Effect of an interstitial fluid on the dynamics of three-dimensional granular media

TL;DR

This study investigates how an interstitial fluid influences the propagation of mechanical pulses in granular materials, revealing elastohydrodynamic effects and nonlinear softening that can be controlled by fluid viscosity.

Contribution

It introduces experimental evidence of elastohydrodynamic interactions in wet granular media and models these effects using an effective medium theory including viscous fluid dynamics.

Findings

Interstitial fluid affects pulse propagation in granular media.

Viscosity controls the nonlinear softening of the material.

Elastohydrodynamic interactions can be tuned to modify material response.

Abstract

The propagation of mechanical energy in granular materials has been intensively studied in recent years given the wide range of fields that have processes related to this phenomena, from geology to impact mitigation and protection of buildings and structures. In this paper, we experimentally explore the effect of an interstitial fluid on the dynamics of the propagation of a mechanical pulse in a granular packing under controlled confinement pressure. The experimental results reveal the occurrence of an elastohydrodynamic mechanism at the scale of the contacts between wet particles. We describe our results in terms of an effective medium theory, including the presence of the viscous fluid. Finally, we study the nonlinear weakening of the granular packing as a function of the amplitude of the pulses. Our observations demonstrate that the softening of the material can be impeded by adjusting the viscosity of the interstitial fluid above a threshold at which the elastohydrodynamic interaction overcomes the elastic repulsion due to the confinement.