Mechanical and Structural Changes During the Deformation of Copprr by Fatigue

CIM Bulletin, 1962


The structural changes which take place in polycrystalline copper under the action of alternating cycles of torsion stress were studied, using the optical microscope and the X-ray diffraction camera, and an attempt was made to correlate them with changes in the shape of the cyclic stress strain curve. It was found that the period of work-hardening was less than one per cent of the fatigue life, and that persistent surface markings, which are assumed to be incipient or actual microcracks, occur upon completion of work-hardening. X-ray diffraction patterns revealed considerable grain distortion at the completion of work-hardening in specimens cycled at a high strain amplitude. This distortion became progressively less as the strain amplitude decreased. Mechanisms for the completion of work-hardening and the formation of microcracks are discussed.
Keywords: amplitude, optical microscope, radian, stress-strain curve, X-ray diffraction, copper, Cycles, Fatigue, Fracture, Fractures, Plastics, Strain, stress, Stress-strain curve