Surface tension effect on the sliding inception between an elastic sphere and a rigid flat

This paper develops an analytical model to characterize the sliding inception of elastic spherical contact accounting for surface tension effect. The distribution of von Mises equivalent stress on the contact interface under pure normal loading is first formulated, and thereby, the maximum allowable local shear stress is determined based on the concept of interface yielding failure. Then, the maximum tangential load that the contact interface can bear, and the friction coefficient at the sliding inception are obtained, which are functions of the normalized interference, the Poisson's ratio, and a surface tension-related parameter. The results show that the role of surface tension in the state of sliding inception primarily gives credit to its influence on the change of contact area. Based on this observation, explicit expressions of the maximum tangential load and the static friction coefficient are derived. It is found that both the maximum tangential load and the static friction coefficient decrease with the surface tension parameter increasing. For a given material, the smaller the sphere is, the lower the friction coefficient is predicted, which is in agreement with relevant experimental results.