Three dimensional crack propagation analysis of spur gear root

Spur gears are widely used in electric power, chemical industry, petroleum, aerospace, automobile and other fields. Almost all these spur gears yield to cyclic load. With the development of modern industry towards high precision, high efficiency and integration, the requirements for spur gears are higher and higher. With this problem, the research on fatigue failure of spur gears naturally becomes more and more important. The vast majority of spur gears in industry operate under cyclic load. Scholars have done a lot of research from theory, experiment and digital methods, and have a certain understanding of material fatigue and structural fatigue of spur gears. In the study of complex models, digital simulation method plays a vital role. At present, most studies are modeled and simulated by digital methods. In this paper, the spur gear model is established by using the ANSYS APDL parametric modeling idea, and the crack propagation process of spur gear is simulated by using the joint simulation technology of ANSYS and FRANC3D.

Cracks on the tooth root surface of spur gears are common. Many scholars have done a lot of research on tooth root cracks by using digital simulation and experimental methods. In this chapter, the crack propagation under different distributed loads is simulated by using the joint simulation method of ANSYS and FRANC3D. From the results, the variation law of the stress intensity factor at the crack front and the variation law of the crack propagation path are observed, so as to infer the influence of the uneven distribution of the load on the tooth top on the crack propagation behavior of the tooth root.

In practice, it is impossible to consider the influence of all practical factors on crack propagation behavior at the same time. The load of spur gears is very complex. When spur gears mesh, the load is not only unevenly distributed in the tooth direction, but also constantly moving on the tooth surface. The size and direction of the actual load are constantly changing. It is difficult to investigate these situations at the same time. In the analysis process, we can only simplify the model as much as possible and control some variables to study the influence of other variables on the root crack propagation behavior. In engineering practice, this simplified method has been widely used.

The key point is to simulate the crack propagation of spur gear root by using the joint simulation method of ANSYS and FRANC3D. Considering the unequal load between points on the contact line during the actual meshing of spur gear, the load linearly varying in the z-axis direction is applied to the contact line of spur gear, and the propagation process and results under ideal load are compared and analyzed. The single tooth finite element model established by ANSYS is introduced into FRANC3D. After the crack is embedded in the dangerous position, the static analysis of the crack is carried out, the values of the stress intensity factors of each node at the front edge of the initial crack under the two loads are obtained, and the changes of Ki, Kii and kiII under the two loads are analyzed and discussed. Then the crack propagation process is simulated, the variation trend of stress intensity factor along the specified path in the crack propagation process is given, and a comparative analysis is made. It can be observed from the results of crack propagation that the crack propagation path changes due to different applied loads. These results are analyzed and discussed one by one. The main conclusions are as follows:

(1) The crack propagation process of spur gear tooth root under ideal uniformly distributed load and actual load is simulated, the stress intensity factor at the deepest crack in the crack propagation process is calculated, and the curve varying with the crack propagation length is given. Finally, the crack propagation result diagram is given. From the diagram, the influence of uneven tooth load distribution on crack propagation behavior can be seen intuitively, Compared with the propagation path under ideal uniform load, the actual load makes the root crack propagation path of spur gear offset.

(2) According to the simulated stress intensity factor at the deepest crack of spur gear, the crack inclination during crack propagation is calculated. Due to the different loads between the points on the contact line in the actual loading, the crack inclination of spur gear changes greatly compared with the ideal uniform load, which affects the crack propagation path.

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