Fig. 10 Dislocation distribution in the model under cyclic loads. Applied loads of (a, d) d1, (b, e) d2 and (c, f) d3. Loading directions are along (a, b, c) the y -axis and (d, e, f) thex -axis, respectively. Only dislocation distribution at the end of the cycle (1, 3, 5, 10) is shown. Other features are the same as in Fig. 9.
The interface is an underlying area for defect generation and annihilation during plastic deformation.48 During cyclic shear deformation, the interface is accompanied by the nucleation and annihilation of dislocations, which results in the fluctuation of dislocation density (shown in Fig. 7). After several cycles, the residual strain in the model hinders the annihilation of dislocations, which is manifested as a large number of dislocations remaining in the model at the end of the cycle. Fig. 11 shows the nucleation and annihilation of dislocations on the interface when d1 is applied along the y -axis. The view in Fig. 11 is kept parallel to the interface by rotating the coordinate system. In the third cycle shown in the upper part of Fig. 7a, the dislocation density first increases and then decreases, which is manifested by the evolution of the dislocation as shown in Fig. 11. The 1/2<111> dislocation nucleates at 2.25 cycles, then gradually grows up at 2.25-2.4375 cycles, and finally disappears at 2.4375-2.5625 cycles. Note that the time for dislocation nucleation is longer than that for annihilation, which is mainly due to a larger activation barrier of nucleation than that of annihilation. The same conclusion was drawn by Liang et al.20 In addition to that, low temperature was adopted to the atomic model, because temperature affects the speed of dislocation evolution.49 Choosing a temperature of 5K could help us observe the process of dislocation nucleation and annihilation more clearly.