INTERPARTICLE SLIDING IN THE PRESENCE OF ADHESION

Contact mechanics theories for the normal and tangential interactions between two non-adhering elastic spheres are well established and the tangential sliding criterion is given by Amontons' law. For micron-sized particles, however, surface adhesion effects due to van der Waals forces become significant. Theories to describe the particle interactions in the presence of adhesion have been developed but a rigorous analytical solution is intractable since the stress distribution in the spheres depends on the surface interaction which depends on the exact shape of the deformed surfaces and that is only known if the stress distribution is known. Accepting the approximate nature of existing analytical solutions, we have re-examined the tangential behaviour and conclude that, in the presence of adhesion, the contact must 'peel' before sliding can occur. This leads to a new sliding criterion which shows encouraging agreement with experimental results, even for negative normal loads.