Dependence of hardening and saturation stress in persistent slip bands on strain amplitude during cyclic fatigue loading

Abstract

Cyclic loading of FCC single crystals leads to the formation of persistent slip bands (PSBs) over a wide range of applied strain amplitudes. The hardening and saturation stress associated with cyclic loading of Cu single crystals are reproduced with 3-D discrete dislocation dynamics simulations. Evolution of the dislocation microstructure in PSB channels and walls during cyclic loading is shown to explain key features of plastic deformation. Screw dislocation segments are found to deposit edge components near PSB channel walls resulting in the nucleation of half-loops that expand into neighbouring channels. The saturation stress is found to be 34 MPa at an applied strain amplitude, , within the range of experimental observations. It is shown that once PSBs are formed, subsequent cycling at lower strain amplitudes does not lead to their elimination, but the cyclic stress–strain behaviour is modified. At lower values of of previously formed PSBs, the saturation stress is found to decrease to 24 MPa at . Plastic energy dissipation in hysteresis loops is also significantly reduced but not removed. However, some reverse plasticity is shown to take place upon unloading at low values of , and is a direct result of strain recovery of loops that expand into neighbouring channels during the loading phase.