A fractal analysis of normal impact between rough surfaces in presence of adhesion

The paper describes a theoretical study of normal impact between surfaces taking into account the effect of scale dependent surface topography. An elastic-plastic impact model is used to study the normal impact between rough surfaces in presence of surface forces. In order to account for the effect of asperities ranging from nanometer to micrometer level, a fractal approach is used in the present analysis. The fractal elastic and plastic adhesion indices are used to consider the different conditions arising out of varying impact velocity, material properties and surface parameters. The study shows that the coefficient of restitution is affected by material properties, surface topography and impact velocity. Results clearly indicate that high impact velocity is desirable in order to achieve low coefficient of restitution. However, there are certain combinations of material properties and surface conditions, given by the choice of fractal dimension and adhesion indices, where coefficient of restitution falls to a very low value.