Rheology of a sonofluidized granular packing

TL;DR

This study investigates how weak vibrations influence the rheological behavior of dry granular materials, revealing a transition from nonlinear to linear force-velocity regimes and introducing a heuristic model for this behavior.

Contribution

It provides experimental evidence of vibration-induced rheological changes and proposes a simple model explaining the vanishing stress threshold and linear force-velocity relation.

Findings

Transition from nonlinear to linear rheology with increased vibration

Identification of geometrical and velocity hardening effects

Weak dependence of velocity hardening on vibration intensity

Abstract

We report experimental measurements on the rheology of a dry granular material under a weak level of vibration generated by sound injection. First, we measure the drag force exerted on a wire moving in the bulk. We show that when the driving vibration energy is increased, the effective rheology changes drastically: going from a non-linear dynamical friction behavior - weakly increasing with the velocity- up to a linear force-velocity regime. We present a simple heuristic model to account for the vanishing of the stress dynamical threshold at a finite vibration intensity and the onset of a linear force-velocity behavior. Second, we measure the drag force on spherical intruders when the dragging velocity, the vibration energy, and the diameters are varied. We evidence a so-called ''geometrical hardening'' effect for smaller size intruders and a logarithmic hardening effect for the velocity dependence. We show that this last effect is only weakly dependent on the vibration intensity.