Granular Rheology in Zero Gravity

TL;DR

This study investigates the rheological behavior of nearly elastic granular media in zero gravity, revealing quadratic shear rate dependence, volume fraction effects, and particle ring formations, with experimental results challenging existing theories.

Contribution

It provides new experimental data on granular rheology in zero gravity and highlights discrepancies with theoretical models, especially regarding particle structures and flow behavior.

Findings

Quadratic shear rate dependence observed.

Power law relation with volume fraction.

Particle ring formations at intermediate densities.

Abstract

We present an experimental investigation on the rheological behavior of model granular media made of nearly elastic spherical particles. The experiments are performed in a cylindrical Couette geometry and the experimental device is placed inside an airplane undergoing parabolic flights to cancel the effect of gravity. The corresponding curves, shear stress versus shear rate, are presented and a comparison with existing theories is proposed. The quadratic dependence on the shear rate is clearly shown and the behavior as a function of the solid volume fraction of particles exhibits a power law function. It is shown that theoretical predictions overestimate the experiments. We observe, at intermediate volume fractions, the formation of rings of particles regularly spaced along the height of the cell. The differences observed between experimental results and theoretical predictions are discussed and related to the structures formed in the granular medium submitted to the external shear.