The gear–spline system consisting of the internal spline of gears and the external spline of shafts is widely used in mechanical transmission systems. However, considering the nonuniform spline clearance caused by the assembly and manufacturing errors, the vibration characteristics of the system and the spline wear mechanism are still unclear. This article proposed a dynamic model of the gear–spline system with nonuniform spline clearance and wear evolution of spline. Compared with the existing models, the new contribution of this article is to reveal the coupling vibration mechanism of the gear–spline system under the condition of nonuniform spline clearance through the dynamic model. On this basis, the support stiffness characteristics and wear evolution law of the spline pair under the dynamic gear meshing force are studied. The results show that under the condition of nonuniform clearance, the displacement response of the system is modulated by the rotation frequency, and the motion trajectory tends to be chaotic. The load distribution of spline teeth and the equivalent stiffness of the spline depends on the number of loaded spline teeth, which in turn depends on the input torque and clearance distribution. In addition, the spline teeth with smaller clearance bear more loads and wear faster, and the wear causes the nonuniform clearance to gradually increase and become uniform. This study can provide theoretical guidance for revealing the vibration mechanism of the gear–spline system and calculating the support stiffness of the spline shaft.

Rolling Contact Fatigue (RCF) is harmful and inevitable to bearings and usually results in the initiation of subsurface damage. This paper focuses on the cumulative mechanism of subsurface damage in bearing steels arose from cementite during RCF. The distribution of subsurface shear stress in bearings was investigated by finite element simulations. A two-phase atomic model of bcc-Fe and cementite was built. Ten alternating shear load cycles were applied when the model was initially in the elastic, elastic-plastic and plastic stages, respectively. The results show that cyclic softening diversely occurs in all three types of stress responses, and the progress of plastic accumulation depends on the amplitude of cyclic load and cycles. Severe shear deformation eventually leads to the damage of the cementite phase, which might be the microscopic mechanism of the fatigue failure of bearing steels. The conclusions presented have general applicability to brittle inclusions in bearing steels.

Rolling Contact Fatigue (RCF) is harmful and inevitable to bearings and usually results in the initiation of subsurface damage. The root cause for this damage is the cumulative plastic deformation accentuated by carbides. This paper gives a new explanation of RCF based on multiscale models. The distribution and change law of subsurface shear stress in bearing steels was previously investigated by a finite element model. A two-phase atomic model of bcc-Fe and cementite was built. Ten alternating shear load cycles were designed to explore the mechanisms of the cyclic plastic accumulation when the atomic model was initially in the elastic, elastic- plastic and plastic stages, respectively. The results show that cyclic softening diversely occurs in all three types of stress responses. Severe cyclic shear deformation eventually leads to earlier cyclic softening and stress yield, which might be the micromechanism of plastic accumulation and RCF in bearing steels.

Fatigue failure usually occurs on the subsurface in rolling bearings due to multiaxial and non-proportional fatigue loadings between rolling elements. One of the main stress components is the alternating shear stress. This paper focuses on the micromechanism of plastic accumulation and damage initiation in bearing steels under cyclic shear deformation. The distribution of subsurface shear stress in bearings was firstly investigated by finite element simulation. An atomic model containing bcc-Fe and cementite phases was built by molecular dynamics (MD). Shear stress–strain characteristics were discussed to explore the mechanical properties of the atomic model. Ten alternating shear cycles were designed to explore the mechanism of cyclic plastic accumulation and damage initiation. Shear stress responses and evolutions of dislocaitons, defect meshes and high-strain atoms were discussed. The results show that cyclic softening occurs when the model is in the plastic stage. Severe cyclic shear deformation can accelerate plastic accumulation and result in an earlier shear slip of the cementite phase than that under monotonic shear deformation, which might be the initiation of microscopic damage in bearing steels.