Dynamic effective mass of granular media

TL;DR

This paper introduces a frequency-dependent effective mass concept for jammed granular media, revealing how acoustic dissipation, elasticity, and aging are influenced by humidity and capillary effects.

Contribution

It develops a continuum and trap model to interpret the effective mass measurements, highlighting the role of capillary condensation in attenuation.

Findings

Effective mass signatures reveal acoustic mode dissipation.

Humidity affects the kinetics of capillary bridges.

Attenuation is significantly influenced by capillary condensation.

Abstract

We develop the concept of frequency dependent effective mass, M(omega), of jammed granular materials which occupy a rigid cavity to a filling fraction of 48%, the remaining volume being air of normal room condition or controlled humidity. The dominant features of M(omega) provide signatures of the dissipation of acoustic modes, elasticity and aging effects in the granular medium. We perform humidity controlled experiments and interpret the data in terms of a continuum model and a "trap" model of thermally activated capillary bridges at the contact points. The results suggest that attenuation in the granular materials is influenced significantly by the kinetics of capillary condensation between the asperities at the contacts.