Effect of Roughness and Sliding Friction on Contact Stresses

The stress distributions associated with smooth surfaces in contact are rarely experienced in practice. Factors such as surface roughness, lubricant films, and third body particulates are known to influence the state of stress and the resulting rolling contact fatigue life. This paper describes a numerical technique for evaluating the complete subsurface field of stress resulting from the elastic contact of nonconforming rough bodies, based on measurements of their profile. The effect of sliding friction is included. The presence of asperities within the contact region gives rise to high shear stresses near the surface. Realistic coefficients of friction for lubricated sliding contacts (i.e., μ ≈ 0.1) causes the “smooth body” shear stresses to interact with the asperity stresses to produce a large, highly stressed region exposed to the surface. The significance of these near-surface stresses is discussed in relation to modes of surface distress which lead to eventual failure of the contacting surfaces.