Cyclic hardening and slip localization in single slip oriented copper crystals

A static-dynamic model is applied to the interpretation of slip localization modes observed in a systematic study of the evolution of dislocation structures in single slip intermediate amplitude fatigue in copper deformed at room temperature. The model assumes that veins do not deform plastically, unless their critically soft interiors are destabilized to produce an embryonic PSB. This assumption is shown to be fully consistent with slip homogeneity. The model predicts that the vein structure remains active during cyclic saturation. This prediction explains the present novel observation that in intermediate amplitude fatigue, after the initial formation of PSBs by ''collapse'' of matrix walls, triggered by long-range internal stresses, there is continued formation of new PSBs by ''splitting'' of matrix veins. The model shows that the long-range internal stresses in the thin PSB lamellae and in the more extended wall structures produced by this process are about equal. Nevertheless, the model and microscopy suggest convincingly that minimization of dislocation line energy in the dynamic structure between glissile walls and veins controls the condensation mode and the equilibrium wall spacing of PSBs.