Creep and fluidity of a real granular packing near jamming

TL;DR

This study investigates the slow internal dynamics of granular materials near jamming, revealing universal creep behavior and internal reorganization processes that precede yield, modeled through a visco-elastic framework with a fluidity variable.

Contribution

It introduces a visco-elastic model with an internal fluidity variable to describe creep in granular packings near jamming, unifying experimental observations across different packing fractions.

Findings

Logarithmic creep observed at all packing fractions.

Creep dynamics can be rescaled onto a universal curve.

Identification of a stress threshold for internal reorganization.

Abstract

We study the internal dynamical processes taking place in a granular packing below yield stress. At all packing fractions and down to vanishingly low applied shear, a logarithmic creep is evidenced. The experiments are analyzed under the scope of a visco-elastic model introducing an internal "fluidity" variable. For all experiments, the creep dynamics can be rescaled onto a unique curve which displays jamming at the random-close-packing limit. At each packing fraction, a stress value is evidenced, corresponding to the onset of internal granular reorganisation leading to a slowing down the creep dynamics before the final yield.