Initiation and propagation of surface cracks in rolling fatigue of high hardness steel

Surface cracks initiating flaking failure observed by Sugino in rolling fatigue were further studied. Surface crack initiation was influenced by either running or material conditions, affecting the residual tensile stress just below the rolling contact surface. The fatigue crack is thought to initiate very near the surface by the stress cycle of small tensile residual stress and large compressive contact stress. The amount and direction of the tensile residual stress due to rolling contact varies with the contact geometry, which probably determines the direction of the surface crack and the appearance of flaking. The transition from the surface crack to flaking failure or complete section fracture is material and running condition dependent and is explained by a fracture mechanics concept.