The role of viscoelasticity on heterogeneous stress fields at frictional interfaces

We investigate the evolution of heterogeneous stress states along frictional interfaces. Using finite-element simulations, we model the occurrence of precursory slip sequences on a deformable-deformable as well as a deformable–rigid interface between two solids. Every interface rupture creates a stress concentration at its arrest position and erases the stress concentrations produced by previous slip events. While the interface is sticking perfectly between two slip events, erased stress concentrations reappear and survive several cycles of ruptures. Such reestablished stress concentrations are smaller than they were before the rupture. We show that the decrease rate of these stress concentrations is exponential with respect to the number of subsequent events and that the bulk viscoelasticity is at the origin of this history effect. During a slip event, the friction tractions at the interface change almost instantaneously, which leads, between two ruptures, to a relaxation-resembling viscous effect that restores the stress concentration. We describe the decrease rate analytically and highlight that it is proportional to the ratio of the viscous over the instantaneous Young's moduli, and illustrate it by varying the material properties in our simulations. Understanding the dynamic behavior of frictional interfaces is relevant for a broad range of applications in engineering , mechanics and geophysics. Despite longstanding research on friction, its dynamics is today still not well understood. For instances, the knowledge of the macro-scopic frictional strength is essential to the design of new engineering applications. Nevertheless, the transition from sticking to sliding, which is closely related to the macro-scopic friction coefficient, is still an only partially known phenomenon. The classic view considers that sliding initiates when the macroscopic shear force overcomes the macroscopic friction force, which is proportional to the normal loading. This simplistic picture does not account for the complexity of local slip occurring during the initiation of sliding. The transition from sticking to sliding was shown, in experiments, to be particularly interesting when the shear load of an interface between two blocks is applied by a pusher that is located near the interface (Rubinstein et al., 2007; Maegawa et al., 2010). In these conditions, the sliding initiation is a succession of local slip episodes that propagate at macroscopic stress levels much below the friction coefficient of the system. These precursors to global sliding initiate at the trailing edge, where the pusher is applied, and propagate along the interface until they stop before the other edge. Generally , each slip …