Fig. 6 Shear stress-cycle responses under different loading conditions. 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. Red and blue dash lines represent the trends of maximum and minimum stress amplitudes, respectively. Red boxes show the yields of shear stress.
The decreasing extent of stress amplitude during cyclic softening depends on the dislocation evolution mechanism under different shear loads. Note that the experimental results drawn from carbon steels show work hardening as cyclic cycles increase under uniaxial ratchetting deformation,11,42 which is contrary to the cyclic softening. The reason might derive from the initial regularity and simplification of our simulation model. Furthermore, there are obvious disparities between the results shown in Fig. 6 and the results drawn from the model under cyclic tension and compression loadings.20 This is mainly due to the differences in the calculated stress tensors and the mode of motion. During cyclic shear deformation, atomic model seems more likely to appear cyclic softening, and the plastic accumulation is faster. And the rapid plastic accumulation is unfavorable to the fatigue life of bearing steels.