Flaking failure in rolling contact fatigue caused by indentations on mating surface (II): Formation process of flaking failure accompanied by cracks extending bi-directionally relative to the load-movement

In rolling contact fatigue, a surface crack normally extends in the direction of the load-movement (LM). However, we have found that flaking failure with bi-directional crack extension occurs on a defect-free roller surface when indentations are present on the opposed roller surface. In the present study, a stress-state analysis using the boundary element method was conducted to evaluate the effects on a defect-free surface of an indentation on the opposite roller surface moving through the contact area. It is shown theoretically and experimentally that the initiation of a small subsurface crack parallel to the contact surface takes place where the maximum stress concentration occurs induced by the indentations on the opposite roller surface. The small subsurface crack grows into a small flaking failure accompanied by cracks extending in the direction opposite to the path of the LM. Subsequently, the small flaking failure expands in the LM direction, resulting in larger flaking failure with bi-directional cracking.