The Mechanics of Crack Initiation at Hard Particles in Rolling Line Contacts

Abstract

The mechanics of crack initiation in rolling contact bearings is investigated by considering the possibility of hard particle debonding from the surrounding softer matrix. The local elastoplastic stress and strain fields around a hard cylindrical particle located at the point of maximum shear stress below the Hertz contact are calculated by the finite element method. The calculations show that if the applied Hertz loading is sufficiently high, the matrix contiguous with the particle deforms plastically. Upon unloading tensile residual stresses will be set up normal to the particle-matrix interface. The particle-matrix interface debonds provided the stored elastic energy in and around the particle is larger than the work of adhesion, and the maximum residual radial stress is greater than the cohesive strength of the particle-matrix interface. The gradual softening of the martensitic matrix around non-metallic inclusions or carbides, which is known to occur after a large number of stress cycles in bearing steels, could result in a residual radial stress greater than the interfacial strength and cause particle-matrix debonding.