Adhesion effects in material transfer in mechanical contacts

A series of molecular dynamics simulations of the contact and separation of a surface with an asperity (material A) and a flat substrate (material B) are performed, in which the A/B interfacial energies vary (leaving other properties unchanged). When the work of adhesion Γ is large, substantial plastic deformation occurs on separation, and some material is transferred to the opposing substrate. When Γ is small, separation of the materials occurs at a critical force, with no material transfer and no plastic deformation. A theory is developed, based upon a capillary equilibrium argument, that accurately predicts when material transfer from one surface to another will occur. When separation occurs without plastic deformation, the separation process can be described by Johnson, Kendal and Roberts (JKR) adhesive contact theory. The simulation results and theory clarify how interfacial adhesion can be manipulated to control surface roughening, material transfer and surface alloying in contacts.