Deterministic Analytical Model of Resistance to Deep Contact Fatigue of a Stressed Material

The stress state of the surface layer in the contact zone of the mating teeth of cylindrical gears is considered. It is shown that under contact loading, the stress state of the surface layer is inhomogeneous and changes with the distance from the surface. It is established that the value of the equivalent tangential stresses does not depend on the standard size of the gears, but is determined by the surface contact stresses σH. Moreover, the depth of occurrence of the maximum equivalent tangential stresses depends on the gear modulus (the reduced radius of curvature of the mating surfaces of the teeth) and, to a lesser extent, on the surface contact stresses σH. The inhomogeneity of the stress state and the structural characteristics of the diffusion layers of surface-hardened gears is a prerequisite for the appearance of critical zones in them, in which fatigue processes of contact failure can originate and develop. A deterministic analytical model of the resistance to deep contact fatigue of hardened tooth surfaces is proposed, based on determining the service life of the gear before the appearance of progressive deep contact chipping of the active tooth surfaces with a regulated variation of the microhardness values in different zones of the diffusion layer.