Friction in rough contacts of linear viscoelastic surfaces with anisotropic statistical properties

Viscoelastic rheology can have great effects on the contact mechanics of randomly rough surfaces with anisotropic statistical properties. In this paper, we investigate such effects in the framework of Persson's theory. We calculate the forces that arise in viscoelastic contacts because of the viscous dissipation occurring in the bulk material. Interestingly, the non-symmetric distribution of the normal contact pressure entails the occurrence of a force in the direction perpendicular to the sliding one. Such force does not carry out any work, and hence does not dissipate energy, but it is important for the global equilibrium of the system. Results are also compared with numerical exact calculations finding a quite good agreement. However, with the present method, we cannot capture the stretching of the contact clusters due to the viscoelasticity and, hence, the resulting change in the anisotropy of the deformed surface.