4 Conclusion
The atomic simulations based on the two-phase model of bcc-Fe and
cementite in this work characterize the microscopic mechanism of
cumulative damage in bearing steels under RCF. The main conclusions can
be summarized as follows.
1. The stress responses of the atomic model appears cyclic softening
under all three kinds of cyclic load, and a larger load leads to a
greater reduction in stress amplitude and a time-advanced cyclic
softening.
2. Dislocations nucleate and annihilate on the interface when shear load
amplitude and cycle index are small. When the amplitude and index are
large enough, regular structures of the material are destroyed, and
massive dislocations retain in the model, resulting in the gradual
accumulation of plasticity.
3. Larger shear load amplitude leads to higher average density of
dislocation and larger proportion of irregular structure in the model.
As loading direction changes, the stress responses and dislocation
density of the model is basically unaffected, but the proportion of
irregular structures, as well as the initiation and movement of
dislocations changes significantly.
4. Large shear load amplitude
causes a mass of defect meshes in the model, further resulting in lots
of residual shear strains and stresses in the model. When the cementite
phase tends to be damaged under severe shear deformation, the material
is usually in a dangerous state, which indicates the origin of failure.
Since cementite is brittle and difficult to deform, it can represent a
series of brittle inclusions in bearing steels. Therefore, plastic
accumulation and defect initiation are more likely to occur on the
interface between inclusions and bearing steel matrix under RCF.