Significance of Elastic Coupling for Stresses and Leakage in Frictional Contacts.

We study how the commonly neglected coupling of normal and in-plane elastic response affects tribological properties when Hertzian or randomly rough indenters slide past an elastic body. Compressibility-induced coupling is found to substantially increase maximum tensile stresses, which cause materials to fail, and to decrease friction such that Amontons' law is violated macroscopically even when it holds microscopically. Confinement-induced coupling increases friction and enlarges domains of high tension. Moreover, both types of coupling affect the gap topography and thereby leakage. Thus, coupling can be much more than a minor perturbation of a mechanical contact.

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.