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.