Evolution of persistent slip bands and simulation of its stress field in a fatigued copper single crystal

The transition from the so-called matrix veins to persistent slip bands (PSBs) in a fatigued copper single crystal was observed by electron channeling contrast (ECC) technique in a scanning electron microscope (SEM). In the four stages of PSBs formation, the different dislocation patterns can be obtained by the experiment, namely, the veins, persistent slip lines (PSLs), embryos and well-developed PSBs dislocation structures. In the consecutive four stages the typical dislocation structures were simulated and the internal stresses were calculated by the three-dimensional discrete dislocation method, correspondingly, the external stresses were calculated by the finite element method (FEM). The simulation shows that in the dislocation dense regions (veins and walls) the stress distributions are relatively more concentrated than that in the dislocation poor regions (channels and within a PSL). At the tips of the PSLs and embryos, the internal stresses were not substantially changed; however, at the tips of the PSLs and embryos the external stresses were much higher than that at the other regions. This will drive the PSLs and embryos to grow.