Deformation-Driven Diffusion and Plastic Flow in Two-Dimensional Amorphous Granular Pillars

TL;DR

This study investigates how deformation causes particle diffusion and flow in 2D amorphous granular pillars, revealing size-dependent behavior, shear band formation, and a transition from ballistic to diffusive particle motion driven by deviatoric strain.

Contribution

It combines experiments and simulations to show that deviatoric strain drives effective diffusion and reveals size effects on deformation and shear localization in granular pillars.

Findings

Non-affine displacement shows exponential crossover from ballistic to diffusive behavior.

Yield stress increases linearly with pillar size.

Shear band width is about twice the particle diameter and size-independent.

Abstract

We report a combined experimental and simulation study of deformation-induced diffusion in compacted two-dimensional amorphous granular pillars, in which thermal fluctuations play negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and non-affine displacement associated with each particle between two stages of deformation. The non-affine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.