Frictional weakening of vibrated granular flows

TL;DR

This study uses simulations and dimensional analysis to understand how harmonic vibrations weaken sheared granular flows, revealing that amplitude and dissipation play crucial roles in contact breaking and flow weakening.

Contribution

It introduces a new criterion involving displacement amplitude and pressure for shear weakening, highlighting a second dissipation-dependent process.

Findings

Weakening depends on displacement amplitude squared relative to pressure.

A second dissipation-dependent process contributes to weakening.

Predicts flow behavior under arbitrary external vibrations.

Abstract

We computationally study the frictional properties of sheared granular media subjected to harmonic vibration applied at the boundary. Such vibrations are thought to play an important role in weakening flows, yet the independent effects of amplitude, frequency, and pressure on the process have remained unclear. Based on a dimensional analysis and DEM simulations, we show that, in addition to a previously proposed criterion for peak acceleration that leads to breaking of contacts, weakening requires the absolute amplitude squared of the displacement is sufficiently large relative to the confining pressure. The analysis provides a basis for predicting flows subjected to arbitrary external vibration and demonstrates that a previously unrecognized second process that is dependent on dissipation contributes to shear weakening under vibrations.