator and ring electrode tests, careful alignment of penet;ra tors, electr•ode:s, and probes, and measurement of loads, de-f.leot;tons,, curr ents, and potentials were required. .- Since it was found impractieal .to h old the component parts by hand , vise, or wooden f'rame.; a .ma chined steel press was designed and built , ~is machine has served for al.1 penetrator and electrical spot we ld tests to da te, A. DESIGN AND CONSTRUCTION OF SPO'l1W ELD TES·rII\ (t MACHI NE/11. . . . . . . . . . ' . . . . . . . . . . . Spotwe l d Test.ing Machine //1 is a laboratory device de.• signed to test the princ1I)les of the penetrator and electrical non•destructitre tests. It has n,o t been d.ea:tgned to take exte:nsive structure.Sp but wil l handle standard s h ear test panels with spotwelded lap joints. Comp.a.ct eon.struction was used to avoid excessive deflections of t he f:t' ame of the ma• chine under loading , The machine combines twe test opera• t1ona in one sequen ce.,. name ly: two ~iide ring penetra tor tests of t he nugget diamet.e r 1 and two side electrical tests of the total a:Pea of- bonding . 1''igure 52 show~ the entire ma chine, 1:i1or t h e r:J,.ns penetrat or test., a hydraulic jack (a) a.pp:Jies I- . .. . . • loads mea.su1,.ed by weighing b lock (b) .a nd indicated on dial gauge (c) to the moving pressure cylinder (d) wh ich slides FIG. 52. SPOTWELD NON-DESTRUCTIVE TESTING MACHINE NO. 52A. o. CONTACT TIPS. A. HYDRAULIC JACK. B. WEIGHING BLOCK. H. I . ANVIL-LOWER. P. Q. c. o. MOVING CYLINDER. R. PISTON CAP. E. CYLINDRICAL GUIDE. J. BALL PENETRATORS- UPPER. K. ANVIL INSERT. L. ANVIL-UPPER. F. FRAME. M. TOP PLATE. G. 8ALLPENETRATORS-LOWER. N. PROBES. LOAD DIAL GUAGE. FIG. 1. SIDE VIEW OF ASSEMBLED MACHINE. ANVIL INSERT. FIG. 528. DIAL GUAGES. T,U. TERMINALS. v. MICROSWITCH. DETAIL OF MACHINE, DISASSEMBLED. ' FIG. 52C. DETAIL OF ANVIL ANO PENETRATOR ASSEMBLY FIG. 53. RING PENETRATOR ASSEMBLIES USED ON TESTING MACHINE No. 1. FIG. 520. DETAIL OF WEIGHING BLOCK. FIG. 54. RING ELECTRODE ASSEMBLIES USED ON TESTING MA CHINE No. 1 . 1:\.5 in an aecurately machined cylindrical gu:l,de {e} eupported bf the frame o:f the ms.chine (f'). 'Ihe ball penetra tors ( g ) a.Pe carried on removable anvil inse~ts (h) held by a set screw in a socket in the anvil (i) $ and a.re carefully aligned on the axis of the moving cylinder• · Similar penetI~a. tors { j) are car• ried on t he a.nvil insert (k) in the upp.er anvil (1). This anvil is set into the top plate (m)which is securely fastened to, but electrically insulated from; t he f r>a.me (f). These upper penetrators are carefully aligned with the lower penetrator balls on the moving cylinder. Probes (n) slide freely in the anvils, nnd have replaceable contact tips (o) which pa ss through small holes in the anvil inserts (k). The beads of these probes are i.n contact with sensitive dial gauges (p) and (q) fastened firmly by posts to the top plate (m) and the piston eap (r) i :respectively,. 'Xttese gauges me a sure the pene""' tration of' t he penetrator ba,lls unde:r loading. In operation, the spotwelded panel is inserted between. the head and the movine; cylinder and the spotweld is carefully ¢entered under the penetra tor a.ssembly . Loads are applied a s desired. Fol' t h e two side eleotri~at . test, either t h e anvil in• serts carrying the b all penet:ra tors, or simils.r insents with ci!'OUlav ring penetrators (s} .may be used as electrodes. Elec- tric current from an external direct current cu;r,rent generator 11-6 is introduced into the top pl ate (m) (which is insulated f;rom the f'ra..rne) at conta ct ( t). 'lhis curr-ent flow s from the up"per penetrator or electrode (j) through t he weld to the lower electrode (g)-, and leaves t h@ ma ehine through the terminal (u) on the moving cylinder, The current then returns to the gene• rator through ru1 external ammeter and c ontrol resistance. The potential clrop across the probe.a (n) is me asured by a. low resistance m1eroa.mmet:er . These probes are carefull y insulated from the anvil inserts~ Microswitch (v) on the weighing blook (b) is inter ... loeked with the current switeh to prevent the switching on of current with inadequate l9lectrode pressure. r.r.ae ~~ng _J;>e~1etr a po1~ a. s ~epipl _ies used o.n Testing Machine # l are sh own in !i'igure 53. F'or laboratory tests, 1/16n di• ameter hardened ste.(S!l balls ( eo:m.-nero.i ally twaila.ble for R·o ek• well Hardness Testing Maohines) were us~d as penetrators. Calibrated sharpened steel p a>ints ( cornme,r oially av itilable .for ' use i n the Ba.rcol I mp1"esso1"') ean be u sed to obtain equivalent penetratol? tests with much lighter applied loads. T.he pene- trators are mo-unted on circles of diameter chosen to correspond to acceptable spotweld nugget diameters in various gauges of aluminum a lloy sheet, and are supported on hard steel anvil inserts, These inserts may b e quickly exchanged when it is desired to test s potv.reld~ i 1 different gauges of alloy sheet. The ;r-ins; _ele_otrode a.sse_mbl;i.es used on r esting !- aohine #1 are shown in fi'igure 54. ' he electrodes a.re ciroula1• eon- tact areas of· diame ter slightly l arger than the total bonded areas .of acceptable spotwelds inoo.ch sheet thicknes.s.. These ele.etrode uni t.'.S' ar-e of the same dimensions as the pene..,. tra.tor anvil iru.1erts and may be used interchangeably in Testing Ma chine 1/l,t B. Priinci;el~ of Onepation of f.ia~hine ·' , . - - ' • The ~ing penetrat.or- tests of spotweld testing ma chine #1 are based upon results of the pe-netrato.v profile tests shovm in Figur~ 34. From these tests it was :f.ound that t h e typical penetration profile h!ild the cha::ra cte:J:>ist~c shape shown in li'i• gure 55. The ring penetrator units of spotweld testing ma• chine lf:1 are designed with the dia,mete:r such that the pene - tra tors fall on the points A.., A ef the perietl"a.tor profile curve for normal good welds in each gauge of aluminum alloy sheet . If' t he weld nugge ts a.re smaller than t he no:rmial acceptable weld nugget the penetrators fall outside the weld nugget ove;t> the t~mper~d parent metal, at points on the penetrator profile ourve identified by B'""'B" It, howev·e:"r 1 the nugget is larger than the normal size, the penet:rators fall over t he ce nter of the nugget aJ'ld the indications corr espond to t he points C-C of th~ penetrator profile., Sections through typical weld nuggets of various size s in 0040" 24St Alelad sheet are s hown in F'igure 56 ' . - -...:~~~ · - ~' -- - - ~ i'~ - _ ; __ ' , I / / \ \ \ \ I \ I \ \ I I I FIG, 55, CHARACTERISTIC SHAPE OF PENETRATOR PROFILE, TOP, PENETRATOR INDICATION PROFILE. CENTER. SECTION THROUGH NUGGET. BOTTOM, FAYING SURFACE OF WELD, DOTTED CURVE CORRESPONDS TO THIN NUGGET. TAYLOR WINFIELD WELDS IN ■ 040" 24ST ALCLAD. • 0 0 ::r ,-I - 0 ~ ,-I :· _ _...._ ~ - ~ ••. ~ r . ; -. ~-- -----=-~ ,. . ~-~~=-.=, ~ __ ,_ 0 0 ~ ,-I -·i .. ~ , 0 0 CX) ,-I 0 0 °' ,-I Cl) z UJ ~ u UJ 0 11. Cl) lC'\ 0 N ..J ..J < ex 0 IA. lC'\ r-N N Cf) t..J 0 > WELD SECTION 0 0 (X) N 0 LL ::E 140 150 160 170 180 RING PENETRATOR INDICATION FIG, 56. MACROGRAPHS OF SECTIONS OF UNPULLED WELD SPECIMENS, AND INDICATIONS OF THE RING PENETRATOR TEST FOR THESE SPECIMENS. 118 with the indentation of the ting penetrator teat vi s ible · on the macxog:raphs. The penetrator test ind.ioation is ehown fo:r each of t he we lds. It may be seen tha t the p enet:r a - · t io n of the ring penetrator mea~ures weld diameter sensitively and reliably, and that s mall we ld nuggets a re d ifferentiated fr .om· l a xg e weld nuggets by significant chanses in indication. '!'he rin g electxode t wo side d irect our:rent test of s pot- weld testing mac hine #1 are _based upon preliminary tests of the two•eide direct current met hod of determining the total b-0nde'd axe r-t a t th e f a ying plane. Fi gures 9, 10 and 11) .-. (See Section 1IIB•l and Maorogra,phe of the fayin g plane of typic a l s potwelds of vaxious sizes in 4 040 " 24 ST Alol~~ sheet ar e shown in Fi g u:re 6?, with the indication of the t wo-side electrical test shown for each weld" It may be se en that t he eleatrioal test indieatione correlates with the total bonded · area of the epotweld, C, Proa~du~e in ◊Eeration of Maghine 'l'o cond uct non-des true ti ve tests of epo twelds the machine is firet calibrated for penetrator tests by using a block of .J.""' homo geneous material of' kno wn hard11e s a ,"'~ and applying a fixed load by mea.ns of a hydraulic jack, The penetration ie measured on t op and bottom dial gaugee and oompated with previous xesults on the same t e st blooK. Any change of shape. in the penetrat ors can be· observed and the penetrator balls ( 1/16" diameter ste el balle J identical -w ith those used in Rockwell * ...... Rockwell Haranes s Testing Ma.chine calibration blooka WELD A----- e~--...- c~--.....- -.....~-, D ...,__---+---+--+---+--t-"t'-'t" E...,__....,__-+--l--+-1'-+-t-t-1""'f'- FIG. 57. INDICATIONS OF THE RING ELECTRODE TWO SIDE DIRECT CURRENT TEST FOR TYPICAL SPOT WELDS (FAYING SURFACES SHOWN AFTER SHEAR PULL TEST.) F ~---i----+---+---1--+++-+-t-t---,G li---•--i---+--+--+-+-+-+-+-1---t-~~ ~ L----+----+---+---IH-+++++---+--1"'-t-1"'-t-r-l .5 ' e 10 ELECTRICAL INDICATION eo 100 Hardness Tes ting !A'.a ohines) may be re placed , i f nece~e,a :ry .. Before conducting eleotzioal teats, the electrical system is checked by applying a. fixed cur?ent to a aimi lar oalib:ation block of' 11.11ovm thickness and res is ti vi ty and oompa.r ing the potenti a l indication with that ob>tained ptevious ly. Corr e ctions are ma de i f indications ar e abnox mal. These aheo ks ehould be mad e before beginning a new set of tee ts and af'ter every t wo hundred welds te s ted. After the calibration of the ma.chine, a epotwelded panel is ineexted in the gap between the eleat:i:o des and the f'i :rat spotweld ifil carefu l ly centered under the potential probe of the hea.d of the tester. A p;te--load of fixe o a raount (200 po unds with 4-ball i mpress ors} is applied by meane of the hydraulic ja.oK, the load being ind icated by the dial gauge on the we i ghing bloct( ., The ind ioation of ea.ch penetxatox dial gaug e is tec o:rded. 'fhe load is then ino.reaaed to the full load setting {1 000 lbs, on the 4-+ ball asse mbly), and the indicat ion of ea.ah dial gauge ie a.gain recorded, If eleetxieal tests a:re being cond uoted 1rvi t h the same set of eleet:ro des the direct our tent is a p plied and the potential ind ioat ion recorded ♦. :rhe cu;rrent 1 i:a then interrupted and the load released so that the -w elded panel may be moved and t he next 1eld te c ted. '1'he sum of the changes in indicat i on of the uppet and lo we r: di a l gauge$ be~ tween pre.-load and full load is tih~n teJrnn a s the ind i<: at ii:m o.f penetration. The tatio of the total testing curr ent to 112D the potential indication is t a ken ae the ind i ca ti on of bonded are a at the faying plane. For great er sens itivity, current electrodes of diameter larger than that of the penetr ator ring may be used to inoiea.te the total bonded area, in a separate ' d i:i:ec t out:r:ent tee't f.ol lowing the penettat cu: t ,e::; t • .£ven on th~ laborato,xy t e sting ma.chine, a weJ..d may be teste d in leslil than a minute, tea.ding all d iale and mete4e by eye. For production measutement,s, a ma.chine capable of' t aJ.dng a.ny shape. of st:ruoture which c an be sp.b twelded coul,d be u.s ed f():C the eame measurements . The p,:e ... load and full load c ou l d be a p plied automa tica lly by oo nnec ting the loading pistons t o e ou:roee of l ow and hi gh hyrlazau lio o:r a it preli:\ sur es, and by r e oording the deflection of tbe weighin& bl.oak and ot the penetrator ind ica tors by means of magneti e ox eleQt;rio ·s ti a, in gaug,es 9 All thi.a mi ght be controlled automatieally by simply pr essing a butt on t o in.:itiate the eequ~no.e of o peration a nd ob~e:rv ing re e ultant indications on a r e ooxding instrument 01 i ndicator device, The only po;tH>n of tl1e te s t which is i nhere ntly slow is the cente:ting of the epotweld under the te e t i ng ass embly. By far the great est porti on of the time req uir ed in the tee ting operation w(mld be xequired for t .h is it em a.lone~ W1th such a mac hine, it s hould be posaib l e .1@ teat 10 to 30 apote a minute without diff iculty. Testing 1t achine /fl hae been used under several eond i tions in the testing of •S pt>twelde in aluminum alloy sheet &o Various penet:rator a.r:rangeme n ta have heen employed and s eve:ral ga,ugea of' ehe e t tee.te.d $. r::.:: ..... 'l'he fi~st arrangement censis ted of th:ree L hardened steel balls plac ed equidistant on the peri• phery ·O f a eirole (See Fig. 53A). Te s ts showed this device to ba capable of discriminating weld stiensth reliably on welds o.f noxmal . shape (See Fi gul,'es 5 and 58) but on welds of type B-4, (See Fig. 3), exxoneoue indications resulted because of the irregular shape of the a:rea of bonding. I t.proved asse rubliee with four and e ix balls placed on the circumfe.r enoe of the cri tioal circle ahowed i mproved performance (See Fig .. t'.:13:B and 530). Lik:evdse, the use of ci:raula.r electrodes o.f diameter larger than the penetiato:r oi:,:ele a s ele ctrodes for the eleo .. trical te s t re e ulted in a n i mprovement in the measureme nt of the area c~f bonding ( ~e e Ffg . 54A to 64C). ~ p_iam,ete:r ' of . .the we ld n\lgjets . . . . is measu red to within plus or m.inus 10 to 15% by the penetrator test alone as s hown i n F i g uJ;'e 59, ty pioal of results on several hundred apotwelds made in d i-f ferent West Coast air craft factories under normal industrial conditions of welding. These tests prove the ma chine to be capable of measuring weld nug get diameter xe liably. It i s be eauee of the reliability of this measure- ment that the machine is oapable o:f' rnea.su:r in g the $tre.ngth of the weld, ~ -- 1400 - -- -- ---- ----- - ~ --- - -· • • i - - -- ~-------i~-__jf-------<f----t-- CJ) ,. ~ i -- - t -- ~1300 12oc-1--- +---t------t- - - - r- - -----r--1.. -:-- ------J 5 ~ I 100 • :...:._.. :.