Rheology of dense granular flows for elongated particles

TL;DR

This study investigates how the rheology of dense granular flows varies with particle elongation, revealing non-monotonic friction behavior and microscopic contact mechanisms through 3D simulations.

Contribution

It provides the first detailed analysis of how particle aspect ratio affects the rheological properties of dense granular flows, including the non-monotonic friction coefficient.

Findings

Friction coefficient increases then decreases with aspect ratio.

Normal stress differences and coordination number vary with particle shape.

Microscopic contact analysis explains the non-monotonic behavior.

Abstract

We study the rheology of dense granular flows for frictionless spherocylinders by means of 3D numerical simulations. As in the case of spherical particles, the effective friction $\mu$ is an increasing function of the inertial number $I$, and we systematically investigate the dependence of $\mu$ on the particle aspect ratio $Q$, as well as that of the normal stress differences, the volume fraction and the coordination number. We show in particular that the quasi-static friction coefficient is non-monotonic with $Q$: from the spherical case $Q=1$, it first sharply increases, reaches a maximum around $Q \simeq 1.05$, and then gently decreases, reaching back its initial value for $Q \simeq 2$. We provide a microscopic interpretation for this unexpected behavior through the analysis of the distribution of dissipative contacts around the particles: as compared to spheres, slightly elongated grains enhance contacts in their central cylindrical band, whereas at larger aspect ratios particles tend to align and dissipate by preferential contacts at their hemispherical caps.