Numerical modelling of fatigue crack's initiation in rolling contact of sintered steels

The rolling contact fatigue is a major problem in mechanical systems submitted to very high contact pressure. Sintered steels are often used to build camshaft so as to save weight and decrease cost production. However, the porosity of sintered steels may worsen the resistance to rolling contact fatigue. Previous investigations have already shown the importance of the surface hardness and its density in the fatigue resistance of sintered steel. The objective of this paper is to investigate, by a numerical approach, the influence of various material parameters, such as work-hardening nature, yield stress, on the stress near porosities during a rolling contact. Residual tensile stresses due to plastic strain near porosities have been particularly revealed after a sliding sequence, which could explain the crack's propagation observed experimentally on camshafts. It is shown that the crack initiation can be explained using Dang Van fatigue criterion. The opening and the propagation of the crack are then discussed with the help of the fracture mechanics of brittle material. The crack's propagation observed experimentally is then discussed.