·· . ,.,. WIOOL-~----l----+---+---+--~.~-~n-=....~.--=-=-+-----t--------1 a:: • -~ ; :.z.,.-: ..~ . : 3 900 ..:~- . ,-_;. " u.. a:: 700 - <i a ooL----L----1----1--------.~ ► .••-__:....!.'--'---f----~ - + - - - - t - ----1 soc-~---4-~-+---+---'--+---~---+-----+----1 ~ 500 a:: 4001---~--4----+----+----+---+-----+-----t------j ~ 300 ~ 2001------+----+----4---+----+------:--l-------t-----1 3 100 ( _ _ _L___ _L __ 0120 130 _ L___ _ L __ _ j _ __ _ _ . _ __ __,____ 140 150. 160 170 180 190 PENETRATOR TEST INDICATION ____. 200 A 140 0 cn13LK. a ~120 0 ~110 0 &11000 ~90 0 =so 0 <{ u.. 70 0 a:: ct 60 0 w ~50 0 a:: 40 l. I ' . ~30 0 ~ 20<.; .. g IOu 0 100 . . ., ... .. . .. • ) i .. ........ ·"· . . .,_.. . 'I'." .. . . . .. .. . .. . . . . . .t' . .. .. .. . .·. . •~ I - ' . ' 110 120 PENETRATOR TEST INDICATION 130 140 8 FIG. 58• RESULTS OF PENETRATOR TESTS USING 3 BALL PENETRATOR ADJUSTED ·FOR 24ST SHEET ON: A. 175 TAYLOR - WINFIELD SPOTWELOS IN .064 11 24ST SHEET. 8. 138 SCIAKY SPOTWELOS IN .020" 24ST SHEET (SEE FIG. 41A). .040• 'i'he .s tatle shea.r ~t;rength of the spotwe lde is me a sured to plus ox minus lO% by the penetrator. tes t a lone i n the :range fox which . penetrat or i s ad jueted ae sh own in Figure 6() on the same sete o! industrial ly mad e spotwelde. This measure~ rnent compares fav orably with the . oo:rrelat i on between the strength. and s potw eld nu·gget d i ameter shown in l'? i gure 41 for the same s ets of apotwelds. It is seen that th.e penet r at ion teat me asu:res wel(l e:txength w:i.th an e~r or equa l to only t wice the median error in the c;, or r elation be:twe~n weld nugge t diameter and st?ength. 'f'h is quality of meas ure ment i n its.elf is ade• q uat~ for t he non•d eetructive testing of epotwe lds :i.:ti industry •. The total. a,:e a .of' !;>on.-d.i lli: at the fayin g plane., i s meaauied 1 to plus or minus 10% by the electrical tes t ( See Fi g . 61). Be- caus e of the variation in the na.tur~ of the corona bond1ng and the dif f ic ulty of visually measuring tb.e oor ona a rea on the pulled welds this aorielation ie appreciably less a oc urate than that ·b e tween pe11et;ratoX' test $ and nugget size, The. di teot o or- :r e lation between eleet:rical test indications a.no spotweld e.ta- t ic shear strength is poor beea.use the t e s t does not d iaaximinate t h e type of bond ing at th e· f aying $Urfae e {See F i g . 62). 'l'l;te ;i,tat~c $heal' strenta;ttJ. of the apQtWeld s is measured to p lus or minus 10% by the co mbined penetrator and eleotiioal indications (See Fi g . 63). test The tot a l strength is determined :i,n aecoxdanoe with the relation given in Secti on IV•D. ·, l \' . ., . ./:· ••• z · • • ••• i ! ' !:: I_ l l '. ..: .. • I :.-- I _ .·_::, i-~ -- I 'I : I II I I •• ' ' :,.1, ,, : .. 1 • I • . I· I .: • I .f •• · r . I .. I I 140 150 ., 160 110 180 • - 19~00 PENETRATOR TEST INDICATION 'I .-; :- I· l I 1 I -- • l ::, o >--- . l I .!. ' ! .... , . . ' 1 ~ I I • ;l .I --,- - -- - - I 1 ' PENETRATOR TEST INDICATION 190 200 - - - --r ---------- ---+- ------ --➔- -- ----- --- .:__'. .,_ f! I -· • •r l •• IJ- : 1 '. - ,30· • - ,~o -- 150 ···-,to ·-- J o -• ,so • 1 ' • l ;I ·• • , • .•;. • : ,. -+----- -- - -~ " -- --'----• -~ - - -----• - I - I ·1·. .... . :'.·. I I I I - . I· ---1·--- - -; - ----+ . .• I II 1· - 120 130 " I . I • 1 I i i I I I I I I I -i -----1 i I - •- -- I I I I ___ 1 ., _.. ~ 1 .. . ,. : - •• I' t - - ' ; t 1 r J : i i l · 1' ------------+I -- -----jI - - -----j·-- - - --- - --- --- - - 1 r • t-.-~g 0 n..-.---,.IJ-,..-- ~ • ~o I PENETRATOR TEST --Jo-- IND! CATION I (5 ; I T~(j" .... 21 00 1 w I o -i - - - - - + -- - + - - - t - - -- - + -----+- --------+-- -- _ _J __- - - 1 z 2.0 ~ :::> (!) -~3.0 ..... C) i::I _96.0 ' 0 ·~· : ·•· -- _ __ T 140 -< 150 l60 170 180 190 200 . PENET~AI0R · TEST INDICATION 8, 85 TAYLOR WINFIEL~ SPOTWELOS MADE ON THE LABORATORY WEtOER AT THE UNIVERSITY OF SOUTHERN CALIFORNIA IN ,040" 24ST ALCLAO. • 7 .01 -. -- - ~ --- --- - .-- rn . ,'.<.; ~ .).'- . '.::f'! ;: . I '-~ •.. .•. i2 ~ -·•· . . I '~~ ) . ; , •~t.--~ 0 .~ 1· -+--- - f - --- u..- . z • (!) '. ::) , • . ~-~-: -.·.· ~40 0 ·• .- <{ ~ 5.0 1- , W. d a ::6.o-w • - ;--1,0 _,./ 105 TAYLOR WINF IELD SPOTWELOS MADE ON THE LABORATORY 0. 105 T~YLOR WINFIELD $POTWEL0S MADE ON THE LAB OR AT OR Y WELDER AT THE UNIVERSIITY OF SOUTHERN CALIFORNIA IN .040" ~ELDER AT THE UNIVERSITY OF S OUTHERN CALIF ORNIA I N . J ij Q• 2 ~ST ALCLAO. 24 S T ALCLAO, NOTE: THESE GROUP S OF S POTWELOS WERE PURPOSELY MADE UNDER WIDELY DIFFERENT CONDITIONS FOR USE IN DEVELOPING NON-DESTRU CTIVE TEST S . C. Cl) 0 ' <t I .0 ::) w . a:: o 2.0 u.. .z . 4,0 -~ ~ 3.0 ...... w 0 <( f,- . • ff ~ -5.o . 0 :---· 6:0 ;--7.0 -·-' A·=-• 1 <39 TAYLOR , t'vl ~FIELO SPOTWELOS MAO< BY CONSOLIDATED ' ' VULTEE AIRCRAFT CORPORATION (SAN DIEGO) IN .040" 24ST AL.CLAD. • ,_· - ··: ; 1.2 0 ··130 - - ' . ,,., - ' •·:::r;,; FIG~ 59. _ MEASUREMtNT OF $POT~ELO NUGGET DIAMETER BY PENETR~TOR lEST -USING 4 BALL PENETRATOR ASSEMBLY. ' -~· ., jt; ' • 04,0 ,· <{ ' ~ • '"':'50 w .• a:: ~LL.I 9&C ·s ;::__7 . 1.,,· ~{;~{i}[!f~-, . ! i· i i r FIG. 6J. MEASUREMENT OF STATIC SHEAR STRENGTH OF SPOTWELDS BY PENETRATOR TEST, USING~ BALL PENETRATOR ASSEMBLY. <nl4uu"'""c=-- -.-- - - . - - - -- -- - - ---- -- - - ----- . - - -, 0 ~1300 li1200 - - - + - - - --+------- r+-- - - 1 IIOU 1£.1 a:: 1000 ::> := 900 ,, ~ aoo--11------+--- - t - - --+---1--~---+----t--------1 ~ 7001-----+- - - ~ sw-·-1--- en 5001 , ct: ; ! 0 3 i -- - - - >--- -- - -- - ---- - ------+_~ - + - - - - - - , . - -- · - -- -, - --+-- - - .------11' - - ,-.- ---+- - ! ·i---~ I - - - . -__ - --t---+-------+-- ~ ~~I---- --+-·- ·_·._:_.._,_ _ _ 1----- - - - - - - - - - - -t-- ---1 iao· 140 150 ~ --,10 190 ·200 PENETRATOR TEST INDICATION 0130 A. 138 TAYLOR WINFIELD SPOTWE WS MADE ~y CONSOLIDATED VULTEE AIRCRAFT CORPORATION (SAN DIEGO) IN ,040" 24ST ALCLAD, [COMPARE WITH FIG. 41 8] 1400•~-~--~---.--------.----,-----..---,--.rr----. W ! I ~ '. ,' ~ 12 0 0 1 - - - - - - t - - - + - ----t-------i----r'~·- -.r:-/-·..- ~ /v' . i 1 ' ;-----.---, .. I ,, : . 1000 1------+---+---+, ,,-,,-,.·~.---+--_.~-~;-/-rt----,--;-------;i Ul 8 00 1------t---+-.--,-,"""'-..-1 / --c-~---+--·----r,~ ' - i - - - - - - t - --1 •• <:, o: 0 v. ✓ I .,.• + I 6QC1--~.........✓--_-_···'--+-~---~-_·✓---✓-~------.----,I / . . ,,,,,,, .,., -r . I 0 ,=/ ♦ :: LL (/) •• z I ,: I ,, g 400>--~1 - · - ~'- - + - - - - - - - < > - - - - + - - - , . . . . - - - - . - - ,! ...:~i'. Q. ,,.. ..:,, z 0 2001-i-•-·~· , ~ - - - + - - --+-- -; - - - - , -- - , .I ~ - -, I ;· -: q~o : 140 150 ,so 110 1eo 190 200 TESTING MACHINE PENE'l:.R"TOR INDICATION _j 8, 135 TAYLOR WINFIELD SPOTWELDS MADE ON LABORATORY NELDER AT UNIVERSITY OF SOUTHERN CALIFORNIA IN ,040" '.?4ST ALCLAD, [COMPARE NITH FIG. H H.] ..:, Ul 140"ur--- ~ - - - , - -----'-- ~- - -0 , -- ~ - -~ --- -- ------, ~13001--------+---+-----t---''--+ - --I-----+----+---~!i &> 12001------+---+----+--- --t----------,-----,1- -· - - - - --1 11 oot-------+---+-- - -+-- -'-+-...:....:...--'--------lf-'-----'-- --+-- - ~ ,ooo-·~--'------+---+----+---+-_.___._--+---+-- - + -- => ; I.,. i I :::! 9001 ~ 8 00/ ~r j - - - - f - -LL ~ ..._ ~ 7001 ; ____ _ _ _,_ _ _ i son;,...----+---+-!-.-. ~-. . .,·rl.~ en 5~1, ~ - ---,r----r- --t--1 , -+------f-- - - t----.----t-~ --t--- - -II- -, , 400! ~~~: ! I• I - - - 1 -- - j- ' i-· •I - - - ' - - ---+----- + - - - - ---t--- - + I ___. - --· ----------t----L ~ ii: -~L 1 L-~;~t __ -- l-~- I --t---~ j __ -~ - I i;; ~oo 10 PENETRATOR TEST ~t :: : _j;O~ INDICATION C. 105 TAYLOR WINFIELD SPOTWELDS MADE ON LABORATORY WELDER AT UNIVERSITY OF SO UTHERN CALIFORNIA IN .040" 24ST ALCLAD. [COMPARE ,VITH FIG. 41 H.] F IG. 61 . CORRELAT I ON BETWEEN ELECTRICAL TEST INDICATIONS AND THE TOTAL AREA OF BONDING AT THE FAYING PLANE OF THE SPOTWELD. TESTS MADE WITH R ING ELECTRODES ON INDUSTRIALLY-MADE SPOTWELDS, :- 90 I I !! I . Ii II a l ~ 801--- - - + - - --,--____j_-+---+-r-+-t------tI i lLI i i fI I .·!, I I ~ 70 I s u. o . 'ti-~ I : -I ~! ' ! . :; ' • ~ • • I I - , - - -- t - --,---+--- •I : . 501--- I 1· i ' -__;___- . -1-_-.-.-.- 1----l l · :___._ ,r.!"t.-4-+·.---..--"--i_- 40 -- - - 0 .... -t I !I I z I ' I 4: 60 1--- f•• !! ·n:= : 1-r ·_ I I I I UJ -t,- -r---t-----:--t-i-1 ! -r-I ~--. -----·---,--,- --- -r • .j I · ! i ' !-: -+-'-~+--,--t-'-;'- -,-·- · i ~ I I ' i :, • ~ 30 I (/) i 2.0 30 4.0 6.0 8.0 10. 29./ 30. 40. 60. 80. 100. • ELECTRICAL INDICATION (AMPS/.-) A. 181 WELDS IN ,040" 24ST ALCLAb MA&E ON FEDERAL WELDER AT RYAN AERONAUTICAL CORPORATION, SAN DIEGO, 9~ LIFORNIA, / 80 r- I i! !: !! !i ! ' I IX 1 · I : 0 50 ·i° i_ z 0 I g; 40 ~ 30 l&I cc ~ 20 I i ·I I I I I II I 2 I I 'I ii Ii i I i 0 (/) I ; I I ! I I i I I I .J I ,. : !I .I : II ! I I I : ! !: .. . .... 1. ♦ •• f r t Ir• .. 1".... I ., 1 ... J.lfl. • I• (.) ,; t 60 ~c{ ♦ I ! ; 1- I + I I l&I I I i § 70 1&.1 ~ . ! I ·""'J r;+ · : t !t • . • I I ii. I t j t ~-\♦ > J.I t . ; :+ .• I I I I : I ! I ! ! i I l I I 60I 80 100 I i I 3 4 5 6 7 8 9 IO 20 30 40 ELECTRICAL INOICATJON (AMPS/---) B, 141 WELDS IN ,040" 24ST ALCLAD MADE ON SCIAKY WELD~R AT LOCKHEED AIRCRAFT CO RPORATION. 110 , 105 / - ,//__ .: < 5 ct / 75 70 ~6 5 ~ 60 (.) . 5 5 .. / ~~-♦ ..,-y ~ 50 r l&J 4 .., a: ct :::> y '40 I / / ~ ♦ , "' ••' . ~Y v.ir 2,:( 1 ♦ ♦ ♦ ♦• .. ♦ ,+ .,, rt..*•/~ . + .. ♦ / ~,!Y' V ,, •' I<- ♦ I ~ ...... ♦ ♦ ~. /♦ ♦ ♦ •t / ♦ T ♦ * v / ,, V / / '~/ . .)..::Y _,w , ' i 2 3 4 5 6 7 8 9 10 INVERi,E ELECTRICAL INDICATION (AMPS/.....) 0 (/) - C. 108 WELDS IN , 0 6 4 " 24ST ALCLAD MADE ON SC IAKY WELDER AT LOCK HEED AIRCRAFT CORPORATION. ~ j 2/J 3.0 4.0 6D ao IO. 20. 30. 40. 6Q. 80. 100. ELECTRICAL INDICATION (AMPS/..........,._,) • r ! - 1.:.J1j tw SU\J u.. 400 a:: <[ , ::::! !I I • .. • .. I I i i i I . .It. .\··.,.. • • I ! __.) J J 60 80 100 I I I I I I IJ I .. .. ~- -. -: ... i i -~ tr I I F IG. 6?. . 20 RRELATION BE TWEEN EL ECTRICAL T~ST INDICATIONS AND S POTWELD S TATIC S HEAR S TRENGTH ON INDUSTRIALLY-MADE S POTWELDS. (SINCE THE ELECTRICAL TE S T DOE S NOT DISCR IMI NA TE Tt-lE TYPE OF BOND IN G AT Th[ FA Yl !~G S URFACE , IT CANN OT SE USED ALONE FG:R RELIABLE PREDICT ION OF WELD S TRENGTH .) 0. 140 WELDS IN .040" 24ST ALCLAD MADE ON SC IAKY NELDER AT LOCKHEED AIRCRAFT CORPORATION. 3 00 ' OI 1 ~200 0 ~200 l)G NE LDS IN . (;6£.. 11 ?'-lST /1.LCLAD ivlADE ON SCIAKY NELDER AT LOCKHEED AI RCR AFT CORPOR ATI ON. • . • I 2 3 4 5 6 7 8 9 10 INVERSE E LECTR !CAL INDICATION (AMPS/......_o..,) ~~oo-- - a:: c. i ' I ~ 300 0 i ! l : I I .. l I I , .. ·. · I I." I 600 ~ 300 ct 100 + ·~ ♦• :. •t - ... ' ••♦ ♦ 3 4 5 6 7 8 9 10 20 30 40 ELECTRICAL INOfCATION (AMPS/...,.,) . -~ ♦ ++ ♦ 1 <( ...J 2 : •I J •• 'I . ♦ ~ ♦ •• --- - •• ♦♦ .. •••♦# ♦ • • -- -- W 0 Cl. ::, C :t: u, 400 0 - .. ·- - -· I --- - - ~--- ~ _c_ f--- · '._j__ I I f 141 WELDS IN .04)" 24ST ALCLAD MAD E ON SC IAKY WELDER AT LOCKHEED AIRCRAFT :oRPORATION. 8. 0- 2 De-:0 z 700 (/) ...J 0 <( 0 ~ 0 LI.I I 40 ) -- ------ a:: 30 o - - -- (/) I LI.I a:: 600 <( 7 0 a:: 6 0 <i: 50 ) u.. ~ ...J => 8 0 a: 140 CJ 13 0 ~ 12 0 ~ II 0 0 Cl. 10 oc I LI.I 9 oc 1.1.1 500 =:! 800 ~ 700 ~1100 ~ I 1000 LI.I a: ::, 900 2 3 4 5 6 7 8 9 10 INVERSE ELECTRICAL INDICATION (AMPS/'......,) 181 NELDS IN .G4)" 24ST ALCLA'o MADE ON FEDERAL WELDER AT RYAN AERONAUTICAL CORPORATION, SAN DI EGO, CALIFORNIA. A. 01.0 400 300 200 100 1400 u, 1300 ~1200 ..J 0 <( 0 u.. 0 a:: C/) I a:: 600 <( LI.I 500 ~ 900 3 800 ~ 700 IL ~1000 0 ;:, 1300 ~ 1200 :::> 1100 1400 ~ / ··-;: 700 920 200 100 500 Cfl I 140 150 160 170 180 / I I I I . I i I 1 I I I I I II i II I I 190 I I II I I I I ---i I_ I = 200 1 - I 1I : _...., I ·J/I ./ - -~r'· I l l Ii·✓, I I I I I A .r I I I I PENETRATOR TEST INDICATION i /I i/1 L, °c, 100 200 400 300 r 200 100 - I 130 60 _, 2. r ... jJ ,- -_1.r: .:.:.:-·· ~--t-· .. ' 30. 40. 60. 80. 100.150.20Q + -- ---- COMB INED PENE l!"RATI ~R-EL ECTR ICAL FIG. 53. MEASUREMENT OF SPOTWELD ' STATIC SHEAR STRENGTH BY COMBINED PENETRATOR AND ELECTRICAL INDICATIONS. 100 WELDS IN ,040" 24ST ALCLAD MADE ON TAYLOR-WINFIELD WE LDER AT NORTHRUP AIRCRAFT CORPORATION , 200 ;.-;;--.r· --- --- ---- --- ------- ------- --- - - -- PENE RATC R TE ST . . ... ..... i:-1 i:-r. TRlf'A T!="C IT _r ..J p - 20. I ELECTRICAL INDICATION (AMPS/4-) 3. 4. 5. 6. 7. &9.IO. ·1.J<F 7.· .,:.JJ/' _,✓.r. . .~--~__...:- . ••"' 20 40 60 80 100 120 140 160 180 ERROR IN STRENGTH PREDICTION (POUNDS) d d 00 ~ 20 0 0:: z 40 UJ ~ 0 LL 3 UJ g 80 (/) z e> 100 a: 0 ::, 01. ~ 100 ..J 200 ~ 0 LL. ~ 300 (I) 400 ~ 500 ~ 900 : 800 c( "- 700,. er: 600 cf .!,1000 01300 ~1200 f1100 U> 1400 ...1 300 400 500 600 700 800 900 1000 · AVERAGE PREDICTED STRENGTH-POUNDS (PENETRATOR-ELECTRICAL) ct 0 0 I£. 