Estimation Method of Micropitting Life from S-N Curve Established by Residual Stress Measurements and Numerical Contact Analysis

Micropitting is a type of rolling contact fatigue (RCF) associated with rough surfaces and severe lubrication conditions. In the present study, we developed an estimation method for micropitting life. An S-N curve, which is a relationship between micropitting life and stresses acting in the region affected by surface asperities (near-surface stress), is established by using data from RCF tests and estimated histories of near-surface stresses (stress history). Changes in the surface topography and residual stresses including the initial condition are measured in order to estimate the stress history. This enables us to consider the influences of surface topography and residual stresses on micropitting. Micropitting life under an arbitrary operating condition is estimated from the established S-N curve and the estimated stress history up to a finite cycle. It is revealed that micropitting life can be accurately estimated from the established S-N curve within the range of our experiment. The median, minimum, and maximum of the relative life ratio (ratio of actual micropitting life to the estimated life) were 0.89, 0.49, and 1.82, respectively. Further analysis confirms that the accuracy is improved by considering residual stresses.