Friction from nano to macroforce scales analyzed by single and multiple-asperity contact approaches

With decreasing contact size and stiffness of the measuring equipment, the effect of roughness is strikingly evident. The effect of surface roughness is clearly visible on the recorded friction loops as fluctuations, which were later attributed to geometrical and adhesive components. Based on our observations, a simple contact model was proposed to describe the nature of localized friction in single and multiple-asperity configurations during a sliding pass. The existing friction model for smooth and chemically interacting surfaces was extended to rough surfaces and it was found that most of the existing experimental claims could be explained as special cases of the proposed model.