Fatigue pitting caused by the friction between the meshing surfaces of spur gears is one of the main failure forms of spur gear transmission system. The initiation and propagation of micro cracks on the meshing surface is the inducement of fatigue pitting. The research shows that the life of crack initiation stage accounts for more than 80% of the surface fatigue life. When spur gears mesh, the tooth surface bears normal load and tangential load, so the contact fatigue of spur gears is a typical multiaxial fatigue problem. The direction and magnitude of near-field stress vector causing fatigue pitting depend on the selected coordinate system, and the methods such as S-N curve suitable for uniaxial fatigue life analysis are limited. The critical plane method considers the plane direction, location and cycle times of crack initiation under multiaxial cyclic load. It is an effective method to predict the multiaxial fatigue life of spur gear surface.
According to the different modes of crack initiation, the critical plane method is mainly based on the following three methods: a) stress; b) Strain; c) Strain energy density. Findley et al proposed that there is a linear relationship between the normal stress in the critical plane and the critical shear stress under the known number of cycles, and determined the critical plane as the plane with the smallest difference between the amplitude of the critical shear stress and the calculated plane.
Brown Miller criterion [7] assumes that fatigue life is a nonlinear function of strain state, and the maximum shear strain occurs on the critical plane. Smith et al. First proposed taking the product of strain amplitude and maximum normal stress as the fatigue parameter, that is, Smith Watson TOPPER (SWT) parameter. Socie modified the SWT parameter and comprehensively considered the effect of stress and strain on the critical plane, so that this parameter can be used for the calculation and analysis of multiaxial fatigue life. It should be mentioned that the brown Miller criterion is mainly applicable to the failure caused by the initiation of sliding type (type II or III or II / III mixed type) cracks caused by shear stress, and the SWT rule is mainly applicable to the fatigue failure caused by the initiation of open type (type I) cracks caused by tensile stress. The meshing in to meshing out region of spur gear is analyzed by using SWT parameters and dynamic finite element method. The research shows that pitting corrosion is easy to occur near the joint, which is mainly caused by mode I crack initiated by tensile stress.
Although many scholars have done a lot of research on fatigue pitting corrosion of spur gears, the fracture mechanism of pitting formation and the behavior mechanism of multiaxial stress are still the current research hotspot.