Micro pitting can be regarded as the precursor of the occurrence of early pitting characteristics, and its geometric characteristics are even less. Compared with the tooth stiffness and matrix stiffness of the time-varying meshing stiffness component of the gear, its influence is negligible. In terms of the contact stiffness of the tooth surface, the micro pitting characteristics of the tooth surface will cause the tooth surface to be rougher, which belongs to the micro effect characteristics. According to the proposed normal contact stiffness model of rough surface, the change of normal contact stiffness under micro pitting can be approximately simulated.
As the geometric characteristics of micro pitting and pitting have not been defined in detail, according to the relevant research results and the formation mechanism of micro pitting, it shows that pitting generally occurs on the pinion tooth surface first, mainly along the pitch line to the tooth root area (Fig. 1 and Fig. 2), and the characteristic size of pitting ranges from 0.01mm (micro pitting) to 0.08mm (extended pitting) The tooth spalling failure characteristics (spalling characteristics greater than 0.08mm) will occur in one step extension. According to Fig. 2 (a), the crack mode of micro pitting (surface crack and this surface crack) is shown. Under the joint action of meshing force and lubricating oil, the maximum characteristic size of surface crack is about 10 μ m, while the characteristic size of subsurface crack is 20-100 μ M. According to the simulation method of micro surface roughness and the fractal mathematical model of rough surface, the mathematical analysis model of micro pitting can be established by approximately changing the roughness characteristics of tooth surface and combining with fractal theory.
The fractal parameter, fractal dimension D, rough amplitude g, and gear parameters are selected to simulate the surface morphology of different degrees of micro pitting. According to the established dimension normal load and normal contact stiffness have certain mathematical expression correlation with a * r and a * C respectively, and through this relationship, the mathematical relationship formula between them can be constructed to predict the normal contact stiffness of tooth surface under micro pitting corrosion characteristics.
Figure 3 shows that the normal contact stiffness decreases obviously after the micro pitting corrosion occurs on the tooth surface, which is 1-2 orders of magnitude different from the characteristic stiffness without pitting corrosion. At the same time, the bearing capacity will also decrease. The calculation and simulation results are consistent with the change trend of the engineering application, which lays the foundation for the later analysis of the dynamic response of micro pitting corrosion and the expansion of micro pitting corrosion.