Dynamic fields at the tip of sub-Rayleigh and supershear frictional rupture fronts

TL;DR

This study combines experiments, simulations, and theory to analyze dynamic frictional rupture fronts, revealing their properties, interface characteristics, and the effects of rupture speed and geometry, especially near the wave speed.

Contribution

It extends analysis of rupture fronts to supershear speeds, providing new insights into interface properties and the limitations of fracture-mechanics theory in dynamic friction.

Findings

Frictional rupture fronts are well described by fracture mechanics.

Interface properties like fracture energy are independent of rupture speed.

Discrepancies occur near the longitudinal wave speed due to transient effects.

Abstract

The onset of frictional motion at the interface between two distinct bodies in contact is characterized by the propagation of dynamic rupture fronts. We combine friction experiments and numerical simulations to study the properties of these frictional rupture fronts. We extend previous analysis of slow and sub-Rayleigh rupture fronts and show that strain fields and the evolution of real contact area in the tip vicinity of supershear ruptures are well described by analytical fracture-mechanics solutions. Fracture-mechanics theory further allows us to determine long sought-after interface properties, such as local fracture energy and frictional peak strength. Both properties are observed to be roughly independent of rupture speed and mode of propagation. However, our study also reveals discrepancies between measurements and analytical solutions that appear as the rupture speed approaches the longitudinal wave speed. Further comparison with dynamic simulations illustrates that, in the supershear propagation regime, transient and geometrical (finite sample thickness) effects cause smaller near-tip strain amplitudes than expected from the fracture-mechanics theory. By showing good quantitative agreement between experiments, simulations and theory over the entire range of possible rupture speeds, we demonstrate that frictional rupture fronts are classic dynamic cracks despite residual friction.