MATERIAL RESPONSE MODELS FOR SUB-SURFACE AND SURFACE ROLLING CONTACT FATIGUE

Material mechanics theories of rolling contact loading can be reassessed by recording the alteration of characteristics measured from the edge to the core of a stressed sur-face via X-ray diffraction. Exceeding metallographic investigations, the developments of residual stresses and line width represent the relevant information carrier. It turned out that material changing permits a specific correlation to failure probability distri-butions. These relationships differ significantly for sub-surface and (near-) surface fatigue. Recent findings from certain bearing applications with higher demands on service life and reliability point to the need for applying different equivalent stress methods for modeling the material response in both types of loading: for classical sub-surface overrolling fatigue that is characterized by strengthening and softening pro-cesses below the Hertzian contact area, shear stress-based hypotheses are indicated, whereas for the surface failure mode that is accompanied by embrittlement, addition-ally to these approaches the main normal stress-based hypothesis should be con-sidered. Cyclic tensile stresses caused by friction can act on material-inherent crack sources. In both cases, changes of the X-ray line width, which mainly stem from plas-tic deformation with rearrangement of the dislocation configuration and martensite decay with carbon diffusion, serve as powerful sensor for material aging. Rig tests under controlled mixed friction conditions give an example of near-surface rolling contact fatigue