Simulation of internal stresses near the surface and fatigue crack nucleation for a copper single crystal in cyclic deformation saturation stage

SEM-ECC technique was employed to observe and characterize the dislocation microstructures during the saturation stage of cyclic deformations in a copper single crystal. Some band-like or spot-like dark zones were found in the dislocation microstructures, which located either at the edge region of the deformed specimen or at the interface between the dislocation matrix and the PSB. To interpret the experiment results, the near surface dislocation microstructure were simulated and the internal stress distributions induced by those dislocations were calculated by using discrete dislocation dynamics method. The simulation results show that near the free surface region, the maximum internal stresses or stress concentration appear at the dark zones which correspond to the interfaces between the PSB and the dislocation matrix or the PSB-matrix-surface interfaces, meaning that fatigue cracks initiate preferentially at these dark zones. The simulated results can well explain the observed ones.