0 0:: -- : ILi :c er: c( if. I w er: => :;! f 1200 1100 1000 900 800 700 600 - ~ 0 1400 cn 1300 [_ ..J 0 ~ LL. ILi o:: 600 c( 500 ~ en 400 0:: 0 300 : J, ~1200 ~ 1100 1000 !5 900 ~ 800 (I) 1400 o 1300 _J 'l'he wel<.l e ueed in tne tests on which Figures 59 througli 63 a:r:e baaed inoluded a large number of la.bor.atoiy weld e , later .found to be excessively por0us and defeoti ve.. Reirn l t s o:t tes ti? on more than 2000 we ld s macle under production c ond i t i on s in ai:roraf t factories are indica ted in Section VII, and indieate thes e te~ts to be mo:ce a .c eura .t e and reliable than was ind icated by the initial te s ts. :E-. CCln{l) ).u~i ons :eased on 1. n~eu lt a o:.t:, ·ree.te . ot: Teetine lilHt:£:li n~ ljl Tb.e ;ri.ns penet:a.to, te~t al~ne oan be a r eJ.iable m.eaeure of vteld nugget diamete r., It mea.suiee t ne with nearly as mlioh a.cou:r~cy as does the diameter of the nugget opserveo by dea tr uotive sectioning. I It d o~e not meas u:re the compon ent ef weld stxength supplied by Alclad bondil11f e (an unreliable contrHnJtion) and so, pro perly oalibra:ted , g ives conservative p:red ict ions of weld s t.:rength, 2. '.the eleot1ioa l te~t alone 1:neaauxes the bonded a.xea t o a moderate degfee of' ae-ns itivity. :By it·-. eelf' it ie not a ieliable meaeurem.ent of weld shear streng th, for shear stxengt.h is not m:eaeu:red reliably by the t otal area of bonding. It d oes detect v,eld s whose. faying s u:rfaoe has bonded poorly o.::;: whose bond nas been bJoken after welding, with absolute reliability. It makes paseible an estimate of the contribution of corona bonding to the weld sheat strength; and so 1s a valuable supplement t ,o the ring penetrator test~ 3. The qh:ief l.imitat,.i.Qn on '~he aooura9y of all forms of meohani,c al and electiioal teats sensi- tive to weld aize results from the difficulty of locating the oentex of the weld by observation of the outer surface af the weld ed sheet. 1'he weld m.ay not be centered under the welder electio de in• dentation. Thus the major pottion of the testing time i e requited to looate the tester above the weld • wni le t he test i ~s e l:f may be near J.y ins tan• taneous.. Automatic profiling to locate the wel<;l ao,~uxately req uires elaooia.te a pparatus and in- oreai:i,ea tee ting time. 4~ Other limitatione result from the fact that penetrator indication• depend upon alloy, heat treat ment, and sheet thickness. Calibration must be made on that all oy and heat trea t ment being inspected, with a penetratox ring af dia• mete:r suited to spotwelds in the &i ven gauge of sheet~ 12:5 Experienoe with. SpQtweld 1,esting Ma.¢hine #l bas .i ndicated principles and px-ae,tical design forms fol' nan-deetxuctive apat• weld t estexe ... L. l?ropoa ed Han.o '!'es tel' A is a s mall portable pene... tiatol' tester, similar · to device$ ,1ow on the market fox hand hatdness testing ¢i f homogeneoue ma terials:.% A ring of sharpened caJ.ibrated penetrator s is sp;ring loacl ea by hand pre ssure to ma,ke a ona.;..sid e fine: pene.;. 'hator test equivalent .to ~hat of 11est i ng Mae.b.ine # l ·, (See F i g \W 64h ('.Sy using emall diameter •, · sharpened pr,obes, a g~eat 1;e(luetion in load ts obtained r'or penet:ratione se?,]sitri,~e to weld n-u gget p;es enc e.) Thie i s a di:rect me.aau:rernent of nugget diamet.e-r~ The device must be oalib:i;ated on the alloy and temper of shee t to be tested .• A change to ring pene tJ;'ato:te of different diar.i'.lete:r ii! :requi.recl when spotwelaed sheet of greatly different thicilt;.; ness ie ta be tested -• Pro perly looa.ted above each weld, the 'hand tester should be neu ly as xeliable a.e the penetrator test of 'fea ting Maehine fJl~ 2; l'ro pesed :Prqdu~tion _t este r B is , intended for proauc'tion line use ....... poasi.bly direo·tly after the spotwe lding Qperatien..;•wi th weld ed pa:r ts being ~~ The Ba.rcol lmpresaor, available from Barber Colman Company, Rockford, Illinois, FIG. 64. HAND HARDNESS TESTER SUITABLE FOR PENETRATOR TE STS OF SPOTWELD S IN THIN ALUMINUM ALLOY SHEETS. (BARCOL IMPRESSOR - - BARBER COLMAN co.) FIG. 65. SKETCH OF MECHANICAL PROOF TESTING TOOL. i i l t I I - - - ·-- - - - - - - - / FAYING PLANE l ELD 126 brought to the tas ter. It 1e equi pped wi t h a tbioat and pxe ss or rocker a:rm of d i mene i one equivalent to t he welders it s erves,. s o that any weld made on the we lder s · can be te;.,te d on it. Two'!"side .ting pene·t:iza.- tor and electrieal tee te a te automatically oa.rr ied out and rec orded each time the operat or f oo t s witch. pi-es $ ee the Air loadi ng and strain gauge reoofding make :p ossible tests ae rapid as the lS potwelding ope rati on it se l f . Strain gauge load meae u:re ments, with p :r:e-load and full lQad a pplied by ai:r pressure and e tr ain gaug e penet;ra tion measurements, eould be rec or d ed a.utoma tio a lly, or aetuate indicato:r davices. 127 y:t De.v~·lopme;nt of Radi<:>sraph ic In~peQi;;iQn Method§.• . . . - ' At the t'.i.me this res eareh was beg"1ln; vs.d;to~ gr~PBY .C!f' ..s:eotw~l¢ls had been proposed a:.s a non... de"" structive method of inspection,. and spotweld radio'"" graphs of hi gh quality had been obtained in.research investigati ons . Long exposures at l0w voltages with fine grain X•ray film were found ne oessary to obtain adequate contra st and de.finition in apotweld radio·• g:r•aphs made wi th standard X- ray equipme n t . Al t h ough such radiographs showed cra ck;i.ng and pQrosity (when present) in spotweld nuggets, and in .moat cases showed ring s which mi ght possibly be correlated with weld nugget diameter., the nature and extent of the honding at the spotweld faying surfa ce were not revealed. Not all investigators a greed as to whether or not spotv.reld strength and qual:tty could be de • termined reliably i'rom spotweld radiographs. The limitations and t he fea~:l.bility of the method :for practical industrial inspection of spotwe.lds had not been established,; as evidenced by the fa ct that r a diogr ~hie inspection of spotwelds in alumi num alloys had not been widely adopted in the aircraft industry, despite the gr•eat need for a non.. destruct• ive tes t tor spotwelds~ 128 The de velopment of pl"aetieal radiogra.p.,.hie spotwel.d inspection 1?equired: 1. The development of radiog:r:•aphic technique is:e that spotwel.d radiegraphs of acceptable contrast and de,finition could be obtained using av:ailable com• martial x..ray e-quipment and films, with exposure times as short as a few seconds per weld, 2. The development of reliable procedures for inter- preting spotwe,ld structure, size, shape, quality; . strength,- and defects fr◊m radiographs 1 and 3. 'l'he applicaticm of' radiographic inspection to t h ousands of spotwelds from many indu.s trial sourees, to determine the validity.; reliability; and ace'l.:U'acy of the radiographic method of spotweld inspection . A. Te~~,~9.ue o,f . Spotweld RadiO£iI'~J2h:Y:, 1. X•,R~z . ~guipn1et1t: No radiogra.p hie equipment suitable for spot ... weld inspection was availabl e at California In""' sti tute .o f ~l'e ohnolog-y. Art~angements were made for the use of equipment o:e Triplett s,nd Bar... ton, Incorporated, of Burbank, California, and for the cooperative !$arvioes of an x-.ray en- gineer and physicist ♦. Calibra ted production ':/~•ray unit No. 6 (150 Kvp. Triplett and Barton, Incorporated; equipment with r e ctifier) (see Pig .66) was ~::::::}K il ;;h,,:Y A PRODUCTION X-RAY EQUIPMENT USED IN THIS RESEARCH. A, 8. PRODUCTION UNIT TUBE AND TRANSFORMER B 129 used for this research . . Standard ~perating oond! tions of 10 ma,. be run eurrent and. 36 inch source•.film~d.ista..noe,. with voltage selectei f:r.om calibration. charts to give optimum contrast with the all()y, material thickness, and .film used., were employed for all regular te-sts. 2. Sat-eo~iqn f),nd Qal_ip;rat;ion . pf .x--~ay Ftlm , Preliminary tests of 80 experimental and eommeroial X• re:y films resulted in t he selection of Triplett and Bart0n Incorporated., Type 60 { eomraercially available as Eastman Type M) film for all succeeding tests. This film is a high contra st, fine grain type rm· use without screens. For all spotweld radiographs; this film was wrapped only in black photo-graphic paper lea.d_backed to prevent back.... sca.ttel' and placed in inti.mate contact with the welded sheet . A complete calibration of thj,s film on mac- hine N-o . 6., with Z4St allo.y in thicknesse s .from 0 .01n to 0 . 25° 6 was completed with t he result s sh own in Appendix I . Due to the inherent fil• tva.tion in this X- ray s.ource,. optimum contrast was obtained in the range of 30 to 45 primary vol ts (approximately 30 to 45 KVP •). 'Ni th spotwelds in . 040ir she e t, t he radiographic contrast was approximately 0,6%1 and t he film den- 130 sity ab<mt 2.7, for 835 second exposures at lO ma, 36" souroe•.t'tlm-distance, 36 primary v0.l ts. These exposure conditions V11ere used for all welds in ,040" 24S '.J.' alley, wi th a n effe·otive field 14" square a.t 36" source-filmdistanee. 3. Radi osral-?flY . of'. _S;ije Oifie:P,S: Trials made throughout the rane;e of ~hee_t th;iqk:n~_$see from .016" to .091 11 in Alclad 24ST alloy indicated that with thicker sheets, optimum rad:tographs could be obtained with shorter exposures, with higher contrast than could be obtained with thin sheets, All gauges were radiographed adequately for re.liable spotv1eld inspection on this equipment. Exposures of normal welds in .040 n 24ST, :Z4S0 1 .3~0, and .. e1sw allozs indicated that the standard exposure conditions were near the op• timum contrast for EHlGlh of. these alloys. Fig. 67) ( See 24S alloy 1. with its 4% copper content, provided the sharpest sp•o tweld radiographs . 'l'he effect of L,)le,qing t~ fj_~m varying, dis~ tanoes pehind t he . welded specime,n was investi• gated, with the results shown in Fig . 68 . With a 36 inch source-fil.m-distanee., the film could be placed as mu ch as 2 inches behind the welds • FIG,f>7. 24ST, A. 24ST ALLCY 8. 24S0 ALLOY I C. 3S0 ALLOY D. 61sw ALLOY RADIOGRAPHS OF 2 4SO, 3s0, NORMAL SPOTWELDS 61sw ALUMINUM ALLOYS. IN .040 11 SHEETS OF 2" C. 8" FIG,68 , EFFECT OF PLACING RADIOGRAPHIC FILM VARYING DISTANCES BEHIND THE SPOTWELOED SHEET, J• I FIG, 9, CRACKS, STEREOSCOPIC X-RAY VIEWS OF A SPOTWELD NUGGET CONTAINING ) 6.8 11 LEFT FIG, -ro. 4. 3 11 LEFT ON AXIS 6.8" RIGHT EFFECTS OF PLACING SPOTWELD OFF THE AXIS OF THE X-RAY TUBE, 131 without notieable loss o.f ·def'init-ion or en.. largement. With the film an behind the sheet, noticable enlar gement; accompanied b y loss at atefinition; oecu:ri"ed, Thus i t 1s •not necessary; fo;r> the film to be i n intim1Stte . contact w:lth the w:e ld;. despite published sta tements to the contrary. ~tereoscopio x-:i:•a]t views o:f a spot weld were obtained ( see F'ig• 6-9) by two e xp osures, ttte s pecimen having been moved bet\veen exposures to obtain t h is eff ect. Viewing t hese radio• graphs with a stereo• lens v.iewe1?, t h e obse:t•ver see.s a t:h..ree dimensional image,. in wh ich the cracks above and below the :faying plane can be diser1m1ri_ated . It is not probable t hat stereo s·petweld inspect ion would be useful in i ndustry, as very little new info..rmation is obtained from second exposure • . Th.e useful . field at the standard souree-film .. distance wa s investigated_, a s shown in J.i'ig,70. Fu1... ther t ha n 7 inches of'f t he axis of t he beam~ t he e:ffective irr-adiation wa s reduced sufficiently to low-e:r film density and reduce radiographic contrast noticeably_. Some loss of definition &lso oecur·red outside t h e u s.e f'ul field (14 in. square,) 132 A speoial tub~ with .fine too.al spot (less than o.7 m.m .~ square)., and thin inverted bubble glass wind.ow,. target ~h i e $l lt and sh ort f l lament·-. target distance W•a s employed in a. s~ries of e.xpo"S.u.re s to determine the mtnimum sour0e~film"", di ste.ne.e pemn:i ttin.g QO-C.e ptable defini tio111 add the minimum exposur,~ providing a dequa. te eon~ tJ?ast and de n sity (2, 5), Excell~nt radio.grap hs we:i."'e obtained ( see ll)ig. 71) at source•film d ' a,.. tanees of 16", an., 4n, and 2ti~, w'ith 30 KVP, l.O ma 0 a,nd e xposure times of 310,. 78,. 19, a.nd 4"' 7 seconds, respeetiv~ly.-. :i:n t be latter case, . the field 9:overed was of 5/a n diameter• and t h e enl.arg~ment was 4~5J&. defin1 tion QccurJ?ed, Negligible loss in 11 l hese re$ul ts demonstrate th& t it ·is P:r;?-qt::t..cal.: .to_ , ~a.diog:t-al)h ipdiVi,~'Ual S£Otwelds .acte9.-qa..tell: wi ~~ .:~~pp,sur·e, ,t;l,mes lftS 1,o,y as 9 see.ondal, us~.n6 1shgrt souree ...filrn dis·• tanees.,. portable light weight equipment, and complete prote~tion f'or personnel against X• ;r-a.ys. With t ype M f"ilm in dental ca E,Jsettes~ a pre.e• tical, low cost spo:tweld radiographic i n speet• ion of' aircraft on the production line becomes possible, with this technique . 2 Inches s. F . D. 4 I nches 8 Inches s . ? . D. 16 In ches S. F. D. Fi g . 71. s . F. D. Effect of Var y ing S ource F ilm Distance In Spotwe ld Radiography. 133 In addition to the short s-ouroe,~:f ilm~d,.-a~ ta:nc,e technique f or inspee-tio.n of individual. spotwelds, many produ etion a sse.rnbli~.s can 1;:)~_ ~adi¢&ragl'l:~'t on produe t.i on ~quipment at la.ttg~: souree<!'film,.·d ist-a nce with resultant large fi~.ld eove!'Elge ,. F'ig;• 7.2 $hows a. part of a single 'e:x-P._o·sureJ i n cluding sever~l hundred spotwelds in an experi mentally spetwelded tail b oom of a pursuit sh ip,. TWo prints were needed to r~p:,;;oduee the .full ran g e of t h e x~ray film, :f'Qr the two layer and three la.yet> welds res-""' peetively. This is an example of a primary airers.ft struct1We which could b~ readily radiographed~ Eh Inter;ereta~1on pt -~p9tweld ~V~p.iQt3V~Pb.~u The following s-potweld propert:i,.es and def~cts (when present) can .be interpreted from properly mad.e epotweld rad.iograph$; ( 1} StruoF~e.~ including the granular and den"'dri tie· zones of the weld nugget., the boundar.y between east alloy and parent · metal; segrega,.. tion of copper· rich ma terial wd, t hin the nugget and ,of eutectic in the parent metal. ( 2) G.e ome tn;, inelucUng tne diameter and shape of the weld nugget in the parent sheet nea;r the f"E:1.ying plane, thickness Q~ penetration of e "RADIOGRAPHS OF SPOT WELDS IN TAIL BOOM OF A PURSUIT PLANE. • • r: ) G,9l't, \ RAD ! OGRAPHS OF SPOT WELDS IN TA I L BOOM OF A PURSUIT PLANE. 