Compaction dynamics of crunchy granular material

¹ Particles and Grains Laboratory, School of Civil Engineering, The University of Sydney, Sydney, New SouthWales 2006, Australia
² Geo-Innovations Research Lab, Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, California 92182, USA.
³ Department of Civil, Environmental & Geomatic Engineering, Faculty of Engineering Science, University College London, London WC1E 6BT, UK.

^* e-mail: francois.guillard@sydney.edu.au

Published online: 30 June 2017

Abstract

Compaction of brittle porous material leads to a wide variety of densification patterns. Static compaction bands occurs naturally in rocks or bones, and have important consequences in industry for the manufacturing of powder tablets or metallic foams for example. Recently, oscillatory compaction bands have been observed in brittle porous media like snow or cereals. We will discuss the great variety of densification patterns arising during the compaction of puffed rice, including erratic compaction at low velocity, one or several travelling compaction bands at medium velocity and homogeneous compaction at larger velocity. The conditions of existence of each pattern are studied thanks to a numerical spring lattice model undergoing breakage and is mapped to the phase diagram of the patterns based on dimensionless characteristic quantities. This also allows to rationalise the evolution of the compaction behaviour during a single test. Finally, the localisation of compaction bands is linked to the strain rate sensitivity of the material.