How granular materials deform in quasistatic conditions

TL;DR

This paper distinguishes two rheological regimes in quasistatic granular deformation, highlighting how microscopic contact behaviors influence macroscopic material responses and the transition between regimes.

Contribution

It introduces a classification of deformation regimes in granular materials based on microscopic contact network behavior, supported by numerical simulations.

Findings

Identification of two distinct deformation regimes in granular materials.

Transition between regimes is different from elastic and yield thresholds.

Microscopic contact behavior critically influences macroscopic response.

Abstract

Based on numerical simulations of quasistatic deformation of model granular materials, two rheological regimes are distinguished, according to whether macroscopic strains merely reflect microscopic material strains within the grains in their contact regions (type I strains), or result from instabilities and contact network rearrangements at the microscopic level (type II strains). We discuss the occurrence of regimes I and II in simulations of model materials made of disks (2D) or spheres (3D). The transition from regime I to regime II in monotonic tests such as triaxial compression is different from both the elastic limit and from the yield threshold. The distinction between both types of response is shown to be crucial for the sensitivity to contact-level mechanics, the relevant variables and scales to be considered in micromechanical approaches, the energy balance and the possible occurrence of macroscopic instabilities