Overview of fatigue pitting of gears

According to the causes of pitting, pitting is a phenomenon of surface metal falling off under the action of cyclic contact stress. Due to the complexity of gear material, heat treatment process and loading, the forms of pitting are also diverse and random, as shown in Figure 1. As there is no corresponding classification for the severity of pitting at present, the following is a brief description from the pitting morphology and size characteristics. The pitting morphology in Fig. 1 (a) – 1 (E) is relatively small and scattered, which can be called the early or middle form of pitting, while the pitting morphology in Fig. 1 (f) – 1 (I) is relatively large and concentrated, which can be called the late form or spalling form of pitting. Whether it is the form of pitting, its performance characteristics can cause the reduction of gear bearing capacity and anti deformation ability, and even cause serious phenomena such as equipment shutdown or equipment damage.

Due to the randomness and geometric complexity of pitting morphology, accurate calculation of meshing stiffness is very important for the study of gear failure dynamics. At present, for the analysis of gear meshing stiffness under the characteristics of gear pitting, three simplified models as shown in Figure 2 are mainly used to simulate the pitting morphology for research and analysis. In order to facilitate the calculation, the geometric position of the pitting geometry is set symmetrically, that is, the geometric symmetry and the position symmetry are taken, and the pitting morphology is set symmetrically about the tooth width centerline . Although there are some limitations in the simulation study of these simplified effects of pitting, which can not truly reflect the pitting state shown in Figure 1, the development trend of mesh stiffness under pitting can be predicted by these simplified geometric models, and the influence of the size of pitting area on the stiffness can be analyzed.

(a) Rectangle (b) Round (c) Triangle

Due to the randomness and complexity of the pit geometry shown in Figure 1, it is difficult to measure and simulate its geometric characteristics and mesh stiffness. But at the same time, it can reflect the influence of pitting characteristics on meshing stiffness as truly as possible. Based on the geometric morphology of rectangular pitting pits shown in Fig. 2 (a), a general mathematical model for meshing stiffness calculation under pitting characteristics is proposed, and multi types of pitting characteristics of tooth surface are studied, such as single pitting, multi pitting and random distribution pitting. It is of great significance to provide basic support and direction for the later fine research, as well as the reference value of research results.

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