Mechanical and Structural Changes During the Deformation of Copprr by Fatigue

CIM Bulletin1962
T. McGRATH ; R. C. A. THURSTON
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
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