Influence of the surface geometry on the friction in adhesive contacts

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Tangential loading and movement of contacting bodies in the presence of adhesive interaction belongs to the least understood phenomena in contact mechanics. In contrast to normal adhesive contact, i.e. the mere approach and detachment of contacts, there is no universal, energy-based approach to this problem. Instead, dissipative forces play a crucial role. The main goal of the planned project is to clarify the microscopic and mesoscopic origin of the frictional forces and of the energy dissipation in an adhesive contact. Based on this, a concept for the modeling and simulation of adhesive tangential contacts should be developed, implemented in a numerical program and validated experimentally. We are guided by the idea that adhesion on the microscale is dissipation-free and that only instabilities - caused by microscopic heterogeneity of surface chemistry or topography - lead to energy dissipation (and corresponding frictional forces). While this idea is not new in friction physics (Prandtl-Tomlinson model), it has not yet been explicitly applied to tangential adhesive contacts. To achieve this goal, theoretical investigations of heterogeneous contacts are to be undertaken, based on the methods already developed to simulate reversible adhesion. This will go hand-in-hand with systematic experimental investigation of the adhesive tangential contact. A well-founded physical understanding of the dissipative processes in adhesive contacts will lead the way to control of adhesive interactions in practical applications. In particular, the influence of the shape, the roughness, the material heterogeneity and other system parameters that have yet to be determined will be examined theoretically and experimentally.