An experimental study of the relationship between surface roughness and stress in EHL contacts

摘要

Contact pressures, particularly those produced by surface roughness, and the resultant sub-surface stresses, are known to be directly related to failure. Measurement of contact pressure is extremely difficult, measurement of the stress appears impossible. This led the authors to consider an inverse approach to the problem. Instead of generating a profile and trying to determine the resulting stress, it was decided to fix the stress level in the material and to determine the roughness profile that would generate it. Accordingly, a soft steel disc was ran against a hard counterface, under increasingly severe load conditions, and the changes in the surface profile observed. Since the yield strength of the soft material is known, the results should provide an indication of the relationship between surface roughness profile and sub-surface stress. The results presented in this paper are from a preliminary investigation using a largely circumferential roughness profile on the soft disc. At each load the roughness was measured and used in a theoretical analysis to estimate the contact pressures and the sub-surface stresses. After allowing for the development of residual stresses, the results show a close correlation between the maximum calculated von Mises' stress and the yield stress of the material over the entire range of loads examined.