Plastic Buckling of Cylinders Under Biaxial Loading

Author: Giezen, Jurgen Johannes

Year: 1988

Degree: Dissertation (Ph.D.)

Advisors: Babcock, Charles D.; Knauss, Wolfgang Gustav

Committee Members: Knauss, Wolfgang Gustav; Babcock, Charles D.; Knowles, James K.; Beck, James L.; Rosakis, Ares J.; Singer, Josef

Option: Aeronautics

DOI: 10.7907/ycv3-kp17

Abstract

An experimental investigation is carried out to study the effects of nonproportional loading in the plastic range on a buckling load. The discrepancy between experimental and theoretical results points to some principal shortcoming in the analysis. The problem has been simplified by applying axial tensile load and external press to simple cylindrical shell specimen and observing the buckling load for various nonproportional load-paths. Results are compared to numerical predictions (BOSOR5) using classical type plasticity models such as J₂ deformation and J₂ incremental theory. Significant discrepancy was found an attributed to inadequate modeling of the nonlinear material behavior. The effects of geometrical imperfections and large deflections were found to insignificant, thereby leading to an idea how much of the discrepancy between test and theory is due to a use of inadequate plastic model. The introduction of the Southwell plot into elastic shell buckling problem reduced the already minor effects of geometric imperfections.

The Christoffersen-Hutchinson corner theory model was introduced into BOSAR5 in its simplest form as presented by Poh-Sang Lam. Results obtained with this model, which allows corners to form on an initially smooth yield surface, displayed better agreement with experimental data. However, increased computational time and problems related to abrupt changes in load-path at the corner are a major concern at this present time.

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