Frictional sliding without geometrical reflection symmetry

TL;DR

This paper reveals that geometrical asymmetry in identical materials can induce coupling between slip and normal stress, affecting stability and failure, supported by theory and experiments.

Contribution

It introduces the novel concept that geometrical asymmetry causes slip-normal stress coupling in identical materials, impacting frictional dynamics.

Findings

Asymmetry induces slip-normal stress coupling in identical materials.

Coupling explains previously unexplained weakening in frictional cracks.

Asymmetry can destabilize otherwise stable frictional sliding.

Abstract

The dynamics of frictional interfaces play an important role in many physical systems spanning a broad range of scales. It is well-known that frictional interfaces separating two dissimilar materials couple interfacial slip and normal stress variations, a coupling that has major implications on their stability, failure mechanism and rupture directionality. In contrast, interfaces separating identical materials are traditionally assumed not to feature such a coupling due to symmetry considerations. We show, combining theory and experiments, that interfaces which separate bodies made of macroscopically identical materials, but lack geometrical reflection symmetry, generically feature such a coupling. We discuss two applications of this novel feature. First, we show that it accounts for a distinct, and previously unexplained, experimentally observed weakening effect in frictional cracks. Second, we demonstrate that it can destabilize frictional sliding which is otherwise stable. The emerging framework is expected to find applications in a broad range of systems.