Slippery but tough - the rapid fracture of lubricated frictional interfaces

TL;DR

This study reveals that lubricated frictional interfaces are governed by shear crack propagation, where lubricants reduce resistance but increase energy dissipation during rupture, with viscosity influencing onset but not dissipation.

Contribution

It introduces a fracture mechanics perspective to understand the complex dynamics of lubricated frictional interfaces, highlighting the role of shear cracks and energy dissipation.

Findings

Lubricants significantly increase energy dissipation during rupture.

Viscosity affects the onset of friction but not the energy dissipated.

Shear cracks mediate lubricated frictional motion.

Abstract

We study the onset of friction for rough contacting blocks whose interface is coated with a thin lubrication layer. High speed measurements of the real contact area and stress fields near the interface reveal that propagating shear cracks mediate lubricated frictional motion. While lubricants reduce interface resistances, surprisingly, they significantly increase energy dissipated, $\Gamma$, during rupture. Moreover, lubricant viscosity affects the onset of friction but has no effect on $\Gamma$. Fracture mechanics provide a new way to view the otherwise hidden complex dynamics of the lubrication layer.