Mechanical Behaviour of Dry Binderless Polystyrene Granules

Abstract

In this paper, the applicability of elasto-plastic contact mechanics to predict the coefficient of restitution of a dry binderless granule impacting on a flat surface is assessed. The granules were prepared using polystyrene particles to avoid complications arising from energy dissipation by solid and liquid binders since only van der Waals attractive forces operated between these particles. The Young's modulus and yield stress of the granules required to calculate the theoretical coefficient of restitution was extracted from slow diametric compression tests using elasto-plastic force-displacement relationships. Significant deviation of the measured coefficients of restitution from theory was found and thus it was concluded that the energy dissipation of the current granules under impact is not analogous to perfect and finite plastic deformation. The granules were shown to fracture in a semi-brittle manner as a consequence of rapid propagation of unstable meridian cracks preceded by irreversible deformation such as densification of the contact zone. However, impact data obtained at velocities corresponding to such fracture were ignored for the purpose of comparisonwith theory.