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

The crack growth in rolling contact fatigue has been investigated with a newly devised testing rig. A surface crack normally extends in the direction of the load-movement, and flaking failures accompanied by cracks extending in the direction opposite to the load-movement are rarely observed. However, in some situations, cracks extending in the opposite direction appear with an as not as yet clarified mechanism. In this study, a double-roller type rolling contact fatigue testing rig has been devised to reproduce the opposite-direction crack growth. Equally spaced artificial indentations are marked on the surface of one roller, while the other roller surface is defect-free. In that set-up, a flaking accompanied by cracks extending bi-directionally to the load-movement almost always occurs on the defect-free roller surface. The appearance of the flaking is consistent throughout the tests, but the cycles to failure vary according to test conditions such as (1) contact load, (2) additional tangential force between the rollers, (3) the number of artificial indentations, (4) whether the defect-free roller is operated as the driver or the follower, (5) rotational speed, and (6) size of artificial indentations.