A mechanism for nucleating secondary fractures near a pre-existing flaw subjected to contact loading

The mechanism of surface failure from a pre-existing line defect under rolling contact has been studied using a boundary element method. A three-dimensional boundary element model has been developed in order to investigate how the pre-existing defect affects the surface fracture behaviour and to determine the geometry of acceptable line defects. Research shows that the pre-existing line defects significantly increases the magnitude of the surface tensile stress on the contact circle. This tensile stress leads to secondary fractures near the pre-existing flaw. Consequently, the secondary surface cracks are formed. These secondary surface cracks dominate the final pitting formation. The secondary fractures can be formed at either the trailing edge or the leading edge of the contact circle. Changes in the crack geometry have a significant effect on the magnitude and distribution of the surface stress. Increasing the gap between the crack faces increases the tensile stress at the edge of the contact circle. Also, increasing the crack length or crack depth increases the tensile stress at the edge of the contact circle. All the numerical analysis based on this model has been verified by a comprehensive experimental study and the predictions are consistent with the experimental observations.