Acoustic emission generated by glass beads in compression and shearing

Alister Smith,Neil Dixon

doi:10.1007/s10035-019-0944-0

Abstract

Acoustic emission (AE) monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials. This paper presents results from a programme of drained triaxial tests performed on densely packed glass beads to establish quantitative interpretation of AE during isotropic compression, shearing and associated stick–slip events. Relationships have been quantified between: AE and boundary work (i.e. AE generated per Joule) for a unit volume of glass beads under isotropic compression and shear; AE and shear displacement rate; and the amplitude of deviator stress cycles and AE activity during stick–slip events. In shear, AE generation increased with shear strain and reached peak values that were maintained from volume minimum (i.e. the transition from contractive to dilative behaviour) to peak dilatancy, whereupon AE generation gradually reduced and then remained around a constant mean value with further increments of shear strain. In each stick–slip event, AE activity increased during shear strength mobilisation, particle climbing and dilation, and then reduced with the subsequent deviator stress drop during particle sliding and contraction. The amplitude of these cycles in AE activity were governed by the amplitude of deviator stress cycles during stick–slip events, which were also proportional to the imposed stress level and inversely proportional to particle size.

Highlights

Proportions of the energy dissipated during deformation of particulate materials are converted to heat and sound
acoustic emission (AE) monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials, for example: particle–particle interactions such as sliding and rolling friction; particle contact network rearrangement; degradation at particle asperities; and crushing [4, 5, 19]
A programme of drained triaxial tests have been performed on densely packed glass beads to establish quantified relationships for use in the interpretation of mechanical behaviour from AE measurements

Summary

Introduction

Proportions of the energy dissipated during deformation of particulate materials are converted to heat and sound. Packed particulate materials mobilise shearing resistance through inter-particle friction and interlocking (i.e. dilation, particle rearrangement and particle damage) [18]. AE monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials, for example: particle–particle interactions such as sliding and rolling friction; particle contact network rearrangement (e.g. release of contact stress and stress redistribution as interlock is overcome and regained); degradation at particle asperities; and crushing [4, 5, 19]. Monitoring the evolution of these processes is valuable in geotechnical engineering, where mobilisation of peak shear strength in dense soils causes shear zones to develop, which in turn leads to reduced shear strength and accelerating deformation behaviour as the soil mass becomes weaker under the same imposed boundary stresses; this ultimate limit state can have devastating consequences for people and infrastructure

Methods

Results

Conclusion