Research status of root crack of spur gear

Most spur gears yield to cyclic load and are widely used in aerospace, wind power generation and other industrial fields. Under the action of cyclic load, modern industrial spur gears produce surface pitting corrosion and tooth root stress concentration, resulting in fatigue failure. Pahen s and blarasin a studied the fatigue fracture mechanism of spur gears through experiments. However, due to the long period and high cost of experimental research, there are many difficulties in studying complex models, and digital simulation method is a very powerful tool in this regard.

Researchers generally study the fracture characteristics of spur gear teeth on the basis of existing fracture mechanics and damage mechanics, adopt boundary element and finite element methods, infinitely refine the crack front area, reasonably control the boundary conditions, approximately estimate the change of stress intensity factor at the crack front edge, and obtain the stress-strain field, So as to study the fracture characteristics of fatigue cracks. In 1999, Michele ciavarella and Giuseppe demelio of the University of Southampton studied the fracture failure of two-dimensional tooth root based on the theory of stress-strain field. In 2001, David g. Lewicki, an American scholar, put forward a super safe design idea, which aims to study the occurrence and propagation law of tooth root crack, try to improve the design, and try to avoid the development of root crack: that is, after crack initiation, try to change the propagation direction of crack, so as to prevent fracture failure of tooth root. Most scholars mostly use digital simulation method to study this problem.

At present, the main models to study the initiation and propagation of spur gear root crack are moving load model and tooth top load model. David g. Lewicki pointed out that the moving load model makes the model process more accurate and close to the actual situation because the load on the teeth changes with the rotation, size and position of the spur gear during the meshing process of the spur gear; In the theory of crack propagation, the danger plane theory can not only predict the crack initiation life, but also accurately determine the direction of crack propagation. After that, he considered the influence of crack closure technology effect on crack propagation under moving load model, and compared it with some experimental results, which was in high agreement. When studying the root three-dimensional crack problem, the most widely used is the tooth top loading model. The model does not consider the movement of the contact line during the meshing of spur cylindrical gears. When the load is applied to the tooth top line, the result is conservative, but it is very helpful to study the root three-dimensional crack propagation path process. When starting to study the fatigue failure of spur gear, relevant scholars speculated on the basis of many experiments that the position with the maximum local stress in the root is often the most dangerous position, and the crack propagation direction is along the normal direction of the root transition curve, which is similar to the reverse method in engineering. The position with the maximum stress is determined by the crack propagation direction at the root of spur gear. However, these conclusions have great loopholes. Firstly, there are too many assumptions and many specific factors in practice are not considered, resulting in the over simplification of the model; Secondly, the root stress is studied by using the direction of fatigue crack initiation and propagation, but the effect of root stress on crack behavior is not pointed out. In recent years, the research on the crack of spur gear has been refined and deepened continuously. Professor Xia Yanqiu studied the effect of tooth surface friction coefficient on contact fatigue, and Professor Li youtang studied the effect of friction coefficient on the crack stress field strength of spur gear; Many researchers have studied the effects of rotating speed, oil film thickness and other aspects on the fatigue cracks of spur gears.

In the study of fatigue crack of spur gear, most scholars study the variation law of stress intensity factor. In 2012, Dong Feifei of Northwest University of technology studied the influence of spur gear parameters on gear three-dimensional crack stress intensity factor. Some conclusions are similar to those obtained by Raghu V Prakash: the parameters of spur gear in the process of crack propagation and final fracture, such as modulus, tooth thickness The influence of deformation coefficient on crack propagation process and crack propagation life. The development of fracture mechanics also provides a good theoretical basis for the research of tooth root fatigue fracture. There are relatively mature results in the research of bearing capacity and stiffness in the process of spur gear transmission. Moreover, the development of computer technology also provides a good tool for the analysis and research of fatigue cracks. With the support of the above theories and technologies, the three-dimensional modeling and fatigue crack simulation analysis of spur gears have been greatly developed. These results have laid a good foundation for the future research on the fatigue crack of spur gear root.

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