Shear Is Not Always Simple: Rate-Dependent Effects of Flow Type on Granular Rheology

TL;DR

This paper investigates how flow type influences granular rheology, revealing that shear behavior varies significantly with flow conditions, inertial number, and friction, challenging the universality of simple shear models.

Contribution

It introduces a comprehensive analysis of flow type effects on granular stress invariants across various conditions using discrete element simulations.

Findings

Flow type strongly affects granular stress invariants.

Dependence on flow type increases with inertial number and friction.

Standard yield models partially explain flow type dependence.

Abstract

Despite there being an infinite variety of types of flow, most rheological studies focus on a single type such as simple shear. Using discrete element simulations, we explore bulk granular systems in a wide range of flow types at large strains and characterize invariants of the stress tensor for different inertial numbers and interparticle friction coefficients. We identify a strong dependence on the type of flow which grows with increasing inertial number or friction. Standard models of yielding, repurposed to describe the dependence of the stress on flow type in steady-state flow and at finite rates, are compared with data.