The Effect of Surface Roughness upon 25 ST Aluminum Alloy Subjected to Repeated Tensile Stresses Above the Proportional Limit

Citation

Ringness, William Merritt (1949) The Effect of Surface Roughness upon 25 ST Aluminum Alloy Subjected to Repeated Tensile Stresses Above the Proportional Limit. Engineer's thesis, California Institute of Technology. doi:10.7907/WH57-T868. https://resolver.caltech.edu/CaltechETD:etd-02022009-093120

Abstract

Utilizing the Repeated Load Hydraulic Testing Machine at the Daniel Guggenheim Aeronautical Laboratory, California Institute of Technology, Pasadena, California, the author, in collaboration with Lt. Comdr. D. J. Hardy, U. S. Navy, investigated the effects of surface roughness upon the cyclic life of 25 ST aluminum alloy when subjected to repeated constant tensile stresses in the region above the proportional limit. The stress impulses are of such low frequency as to allow consideration of single impulses. The rate of build-up of the impulse and the duration of the impulsive load are such as to create an equivalent static load of substantially the same magnitude as the peak of the impulse loading. It was found that surface roughness has some effect upon the cyclic life. In the lower stress regions, the greater the degree of surface roughness, the shorter the life appears to be. However, for the range of roughness investigated, 5μ to 200μ, the effect is not so pronounced as is usually found below the proportional limit. Where the applied stresses reached far up into the plastic range the effect of surface roughness does not seem to follow quite as specific a pattern. Since the loading impulse featured a 0.33 second duration of maximum load, the effects of creep may well have taken over in shaping the life cycle curve with little regard for surface roughness.

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