134 the nugget into the par•€mt sheet, contour of nugget wall; diameter and shape of eorona. ring, location of s eg!"egati ons withtn the- nugget, a.nd in t he pa rent metal outside t he nugget; and t:he ge orne t:c>y crf erne.k s, porosity, inclusions, and expulsion of metal., ( 5 ) Defect~, includi ng absenee of weld nugget, ina.dequa.te pe ne tration ( or doughnut welds), undersize weld nuggets, excessive penetration in oversize weld nuggets, c:r•a eki ng, porosity, inelusions, expulsion at t he faying plane , seg-. re gation of eu teQtic corresponding to excessively l arge heat affected zones .(I m:ts,• shapen welds, and excessive tip skid. ( 4) ~tr\?n;fktp, in normal welds free of unde sir- able defects and exceasive Alcla.d inclusions, whi ch Qa.n be reliably predicted from weld nugget area.. L , Interpre~atiqn of Fea tures of . Spetweld . - . . . . Had:l<-..>&ra£hS;i1 . . ' . • . - . . , ' a .. f rominep,t Dark Ri,~ei A,•A, shown in Pig, 73 a.n d succeed• ing rad iographs, in.d i.• ·•c~tes sp.otweld nugg. e t diameter and ' ' . . . • . .. . . . 1 .. . . shape. It occurs because t he boundary zone between the c a st weld nugget and t he parent metal is radiographically less dense t han either the body of t h e nugget of the parent nugget or t he parent alloy. Thus a larg er pprtion of the incident X- rays pass through the metal in this region Weld 37 Weld 25 Ra dio g raphs Section Radiogr aph s Section Ma crographs Fig . 73. Typi c a l Spotwe ld Rad io g r a phs, With Rad iog raphs and Ma c r og raphs of Weld Se ct ions . WELD Q, # 73 Radiograph _J Cross S ection Radio g raph Cross Section Macro g raph F i g . 73, Cont 1 d. V.ELD 100 1 Radiograph Figure 73, Cont'd. _-----..,- Cross Section Rad io grapp l35 than else.where, with consequent additional darkening of t he f'ilmi This dark ring 5. s i~Vi§il;'>li;) if the v1eld . nugge·t is abse nt ( see weld fl\•12, Fig, 74 and Weld F..;167, F'ig . '75) or ;if the ra.diograph is inrprope:r-ly made . The dark ring may ta.de or disRppear if' weld nugget penetr·a tion is very low (below 10% to 20%) ( 8.e(:} We l d F....19, Jf ig . 74) . The da;r>k r -ing becomes ri;iore dens~ as t he vertical pro- . jection cf the nugge t we.11 inoreases,. i -11e• as nugg~t penetration int o the parent sheet increases, or as the wall becomes steeper~ (see welds 3? and 73 1 Fig, 73) 'l"he w;td t h of the dark ring increases a s the nugget wall becomes less verti ca l -. ( Compare Welds 25, Fig . 73; and F'.-19, Fig. 74 with we lds 37, Fig . 73 and F• 72 , Fig . 74) 1'h.e (;lirame.t~r, afld sha£e of . t;h~ d~H'lt rinj?; correspond faithfully t;o th~ outline of the vertical wall of the nugget, whi ch :reaches 1a ma,ximum dia.me,ter in the ;parent • - sheet near t he faying plane. The actual diameter of the weld nugget at1 th~ .fayine; plat;iemay be considerably reduced from the out line indicated by the dark l"ing by excessive Alclad in,clusion~ ( However, in production welds, exoe ssive Alclad in-clusions usually occur only in welds of low pe n€rtration, which would be rejected) . ( See entire sequences of F1igs. 73 and 74 for change of dark 1:• i ng diameter in corx•espondence with changes in nugget diameter) . See especially Welds p,..4;:~ and F•44, FIG.-Jff- PART I WELD Fl2 - STRENGTH 0 WELD F-19 STRENGTH 260 POUNDS FIG. 12• MACROGRAPHS OF FAYING SURFACE (A), SECTION (8), AND ENLARGED RADIOGRAPHS (C) OF TYPICAL SPOTWELD SPECIMENS (10 DIAMETERS, EACH SCALE DIVISION =0.01") FIG. 1.'! - PART 11 WELD • F-39 STRENGTH 330 POUNDS WELD F-56 STRENGTH 500 POUNDS WELD F-72 STRENGTH 580 POUNDS WELD F-76 STRENGTH 560 POUNDS FIG. -._, - PART IV WELD F-90 S TRENGTH WELD F-11 2 S TRENGTH I I I WELD F-122 STRENGTH 1385 POUNDS WELD F-126 STRENGTH 840 POUNDS FIG. -J:S - PART I WELD F-16 FELL APART FIG. 13. MACROGRAPHS OF FAYING SURFACE (A), SECTION THROUGH NUGGEr BELOW FAY~NG SURFACE (8) AND ENLARGED RADIOGRAPHS (C) OF TYPICAL SPOTWELD SPECIMENS (10 DIAMETERS. EACH SCALE DIVISION =0.01") F.IG. 915- PART 11 WELD F-30 STRENGTH 200 POUNDS WELD F-42 STRENGTH 330 POUNDS R[STRrc FIG.~ - PART IV WELD F-43 STRENGTH 310 POUNDS FIG.,5- PART V WELD F-44 STRENGTH 260 POUNDS RESTRICT[D FIG."15- PART VI WELD F-62 STRENGTH 460 POUNDS FIG. --,S- PART VI I WELD F-83 STRENGTH 575 POUNDS WELD F-100 STRENGTH 605 POUNDS WELD F-117 STRENGTH 850 POUNDS WELD F-133 STRENGTH 880 POUNDS r _ PART XI FIG. a;, fl ! -· /4 .II ,, . WELD •• l ' .>-, ' .f'- ~-;- F-13q STRENGTH 1200 POUNDS 1 36 Fig. 75; for correspondence of shape of dark ring t o sha.~e of' weld nugge,t just below Alclad layer at faying plane . ) b . 1111.e ou~e~ pQund~rz B,.;~-- of .the, ,-uniforn1l,1 1:te;ht are~ shown on ! 1'ig .. 73 and succeeding ~adiog1"a.phs, del,,i nea tes the outer boundary; .of the eoro~a.. rea;~on at tl;l,e ~n;terfaee . sequence of Fig . 74.) ( See entire It usually resuJ.:ts from changes (due to heat and pressure) in the Alela.d l ayer at the interface; and is most evident when mater ial of the Al.clad layer is pressed away from the nugget region ,. sp:x-,e ading the sheets and filling in t h e interfacial volume as shown in the section s of Welds F• 19 1 F..,39 , F•56 and others ot Fig . 74. The boundary B;,i,,}3 need, not . neeess~:r;tly. ; be the oute~~r.no:s~ . . . .. t,in5 o:f the spotweld radiogI'a.ph-.- in some cases~ t he seal• loped white ring 0-0 resulting from extruded pools of eu..., ,·:,· t e ctie may he ou termost . Boundary B• B can usually be xiec ... ogµi z e.:a. by its relatively smooth contour and pearly ·,niform density. it is not necess arily true t hat the diameter of b oundary B.. B bears. any .fixed ratio to the nugget d iameter••as shown in. Yeld F' ... 12, Pi g . 74 1 whicl1. ha s no nugs;et, yet ha s a faint boundary B• B d.ue to sma.ll effeets i n th.e Alclad layer at the interface . ( See also Fig , 42, showing measuremen ts ~ for a single group of welds in which the ratto of the cor• ona. di.a.meter to the nugget diameter var ies from 2:l to 11:1 ) c. The . s.eallo;ged white r,ins o..,c, shown prominently on ·we l d 73, li'i g . 73 and on Welds F- 112 and F""'l22 of F1i g . 7 4 , i ndi"!' cates t he, presence and location of radiogr a phioa.lly dense 137 ·, :go,o;I._s and stpingers 9f eµt~c;ti _c in tl+<? par~nt· met~l _?Ut$1de tJ:i.e we'.Ld ,n-U,t,se;e~• These stringers and pools of eutectic &re shown cilearly on the r a diograp b. o.f a vert1Qa.1 section of' the . ?eld 73 .o f F'ig . 73, and are seen to lie in the parent metal;, near but not necessarily at the faying plane. Occa sionally sueh a conducting channel f'or the . 10-,N .melti;ng alloy breaks through to the Alelact layel? at the interface , fo:t"ming a bliste!" or bubble of eutectic between the Alelad laya:r and the parent metal , The pools a.nd stringers of eute_ctic usually beeome 32romit1~:nt, -onlz pn h:iS16er $nere;;i w~l,da~ and ms.y be taken as evi• dense that the i:arent metal has been we akened along these channels .out to the boundary c"!'c. 1he effect is probably synonomous with that of an excessively large heat af.fected. zone outside the we l d nugg~t • . '.11he eondition is evidence of excessive heat in t he r eld, and usually accompanies over• sJze nuggets with excessive penetration. On low energy welds t h e scalloped white ring C"i"C is usually absent, since little or no e.xtru.s ion of eutectic :ti...as occurred. d. Lit3ht Zone ~]?.;;, . just insid~ d:a:rk .r ing A• A_,, ~hown on welds 37 and 73 of fi'ig. 73 and visib le on most spotweld ra.<liographs; g~~ms . to . co;r>rE3la,t,6r wi~P. _t:pe ~Q.l ;~ar . .zone 9t, ~he; }V~~~ n~g5$.b • . Where the dend:r1tic zone is bro~d and thick in ve:i:•tie!;\l seetim, the light zone D.. D is clearly evident on spotweld ra.diographs. 138 Attempts to c-o rrela te either bounda:ry of Zone D- D with the inner extremity o.f' the Alela.d inclusion have failed. In general, variations within zone D•D seem to mask r a diographic images of the Alolad inclusion, so that the latter cannot be reliably deteeted. 11 On rare occasions, se gregation of' copper ... rich material ocet;l-t's prominently within the spotweld nugget; resulting in light radial striations~ (See Weld 100 Fig,4 '73), 'I'his com• ditio.u occurs a..s weld heat is increas©d towa.J."d t h B limit at which era.eking occurs in t h e nugget. ZonE} . D• P has no pro~,en. Eiignifieancfi> in p;redicting weld streng~h or 9,uality,. as no correlation has yet been obtained betwee-n weld strength and differences in the eas.t s tructure within the nugget . e. ~~ Zone E,..E :l,p t11~ ; _Qen~e.r of.' the nugrw~~, ins~ the inner hcnmdary of the lifi!lt. ~one D•D, shown on Welds 37 and 73 of Fig . 73t ;ppssib;I.:;r corr ela:tias with the 5ranu.l a.r z op~ o:f the weld nusfiet . It_ kta.e1 . no p;r-ov~n ,tu,~tuJ,. sis,:n;i..,l!;panc,e in ,~n.. te~I,?;ret1llS welrl_g,-u~_litz. Tb.e e.ffect of sheet indentation by the electrodes of the spot ·weld~r is also oeea.sionally evi• d.e.nt in a gradual darkening of the image as the center of t he w@ld is approached.. However, in .<a peeim{!)ns whose out$r surfaces have been ground flush and parallel,. the d arkening is still evident, Zones n... n e.nd E• E may vary greatly in shape and de nsity. 139 With .misshapen nugget$, such as F--42 and p.44 of 1r1g . 74, these variations are obviously correlated v.rith nugget shape., appar• entl.y still following the dema.:rkation between granular and dendritic ca st structure in t he nugget . f .. Cracl-t$ and, Poro~iti ip. the weld ll:tlSS~t a,~pe-a:r a~. ,P1~ominent bJ;a2~, m~r!fdi:!1SS 1t~..F often radiating spokewi se from the center 1 of the nugget. They are actual voidis, henoe mol"'e x... r ays :· pass thl'ough those parts of the spotweld to produce i nte n se blaekening of t he x-adiographic film. Cracks usual j:y are the reault of excessive heat or. inade .... quate tip pressure during welding. There is no e'l!ide,noe that c::racks reduce the static shear strength of s potwelds. Recent tests indicate that cra cks may reduce t he f~:t~a;ue strength of spotwelds in ~tressed atta¢hments. g. Sesresation of_ copper ri~h material withi.n the weld nugget a.2a;gears . as l~5ht., (usually radial) s _tria~1on $ G..-Cl. 100 in Fig . 73). ( See ~ eJ.d These light str:1.ations :result because the segregated material is r ad.i ographically more dense than th~ surrounding cast alloy of t he weld nugget. The condition of extansive segregation witb.in the nugget is re l atively rare. It occur s in l arge nuggets whi ch have been subjected to .more t han normal heating, o1'ten under con... d i tions elos·e te those producing era eking ~ Possibly t h e copper rich material g · t r~r s in incipient cracks--radi o~-raphs have been observed in which a network of bl s. ck cra cks {voids) 140 connected to a netv.rork of light striations within the nugget .. ]:here is n0 experimental e"(Tidence t ·o date, to show that the 1 segregation within the nugget weakens the weld,w However,, . the condition is undesirable., since it occurs on the borderline of excessive weld he ating which pr·oduees cracking and an ex:- cessively laJ?ge heat affected zone outside the weld nugget. h. E*pulEd01}, .o.f, metal (,tlspit"t ~t ,the fa~rint3 plane H-,,tf appe~xs as an irre~uta~ liSh.t a~ea outaide the nqrmal w~ld region ( See Weld F-•l2 6,- Fig. ?4 and weld F~l33, Fig •. '75) with the Qhilracteristic sh~pe of exr>el+ed matepial seen on actual welds . It is easily recognized, and occurs usually on welds me.de with exce ssive heat., insu:f'fieient electrode pressure~ or impropex•l:y prepared sheet surfaces !> In general,. welds with 11 spitH are founc1 't o be of lower strength than norxnal welds made under similar conditions. i. M1s-sha.£en wel~s! .~characterize-d bz ~rr_esul,e.r . or, ova!_- ~l~tilp~d..nus;se~ _bpt~ndariies {daf:~k_ping A-A) are easily recognized, ( see we.lds F•42 and F''!"44, Fig .• 74, also examples _ in F'iguJ?e 72) Such mis- shapen welds usually result from impropel" or nonuniform s heet surfa,c e pre par-a tion, from d1:rty or mi ssh.a.pen welding electrodes, or other local inconsistencies . Although individual mi.s ... shapen welds may have adequate strength (if nugget al"ea at the :raying plane is aaequate}, t he condi tions producing mis~sha.pen welds also produce weak and defective welds . Hence this eond.ition is undesirable. 141 j E4eess,;l.v:e. tip $kid may b€l evident on the radiogra.ph by a mal?ke-d di.f:fe:renae !.n the density of the uniform light; a~ea normally re.p :r-e$enting the eo~ona and bounded by B-B,;, as shQwn on several of the two layer welds of F1g., 72 . The ma;rked lighteni.n g of this zone Qn one side of the weld result.$ £~om th~ increased thickness of Al els.d mate.rial on the $heet surface, pushed up as a. resttl.t of tip skid,. This condition should be ohe,e ked by examination ef the surface of the actual welded part . Tip skid is undesirable beeaut:Je, .it may introduce in.• consistent pi~essure conditions during welding, and usually introduces loek.ed""up stresses in the welded pa:r-t;.• C. In,spec.t.;l9r1 . P.f "gdedur~: Radiog~aphic inspection of spotwelds is a useful supplement to~ bu'G not a replacement for, process control and visual inspection. It prerndes the inspe ctor with far more oomplet.e information concerning the weld than does. visual inspect.i on. This information should be used by the i n spector in exactly the same manner as equivalent in.forms• tion obtlaine-d by de ,s truotively sectioning speeimen welds would be 'lrned. No change in $tandards of weld quality and strength, as established through specifications and industrial e.xperience 1 is required. Radiography simpj.y provides more comple ·ce information on which to ba s e judgeme nt of' weld qua·l- l42 To fur-nish a ;r:eferen-oe standard for the analysis of weld quality in any .give.:n ;factory~ a series of et a. tie sh~a.?' test specimens in each gauge and alloy should be prepared and r adiographed• then subjected to static $hea.r pull tests and destructive sectioning.: In .making these specimens, normal production conditions sh ould be used, excep t tht~t one or more welding v ariables;, such a s weld current or e nergy•, should be varied throus,h the wide-st possible range to obtain a wide range of strengths and defects,.. 