Abstract:

Gear is an important component in mechanical transmission, and its fatigue performance affects the reliability and safety of mechanical equipment. However, in the current research on contact fatigue problems, the joint mechanism of residual stresses and inhomogeneities is unknown, and the effect on contact fatigue life is difficult to predict. In this paper, a numerical algorithm model is proposed to analyze the distribution of common residual stresses and inhomogeneities in gears. To reach this goal, the classical distributions of the residual stress in the gears are obtained from references. Then the gear loading tooth contact analysis of straight tooth cylindrical gears is carried out to find out the contact load at a series of key contact positions and the size of the equivalent contact radius. Finally, a microscopic contact calculation model combined with the residual stresses and the inhomogeneities is established. In the establishment of the model, the inhomogeneities inside the gear are transformed into inclusions containing eigenstrains using the equivalent inclusion method, and the coupling effect of the residual stresses and inhomogeneities is considered in the equivalent equilibrium equations. The stress distribution under the joint action of different residual stress fields and inhomogeneities is computed by the presented model. On this basis, a gear risk assessment model is established. The equivalent stress is calculated using Dang Van's criterion, which is then incorporated into the Lundberg-Palmgren life model to find the minimum number of cycles. In this way, the risk assessment of contact fatigue inside the gear is completed, and the effects of different meshing positions, residual stresses and inhomogeneities on the contact fatigue of the gear are analyzed. The model was verified by the finite element method, and the results agree well. The impact of inhomogeneities on the contact fatigue life of gears far exceeds the influence of residual stress, and they predominantly determine the earliest point of contact fatigue on the gears. Under the combined effects of residual tensile stress and inhomogeneities, the maximum stress value in the sub-surface layer increases and shifts towards the material surface, making gears more prone to contact fatigue.

Key words: residual stress, inhomogeneous material, spur gear, contact fatigue, risk assessment, Dang Van criterion