Spatial repartition of local plastic processes in different creep regimes in a granular material

TL;DR

This study investigates how local plastic events distribute spatially in granular materials under different creep regimes, revealing the relationship between creep behavior, plastic activity, and material fluidity through spectroscopic analysis.

Contribution

It introduces a detailed analysis of the spatial distribution of plastic events in granular creep regimes, linking local plasticity to macroscopic rheology and aging effects.

Findings

Hot-spot dynamics correlate with effective fluidity.

Local visco-elastic rheology explains creep features.

Creep regimes differ with and without mechanical activation.

Abstract

Granular packings under constant shear stress display below the Coulomb limit, a logarithmic creep dynamics. However the addition of small stress modulations induces a linear creep regime characterized by an effective viscous response. Using Diffusing Wave Spectroscopy, we investigate the relation between creep and local plastic events spatial distribution ("hot-spots") contributing to the plastic yield. The study is done in the two regimes, i.e. with and without mechanical activation. The hot-spot dynamics is related to the material effective fluidity. We show that far from the threshold, a local visco-elastic rheology coupled to an ageing of the fluidity parameter, is able to render the essential spatio-temporal features of the observed creep dynamics.