Force and flow transition in plowed granular media

TL;DR

This study investigates how granular media respond to localized forcing, revealing a bifurcation at the onset of dilatancy where flow patterns and force fluctuations change character, with a model explaining the observed dynamics.

Contribution

It identifies a bifurcation in force and flow behavior at the critical volume fraction and links it to shear band formation, providing a new understanding of granular response.

Findings

Force fluctuations are rapid below $ ho_c$ and periodic above $ ho_c$.

Stable shear bands form above $ ho_c$ and cause the bifurcation.

A friction-based model explains the behavior for $ ho> ho_c$.

Abstract

We use plate drag to study the response of granular media to localized forcing as a function of volume fraction, $\phi$. A bifurcation in the force and flow occurs at the onset of dilatancy, $\phi_c.$ Below $\phi_c$ rapid fluctuations in the drag force, $F_D,$ are observed. Above $\phi_c$ fluctuations in $F_D$ are periodic and increase with $\phi$. Velocity field measurements indicate that the bifurcation in $F_D$ results from the formation of stable shear bands above $\phi_c$ which are created and destroyed periodically during drag. A friction-based model captures the dynamics for $\phi>\phi_c$.