Crossover from negative to positive shear rate dependence in granular friction

TL;DR

This study investigates how granular friction changes with shear rate, revealing a transition from negative to positive dependence at a critical inertial number, driven by frictional healing and anelasticity effects.

Contribution

It experimentally demonstrates the crossover in shear-rate dependence of granular friction and explains it through physical mechanisms, confirming simulation consistency.

Findings

Friction coefficient decreases with shear rate in quasistatic regime.

Friction coefficient increases with shear rate in inertial regime.

Crossover occurs at a specific inertial number, independent of grain shape.

Abstract

We conduct an experiment on the frictional properties of granular matter over a wide range of shear rate that covers both the quasistatic and the inertial regimes. We show that the friction coefficient exhibits negative shear-rate dependence in the quasistatic regime, whereas the shear-rate dependence is positive in the inertial regime. This crossover from negative to positive shear-rate dependence occurs at a critical inertial number. This is explained in terms of the competition between two physical processes, namely frictional healing and anelasticity. We also find that the result does not depend on the shape of the grains and that the behavior in the inertial regime is quantitatively the same as that in numerical simulations.