In the process of spur gear crack propagation, the stress intensity factor changes with the crack propagation. Compared with the crack propagation of spur gear under ideal load and actual load, the change process of stress intensity factor is very complex, and with the increase of propagation steps, it brings great difficulties to the drawing. In this section, it refers to a node determined in geometric relationship in the fixed crack front edge of spur gear, as shown in Figure 1. This node is the midpoint of the crack front edge of elliptical sheet spur gear; Then, the path is formed by connecting these nodes, and then the stress intensity factor on this path under different loads is calculated. The results are shown in Figure 2.
It can be seen from Figure 2 that ki increases at the midpoint of the crack front with the crack propagation of spur gear; Kii changes little after the second step expansion. Numerically, Ki is much larger than Kii and kiII, and Kii is the smallest.
In general, under the action of ideal uniform load and actual load, the change trend of KI and Kii is the same. With the continuous increase of crack propagation of spur gear, the value under actual load is larger than that under ideal load. Kii under ideal uniform load and actual load is very small, and the change with crack propagation of spur gear is not obvious. The value of kiII changes obviously under different loads. Under the ideal uniform load, because the loads between the points of the contact line are the same, kiII is basically unchanged in the process of crack propagation and its value is close to 0. It should be noted that in the two loads, Ki always increases with the crack propagation of spur gear, Kii still changes little after the second step of propagation, and kiII decreases with the crack propagation of spur gear under the two loads.