Repeated Loads Above the Proportional Limit on 24-ST Aluminum Alloy

Citation

Nelson, Conrad Nathaniel (1948) Repeated Loads Above the Proportional Limit on 24-ST Aluminum Alloy. Engineer's thesis, California Institute of Technology. doi:10.7907/V6ZX-5G92. https://resolver.caltech.edu/CaltechETD:etd-12192008-105659

Abstract

The purpose of this investigation was to study the effect of repeated tensile stresses above the proportional limit on 24ST aluminum alloy. The investigation consisted in obtaining data on prepared specimens of 24ST aluminum alloy in a machine capable of applying a pure tension stress, repeated many times a minute, without shock but with a high rate of loading. It was found that permanent deformation caused by overstressing is not a useful factor in forecasting the life expectancy of the specimen being tested. It was also found that the effects of "aging" (elapsed time between overstresses), initial stresses, and magnitude of overstresses applied, all have a definite influence on the ability of 24ST aluminum alloy to withstand further overstressing. However, these effects are so scattered between different specimens of the same material that they cannot be determined accurately, either qualitatively or quantitatively, without a thorough statistical survey. It is considered that this investigation merely points the way to a further study of the behavior of all aircraft materials above the proportional limit. The investigation was carried out at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California. (referred to hereafter as GALCIT.)

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