Granular packings with sliding, rolling and twisting friction

TL;DR

This paper uses discrete element simulations to explore how different frictional constraints like sliding, rolling, and twisting affect the microstructure and stability of granular sphere packings, revealing conditions for stable packings at low densities.

Contribution

It introduces a comprehensive simulation approach to model granular packings with complex frictional interactions, highlighting the effects of rolling and twisting friction on packing stability.

Findings

Stable packings at low volume fractions with high resistance to all friction modes.

Rolling and twisting friction are essential to replicate experimental packing densities.

Microstructure constraints increase with additional frictional interactions.

Abstract

Intuition tells us that a rolling or spinning sphere will eventually stop due to the presence of friction and other dissipative interactions. The resistance to rolling and spinning/twisting torque that stops a sphere also changes the microstructure of a granular packing of frictional spheres by increasing the number of constraints on the degrees of freedom of motion. We perform discrete element modeling simulations to construct sphere packings implementing a range of frictional constraints under a pressure-controlled protocol. Mechanically stable packings are achievable at volume fractions and average coordination numbers as low as 0.53 and 2.5, respectively, when the particles experience high resistance to sliding, rolling and twisting. Only when the particle model includes rolling and twisting friction, were experimental volume fractions reproduced.