'l,be significan ce of' each def'ect and the relation of nugget size to weld strength can be determined from these .speeime:ns ♦, A table of standard reference spee.i.me-n s, including welds of each nugget diameter and penetration, and specimens of each defect, e.an be pre,. pared. Such a table should show,. side by side, the weld section, the weld faying surface• and the radiograph for each weld type, as well as the wel,d strength and its acceptability. A ~urve can be drawn relating weld nu·g get size (measured by t he dark :r:-ing A• .A ) to weld strength,. trom which the st.r ength of produ ction welds can be predicted from their radiographs • '1:he reference table at.id curve should be placed where tne inspector> ean re.fer to tn.~n1 while examining radio ... graphs , (Fig. "/4 shows such a table. of' data prepared :from '11aylo1" Win.field ·welds made at the Uonsolida ted Vul tee Air• . era.ft Corpora·i.;ion .of San Diego,; and Fi g . shows the correla- tion of weld strength to da.rk ring diameter for the weld.s .) 143 te~P~ ~.t;ttop nules l •. 1l1h e weld s h ould be rejected if the ra.d.iograph shows no ......._, ~mp.se of the we.lo. nugget .. The- da).?k ring Jl;;. A outlining the nugget may be absent if there were no weld nugget, if the nugget were of doughnut or crescent type with 1e·ss than l07J to 20% penetra tion (usu.ally possessing large Alclad inelusions), or if the radiograph we1"·e ma.de with i mpr oper technique . 2, The weld should be rejected if the dark ring A• A outlining the welti n.µg €ie>1.l, i/s ·too ~m;e.ll . ir:i. d,;ta.met~,r to permit the re- quired weld strength to be develope4 in the nugge t, Corona bonding outside the nugget should riot be relied upon to provide weld strength, a s poor surface pr_epat-a.tion may result in no corona bond.ing. 1be nugget diameter re-. quire<i to maintain weld st:t>eng th above minimum ae.c.eptable standards oan be dete;r-mined from the ourve relating weld s.trength to dark ring diametert tor the g iven Sh$et thick- ness and alloy . 3• r:rhe we ld s hould be ;re jected if ~~e~ss1v~ e»:'1:1,9kin;S ('>X' . po:r-. osit_u occur in the nugget .• The limit of a cceptable cracking and porosity must be established through experience, with due re gard for the - ll!S~. for which the spotwelded struature is intended, 01-.ack.. • ing is excessive when -e~a.eks $:x:tend to the sheet surf'ac.e o~ the boundary ot the nugget, o:i, when the¥ are such that they 144 will extend to the sheet surface or beyond th.e nugget boundary under loading. Sueh extended cracks may intro- duce corrosion into the weld, or propagate- under i'atigue l ,e ading. Cracking indicates excessive heat and inadequate elec;,..,; t:t?.o..d:e pres sure during welding• Limited dull porosity is probably not ea.use for 4'ejeotion. Po.rosi. ty suf'ficient to reduce appreci ably the, effective bonded area at the faying plane , will decrease weld strength and is cause for re-jeetion. ( See Weld 73, Fig . 73.} 4. 'I'he weld should be rejected if m1:5J5et Fenet:ration is i:p.• ad~guat~ o:r e:/l~c.e ssi,re. . . ' . ' ! Nugget penetration between 20% and 80% of the sheet thiekness is usually consldered acc.e ptable. Inadequate nugget penetra tion can be recognized if the dark ring A A is broad, faint., and of small dia• meter, fading into i nvisibility locally, through oem..parison with standard specimens with inadequate pe-neti•ation.. Inadequate penetration usually :i:..esults in e:xten.... sive Al clad inclusions into the weld nugget.,- wt th :tn~ consistent, poor, or zero bonding •. Excessive nugget penetrat-ion can be recognized if the da.;rk ring A A is unusually dense., of large diameter, 1 45 and oth(;}r evid~ne~ts of excessive heat, such as. a pront.-. inent s -c alloped whi te ring C-.Ct are present ... by com:.. parison .wi.th standard specimens. with excessive pene.t~ation .. Rxcessi ve nugge t penetration may be accompanied by re• duced corrosh;in resistance or even breaking of the Al elad layer ~t the sheet surface• and is a definite cause of lowe.r e d sheet e_ffieiency .• 5,.. Depending upon quality sta11da:rids and the use to be made of' the spctwelded. sttauc-ture, the weld may be rejected if' $P~?es_s:t ve:lY l1'\;r5e p.eat a.ffe.c:t;ed_ zon;JS exist outside t he weld nugget ,., Excessively large heat affected .z ones are indi.cated by the presence of' a p!•ominent wh;i. te s0e.ll0-ped _ring c.c •. Such zones, weaken t h e weld ed joint under fatigue loading ., 6~ The weld may be rej e cted if fi~pe.§~~;v,e ~~;eµls 1ipp o.f meta,l , tl,~Pi t"J . oocurs at the faying plane .. ( ,' . A small,-, infrequent na:pit 0 may oecs.aionally occur under normal welding e._ondi tions due to an unusual loeal sheet surface eondition,, Such is not cause for re.ject1o.n. Expulsion of large amounts of metalJ• coupled with nugget p ;:ros1 ty and bl_a_ckening of the radiograph due to absence of metal, is cause for rejection.,, as such welds are usually weakened appreciably by expulsion., 7 -· If the weld is not subject to an~ of the listed causes tor rejection; - if' 1 t paases visual inspeetion, h a s a novmal :radioga.ph,. acce.pta.bl.e penetration and shape_, and if the 146 nugge,t diam~ter is sufficient to guarantee acceptable strength in the weld nugget., the weld should be ae-cepted. A normal weld radiograpb _,- sho~rn olearly the nugget outline f:i...,.A/) with width and density c.0 1•responding to acceptable nugget penetration, and shows no weld def'eots. A nugget diameter sufficient to guarantee acceptable st:rength can be determined from the curve relating strength to dark ring diameter on standard specimens- in the same sheet thiekne$s a.ncl al l oy •. Be The feature~ of' Zones D-.D ap.q. ~~1:il in the weld nugge~, and the presence of 1:tg:P.t striations o...,Q ( segregation) in the r).UE)ge-t, b.a.ve as ye1j no proven sign1f!oance in the interpre• tation -o f weld quality and strength fr-om ra.diographs . ~h '.!'he frequent oecurnance of missha pen welds., por.osi ty ., and spit may be taken a s evidence ot improper or inadequate sheet sur.face preparation for welding, or of bad tip conditions during welding • 10.- ..: ~ he combination . of' very la.X'ge nugget diameter ;, A..,A, ex-. cessi ve penetration• ~raeking, l\lld exeessive segrega tion of eut-eotio. in the parent metal is evidence of e x cessive eurrent or energy (resulting in excessive h eating) in the welding p.:t"ocess . 11. The fr-equent 0ccu1"x>ance o.f' era eking and/ or of porosi t y in the nugcet, ~ven in weld.s of normal .size, is eviaenee of inadequate eleet:rode pressure during welding, or delayed or J.47 inadequate forging pressur-e.- 12. In a stx,u.eture containing a cceptable and rejectable apotwelds• the use planned for t he strueture;,. the loeation and type as well as the r.i;u.mber of defective welds_, and the probable eause.s of the d efec.ts; must be considered inoo• te!'mining the acceptability of the welded structure. P:t>imary aircraft s.t:ructures·., whose failure would exi... danger personnel and t he plane. should be welded to high standards. SeeondaI'ly structures, whose failur-e is of little aign1f1oance, dQ not merit the high eost of high quality Vlelding and inspeet:ton , Weld location ls important. Failure of the end weld$ in a row of weld$ may lead to suoc.:;essivfit failure . _, or it zippering" of the joint. On the other hand, a weak weld in the center of a la;rge area containing hundreds of n ormal welds might do no 1'i.J1:mn1- mince usual practice is t .o include many more spot1Yel.ds than required by the anticipated lQads. A few defoet1ve \-Velds among many normal welds may be harmless; but a few def'ective welds in a group of bordel:•• line acceptable v1elds might be dangerous. '.lhe type of weld defect may be impo:rtant as a result of loeat10t1 or of' type of loading, and sheyuld he evaluated with the$e factors in mind, Defective welds resulting from bad W$l..d ing pl?aetiee , improper $heet surfa ce preparation, carelessness, or 148 easily remedied causes shou .d not be accepted, Defe9ts \Vhich occui- undez• optimum proce$s control and weldinb qond'.l.ticms due to sma.11 and uncontr@llable factors may he tolerated when no possible daiuage can :resu'i t tQ the structure. 1 49 VII RE SULTS O:ft1 TESTS ON I NDUSTRl'. AL SPOTWEl,;.1)§.! A large munbe:r • ot in.dustvi..al:ly made spot"eldtl from Southern Calif'ornia ai:rora.ft faeto:t•:l.ea wer~r radioJg~aph$.d 1,. subj ected to penetr ator and ring electro-d $ t:ests, arid pul.,J:.ed to destruction as tlngle spot static shear test atri'ps.-. Th e welds were t h en .s ectioned,, · polished and e. tehed to de\i!'i termine metallurgical structure and weld geom(l}tr:v, Th.$ radiographs and the welds were care£ul.ly inspected and mea'"'' $1.lred,, and the corTelation between radiogvaph ie t'@atl1res and weld properties W8r·e deter.ruined., The r ~sul ts of te.sts of three typical gr·oups ot in..dustr.i al w~lds ·t 1~ 166 J?ede1:1al Spotwelds Made By The Vega Aircraft Corp- oration ot Jilurbank,, Califorri..ia. ., 2.., 100 Taylor \iJi.nf ield Spotwelds M&e.e By Nortbrop A! .;rw CJ:>aft,- Inc., of Hawthorne,, California~, 3., 138 Tayl or Wi ndfield Spotwelda fllacle By 'lhe Co:naolidated Vul tee Aircraft Co:rpO.l"'tation of 1'3.an D:l; ego a.,..r1d one group of laboratory w.elds., 4,.: 326 Tayl or Winfield Spotwelds Made At t he Un;t'7e;t-$1ty of Southern C~l,if orni~ .., are n ow presented in the .form of graphs., ph otograph:s ;, , and tables of data . For each group of' welds, there appear in sue ce $sion: Table r-. ... Data On Condl. tion s of Welding Pig . l . Contact Reproductions of Ra.diographs of' ':Bypieal \'v eld Specimens . 150 Fig .. 2. Correlation Between Static Shear Strength and Net ~Veld Nugget AFea at Faying Plane (me asured on Welds) Fig. 3. Predietion of' New \Veld Nugget Area at t h e fay-+ ing plane by Ring Penetrator Test. Fig. 4. Prediction of Stati0 Shear Strength by Ring Penetrator 'l'est . Fig, 5. Prediction of Net Weld Nugget Area at the fay• ing plane by Eleetrieal Test . Fi g. 6. Prediction of Statie Shear Str$ngth by Elee"'" trieal Test . Fig. 7, P:rediotion of Net ' Weld Nugget Area. by Radio .. gt-aphic Dark Ring, F1g. 8 . Prediction of Sta.tic Shear Strength by Radio-, graphic Dark Ring. Fig . 9. Comp1.aris.o n of Aoc:ura cy of Static Shear Strength Measurements by Different Non ....ne structi ve Tests.• Table II..-. .... Qoraparison of Accura cy o:t: Mea.sur-ement of Spot• weld Static Shear Strength By Weld. Nugget Diameter and By Non""Dest ructive Te sts. tra.ble :tr1 ....0etail of Radiographic I ndica tions. A. Results of Tests on 1 66 Federal Sp otwelds Made By The Vega Air craft Corp.o rati on of' Burbank, California,. Alctad Aluminum Alloy . Sheet. .040 11 24ST Tl,. BLE l SP(;:c n .;m;N DAT.;.. E\, : ::E)oTw;: -u :.:- sp:;cn,r,,;:r. s 1L•J r~ AUGVS·~ 20, 1943 l<'<D 0AI,IFO:J.tI A HISTI'l'Ul'E OF ~x!CHNO:t.OGY M.\ TI~ c.; I 4.L : hl..ti.CRINJ5 : 0·;:..,lAlHNG : M.ACH i k~ S':•~'11S: rnGS: . 040 to .040 24ST Alol P...d }:l' ederal Ty~ ,1?2-36-R..-oa-.:ierial 8918 0ondenser DiscMt!'g& Oa.k i to if 84-A Time,-12 minutes Welds No. Spec.No. Kilovolts '.Jondenser Weld l<"'orge Electrode Electroc e ;,.ppr ox ..· Smar l.b.,P:ress, Pre. s s • .'Press. Bottom , ~1¥ .D • !, .• -' 112 "+2 ½ ' 1"l a t 175 " rt 796 ,, If 22~ " It .. " ,, 800 IY Tl " u 32() 2.20 800 " ~75 2.30 800 " ,., " 7 " ,, ,. ff -f.2i Cl33-94 8 2 .48 800 n II It It ..Q95-106 9 2.50 800 ., .~ 480 If ,; Oi07-ll8 10 2.54 800 " 0119-130 11 2.i5 800 "' 11 ff ... . il5 0131-142 12 2.76 80P H tS " ft i89 0143-1 54 13 2.so 80 0 " " B 725 0155-l Go 14 2.78 1000 If .01-1 2 V• 1! 84 • 800•. 450 1-400 013-22 2 2.80 1000 " n ,0 23-34 3 1.86 aoo ,, ~ 5 ...4 6 4 l.97 800 .047-58 5 2.05 059-70 6 .()11-e2 ~ •.;; ,_ , . " 5 / l.G •t " n 275 ' . It ,, ·495· ,so ?~Q ,. Contact. :Rad1ograplu3 of' Vega Weld.s, Figure 1. ...-S) Q cj ,· (:) <:) - ~ 't 0 ~ a <:) - -~ 0 ..., 0 - 0 <) 0 -- <:r "' 0 • . a0 • • t. 0 - Oo 0 • •• • C"I 0 • ..J) 0 • 0 i . T11 : --t IJL . 1 • A 3G 23 .1, .JJ 11uJ>t .A . .- .U V: I ~ut, '.' 1 i_ ·: :'!_'. ~-;:i. FAYING PLANJ!; BY RING PENETRAT OR I'J1.S l 1 I , -, IlG1IE.E 3--PREDICT I Q;\l O! NET Ni~LD NUGGE'1 _AREf ,A ~ THE • ' 1 ·- ; , , I: V "<'(H 1V:~.ns p~~gg~1'0 43 ·--s- ... ,,., . 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I ·1~ -,·,,· ·:;,t; ~~~, H-: 1· .. . . --4-:-;: r·:-! I -, '• l " ,-, "l !•~ . :: I ,1::1 :t- • I r ' ,I :.lJ! I 1 _L_ :- t(',11; ,- r·--- : I - :,' I .~ / ( 1-- I PENETRATOR TEST I .NDICATION i• '}QJ¢JJ11 k"s'8, •lijct~-:;B~#~h:l Im ~r ~-:~ ~if~;~ -;ia~:C i'• ';j_]J[i 1: 1,;,~nl] 1H~tJi~faj,o (/) ~ Cf ~· 0 ~ z g! p i ~l ,:il' l ·'1! l·-i q! ~ ix: (:q H ,.._, 'l I 1 _··. [••.•' .. o:i ~if I :13 .:\i:i; r:w:ir: 1_r :;i }Itil1l j Jtil }_,lm rrrn[:) _i)lj:¥~; r~~4.0~1j; >H::1~e~i~ -~:nq:_mt :y:!::i I,.-:~,J:,,.,.I ,,, . Y . ►i .h~1fl •)·,:,:: -: ·,11 i! ,i; (; , r:·.rn i 1ii-.it ~1tJ O ! Vi ,,: t=i . n i hf .. _ -: , ').:11 i·.-s.;·:l,l n: l r r~s-2 -:: .011 U} A 11 1 1 i 'to. , ·· ·r I I ·J I I : l - ~ • I ~ •- : : ~ : , :.. I 01. I ·.: i:f ~st .l:itHLI~[ '!~ ' • • -- ~ Jf[~~t;~ -:~:-+~--~ JJ"; '.:!u3}i ., •• .: ".T'i ! " ';•. : :JJ# _ j''_ ••••lI • ft,; 1:;!.· :· ?:1·:i;:.';.•; 2 ; ••: Ii'.:' I·:!1, !,t: ~ f'. : f II j' .. I, .I JL ·H '' - I ,- ' i I . rt :--, l"' .l -r'-•· . PROJECT 43 GROUP 0 V:J:ti LlA W~d:Ji) S -, 1 1 ' I !~:. I • ,,J ..- •• ', 1, _ 1;•·1 • ." . ';: •· t . . . . , ( ,--~ '~ : 1 ! ' , .: -: I Tl ·/ _)':,ill , W" I , ,·•-· , , , . , • , .t ... J1 :, ;;,;. i? . 1 • .• , • •. 11 .. -~ ! I . • ' ' · :· I . I ., ! • ,,zj . \.. . , ~ '1 ! ; : •..• '. ' , .; .; .•.:..:. ... a. ,I .:.,--~r-•·-~~·- .+.--~ · • · / . . . • .. •: . . I . . · -· 00 !/.J~A ;-. u •· • ..;-- ·· ·, :,l:! T ·. !: . I· .. , ;; i': : -~~..:,~:t ' -:-:t - u.,... . ; ," : .':+ ··; :;:' PENETRATOR TEST INDICATION 1 r ·.