Unstable cracks trigger asymptotic rupture modes in bimaterial friction

TL;DR

This paper investigates how the mechanical differences between two materials affect the rupture dynamics at their interface, revealing instability and new rupture modes driven by bimaterial coupling at high velocities.

Contribution

It provides a comprehensive physical description of bimaterial interface rupture, highlighting the role of bimaterial coupling and identifying a critical velocity for rupture instability and slip pulse formation.

Findings

Bimaterial cracks become unstable at a subsonic critical velocity $c_T$.

The critical velocity $c_T$ is the subsonic limiting velocity when rupture opposes shear in the softer material.

Slip pulses are generated when rupture propagates in the direction of shear in the softer material.

Abstract

The rupture of the interface joining two materials under frictional contact controls their macroscopic sliding. Interface rupture dynamics depend markedly on the mechanical properties of the bulk materials that bound the frictional interface. When the materials are similar, recent experimental and theoretical work has shown that shear cracks described by Linear Elastic Fracture Mechanics (LEFM) quantitatively describe the rupture of frictional interfaces. When the elastic properties of the two materials are dissimilar, many new effects take place that result from bimaterial coupling: the normal stress at the interface is elastodynamically coupled to local slip rates. At low rupture velocities, bimaterial coupling is not very significant and interface rupture is governed by `bimaterial cracks' that are described well by LEFM. As rupture velocities increase, we experimentally and theoretically show how bimaterial cracks become unstable at a subsonic critical rupture velocity, $c_T$. When the rupture direction opposes the direction of applied shear in the softer material, we show that $c_T$ is the subsonic limiting velocity. When ruptures propagate in the direction of applied shear in the softer material, we demonstrate that $c_T$ provides an explanation for how and when slip pulses (new rupture modes characterized by spatially localized slip) are generated. This work completes the fundamental physical description of how the frictional rupture of bimaterial interfaces takes place.