Critical packing in granular shear bands

TL;DR

This study uses 3D simulations to investigate how granular materials localize deformation into shear bands, revealing a critical packing density within these zones that depends on friction and grain shape.

Contribution

It demonstrates the existence of a critical packing density in shear bands during granular deformation, linking it to dynamic equilibrium and frictional properties.

Findings

Critical packing density exists within shear bands.

Density outside shear bands retains initial packing memory.

Friction influences the critical packing state, approaching dynamic random loose packing.

Abstract

In a realistic three-dimensional setup, we simulate the slow deformation of idealized granular media composed of spheres undergoing an axisymmetric triaxial shear test. We follow the self-organization of the spontaneous strain localization process leading to a shear band and demonstrate the existence of a critical packing density inside this failure zone. The asymptotic criticality arising from the dynamic equilibrium of dilation and compaction is found to be restricted to the shear band, while the density outside of it keeps the memory of the initial packing. The critical density of the shear band depends on friction (and grain geometry) and in the limit of infinite friction it defines a specific packing state, namely the \emph{dynamic random loose packing}.