Evaluation of Rolling Contact Fatigue Using X-Ray Diffraction Ring

In this report, a novel approach for evaluating the progressive degree of rolling contact fatigue (RCF) is introduced. The rolling contact surface after two-cylinder testing was evaluated by a new X-ray analyzer, which can rapidly obtain tri-axial residual stresses and the orientation of crystallite from an X-ray diffraction ring (Debye ring) on a two-dimensional detector. The non-uniform intensity of the Debye ring was observed for the tested sample under boundary lubrication. This makes it clear that RCF, under asperity contact conditions, accompanies the formation of an oriented texture of martensite grain. In addition, characteristic residual stresses that differ from the plane stress condition were observed for asperity contact surface, and residual von Mises stress, derived from their tri-axial residual stresses, demonstrates severe plastic deformation close to yield stress of hardened bearing steel. The behaviors of martensite grain orientation, tri-axial residual stress, and surface damage were investigated for several samples under different RCF conditions to clarify the mechanism of surface-initiated failure. The Debye ring analyzer can rapidly obtain more information regarding accumulation of fatigue, criteria of fracture, crack development, and shake-down in rolling contact subsurface, as compared with conventional X-ray diffraction analyzers. This new system is a promising method, not only to investigate the mechanism of RCF, but also to allow for the quantitative estimation of the progressing degree of RCF.