Friction weakening by mechanical vibrations: a velocity-controlled process

TL;DR

This paper demonstrates that vibration velocity, rather than grain mobility, controls frictional weakening in both granular and solid materials, with a critical threshold around a hundred microns per second linked to surface asperity roughness.

Contribution

It reveals that vibration velocity governs frictional weakening in solids and granular media, challenging the previous assumption that grain mobility is necessary.

Findings

Friction weakening occurs at a vibration velocity threshold of about 100 microns/sec.

The velocity threshold is linked to asperity surface roughness.

Vibration velocity controls the transition from stick-slip to continuous sliding.

Abstract

Frictional weakening by vibrations was first invoked in the 70's to explain unusual fault slips and earthquakes, low viscosity during the collapse of impact craters or the extraordinary mobility of sturzstroms, peculiar rock avalanches which travels large horizontal distances. This mechanism was further invoked to explain the remote triggering of earthquakes or abnormally large landslides or pyroclastic flows runout. Recent experimental and theoretical work pointed out the velocity of vibration as the key parameter which governs frictional weakening in sheared granular media. Here we show that the grains mobility is not mandatory, and that the vibration velocity governs both granular and solid frictional weakening. The velocity threshold controlling the transition from stick-slip motion to continuous sliding is of the same order of magnitude, namely a hundred microns per second. It is linked to the roughness distribution of the asperities at the contact surface.