CYCLIC STRAIN LOCALIZATION IN POLYCRYSTALLINE COPPER AT ROOM-TEMPERATURE AND LOW-TEMPERATURES

Copper polycrystals have been cyclically strained with constant plastic strain amplitudes at temperatures of 295, 178 and 88 K. Hysteresis loops were recorded, and stress amplitude and loop shape parameter were plotted vs. number of cycles. In room temperature cyclic straining, the surface relief and dislocation structure evolution was studied. The mechanical measurement and surface and internal structure observations indicate the presence of the characteristic stages in the fatigue life of polycrystals. The fatigue mechanisms maps were drawn for polycrystalline copper, demarcating the region of homogeneous straining, the region of progressive localization and the region of stabilized repeated localized cyclic straining, leading to the initiation and growth of primary fatigue cracks.