Criticality in vibrated frictional flows at finite strain rate

TL;DR

This paper investigates critical fluctuations in vibrated granular flows, revealing a unique critical point at finite strain rate and vibration strength, explained by a mean-field model involving self fluidization and friction.

Contribution

It introduces a novel critical point in vibrated granular flows at finite strain rate and develops a mean-field model to explain this phenomenon.

Findings

Critical fluctuations occur at finite strain rate and vibration strength.

The rheology and fluctuations are consistent with a Landau-like mean-field description.

A general model captures the competition between self fluidization and friction.

Abstract

We evidence critical fluctuations in the strain-rate of granular flows that are weakly vibrated. Strikingly, the critical point arises at {\em finite} values of the mean strain rate and vibration strength, far away from the yielding critical point at zero flow rate. We show that the global rheology, as well as the amplitude and correlation time of the fluctuations, are consistent with a mean-field, Landau like description, where strain rate and stress act as conjugated variables. We introduce a general model which captures the observed phenomenology, and argue that this type of critical behavior generically arises when self fluidization competes with friction.