The influences of a single bump (dent) or regularly arranged bumps (dents) on the film thickness in impact circular elasthydrodynamic lubrication (EHL) contacts lubricated with a Newtonian lubricant are investigated numerically. It has been found that the deformation of the bump or the dent at the contact center depends mainly on the macroscopic pressure distribution produced between the smooth surfaces by impact. The macroscopic pressure distribution is influenced by the initial impact gap, the loading speed, and the mass of the moving body. The central bump or dent hardly deforms when the initial impact gap or the base radius of the bump or dent is small. When the initial impact gap is large and the radius of the base of the central bump is not so small, the oil is entrapped in the bump, and micro-dimple is formed. The deformation of noncentral bumps or dents is mainly influenced by the film profile under conditions of smooth surfaces.

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