Relationship between the propagation of fatigue cracks and the behaviour of plastic flow under rolling/sliding contacts - effect of slip ratio

The relationship between the propagation of fatigue cracks and the behaviour of plastic flow in the surface layer was experimentally investigated under lubricated rolling-sliding contact. The test specimen material was medium carbon steel (S45C) with hardness H_v 187 after annealing. Results show that the displacement of plastic flow in the surface layer of the follower increased with increasing number of revolutions. Crack propagation occurred in the surface layer of the follower when the displacement of plastic flow on the centre of the contact reached a saturated value. On the contact surface of the follower, the propagating angle of the fatigue crack was found to be correlated to the angle of plastic flow, which was independent of the slip ratio. The rate of plastic flow increased with increasing slip ratio, resulted in a reduction of fatigue life. The displacement of plastic flow beneath the contact surface could be evaluated from the profile change of the plastic flow on the contact surface.