Sounds of Failure: Passive Acoustic Measurements of Excited Vibrational Modes

TL;DR

This study uses passive acoustic measurements to monitor vibrational modes in sheared granular materials, revealing how their vibrational spectra evolve before failure, offering insights into predicting material failure.

Contribution

It introduces a novel experimental approach to track vibrational mode evolution in granular materials approaching failure through passive acoustic monitoring.

Findings

Broadening of vibrational mode distribution coincides with plasticity.

Shape of vibrational spectrum changes before and after failure.

Passive acoustic monitoring reveals evolving material state.

Abstract

Granular materials can fail through spontaneous events like earthquakes or brittle fracture. However, measurements and analytic models which forecast failure in this class of materials, while of both fundamental and practical interest, remain elusive. Materials including numerical packings of spheres, colloidal glasses, and granular materials have been known to develop an excess of low-frequency vibrational modes as the confining pressure is reduced. Here, we report experiments on sheared granular materials in which we monitor the evolving density of excited modes via passive monitoring of acoustic emissions. We observe a broadening of the distribution of excited modes coincident with both bulk and local plasticity, and clear evolution in the shape of the distribution before and after bulk failure. These results provide a new interpretation of the changing state of the material on its approach to stick-slip failure.