Generally, the models used in simulation analysis are simplified, and it is impossible to fully consider all factors; From the idea of control variable method, highlight the factors that need to be studied and ignore other factors in the research. Therefore, there are defects where there are innovations. In Chapter 4, although the effects of two different tooth direction distributed loads on crack propagation behavior and crack propagation life of spur cylindrical gear root are simulated and analyzed, the actual situation is that the uneven degree of load tooth direction distribution is constantly changing with the gear meshing process, and with the change of the actual situation, In order to study the influence of different loads on the root crack of spur gears, the initial crack position is fixed in the middle of the root; Later, the influence of initial crack position on crack propagation life has been studied by many people. In this paper, the change of position is changed from the change of tooth width to the change of included angle with the determined plane. Generally, in order to facilitate the research, simplified models are used. Although this method brings convenience to the research work, the actual gear meshing is a very complex process, and there is a big gap between the analysis of single tooth and the actual situation.
The research on fatigue crack of spur gear root depends on the development of fracture mechanics, and the fatigue fracture behavior of materials in practice depends on the development of elastic-plastic mechanics. Although many software tools can be used to study the fatigue cracks of materials and structures, they are basically established in the scope of on-line elastic fracture mechanics. Within the scope of on-line elastic fracture mechanics, there are also great limitations. K factor is an important parameter to describe the stress field at the tip or leading edge of spur gear root crack, but there are still many problems in the calculation of K factor. For example, the calculation of K factor under the specific spur gear root crack geometry has not been solved. As far as the content of this paper is concerned, the main research work in the future will focus on the following aspects: first, find out the definite relationship between stress intensity factor and shape factor, so as to accurately calculate the stress intensity factor at the tip or leading edge of different crack shapes; Secondly, the influence of material plasticity on the fatigue of materials and mechanisms must be considered; Thirdly, the influence of tooth load distribution coefficient on the fatigue crack propagation behavior of tooth root is determined; Fourthly, the variation law of the uneven degree of load distribution in the tooth direction during the actual meshing of the gear is determined, and the relationship between the gear fatigue life and the load distribution coefficient in the tooth direction is established.