< ; •• •t !i - -~- · ; ·' . ' ' ,_ , . · •-;/ ; • 1, , 1 i 130., ;... ,; ,, l~~i. l."i Q. ._L: ··-~• .• . ,... , .' ~ ""' -,~ .. :: !: ; • ;; . L , .4 ,.,,. . ,: ·1 i:[l ifit:[}fu:• l~~ ;;: {f} ?¥!:~fl~-~~t~ :-,]~-:Tt4 lI -1 1~·: ~\;-, !:)~_ :':: . c; ••Hl \~t :. :· :1:::•·~ ,·-· •.. ,L . - ' +---+ -~~~-c.: : I:••·• I c-., " " L.......!.. c ;::-: :.1·:: ~::o.t· :(m@:~t, r·-: : ..... - 1::rt cc: , ·-· P- , , ·· , :--- ,. · w l 11 FIGUllli 4-PREDICTIOH OF STATIC s HEAR "ifTkEtlcfTH BY RI NG PENETRATOR TEST !~ ·-!-- ~f-:- ·. ! - -~ - -._L,_ 1-~~ ~ :-~ +-:-- ~"-:":-;-~~:- : . '. ! . , I .. ..· ·I ::l ~. . .. • ..,· - .1 ,, . J ., .•• : , I;J: '••• :,· -· t-=• ••• ,, ;••, -•• •, • ·• / • ·; . •. , ..... ; • nn · ·· • ·· r '' ..'l.. :r t~Bf""r::lh: I 1a , 2,0 t--l 0 ~ pr, 0 ~ Cf) ....... 1-,.-1 ~ Cil ~ ,-.T.j s,...:.i H ::: r,- ~ I I ~ D ;::) ,.:.; f-.• V2a ~ 1 l .?J 11; ,; , :bfif 111.:! :.trl J o; OI ;, ,,; . Y . i1 .. o::.i A3C2: J .h•;J 11<r•·n ; ~-;11 ;1 r r - e c:e .t.:> :-i I ' 1 i I: ---r I iI I ' I :' ' ~~- ' l I I ' i I Cl) - -·I i ; I' ' , I :··;• j - -, ! 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' : ' ~I •• 1 JT - 1 -11 ri!loo. j : : : I' ,,: : I i · 1· i j . + 1 16lO.. •1 :SQ. 1 , . : : • ! ' i . :1' ' . : . : I I l' i .. ;I I! ·1 : ' I I 1 ·r-- ---;-- --~- -- --·- --- -- ~ - 1 ' , , I • I I ' : ·' 1· ,. .I ·- --r1 , ---::- ' 'I ' I ! ; . ---+----; -·- - ---~- --i--~- -- . _J___ •) , I i 1· • '_J .. ' • I ; I i I ' ·1 I : I ' I I I !· ·· 1 _j___1!_ __ [___ -_:___rl·- +-I__ J: J-! : ' I l .1 i .•·'i ➔--~-~----,- I 1 · • ..-, 1-- II !. • I I I I i \ • I. .'' ' ' I i I _--1_____: _ 1__ __ _ _1 _ __ ! ! ! i I -, 1·· : 1 ' .. I 1 ·· ' - I ' t · _ _J_~_ • _: 1J:-.• ~ ➔. ' !I I i! i l I i lI J?RQJEcy ~ o, :I Gm1UJ;l O _I _.~.., I J~ - ' •J 1 l I I ; •I __j_ I ! I f I ~_j______ i__ _.__]__ __! ___ I ft·: : ' . ' ! • ' I . r-I _I _. ·--~- ---; --------- ·I -~-----~:,;-~ :-:-, ' • • • 1 •• -· · !I • • • ·I . -' • . 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' I i- ! ! r--, ! .,I _-__J__ ! _i___, _____ -· ________ J_____ ___ -~- ' I I' ! I i' . ·~ ii '' I ii ' I -:1--t -i-+ ·I· , l . ; I -: ' ' ,. ' _,______ _ __ ~_[___ - ___ j _____ I · ' -' i . I' •• 1_ __ -I! FIGURE 5- PREDICTION OF N~T WELD NUGGET AT TJ;!E F AYIING~PLtNE ~"Y.°ELECTRICAL. TEST - - - - - + - -- 1- - - - .,---'---- I ' ,_ t I ~' ! t\) i<r ,., t !:.· ind1, '5t h Jin,,_.,. u,·cl·n t,,d "'4-' ,H . . r-. u . '>. ,_ I,·-. ~o il ----- --- - - --~-------- ~----- - ~-- ---- --- --- :-- - 1---~ - - ~- i---1 ' _ , r-1 I ;I :-I--~-- - -,- I . ! ! ----i-- ----------- -- :- ~ I : ?. 0 - .... ~1•m: - l ,o~:11rith11ii,•. :::! < ' I I i -~ • . - I ' ·; . ,., .I'\ ' GOO ' : •• I i .t-; , • ' i : i ' . ' : . • • . . I -- • V N. !, . A Y. N O . 3"5 9 · 81 • : i . 1 [ I I I I .: .1I r- : .. ' ' i .. O ' . ---- -- . gt. • i I I I, ' .. •. • I : 1 ' ! ' : . '' ' i '1 ,t 1_ · _1 I • I I I ' l _i I ' :. : ' i ' i :. I ' ! I : 1 I ., • . •· . 1 • • :I . :' I I i' •• 1 I • • : I 1·· r.: I I I . 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'..: , ·y ,·!,·~ TABLE !J: Comparison of Accuracy of Measurement of Spotweld Sta.tic Shear Strength by Weld Nugget Diameter and'. by Non~des""' true ti ve Tests. Err.o r i _n Prediction Test Method Median Error f Maximum ~r C><I' '· For. 90% Wel·~~. ·FQ,r 100% of W~lds Pounds 205 Pounds 55 Pounds 145 Pounds 255 Pounds 55 Pounds 145 Poun4s 305 Pounds 25 Pounds 75 Pounds 185 .Pounds Weld Nugget Diameter 25 Ring Penetrator Test Electrical _Test Radiographic Dark Ring Pounds 65 > I . T.:',BLB I II ~1ii.DIOG '1U:lfl; I::: Il'•D I J.',:,.' IOI~S I Defeots Weld / otu'.:!l Pr ediot8d Aa ce~ta ble L ow PeneHigh PaneNo. Strength ~trongtb Penetra tion tra.tion or tra tion and , Oversize ~nd l~o rmal Undersi ze Size o UJ rti ~ o 0~ pj' VJ 'O Q S' 0 c+ 0 t 1 Cll::,''1 .... \l) c+ •g ~::1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 230 370 320 320 290 230 180 220 290 320 650 640 740 620 ?20 660 640 ... 740 820 23 28 330 180 140 180 • 60 170 29 160 26 27 * .. 31 35 36 37 38 39 40 41 42 43 44 45 46 320 300 240 340 280 250 230 160 110 260 2 40 350 1 30 240 1 40 X X X X X X X X X 838 X 79 5 .x 758 810 765 730 783 740 740 812 :x X X X X X X X .x - X X y .,,. X 30 32 33 34 X X X 320 22 24 25 - - X X X X X X X X X X X X X X . X X X X X r-· (l)~ '"1 'd o ,- c+ Ill..., '"1 oo X X X X X X X X X .x 0 Cl) Cl) .;-c+ Cl) Cl) p, p, RAD IOG ilti.?H IC INDi v .·s ION S Defeo ts 'Veld Jcotucl No. Straµ g t h 148 1 49 150 151 152 153 154 155 156 157 158 1 59 160 161 162 163 164 165 166 Note: 650 630 689 740 820 1 40 820 810 890 8 30 940 850 8 60 '750 700 1020 880 Low Pen e- Hi gh .Pane- Pene t :ra. t ton tra t ion or tra tion and Cl t;, !ti ~ C '1 ta O t- c1' I\.) .... '1 {/l and Nor mal Size Unders1 1,0 Over size I';' 'Predicted Accep t abl e .S trength • 690 715 . 730 730 758 768 730 740 800 825 800 (,) c+ 0 i' '1 ..,.i a) .... tQ C4 ts X X X X X X X X X X X X X X X X 945 927 (I)$ 'O . .... c-t(D (I) p. p. X X 865 740 Cl) X ,X X Q X 810 825 X X X X X p,, ~ 0 c..,, X X X X X X X X X X X X X X X X X X X 78 3 730 l'4 i X V'ihere no Actual Strength is g iven, t he sp e cimen wa s sectioned. Where no Predicted Streng th is gi ven , no dar k ring was visible. 151 Bo. Results of Test.s on 100 T~yl~r"'Winfield Spotwelds ll!aee By the Northrop Aircraft CorpQrat1on of Hawtho:rne California. In .04o n 248T Alolad Aluminum Alloy Sheet• l "c:. TABLl!: I Speci~en data for spotweld speoimena made July 13, 1943 for California Institute of Teohnology. .040 to .040 24ST Ala. Machine Taylor-Winfield Electrode Weld Pressuxe: 980 lbs. ~lectrode Forge Preas : Constant) 1500 lbs. Capaoi tance ; • 600 Mfd. Constantl Voltage : Variable Radiue top eleo. i 4 11 \ Cone tan t Radius bdttom elec. : 10" {Constant) Material cleaned in Nelite for 16 minutes Material Welds . No. D.C. Voltage Ml-10 1875 Mll-20 1975 M2l-30 M 31-40 M 41-50 M 51-60 M 61-70 2150 2275 2420 2550 2660 M 71-80 2790 M 81-90 2900 3000 M 91-100 TABLE II Co mparison of Accuraoy of Measurement of Spotweld Static Shear Strength by Weld Nugget Diameter and by Non-destr1,_1ctive Tests. • E~roz 1n l?l:ediot1on Median Maximum Error· J?o:r lOQ% of ____T_e_s_t_lo._-e_t_h_o_d______~_ -.~t<Ux1 ~•or 'du% Welds ----- - •--,- - welds Weld Nugget Diameter 25 Pounds 75 ?ounds 160 Pounds Ring Penetrator Teet 35 Pounds 75 2ounds 230 Pounds Electrical Test 25 Pounds 75 Pounds 130 Pounds 35 Pounds 85 Pounds 125 Pounds Radio graphic Dark Hing O) H iS zH '0 I I i 1 : i f •• . l -.J- • , ., I l I I- f • : ' - ~ - - - - - - - -~----!--- - ------ i --~J~-~-:-1-~--~-+~--- • I , j , 1 00 r 1 l , \ ' ' -~ - . 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J.... ..... .J ! , L . i:/t,o ·_ .l,_ ____ :2(?0 ! •1 ; ·--r--- - : - -- 1-_ • - - .- · - l , _- :__1~0~--- ___ _! _1~01_-~ 1 -- . - ~ -· · 1 ! 1• l ! - r i- -7---.----~--r-···- ~- - , - -- -r -· ~ · - ·- ~- ' i :- -· , ' ... . . I ' i • I i ..:~ ~ ,' • i : ~L.l,-- -- -1----~ ! ; I • •: i ' ! • 1 -;--·t··-~·t• -•-,-·L ___ I· .. • :---- l ,., , t· . , . · I· , • 1 • , ' ,·: ~ '. ' ·-·t-·-...~··-·i ;- I t ; . ·--:-->--~-,- -,-------.. T . ,i i.,- ! . I :.:_i[:_'._t...:.~: t \ i ' l~ I r---+.:..Lf--7 , 1, , ] i 'I -- l I !• / ~~-;---c- ' I •- - , 1 ·- - i ·-·- ( ;. L •• ; ,• J I , i . '. . : • ·- . ; '~-- t - --.- -- ____· _·_·~--·,l--+--.:. -+- - -- · r. - - ,- - -- i '.-- · i•· i _·- ~- - · ··-•- - - - · -·· - ·- . - - - · , .. · - · ~ -- .,_l _, _ _ _ _ __ ...... 1 i 1 1 r ' , ;-··-- , : ! , 1 I ! 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I ... , . - ,T • ~ ' • I f I. j ' \ 1 j - !I , , f • .r ! .. •: , - -· ,,- - -t - - I - :- • -- -- -1-' - -I ---,---r, ----:.+-:-t-·--·-\---.· 1 --- , '~ I I t• • • , I I --f .:..- ~ rl--1Gt·____:___ · -!- ---- - --;-- - ~---:---- -- _.... i r.:.1 1 ! : -· ---' Z • ~ -- -'- - -------,- : '-"f : 1 --Sf'- ---·---+- • 0 C . i. .. .. · -t-· -- -J---; •· .... ,~-- .. ···-- I,--, , , • ' i 1 I 1 1 • • , ', - - - -•- - - - • , • • - -- •• --- - ,• - -- •• ---- r• -- 7~t---·:-- -+I T ! -· I--.. • l - - · - f -- -', - - --' -- - •j1 ' I -t-~ t~~t~-t ~ :~- ;I l.· :·-.--i·---1:~ ·t --;·--_tj-~--:~.-f--(:/ (:~-t -•1---..J~-:-hr+·---\ 1- ' !.r -·-!--:-J.__ _ I . J i ;, i ' i I . ~-,~- :.·:··:~ ---r-~..:t ~-- ~ :~-=~-:--+--:----;---:+ __:i:. -~---- ~----) ----i--:--~-; : :~-:-: -~--:.r :. ; ~--;,.. :.:.: l!,, :: . L- .. .~ -~---:- -1-... y-·-i ~-: •·;::..,····:·- -·: : . !-··:1·-;~i --,.t-1~1.--·t-·· ,---r- l--;..' r-r--r ,1---~1Ff ·- ! ' ·i -:--g{J,--~--:- -·,.·---._ .-:-:· c· -. , . ' ' .. : .. . ' . , .. -·~-----~---+~; i r~ . ~ 1 ~~ , H ' 0 Xt : ;t ~ · 1~~-t ·--r----i---t-·1-·:; - :=, ....... r, . ~ c/.l J ~ m: ~·.h·-t=!· !••d.=~1=:~1 =b~=~~=L'. ,.:~~~i; +J~=LI: r~ul~-ri, .;=t~~=::t-:d.:.t .! (j . 0 1"' .: ,•: Jw , ·,•, ,1 ~-, ,•:l :1 1·: . rl •,i: r ! L :•i ·,.!1 o l Ul ·"- 1: : I :- (' d..: FIGURE 9 - COMPARISON OF ACCURACY OF STATIC SHEAR•·•" "' '"'" STrufl{ GTH fil'EASUREM~N'l' S BY DIFFERENT NOft -DB STRUCTIVE ~ESTS 'f-- TL~BLE I I I Radiographic Indications Defects }leld No. A.ctua.l Strength P:rediot · , Acce-pt a ble Strength Penetration an6.lfo:r:1"1.l '.31:m Low ?.enetra.tion or Under Size High Pena- ttiation and Overshe <.:~tf.lf·om:o 0 0 o· 'i •·d oc+owro W (A ca .... "' 4~p 1 2 3 4 5 6 360 380 350 7 320 3 g 10 320 370 11 400 12 13 14 15 16 490 ;1.7 18 19 .20 21 22 X X • .x X X X X X X - 340 430. 4 :) 0 430 500 440 520 440 550 570 X X 470 430 470 450 X X X X 470 X X 460 X 490 X X 550 560 555 540 X X 23 540 24 520 25 26 525 X 560 520 27 540 520 28 X X 520 544 29 30 31 32 540 520 500 560 520 565 X 570 565 ·x 33 530 5:30 58 0 X X X 34 35 36 3? 38 39 40 41 · 42 43 44 45 46 47 48 520 530 540 570 540 620 590 600 520 640 620 600 665 595 590 597 580 563 53 5 670 660 700 660 X X X X -v- ,A, X X X X X X X X X 673 673 670 X 660 X X X t> !::U . "i •, jOt-C'"I\.) '"'"'i C/l P" (l) (I) c.... (D o rt (D p. p. c+ (l) rZadi o~~·s-ohic Indic a tions Jont. µefe-:: ts Neid. .ii.otual N o. Strength Prediet • Strength Low Penetra.tion or Under- Righ Penetration c.nd Ovar- '"l't:!Ot-rt ill I-'• '1 Cll• &nd Normal Size size ~ Size 660 682 742 760 725 702 670 X ,} 690 680 740 720 720 740 790 800 720 X 702 X 280 730 49 50 51 580 52 68 0 740 680 53 54 55 56 57 .., 5 ·::i 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 ?40 760 720 740 ?90 820 800 840 810 75 77 720 860 78 730 79 80 81 800 830 840 840 660 ?80 76 32 83 34 d5 86 37 88 89 ·• 90 91 92 93 94 95 96 790 780 820 850 840 800 840 760 860 - 97 700 720 9IB 960 99 100 930 X X X X X X X 738 X 750 X X 308 8 12 800 825 '7 63 c+ X X X X X X X X X xx X X X X 370 872 885 900 898 X X X X X X X X X X X X X xx X X 845 900 885 922 X X X 96? :x xx aso 922 970 790 880 922 763 752 835 X xx 838 ,3 0J 8.25 305 16 ~ ::i if. X 690 660 725 770 770 747 738 735 77 5 ~ it •i X X 682 725 o t/l iv ~o g' oc+ocn ;,ooeptable Penet:ra.t1 on X X X X :x X X X X X X X xx X X X X .x XXX X xx X X X X X X ~>' 0 ~ ct> :rj ~l:1 (II c..,. Cl) Q • c+ c-t (l) {1) p., p., 152 C, Results of Tests on 138 Taylor Winfield Spe:bwelds Mao.e By the Consolidated Vulte e Aireraf'b Ceri,orat1Gn of $an Diego 1.n ., 0,40" ~4ST Alelad Alumim:un A.110¥ Sheet . Mote; :Macrographs o-f' Se<ttions of unpulled welds in this group we:t>e g,i ven in Fi gure 66. Enlargements of radio- graphs of typieal welds in this group were given in Fig. 74. The electrical test was omitt:ed., for these welds . 1 1400 50( _J 0 - --- 1001 0 ~ 200 u.. 300 0 a::: 400 Cf) :r: "j 600 a::: 700 LL 3 900 -<l: 800 a::: w1000 ~ 1100 o -1-2 00 ::> ~ 1300 Cf) •' -·--·· : ' . • - - 4• I , I - • ••• •• .. -- .• . • ~ I I • • •• --- -- -- -+ ---+-- - - - - I -- t-·------ - • • . ~ ••• •.• • • --- ----------- - -- - + - -- - -------- - I I -• -• . I• •• • • --- - ··-- ·- ·t - - - ·· I • I • ~ I I 7.0 • FIG . 4. CORR ELATI ON BETWEEN S TAT IC S HEAR S TRENGTH AND WELD NU GGE T AREA AT FA Y IN G PLANE. 1.0 2.0 3.0 4.0.0 6.0 SQUARE OF NUGGET DIAMETER (O .l 11) 2 : -·. . ••• • • • ..4!~ . . - ·- ·--• -·--- -· - - - I i ---- ---------- 1 ·- - +-- - - I I I • . l8.0 -l I • ---------,. I . ---- -r-·- 7.0 --- • i I I I --·-I .96.0 i I I I I t i <l: i 04,0 I I• t- w ~3.0 ~2.0 w a:: <l: I. 0 0 i . ~ .. .. ~ ' . .. !' ' '\ ' \ I i i \ \ I i i I I .•·· . - .:. •1••; .. . .. z .J I . ::, 7 ! i iI '\ . . .• ► I . I I .. .. .. .. .. . ' i I i ; ' ! ~ ~ i I ; ' w ~5 .0 -- l I 0:: Cl) ~ I I = ::, 0 r ---~- . .--· t- ! . .. . . . . . . I I I I I \ I ' I I i I ' i I 120 1..,0 I 140 150 160 1ro IBO I90 PENETRATOR TEST INOICATICYN 200 F I G. 5 . PRE D I CT I O'I OF IVEL D ~ UGGET /\ RJ t. 9Y Rl~ G PE~ETRAT OR TEST. en 1400 0 21300 ::, . ~1200 1 I I 0 0 ~- - - + - - ~ - + - -- + - - - + - - - - 1 - - - - - - - 4 - - - - - i w ~1000 ~ 900.-----+----+---+-- <r u. 800 . .. ~ 700 ~ 600 Cl) 500 ~ 400 u. ~ 0 J -• I : • •· 300 2 0 0 1 - -- - + - ~ - - --- - + - - - - - - + - - - + - - -- -+-----1 100 140 150 PENETRATOR l60 TEST 170 180 INDICATION F I G. 6 . PREDICTIO ~ OF ~ TATI C S ~EAP 3 TQENGTH l Y ~ l'IS P E~ ETaATOR TEST . 190 200 .._ 70 -~ I • 0 ..... . •• 60 w ~ ~ 5.0 0 t; 4 . o i - - -- - -;- - ----- - -- --- ------ -----------1f - -- - ------j <.!) <.!) :::> z 3.0 I I LL 0 •• ~ 2.0 ..•• ~ :::> . ~ 1.0 .1--- ---,-½--- 0 1.0 I • -='---=---'---------+-----'-=------:::-i----=-_----=~--- 2.0 3.0 I. 0 5.0 6.0 7.0 8.0 .. .. .: . . . II SQUARE OF BLAC'< RING DIAMETER (0,1 ) F I G • ry . P R E D I C T I O \J O F ·,',f. L C -~ U G::: E. T 3 Y f< A D I O GR .\ P •ii C [ ,\ >< K : , ; ., .a . [ I AME T E. ~ 1400 ~130 0 31200 ~110 0 I w 100 0 ~ 90 0 _j 80 0 ~ LL 70 0 ~ 60 0 ' • i • .. .: . . ~ 50 0 Cl) a::: ' : 40 0 . :··. ~ 30 0 0 ... . . .' 20 0 . . . a ,ou _J 0 1.0 2.0 3.0 5.0 4.0 SQUARE OF BLACK RING r I G . '3 . i=' R [ D I C T ; u ·, Cl F 6.0 DIAMETER (O.I 11 ) :- T ;, T I C . ~ I: :. ~ 7.0 8.0 . C d a:'. w ~ w . ... ~ 5. 