On the Propagation of Slip Fronts at Frictional Interfaces

TL;DR

This paper investigates the dynamics of slip front propagation at frictional interfaces, highlighting the limitations of static stress ratios and proposing an energetic criterion based on energy density for a unified description.

Contribution

It introduces a dynamic stress ratio concept and an energetic criterion to better predict slip front velocities, addressing previous static stress-based limitations.

Findings

Static stress ratio correlates poorly with slip front speed.

Dynamic stress ratio improves correlation but does not fully resolve directional and acceleration effects.

Energy density rise at the slip tip provides a unified predictor of slip front velocity.

Abstract

The dynamic initiation of sliding at planar interfaces between deformable and rigid solids is studied with particular focus on the speed of the slip front. Recent experimental results showed a close relation between this speed and the local ratio of shear to normal stress measured before slip occurs (static stress ratio). Using a two-dimensional finite element model, we demonstrate, however, that fronts propagating in different directions do not have the same dynamics under similar stress conditions. A lack of correlation is also observed between accelerating and decelerating slip fronts. These effects cannot be entirely associated with static local stresses but call for a dynamic description. Considering a dynamic stress ratio (measured in front of the slip tip) instead of a static one reduces the above-mentioned inconsistencies. However, the effects of the direction and acceleration are still present. To overcome this we propose an energetic criterion that uniquely associates, independently on the direction of propagation and its acceleration, the slip front velocity with the relative rise of the energy density at the slip tip.