Effects of surface roughness pattern on the lubricated running-in process of pure rolling and rolling/sliding contacts were studied using a twin-disk machine. Three roughness patterns, i.e. longitudinal, isotropic and transverse roughness, showed different running-in processes. A simple model of surface truncation was introduced, and the roughness leveling depth was employed as a parameter to represent heights of surface microasperities. Plastic deformation was proved to be dominant in surface microtopographical change. It was shown, however, that wear was essential to the decrease in metal-to-metal contacts. Discussion was made on the formation of lubricating films in the running-in process, and it was suggested that the average effects of roughness in combination with local microscopic effects of roughness contributed to the process. In the rolling/sliding contact with the longitudinal roughness, very thin and steady lubricating films were developed.
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