Based on linear elastic fracture mechanics, the crack propagation and life of spur gear root are studied by using the joint simulation technology of ANSYS and FRANC3D. The main conclusions are as follows.
(1) At the beginning, the research status of fracture mechanics is introduced, and the research status and methods of tooth root crack of spur cylindrical gear are summarized. The second chapter introduces the basic knowledge of linear elastic fracture mechanics, without introducing the theory of material plasticity, such as cod theory and J-integral. In the range of on-line elastic fracture mechanics, energy release rate and stress intensity factor are the main methods to study the fatigue crack of spur gear. Energy release rate studies the crack propagation behavior from the perspective of energy in the crack propagation process of spur gear, and stress intensity factor is a physical parameter to describe the strength of stress field at the crack tip or leading edge, By deriving the calculation formulas of energy release rate and stress intensity factor, the mathematical expression of their relationship is given.
(2) The program for establishing the gear is compiled by ANSYS APDL. Considering that the failure of the gear is the failure of the gear tooth, in order to simplify the calculation, a gear tooth on the gear is cut as the research object, and the initial crack position of the spur cylindrical gear is determined by static analysis. Finally, the single tooth model with the initial crack of the spur cylindrical gear is established.
(3) When simulating the crack propagation of tooth root, the uneven distribution of tooth load in the actual work of gear is considered; In the actual meshing of gears, the shaft is bent due to the radial load, resulting in the uneven distribution of the load on the gear in the tooth direction, which affects not only the crack propagation behavior of the tooth root, but also the crack propagation life of spur cylindrical gears. The crack propagation process of tooth root under different tooth direction distributed loads is simulated by using FRANC3D software, and the deepest stress intensity factor and crack inclination in the crack propagation process of spur gear are calculated. Based on the simulation of crack propagation process, the fatigue life of gear is predicted, and the crack propagation rate under different loads is calculated. The results show that the uneven distribution of tooth load not only affects the crack propagation path of spur gear, but also shortens the fatigue life of gear.
(4) Finally, the effects of different positions of initial cracks on the fatigue life of spur gears are studied; Many literatures have studied this problem, and consider the crack propagation life of spur gear under different included angles between the initial crack plane and XZ plane. It is concluded that the larger the included angle is, the longer the crack propagation life of spur gear is.