0 0 ... . . "t . ~4.0 u.l I I .: I I I I •• • t!) t!) :::, 3.u z u. w I . 60 <{ 0 .. . . ... . .. . ' 2.0 " a:'. <{ 51.0 ' . ...:-• . •1 ... . .. I .,,,. . I I ! (/) 0 1.0 I 2 .o 4.0 3.0 5.0 6.0 11 7. 0 s.o SQUARE OF NUGGET DIAMETER (0.1 ) X-RAY FIG, 9. P REDICTJO'J AREA BY K ADI OG RA P HJC OF WEL D NU SSE T FAI H i<l 'JG , . 1400 cnl300 0 51200 ~1100 < 1000 w a:: 900 ::::::> _J800 I ~700 . •• i I '' ! .. . .. .. .. • • ~600 ~500 (/)4 00 a:: . . .. .. .. . .. . I .. . ' I I . I ' \ , ·.. •. ' I ..... . •. . 0300 LL. 0200 I I I I I I i 100 ....J 0 1.0 2.0 3.0 4.0 5.0 6.0 70 SQUARE OF NUGGET DIAMETER (X-RAY) FI G. 10. '.: T RESJG TH PR ED I CT I O '< 0 F -:; T A T I C S HE AR B Y k A D I OGRA P H IC FA 1:H R 1 .;G . 80 THE ORDINATES IN THIS CURVE :MEASURES THE PERCENTAGE OF THE GROUP OF WELDS WHOSE STRENGTH WAS :MEASURED WITH AN ERID R GREATER 'IBAN THAT INDICATED BY THE ABSCISSA. PERCENT IO 0 _. 0 ., -..,, Gl..,, m ;n m z 1--' 1--' --1 z 0 z I 0 m (/) 0 0 :s: -0 > ;n - --1 (/) ;n C 0 z () --1 0 rn > -< ..,, --1 () () (/) C ;n rn --1 (/) > () -< 0 ..,, (/) --1 > --1 - ::D ::D :I: rn > ::0 (/) --1 ::0 rn z c;, --1 :I: :s: rn > (/) C %) rn I: m z --1 (/) CD -<; N) 0 g .!j ::D 0 • ! I I r• r-·. _:___, i i : __ ,_J I ,-J I , • I : I I __ Lj ,- __ .JI I I I • I iI u, -t 0, ::D 0 ,---' 1 I ,,, II• QO iI I • z~ ,,, g :--·-' : I : -o os z I I I _. .... • .. J I ,---' I I 1I ' : rI I ! ,.J ' I : :____ _,' I N) ,.. J : : -0 (al ,·-- C: 0 I : z- ~t !•,: .,.. ~ ii -..J- Ot 0 -• I;,,•! 0 .-0... a,, I ~ ii · i: 0 "~: I I I ! : I I I :D-VZ ■ >"'c: C> Z GI 0~111 .,◄~ ◄ :D > ■ :D > _. -v~a :r O - :D > a: ~ ◄◄~ ... a >~ 0 > :II to :D - ,. ◄ z◄ » i •0 ◄ "' .~ 0 1' - r I I • ~lr: N) I 1I ,' (0 0 0 I I ,J ; -o I • ' ... : ,____ J ! 0(") 0 : .-•---' r···-· xg -0 ::D I I -t - ii · -' ' 'I : : i zg 0 : ; ~i - - j ' ·y-- o_. () (/) 0 0 I . . 0 ,,, - OF WELDS IN GROUP Ot o, ~ CD cO 00000000 0- 0 C,I ◄ 153 D:tt Results of Tests on 326 Tayler Winfield Spotwelds Made on the La.borato•PY Welder At the Univer,a1ty of Southern Calif., orn.ia in ,04on 24ST Alclad Aluminum Alloy Sheet ~ Note; The electrieal test was omitted. typical results is included~ A selection of TABL$ I Specimen data for spotweld n:pe e.:imens made M.a;v as, and . Jun~ 19, 1943 at University of' Southern Cal:U'orn1.a f'or California In• stitute of Te chnolog-y . Material Machine ,. 040 uo .04;'0 24.ST 4J.Q ,. .• Taylor-W infield Hi•Wave \• elde~ Electl:lode Press'\U"e Capacitance : : Volt.age t R~dius top electrode. Radius bottom elec. ; : 440 line volts (variable) 3'' 3tt Mfl.te~ia.1 ale-a.ued in Oa kite # 63 at U3o·° wire brushed. Panel lfo . 1 2 3 4 ' 6 7 8 9 Welde l'fo ,. Bl•ll 12...24 25•36 57 ..,49 49•60 61•70 71-82 a3 .. 94 95 ... 104 ll{)O 20 2l 11-11 1400 1400 28 29 30 45 ... 54 55 ... 54 65 ... 76 720 900 960 1400 26 27 480 elSO· 1175 1175 1175 1400 22-. 31 32 .... 43 44..,5,3 54+63 64..,,75 76-85 86•95 96.-105 25 360 480 840 13 14 15 l. 6 17 18 19 12 ... 21 22•31 32•44 C~pacitanoe 240 11 0 105,.. lJ.6 ~2 23 24 F tor 4 mi nutes and Electrode Pve $SU."re 1100 1100 1100 1100 1100 10 11 12 Hl•ll 12•2l (variable) (variable) 1400 l.400 1400 1400 1400 1400 1400 1400 1400 1400 1400 1400 1400 960 900 960 960 900 900 960 1200 1.200 1200 1200 960 960 960 960 960 960 1200 1200 Voltage 1800 1716 1680 2060 ).960 1900 18 40 1 8 00 , 2000 2200 1800 2000 2·~ 00 2400 2600 2800 2200 2400 .2 600 2800 1800 2000 2200 2400 2600 2800 2200 2400 77-86 1400 87""96 1400 1200 1400 2600 1200 2800 97.105 Spt,tl1~e:n d~ t~ f t}!J/ n11otw~l.d _s.p~eitQi(rn-i -<S~ June 41 194i ,f Gr Oalito1,n1a lti$t1tute t:1t 1~enno·1 ()a, .,,040 to Ma t1$!r i~ .o~: fat 81' Al,:t o g' l,t;t,-,W:b'lfi~'1 . d !\'l •Watt'l tiel.de~ • liQ.e V~lttlt .: 1 t~~ehin& r • I~le-~tf'Q(tt, ls?$·$~ 1225 lb•• . t~~ ~~at 1.5 2aao .w«,. • atl t~n0$ ,. 3$ft f~Jn .. 5u natitus t p $l~ih ., •· H.tl,t.U.us botct• alee, " f$ l$t-·:tal ~~~ned in 01;l.Jd,t . , es P&nel No. l a- s 4 5 6 7 a Ooropi\~ison (t-f (}Ou.r~cr !l> • &at!Jua!ie- lattt at' ~:pe.twl2ll.d ~ta tie Sh<t-t U... SW$ngth by ~ld- l-iu~~t lltat~et~~ and 'b 7 Non•ti~H:itruotiv-e ' 1:$$.t~h !r:NJ:r ipe~t -Jit'b.b<li 6. -,e~.UI 1· 4 I\ (1 .47 Jt ' l'd9tdl11ll'l . .· ~ U$.'i.flf~in 0lf;•rt .,@!W!II T2>✓~- t . ,:-,eo·~ ·if·, nJ.-~-t•tru; ,~~1¼111. ~J: •~rr>~ f 1Qri 90:'¾i et_ 1'eldeE . .. Fol?a~lfl.OOj oti ~_ )t-tei!Q ~ -~UL ·; ; ~ f · ft;t .. Ot '. ; :1• ·11ifJJI ' w 'IM , g"rt'9t -· r - K {ij.', .. , 1•u~.1 ·1 tf -i.•llllr f Radi Ost"a1,1d. e Da~l<i Ri116 R~dtoiwa.p hitl )'1Q.l.t tt !tin.@ • • - . ;J J . H I- w w :c: (/) 0 < _J r,/\ (.) _J ~ < I(/) ~ 1-f :::t en0 (\J = 0 :::t ,J ,.,, 7 z H J 0 . - H 1-1 (/) 0 - _J w -~ -H-r 3: . (/) :c: a.. < a:: er H (.!) 0 - 0 < a:: H • 0 0 _J w ~ R H fr a- 3: I0 ,. -tf• a.. (/) u. 0 (/) z I- (.) H :::, 0 0 a:: a.. w a:: I(.) < 01 1-1 I- z H - M -\.f H ~ ,. ~ 0 u . ~ . (.!) ....,. 0 ~ 0 0 ~ rf:1 - (-f ~ H LL J t-t ~ 8 -H ~ -t-10 ~, FIG. l ■ CORRELATION BETWEEN STATIC SHEAR STRENGTH ANO WELD NUGGE T AREA AT FAYI NG PL ANE. ii! II~• ,m n .. I, R :si!i!il'JI ' 1400 ,.l !Ii ·- CJ> 1300 ~1200 51100 Q. I 1000 ~ 900 ., 3 800 - : 700 ... .. a: 600 ~ 500 i 400 ~ 300 .. ... ' -· ~ 200 . Q ~ 100 - 00 '· ·(. 1.0 2.0 3.0 5.0 4.0 ao 7.0 6.0 SQUARE OF NUGGET DIAMETER lQI•) GROUP 8 - -115 WELDS 140O..----.----,-----,---r----,---r---r--, 13001---1--- - +---t-- ->--t-- -t--- r - --r-- - , 12OO1-----+-- - t--- ~ 1100 l----+----l-- ~IOOOt----+-- ~ -; -- - - ~- - - - ; -- --t--- r - ~=---~-- f 9001-----t-- ----ti----t-- . +---. .!, 800 ·: :·-~:- ~ « 700 ~ 600 ,_____ ~ -,---, -+-----r-J- ~---'l-- ----t----t--1 - ----t---t--- -, -+- - - - - + -- -t - - - - ; •• . _,___ _,....,..- - - - ·- - - + - - -- - + - - - - c - - - --i-------1 - "- 500 r----- - - , - -- , - --·- ~ 4001----l---~1----+---f-----+------tf-----t----1 ~ 3001---+.'~~--+--- f-----t-- ---,f-----t---'---1--7 (/) 2001----l-- -1--- -+--- f - - --t------,f-----t-- --1 ~ 100~---+- -t - --t--- t - - - t - -----,f-----t-----1 o Oo LO 2.0 3.0 4.0 ~O 6.0 7.0 8D SQUARE OF_NUGGET DIAMETER (O.I') a: 9 GIOUP .H - 105 WELDS 4\1\, 301. . . 200 10(. UV\. :,\J\, 8\X. . .. ... ' • C OU\, .... .1VI,, 400 2\1\, ~ l • I• {\A ,JV\J .., - . . .. . . . . . 10\J I) IU j,.u .. ;,.v -e,J,J LO u.v .i.u SQUARE OF NUGG~T DIAMETER (O.I ) GROUP I .- 105 WELDS. ' I.O FIG. 2■ PREDICTION OF WELD NUGGET AREA AT FAYING PLANE BY RING PRN£TRATOR TEST. RE ~7------"---,::....::"----"=r--"""-----'"4- ~ a: w ..... w ::I! 5. 0 1-40 < w (!) .. ~3. z l40 150 160 • 170 180 PENETRATOR TEST INDICATION GROUP 190 200 8 - 115 WELDS ;--7.0 Q • a: 60 . w ....i5,u-f--"---+---+----+---+---<~ .~-... -f-"'-'---r-----.-; !! . . '• ·. •••• ' 0 4.of---+---+----+---+-----.11-"·,_,.:~--+---+----i ....w -~ ~ ~ 3 ~0 1 - - - - + - - + - - - - + - - , - , - '_•• _.-<c--~--+---+--~--i ::, z . ~2.0 ....... w er < l.u ::, 0 (1) 0 '-eJJ 150 140 150 160 l'O l!!O PENETRATOR TEST INDICATION GROUP 190 200 H - 105 WELD~ ,. .7.0 ~ s.oi-----t---t---..c.+-~.,._--+-----+-~-:-+----i 0:: ~ 5.ot--c----+---+-~~---+-'----+--<- --+----1 w ::I! !!: 4.o,r -----r---t----t---+----1---+--+--~ o · .. : ... .... ~ 3.o,t----+--+-,-----+--+----1---1---+-----l . (!) ::, z 2.1.,nr---t---:---+--+-'----+--+-- - - ll - - - l - - - - - l IL 0 . ., !'·u ::, 0 (1) 0 ~,i:~u--i,,'ii1v~~,ra't~V-,111:)U~-."' l:,V.,..-----~,...u" • PENETRATOR -·,so· TEST INDICATION , GROUP l - 105 WELDS I iK.J 200 FIG . 3. TEST. ru ~ ~ r ~.r PREDICTION OF SPOTWELD STATIC SHEAR STRENGTH BY RING PENETRATOR Rf I "' 140'U !lJ pie, t ,!. l ~ ·- I Cl: I I I ~ I • , ~120 0 ~ 'i, u:,oo 0 c( .. ,I I ~ ✓ Ill ✓ :c .. ✓ u, 80 0 Cl: 0 ., i,,• LL f . .• . . .. . ♦ . • I I .• • I / i,,, .... / •/ 0 ., ., I ,I. '·: 0 ,.l. _-:,,. g~ a. I / I ,. :, - 20 0 , . 0 c( 1· 9 Cl I ~I , • :J z I j • I I ♦ + ~ u, 600 z . I • .. . .,., . . . ,,, ,,, . ., -". . ,·::"t . .,.., ---.· ...·: - ... . ~--... --- .,.. • . ..... --.. .,, .,-• . .... ,I . : ..,,1,, .... I • I I I I 7130 140 150 160 170 I80 190 2 0 0 TESTING MACHINE PENETRATOR INDICATION COMBINATION OF GROUP BADLY CRACKED WELD • 8 (115 WELDS) ANO...:'~ GROUP H (105 WELDS). ' (+) INOICATtS ....,.........--,-----,-----.---,----,---r--;----,-r----,--- ~140 u ~1300'1----4----l---,---+--'--l---'-~ --+--+---t----~1200 ~ 11001-----+---+---+--~1-:-..: . .;.=-_'-+,_.•.,-·:--,--+---=---t--- u: IOOCJ •· ~ i----~------1f-----+---':-'-\.+'-=-·- - + - - - t - - - - - i - - - - i ::! 900 : eoo1----i---t----+--. .-.+--.-+--'--1__,_--r--, ~ 700 \ / • •• ~ 60(;-1----+----+--....,--,_...+--:---:+------+---t-----i-----1 U> 500 ~ 400 3001-----+--:- .+ - - - + - - - t - - - , - - - + - - - - t - - - t - - - - ' - 1 LL ~ 200·1-----,1-------+----+-----+---+--------ii----;---~ 0 -1 I Ou ·0120 130 lctU •• ·150 PENETRATOR GROUP I 160 TEST 170 180 INDIC.ATION - 105 WELDS 190 FIG. ti. ,REOfC~ION OF WELD NUGGET DIAMETER BY RADIOGRAPHIC DARK RING. ~ ~·- =.... d 7.C Ill'~, lll ~ !II • .' •.·. . 11' • ~ ~ ~1 l, ~ I 1 ~ s.ol-------lf-----+-----+--.. ' ~ --------1----+s- -~ - - - - - . .,,., ..... \ . UJ a: < . 1.0. ::> 0 . '•,• _· , ... en 0 1.0 2.0 . . ~o . 4.0 5.o s.o " -1 .0 • .ao •. • • $QU~RE OF DARK :AING DIAM~TER (0:-t~ t : ,· : ·.1::. GRouP B -:- ·11.~·),ELo.s · a d 57.0 ..J .. ··- ~ ~6.0 La.I l- i5.0 •' ·•... . . -~..... . . • < 5 - 1-4.0 w (!) (!) ::> 3,0 z IL. 0 La.I . ' 2.0 ••s a: < ::> I.G 0 en 0 1.0 2.0 ~,.O -· 4.0 5.0 t~O .0 1: 0 SQUARE OF DARK RING DIAMETER (O.I") GROUP l - 10~ WELDS FIG. 5. PREDICTION OF SPOTWELO STATIC SHEAR STRENGTH BY RADIOGRAPHIC DARK RING. .. .,. 140(: CJ> 1300 i 12(K. 5 II 00 ~,o00 . ~ 9 00 :::> -' 8 00 :. 7 vu a: 6 0\. cl l.&J 5 00 J: Cl) 4 00 .. . . .. . . . ~ . ...... .. . 3 3 00 "!.. lL o . 2 00 ~ I 00 -' C LJ ~o 2.0 ol!l.O ~~o TO H-0 SQUARE OF DARK RING DIAMETER (0.1 •) 8,0 GROUP B - 11~ WELD$. WELDS B I THROUGH B 50 FELL APART, SHOWED NO DARK RING ON RAOIOGRAPH. 140I\, CJ> 1300 0 g CL I . IQO0 • ~ 90 0 3 80 0 : 70 0 a:: 60 0 cl l.&J 50 0 J: Cl) 400 .• . .. ~ 300 20 0 g 100 -' 0 I 0 1.0 ... .. . .... ..• '' . - . • • • . . . . -• . . ... Zl201( 1100 • . . . .•.· . . .. ~ •• I• . 2.0 3.0 4.0 o.O 6.0 7.0 SQUARE OF DARK RING DIAMETER (0.1") GROUP l - 115 WELDS 8.0 FIG. 6, PR EDICTIO N ~p.o w 3 - 6.0 er w I- ~ 5.C C Q 4 .ol--- _ j _ -- - 1 - -- - - l - ----1--- 1 - - - _ j _ - - + - - - - 1 I- ._ , .. w . • g 3.0 ·:::, . z I• ~ 2.0 "'~1.c-11-~ ~ - -~ - ~ - - - + -- ~ 1 - - - ~- - ~ - - .,:::, 0 IO 2.0 3.0 4.0 5-0 6.0 7.0 8.0 SQUARE OF NUGGET DIAMETER (X·RAYI 0-1" GROUP 8 - 115 WELDS ·-: 7 .0 0 .. 0 ·- jj 6.0 ~ 5~0 . . . ,. ~ ~~· ~ 4.u"'f---- - - + - -- - + --+----+--------"f-----+----+---; 0 ~3~,-f--- - + - - - + - - + - - - - - - - 1 - - - + - - - + - - - +- - (!) I!) ::, z 2.0 ., . u. 0 ~ 1.0 ~ a U) 0 1.0 2.0 3.0 4.0 5.0 6.Q 7.0 SQUARE OF NUGGET DIAMETER (X-RAY} 0.1" GROUP I 8.0 - 105 WELDS FIG. 7. PREDICTION OF SPOTWELD STATIC SHEAR STRENGTH BY RADIOGRAPHIC FAINT RING. U>I 400 zl 300 0 gl 200 a.. • I 100 ~I vvu :::, 900 800 u. er 70C ..J ~ C t,(JI.. "':c 500 25 400 u. 300 0 20C C 0 IOC ..J 0 " { h U) . .. . 1.0 2.0 SQUARE 3.0 4.0 OF NUGGET GROUP '0 6.0 7.0 DIAMETER (X-RAY} 0.1" 8 - 115 WELDS 8.0 F IG . 8A CORRE LATIO N OF RADIOG RAPHI C IMAGE WITH BO NDED CORONA AREA. -d .. -~ ac-'~-~--~--~--~---~--~--~----4 Cf) : ,•. 97.0 w ~ w .I. I- ~ 5.0 <{ 0 :. ..' , '. . . .. . . .. c:t 4.0 ~ ~ . . O3.0 0 ~ 0 2.o·t----~-~----+---+---~----+----+-----i w ~ <{ 5 1.0 Cf) 0 1.0 20 3-0 • 4.0 SQUARE OF CORONA 5.0 6.0 70" 8.0 DIAMETER (X-RAY) 0.1 FIG. 88 CORRELATION OF BONDED CORONA AREA WITH SPOTWELD STATIC SHEAR STRENGTH. en 1400 ~130 C g120 0 a. I f 100 ~1000 3 900 -. ~ 800 ~ 700 ~ 600 :I: en 500 ~ 40 0 ~ 30 0 ~ 20 0 0 ....1 100 0 ..... . . . . .. . . . 1.0 2.0 3.0 . .. ...I ... . •. . . 4.0 ~ . .... • 5.0 6.0 .. 7.0 SQUARE OF CORONA DIAMETER . (0.1 ") 8.0 154 On the typical groups inelud$d in this thest\$ 1 and on groups of welds from four other ai~er~!'t t'aeteries, the .radiographic test measured weld strength and nugget size mt,re accurately than the penetrator or electrical tests.11 M.e dian er:ro~ for the :Padiogrs.phie test was t:rom 25 to ~5 pounds., fo1"' welds whose stPengths ranged from 200 to 1300 pounds; with riorrmal weld strength 500 to 000 pounds* M$• d.1an error wi. th the penetr•a tor test varied from 55 to 86 pound$,, with the el$ctr1cal test i"r-em 25 to 95 poundsEaeh of these tests would $Eti?V$ for :tndus·t:!£':ta.l inS:pl;}etion:, sinee 60 to 9056 of' the welds would be measured to within 20% of a ctual weld strength.,, n1e additional information on weld geomet~y; structure, and defects provided by the radiogr .;.t phic test., :ln addition to its superior accuracy and reliability 1 make it pre1"! ferable to the penetrator and electrical non"'"destruotiv~ tests,. 155 VIII CONCLUSI ON$ :. It is possible to measure s pot;w:.e-ld nugget size and static. shear strength by th·e penetrator and elect:rical non .. destr:uet• ive tests., .foz, spotwe lds in equal thioknef!s two la.yer ahJUn• inu.rn alloy joints. The accuracy and reliability of measure• m~nt are .s ufficient to make the meth ods useful in industrial inspection. The chief disa dvantage. of both of these methods is the necessity .for accurately eenter;i.ng the test assembly over the spotweld, to avoid large errors in indication ~ The penetrator test also has the disadvant$.ge t hat it marks the s h ee-t surfa ce., but in tests on thousands of welds 1. no case of failure resulting from the penetrato;r• indenta tions has been observed., Correlation of radiographi c de tails with weld geometry and structure showed that, for• spotwelds in equal tb.ick-- nesses of 24ST Alalad aluminum alloy sheet: 1~ Spotweld sta.tie she ar st~e,n gth, nugget size, geo- metry,. and defects can be det~n-•mined l'.'eliably and accurately f::eom the radiographs or production spot·welds . 