An X-Ray Study of the Changes That Occur in Aluminum During the Process of Fatiguing

Abstract

Carefully prepared test bars of 17S-T aluminum alloy have been fatigued; x-ray diffraction patterns of each specimen were taken at intervals as fatiguing progressed. Approximately thirty different test bars have been studied. Seven series of diffraction patterns, corresponding to seven different specimens, are reproduced and discussed in this paper. This study shows that (1) fatigue failure of 17S-T aluminum is always preceded by fatigue damage which is detectable by the use of x-ray diffraction patterns; (2) nearly all of the detectable changes occur in the last stages of fatiguing and consist of rotation of grains, introduction of strains in some of the crystallites, and fragmentation of some of the crystallites; (3) these changes do not occur when the specimen is fatigued below its endurance limit, but always occur prior to failure when it is fatigued above the endurance limit; (4) failure is probably intercrystalline rather than intracrystalline in character.