Controlled viscosity in dense granular materials

TL;DR

This study explores how dense granular materials transition between jammed, fluidized, and frictional states under vibration, revealing material-dependent viscosity recovery and supporting findings with molecular dynamics simulations.

Contribution

It introduces a comprehensive experimental and simulation analysis of viscosity transitions in vibrated granular media, highlighting the material dependence of the viscosity recovery frequency.

Findings

Fluidization occurs at a material-independent frequency.

Viscosity recovery frequency depends on material properties.

Simulations confirm the experimental and theoretical results.

Abstract

We experimentally investigate the fluidization of a granular material subject to mechanical vibrations by monitoring the angular velocity of a vane suspended in the medium and driven by an external motor. On increasing the frequency we observe a re-entrant transition, as a jammed system first enters a fluidized state, where the vane rotates with high constant velocity, and then returns to a frictional state, where the vane velocity is much lower. While the fluidization frequency is material independent, the viscosity recovery frequency shows a clear dependence on the material, that we rationalize by relating this frequency to the balance between dissipative and inertial forces in the system. Molecular dynamics simulations well reproduce the experimental data, confirming the suggested theoretical picture.