Some Effects of Tensile Stressing on Rolling Contact Fatigue Initiation 961829

The effects of surface and near surface tensile stresses on rolling contact fatigue initiation are discussed, based upon measurement of residual stresses and observations of bearings run under both full lubrication (high lambda) and thin film (low lambda) conditions. Previous work considers the applied tensile stresses of interference fit and high speed rotation which effect the macroscopic Hertzian stress field. This paper also takes into account the localized contact stresses and residual stresses at the microscopic sites of stress concentrations. The origins of most rolling contact fatigue failures are at or very near the rolling contact surfaces. Residual stress data for through hardening and case hardening steels are presented. High tensile stresses on the order of 700 MPa (100 ksi) from poor grinding and 480 MPa (70 ksi) from high DN operation cause early failures. A low tensile stress of 70 MPa (10 ksi) is used frequently for interference fit and has no significant effect on life. In between these levels, the failure occurrence for applied tensile stressing is statistical, with some parts failing while others survive. Additional possible sources of tensile stresses are residual stresses from heat treating, residual stresses developed by micro plastic deformation when rolling over asperities, and stresses of rolling friction which are caused by sliding motion and transmitted through the lubrication film. Stresses from different sources can combine to reach the critical threshold for crack initiation. The chance of this happening accounts for the statistical nature of life results.