Crack Growth in Rolling Contact Fatigue and Mode II Fatigue under Compression Stress Field

In the first part of the paper, the crack growth process in rolling contact fatigue has been investigated on ring type plate specimens, in which crack growth is two dimensional and cracks are observed on the side surface of the specimens. The results have shown that cracks are initiated from the contact surface in tensile mode in the direction approximately normal to the contact surface and after some short length of growth, shear mode growth occurs from the tip of the crack and it grows until the separation of the surface layer, namely flaking type failure, occurs. In the second part, mode II fatigue crack growth tests have been made by using an apparatus designed based on the concept that the subsurface fatigue crack growth in rolling contact fatigue is the mode II fatigue crack growth under the stress state where the tensile mode growth is suppressed by compression stress field. The test results have shown that the mode II fatigue crack growth occurs in steel if the superposed compression stress is enough to suppress the tensile mode growth.