211 Spotweld defects suoh e.s inadequate nugget pene• tration (with possible lack of bonding o:r excessive .Alclad inc lusi on into the nugg$t) ~ excessive penet.rati on in ov·{n•size nuggets, cra cking , porosity~ spitting, or excessively la:rge heat.affected zone s a.re clearl:y: evident in the spotw~ld radi°"'" graphs, ~-s . In groups including hundreds of industrially-. 156 mad$ spotwelds in .040'~ 24St Al clad sheet, with 1..u-iifo1:m dis .. tributions of static shear strength from Oto 1500 pounds, the nugget diameter in the 24ST alloy was determined vri th a niedian err or of only .Ol », and strength predicted with a median error of fr om 25 to 45 pounds; b:y visual examinati.on and mea ... su:rement of the s potweld r a dio.graphs~ On production spot we l d s, the penetrator, electrical, and radiographic tests ea.eh measured spotweld sta tle shear strength with a reliability and a <rnura.cy well above the re• quirements of pra.ctiea.1 industr:J.al spotweld inspection. The ra diographic test offers advantages over the penetrator and electrical tests by pr oviding not only a measure of weld strength, but by showing ln clear and unquestionable form the presence, of' defect s such as la ck of penetration , crack:3 1 porosity, spitting ., misshapen nuggets , e xce ss ive pene• tx•ation, a.n d excessivsly l arge hfH1t affected zone s. It make$ possible complete weld inspection in a single opeI•ation which is absolutely not damaging to the weld. Three necesse.Fy prere quisites to the genera l ac eep tanee of radiography as a l'"'eliable non ... destructive test for spotwelds in equ.a l thicknesses of 21ST Alclad she.et have been met by resear ch: l, ~:he method of interpreting weld ge omet:t•y, structure, strength, and d~•feots from radiographa has been established. 2. 11he technique of.' ra.diographing spotwelds., using avail able pr oduction x... ray equipment and oommercia.1 .f'ilm-, has 157 be<iln develope<l to give e:>teellent ~$.dic~.r?aphsJ: ~'i.t,h 0xposur~ t:i~~ tHl :l<it~ e.a 6 t}e~1(l,ij l'~r w-eld. Low 0'0St :i:re~table lt• ~ay equ.ipm$nt for~ apo1rt7eld r~t\dio.griaphy c;.ould oe .mtu:iuf'®it ~t~ed oJ: GOiil."m~;r<;.1nlly uvail~bl.- ~ompQnentfh a. ,·be :re.11i:i'b1J.i ti and ade<1uaey of' ra.eU.ogtaaphi0 tn• speottcm. htu1 been prt>veu, by the- N ·sult$ of ttHTJt -e on tl'ac:,u... Gattti-s. ox :.tndusts:i:\fi..$ llly m~de $f.Hi•tweld$. .rvom t-11iua,y f aot .o~'!E1',$ , :Che !,i,{(}e\UNit~y o-t pt?e(l.1ecio.n t)f wel d i -trem0 ,,.h and :si~e was !l&.11 al.Hive- i :u:lu:3.tritil inspeution r.equit?-~UMHltai. ~ud ~ ton,, ln0,.., a.n d of' the- "v$'t:1':J' ~,ta:t n,$l.p 1n w~~t>7ing out th:l.~ l'.'tHi<:Hlr•Ql'l. ot i('U,'f,__ J' •ff• ~-n:lldi, Mr, (l11 C. "'iool sey , ~n<a, a c4 o;ft tbtl! znembe;t•s o.f tlw ~·~ eldi11g '{e$ft(1Z-ch G1~m.ap ot C~lif• REFEI\ENC:E$ .. . A:tm ~ll3L;,[OGRAi?fIY ·' , ,- (l} u Al coa .t\li:.uni;nwn nnd Its Alloys.t', e. data and inf'ormation pEtmphlet published by the Aluminum Company of 4tneriea, Pittsburgh, Pennsylvania., 1948. (2) nRevealing the !di .o rost:ructlilre of 248 Alloy't, by F . K:elle,Ii and R"A.Bos.sert... .,. 0 Metal Progressu Vol. 41 Nth, 1 January, 1942. (3) "Structun_a.1 and Meta.l.lurgieal Properties of Condenser Diaeharge Spot Weld.$ "', by . G.• s.Mtk.ba.lapov and T.F., Fall$: 1 in u-Tlle Welding Journaln Vol" 21 Wo.- 4 April, 1942, (4) "Radiog:raphy of Spot Weldsrt by RQb,e rt c. Woods; John o. Barre tt and '11 . w. Dietz, in ''Metal.$ and Alloys,. for• Sept• emb~:r;>,; 1942: also 1'Metals and Alloysn, December, 1942, pages 1080+-1083. (5) 11 Standa.x-ds and Recommended Pr actices and Procedures F'or ,··, ( 8potwelding ot Aluminum Alloys" by Airr;:(•aft Welding Standards Comtni ttee of the Ame:ric&n Welding Society, February 1, 1942, Revised April 15, 3.942 .....s ection I-B'I'A!-l'DJ.IBDS OF WELD ~ITALITY (5) Weld Penetration. ( 6) ncorr elation of Metallograph;i.o and Radiographie Examinat1on s of Spoi;;,Nelds in .Aluminum A.ll.oys" by D. w. Smi tp. and F, Keller, in nWQlding Journal."" of December, 1942. (7) uxifetallurgieal h a,pects of Spotwelds in Aluminum Alloyatt by J. R,Ji ~ising and E. H. Burkha:rt, in " Metals and Pro- gressl', December, 1942,. (8) nExami.na tion of' Spotwelds. in AJ.ola.d 243... pu by W.F. Hess,1 R.A ♦. Wya.nt and 13.,L. Averbaeh, in " V,l~ldi.ng Journal " of July; 1942• (9) uRadiography of Light Alloys 11 by Robert a. woods and V* C. Cetrone ·"" in °I:ron Agen; March 25, 194,3 , ( 10 )0 Mio:roradiograpb.y 11 in "Iron Agen, July 22, 1943; Volume (ll} Navy Department , 1:hird Ptirtial Report on Eddy..-eurrent Typ.e ._ Flaw Dete et.ox-a .... 11:e sts Qf Sp<1>twelds in AlUininum Alloys,. by Naval I esearch Laboratory, Anaoostia Station, Wash• ing ton, P, C_, :t~L Report No. o-1792 ( RES' .t1RIC tt1ED ) ~ {12) nA.n :Eiddy"'"Current Method of l:jllaw Dete0t:ion in No:n-.ma.gnetic Metals'• by Ross Gunn, Anaoostia, D. c., in 1tJ.Q urna.l of Applied 11eehanios u, 111areh, 1941. (13),.Modulus of Elasticity and Damping in Relation to the State of' the !vla terial" by F.Fo:r ster, D:r ., Phil., and Profe ssor v,. Koster, Dr. Phil .. • in "Journal of the In.. stitution of Electriee.l Engineer$", London1 B.I . 1 Volume 84;, January•June, 1939 1. Pages 558-564. (14) '"New Method.a of' Spotweld Inspe~t:ton by x-~ay" - by Na. ta.lie Godalsky ... Paper furnished by Sciaky Brothers,4915 W• 67th Street,. Ghio.a.go,. Ill.inois . (15) "I~1atigue Cha..raeterist!cs of Spotwelded 24ST Abnnin:um Alloy" by H. W. B.uss o11 1 L . R.Jaokson, Ht-J. O-rove.i··., and w.w. Beaver, Battelle Mem@ria.1 I nstitute,. for National Advisory Committee fo:ri Aeronautios, Copy Mo . 150 ARR No. 5Fl6, June; 1943 ( RESf.I1RIO TE1)). SOURCE,S OF PRQPOiSED '.l'.ES,'.:[1 l\1WJ!HOPS {a) Two $:1.d, Di,~ect 01-U'rent •.r.est, . A fol"m of t e st similar to the t wo side d:h•e,ct current test was d.eveleped by Andrev1 and Faville for the Glenn _Ma.l'tin A,t roraft Compan,y of Baltimore, IVtaryland.~ (b) (Reefer to Wr. Paul 14erriman tor details , ). 0µ(!) S1¢i~ D:\.reG'.t G\l.4'r~nt Te$t:e'_ A preliminary form of this test was d-eveloped in tne Electrical Re-seareh Seet1on of the LoekhE:Jed Al.:reraft Oorpol."e.tiop, Eurb.ank.t Calj.fornia . (Refer• to Mr . ~ed Bowden for details). ( c) L~p Joi:p.t .,~ndµqtiPti 1.l:'e.~t., A test which may be similar to the lap joint induction teet was developed by Niw ... Norman Bonn,. .of' Philadelphia, Pe:nns yl Vania+ ( d) rl,(}}c.,.u;p Cqil _Edd:z Ow... re:3t. T~$ti: 11 Developed in the Naval Reeearch Laboratory and reported. by Hoss Gunn in nAn Eddy... Current. Method Qf Flaw Det<eotion in Non...Magnetit :Materialsn in the "'Journal of Applied :tl eehanicsll, Maren., l94lj ( e) ~~otweld, ,~ddy T~s t:i~-S tI:ri!t;i,, Develeped in tb.e Naval Re• search Laboratory and :reported in a preg:ress report, July 1 1942 . t:ric.al ReseetJ?Oh Section oi: the Loekheed Ai:reraft Go~porat.ion by Dr. Philip Carl$on. (g) ffeat ije$el'.'v:o.l r Tllerrnal T~:sih Developed by the Cfeneral Electric Company,. Schenectady, New Yo:1:1k, and tested in the Lock• heed Airera.tt Corporation Resea;reh Laboratory, Burbank; Calif•o rnia . Vib~ation ?amPlng Test, Method is disou:ased in ttreodulus (h) of Elasticity and Damping in Relation to the State of the Maby F. J:t":lorster, Dr, Phil, and Professor W., terial" Koster, Dr, Phil., in Journal of the Institution of Electrical En• gifl.ee:es , London.; BtI ,(! Volume 84;-1 Jan\'la~y•lune_. 1939, pages 558•564 . (i) Wave Refleet:ton 're at~ 1.,1 Proposed by Profe.ssor .,. -., A. Fi~e.- stone of t he University of Michigan, in conneetion with the Sup~rsonic Refleet0$eope. ( j) Weld Outlin~ 'l1est. Mlle,. Natal;te Godalsky in a paper furnished by Sciaky Brothers, Chicago, ;tllinois. Note: R:roposed test me t h ods ;1:dentified by the sign f, were in• dependently proposed and developed by the Welding Re.. se arch Gt>oup of the California lnsti tut;e of 'l1eohnology. APPENDIX I RESTRICTED TRJ£-r.~~t:•.:~·'I 1 f-.~ ~:3AR11 c1~ .t' 11\·c: ~ :fi ~ li)J. 1 2 J:e ;(=xvs RADIOGRJ\P}LC FILM. TrffiMS USED SPEED Film spee ds for compar:i.son purpose~1 ar•e sens 1 tometrlc measurements under specified con.d:lt.:Lons ,. Th.es e con.di tions have · been so chosen as to be representative of a large percent of product ion work. Speed is aspressed e.s the !ifJJ\ S necessary to produce a den•sity of 2.50 through .50 11 of 24 ST rolled alum:1.num alloy. The film is in, a paper envelope and e xposed on x=ray· unit number 6 at 79 primary volts ( approximately- 100 KVP). The exact MAS valHe is obtain~d from a plot of density versus exposure time for .50 of me.terlaL CONTRAST The quantit~tive expression of radiographic contrast as indicated in this report by d:1.glt.s along the various _plots., is the percent of the total thickness that will prod.uce a density d:tfference or . 02 ., 'I'his pe rcent represents the pe rce nt of the total th.1.ckness that would be ji..\st. detectable ln the inte:r•pretation of a radio= graph. The hume.n eye can only differentlate a minimum dens 1 ty value~ Under ideal laborar.orv condi ti ons t.his mi.nimum value ls about •. 0050 F'or calcu la.d.ng contrttst applicable to px•oduction conditi ons ttw conservative density difference . of .02 is used. Thi s contrast value is calculated by assuJning a straight line relationship bet~een two densities, usually those produced by a thlckness difference of . 10 11 of r11a'terial. The thickness re·- presented by a density difference of .02 ls calculated and divided by the total e.vex•age thlckness over which the density differencG 1;1as measur ed. rrh:ts is mu:i.tiplied by 100 to express 1 t in pe1•cent. For example, if .10" of mate rial will produce a densit~ differ - 11 ence of . 20" then a density d.iffer~mce of .02 'W'ill :represent 001 dens1 t y of material. If the awars.ge thickness mre :r• which the of. of the total was measur ed was Loo·· 1 p then "01 I'• wo uld :c>epresent 110 thickne ss. This percent is u~ied to exp re ss t _he • rad:log1~aphl.c contrast. When it 1s necessary to apply a sing l e contrast value to a fllm for comparlson purposes, the value used ls that found f'o r 050 11 of 24 ST rolled aluminum a lloy, at a density of 2 . 5 0, exposed for 424 MAS and variab le vo lts.ge o.n x-ray unit l').umber 6. This ls generally supp l imented by the value found for the a a.i11e thick·nes s of material at the s a m1;1 12,ens 1 ty exposed at 79PV and variable time on the same x-rs.;y- uni t . Cont1.~a.st val ues for given thicknesses a r e found by a plot of contrast versus thickness. These plots are not limited to any thlckness, voltage or ma.terlaL 3 D,!J/I'A 'l' IT-LE- - =·-~··-,· - - - -•-··'" Sr_;ecd ,. " ,. I,}j\.2l, d8:C l n 1.t:Lon) ts c.11") :1tu1d~~:.,e Gt.hs .... ;, c~ orle .nJimbe:..) Fog , .. G:r·r1J..r1 ;, .. ,• ~ • f• {~,t:!f; JJ~r2s .1. t;y 1 J..r.1 l . B' ilm . ,. .· ., ., (;orle r.1titUl)e:r") De11clopment .l - Machine d~velopmcnt 2 - Hand development vith agitation 3 - Hand development without agitation Developer ..... . .... Gode number i/ inL-It~~ r~ rJr= t,cntl1s C)f r:tinui~es Dev., Temp, .. , .. , , ... Dcgx'®1:;S F'ahre.n.hel'i:::. .A ,. C "\ "'> t( .0. ., , < , • ,o ·i 1 -D~--:r~, ''"""'' """ ' " ·'"•''. . , J.'I {· \:... ,v -- Q.- .•'!~ll!a. fie-...,;·~ 1'tr.a~ ') ,. ,. (• e ._. (". r, ,. n ,.,11rL1 . ) 1•• O . t D.l..;Ju .::,.., . -? .;.0_:1 6 thru 9 or 46 - steel 10 thru· 13 z 47 or 178 - copper or bras u 37 or 177 - lsad Machine ...... . , .. . . Type of x - ray machine l - 220 .KVP re & B C}qu. :tpment ~~· 22() l't1lI' CCHi1D:!E:Li" )Gi t: l eqt1:L1)r1cx1t 3 2r-~o mr:P C<)mm,~ :rcl~~1 cquiprnor1t t:. - li,00 KVP comme:rc l,E~:. equipment 5 150 KV:P T & B eqi..1tpment h·ii thot:tt x•uctlf ::.cx 6 •• 1.50 KVP T &. B B{llJo '.~pv.wnt ( w:1.th :rc,ct:~.fier} "( -- 1110 KVP commo:c'cil~:.1 cqu1.pmt5nt 8 - 100 KVP corr.une :rc:'Lld . me;d:u:~al 0qu:Lpmen t 2 9 - Miscellaneous equipment J.O~ Radium. ( q u12.ntl t.y e;i ven un,}cr Y.tA) J.1-· 1000 t~P COJmT!~:K'CJ.al equ5.}_)!1l.(:Jl1t J:i1r,.e .. ~ (· .'. ~ ;, ~.r~1A ~ t' •' ,• •• ,; ·~ r, t, .~ .. . , I• ~ ·~ ... " ,; •J ·, . ; ,, E~J<1)0S u.~ee t.t!Tie -- ~;G(!O.n.rls or t.c11tr.1s of 8 tJ<.~or:.c1 ~:: ~J\li.:tl:t ;;,,rnpEres 0!' ten.tl-.ts of rn~i..111.ampe:t'(;S " VoltHge . ........... Primary voltage Sc:reor,1 J.. ·) ., ~., 'J:yr;.H;1 <.J:{ :3c1'leer1 or i""iJJ.u J1oldex~ u.so c1 1 c• ., ... •) - }.;, 7.I '1 - (~J.' ....1~ 7 0 ;}h- ~- 1) (rl v-.. """ 1'. Clpf~.,. )~ l -- "' "~ .,::} t:::1 -,,-: .J,;.l ,;~.U"'J.• t' ":"> ... - . ~, l~J..lJ ·~ t-"l ~ :n n c..::i ·1 -.~ -~.... ·i ~,., r-· ..t.. 1,._:_., iv1.~l w..,_ __ ,,'.! ..,!,..,'.. ,-l.~=,, ;:; err~; e r:.2 ) 2, 3 or 38 -- Front ~nd back lead screc~s ::, •- - - __,._-- - - - -· •- Tungs ta tG s c re cn.8 f?il te:e C~cid.e r.\Llrr/be:r F' ilm X\To, , , , , .. , , , , , Ident :U .' ication m.xmbe:v on film 'uc:st st:r-:Lps t,r ., o .. ,.;~Project r1urc1.1J0r .former DatG Spa.co "" ProjEc:·;:. di vis ion ::1.umbor Ei:n, Ifo, ,, ,, .•oPai~t of film emu:L8:l.on nu.1.u.be:e c,. 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Thlckness Density Cor.trast V-5 V-3 V-4 V-2 (:: ! ! , ~ - ..'.:i i -~ 13 : .5t, E..'rn. No. Subject (,,,1(.<.- ' 4-72- Date \./. o. --· Voltage i -1:,Q___l'.) -·1-- 3 1 iSc. rern i Fi lCer 1F'1lm No . MA ' I De vel opment I I De velope r [ .5' 1 Dev. Time 47 Dev. Temp. ~R Part 3 Mach in e ' Tube Dist. ! ,3(,, Time V F'Um Grain F'og Spee d Rep ort: No. __page No . BURB AN !( , CAL IFORN IA ;a DIAGnOSI$ BARTON INC. iT16TRLWIIOICAI. ~ f, -& TRIPLEIT 1.- ...:;.,·•~:-:l --~.. --. _l _........ -< ., : . ::,,~ ..,,-""'." ·~.:...> ~---- -.,,,,,__ ~~"i:-:.:rcc"---· ---L,.,.,-1 ·--r:·- ... ,_l ... . 1--_-_;;;f-,--=: ~ -1 ---- ·•----·· I ·· .. J,;.>·/ '...... - -+-- - +----+--- + - - - ,e· ::: .. .... - _,. · ..-~ ~ J...-· ... -:·· -••"". ---- L· l ~ \~J .J,·, ~ .? ~-,·:.,-,---; ~ ~--- ..,--::;. ;) Cl . "·t- -1 -::; b:-6; __ .,,.., .,. . / ·~ ••• • -- ·-· -- _ , . , . .. ......t,J - - , . , # ... 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