In the process of gear transmission, if it can not get good lubrication, a lot of micro pitting corrosion pits will be produced on the tooth surface, which will cause more serious tooth failure. At the same time, the lubrication state of the gear changes constantly in the actual operation process. Therefore, it is necessary to conduct in-depth research on the micro pitting corrosion on the tooth surface, clarify the formation process of the micro pitting corrosion from the initial crack propagation to the surface, and reveal the micro pitting damage characteristics under different lubrication conditions, so as to provide the basis for slowing down the gear wear and prolonging the gear life.
The experimental study on micro pitting corrosion of gears shows that the formation of micro pitting corrosion is affected by many factors, such as material, working condition, surface impurities, residual stress, roughness, contact stress, lubrication state, load, heat treatment mode and temperature. Because there are too many factors affecting the micro pitting corrosion, it is obviously difficult to establish a model to take these factors into account. The current research focuses on the contact fatigue model. Chu and Chung used the finite element method to analyze the propagation characteristics of microcracks under different loads. Fla š A two-dimensional numerical model of gear pitting under contact load was established, and the formation process of micro pitting under different equivalent contact radius and different contact load was simulated by this model. Aslantas and tasgetiren proposed a pitting failure model based on finite element analysis and linear elastic fracture mechanics. MTS criterion was used to determine the crack propagation direction. Glode ž The team established an equivalent numerical model of gear tooth contact fatigue, predicted the crack propagation path using the modified MTS criterion, and simulated the formation process of fatigue crack from initial crack propagation to surface using the virtual crack propagation method, and obtained the functional relationship between the stress intensity factor at the crack tip and the crack length, The number of stress cycles required for the initial crack growth to the critical crack length is calculated. Ding et al. Established a prediction model of gear spalling depth, and used the model to predict the spalling depth of spur gears with different geometric shapes and materials. The calculated spalling depth is in good agreement with the measured data.
In recent years, scholars have proposed a new model to study the pitting problem of gears. Xiong Yongqiang et al. Established the thermal elastohydrodynamic model of wind power main gear, and calculated the micro pitting corrosion safety factor of wind power main gear by using the multi grid method. Cheng Jun et al. Established the local contact model of gear pair under the condition of elastohydrodynamic lubrication, and used the extended finite element method (XFEM) to simulate the propagation process of surface crack initiation. Considering the elastohydrodynamic lubrication, Li Xuping calculated the contact pressure distribution of the two-stage sun wheel and the three-stage driven wheel of the wind turbine, thus using XFEM to simulate the formation process of micro pitting under different initial cracks. He et al. Established a fatigue damage numerical model of gear with initial residual stress of 380MPa to simulate the contact fatigue of gear tooth surface. The results show that the initial residual stress will increase the fatigue life of gear tooth surface by 20%. Xu and Max proposed a numerical model to predict the initiation and propagation of micro pitting corrosion on the tooth surface of spur gears, respectively. The mechanism of pitting corrosion initiation was described in detail by establishing the wear equations of wear, micro pitting corrosion and pitting corrosion. On this basis, the effect of crack density was considered, and the propagation of micro pitting corrosion was predicted by using the model.
It can be seen that the previous research work of gear pitting crack propagation is mainly based on Hertz theory and elastohydrodynamic lubrication theory to establish the equivalent contact numerical model of the gear tooth surface with microcracks, but the contact relationship between the crack and the opposite gear in the process of crack propagation is ignored. In the latest research progress of tooth surface, whether it is the study of normal contact stiffness considering micro pitting or the study of predicting contact fatigue life of tooth surface, it is necessary to clarify the change of micro pitting scale characteristics on tooth surface morphology, so as to establish the analysis model considering the influence of micro pitting. In addition, compared with the extended finite element method, the contour integration weakens the relationship between the stress intensity factor at the crack tip and the grid density to a certain extent, that is, the contour integration method can directly calculate the stress intensity factor with high accuracy through the sparse grid elements at the crack tip.
Therefore, based on the contour integral, the finite element numerical model with lubrication contact pair is established to study the formation process of micro pitting corrosion on gear tooth surface, and the influence of different lubrication states on the crack propagation process is further discussed. The change law of stress intensity factor in the crack propagation process is obtained. By analyzing the crack propagation path, the micro pitting corrosion morphology under different lubrication states is quickly determined, The results can provide a basis for the analysis of contact fatigue life and the calculation of gear meshing stiffness considering the pitting corrosion.