Repeated Loads Above the Proportional Limit on 24st Aluminum Alloy

Author: Joga Rao, Chintakindi Venkata

Year: 1948

Degree: Engineer's thesis

Advisor: Sechler, Ernest Edwin

Committee Member: Unknown, Unknown

Option: Aeronautics

DOI: 10.7907/V8T5-YS83

Abstract

The purpose of this investigation is to study the effects of repeated tensile stresses above the proportional limit on 24ST Aluminum Alloy.

The investigation consisted of three parts:

  1. An investigation of the effects of the application of repeated tensile stress above the proportional limit for 500 cycles followed by a higher repeated tensile stress up to 5,000 cycles.

  2. An investigation of the effects of changing the number of cycles of pre-stress.

  3. An Investigation of the effects of aging.

It was found that permanent deformation caused by over-stress is not a useful factor in forecasting life expectancy.

It was also found that the effects of aging, initial cold work, and magnitude of overstresses applied all have definite influence on the ability of 24ST Aluminum Alloy to withstand further overstressing and require considerably more thorough investigation.

It is considered that this field offers attractive possibilities for further study of the behavior of aircraft materials with the objective of increased accuracy in airplane design.

The investigation was carried out in collaboration with Conrad N. Nelson, Captain, U. S. Air Force at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California.

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