Regensburg 2007 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 20: Poster session

MM 20.13: Poster

Tuesday, March 27, 2007, 14:45–18:00, Poster C

Experimental and Theoretical Analysis of Fatigue Phenomena in Rolling Contact — •Jürgen Gegner and Wolfgang Nierlich — SKF GmbH, Department of Material Physics, Ernst-Sachs-Str. 5, D-97424 Schweinfurt, Germany

Material mechanics theories of rolling contact loading can be reassessed by recording the alteration of X-ray diffraction (XRD) characteristics measured from the edge to the core. Exceeding metallographic investigations, the developments of residual stresses and XRD line width represent the relevant information carrier. Material changing permits a specific correlation to failure probability distributions. These relationships differ significantly for sub- and near-surface fatigue. Recent findings from demanding bearing applications point to different equivalent stresses for describing the material response in both loading types: for classical sub-surface rolling contact fatigue (RCF) that is characterized by strengthening and softening processes below the Hertzian contact area, shear stress-based hypotheses are indicated, whereas for the surface failure mode that is accompanied by embrittlement, the main normal stress-based hypothesis should additionally be considered. Cyclic tensile stresses caused by friction can act on material-inherent crack sources. In both cases, line width changes, which mainly stem from plastic 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 RCF.