The Role of Particle Size in the Shock Compaction of Brittle Granular Materials

Abstract

Granular materials can consume large amounts of kinetic energy through deformation of their inherently complex meso-structure. Little is understood about what effect the geometrical variations such as particle size and shape have on their response to shock loading. With this in mind, this thesis attempts to measure the effects that particle size has on the compaction curve of brittle granular materials. Three monodisperse and one polydisperse samples of soda-lime glass microspheres were chosen for this study. A quartz sand was also investigated to determine if the microspheres were a sufficient analogue whilst additionally introducing morphological differences. Beds of these materials were subjected to quasi-static loading therefore measuring the stress-density compaction response. Post-loading analysis of the samples revealed a strong dependence on particle size and morphology. The macro-scale shock compaction responses of the granular samples were measured using plate impact techniques and piezo-resistive stress gauge diagnostics. Similar trends were observed in the quasi-static loading behaviour. Smaller particles appeared to have higher strength in the macroscale which, due to scaling effects at boundaries, contradicted trends from meso-scopic fracture tests. It was concluded that beds composed of smaller, spherical particles show the greatest resistance to shock and quasi-static compaction. For convenience, a single Hugoniot relationship is typically used to represent the shock response of granular materials. This assumption was challenged in this thesis. Identical incident shock loading produced different loading states with a changing bed thickness. The terminal loading states varied considerably with bed thickness in the samples of larger microspheres. The majority of this variation was due to dispersion within the initial portion of the wave. The study concludes that particle size has a significant effect on the shock response of granular materials if the particle geometry is suited to inducing a total-fracture particle densification mechanism.