Influence of inclusion pairs, clusters and stringers on the lower bound of the endurance limit of bearing steels

The lower bound of the endurance limit, defined as the maximal Hertzian pressure that does not induce any micro-plastic strain around inclusions, is computed for groups of inclusions in a bearing steel subjected to contact stresses. An extension of the Eshelby analytical method is used for determining local stresses around inclusions. Configurations such as pairs, stringers or clusters of identical spherical inclusions of alumina in a 100Cr6 matrix are analysed. In the Hertzian stress field, the interaction is revealed to be anisotropic, with a large decrease of the endurance limit for stringer axes close to the normal to contact surface.