Spalling Life Model With Relaxed Distribution Constraints, for Rough Hertz Line Contacts

Abstract

A Hertz contact spalling fatigue life model is constructed without the constraints of a two-parameter Weibull life distribution. The model is based on the time of crack propagation following a simple Paris law, through the Hertzian alternating shear stress field, from populations of surface defects with depth (severity) distributed according to the Greenwood-Williamson asperity model, to the depth of the maximum alternating shear stress. The life distribution shows moderate deviations from the Weibull form, with the dispersion strongly dependent on the contact parameters. The 90 percent survival quantile is obtained as a function of: Hertz pressure, EHD film ratio, asperity traction coefficient, asperity height, slope and spectrum width, fatigue limit stress and stress concentration factor. This model provides insights into the interrelationship of life with its parameters, not available from models adhering to the power law constraints required to produce a Weibull life distribution. No unbridgeable contradictions emerge between the present formulation and published engineering models.