A random surface model has been developed for the deformations of contacting surfaces subjected to both normal and tangential load. The model is restricted to nominally flat (rough) elastic surfaces in contact with perfectly flat (smooth) elastic surfaces. The deformations of the asperities are assumed to be independent of each other and the heights of the asperities are assumed to be randomly distributed. Depending on the height of an asperity, it will either slip or stick. The relation between tangential deformation and load will consequently be non-linear and this effect is often named micro-slip. Results are presented for two types of deformation laws for the individual asperities, with three different asperity height distributions. The results show typical micro-slip behaviour, independent of both the individual asperity deformation and the type of asperity height distribution. The influence of the standard deviation of asperity heights is strong and is an important factor when determining the micro-slip of nominally flat surfaces in contact.

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