Discrete element modeling of shielding and size effects during single particle crushing

Abstract

In granular assemblies such as soil, ballast, cementitious aggregates, food and medical products, particle fragmentation and crushing alter material properties. The goal of this research work is to better understand the microstructure parameters that control the triggering of fragmentation, and to predict how microstructure evolution consequent to crushing can actually enhance or reduce material properties. We focused on size and shielding effects, which respectively refer to the decrease of particle strength with increasing particle size, and to the increase of particle strength with the redistribution of stress towards hydrostatic stress conditions upon crushing of neighboring particles. We calibrated the parameters of a Distinct Element Method (DEM) cluster model of crushable particle so as to match the displacement and axial force obtained experimentally at the first particle fragmentation. In order to study the influence of the coordination number on particle crushing, we modeled the mechanical confinement effect of neighboring particles by placing rigid walls around the DEM cluster. In order to understand why larger particles have lower tensile strength, we studied size effects on the crushing process of clusters with and without internal flaws. We found that for clusters with a porosity ranging between 0% and 30%, tensile strength only depends on porosity and not on flaw size. Overall results show that particle strength depends: (1) linearly on particle coordination number; (2) quadratically on particle porosity. Theoretical and DEM modeling of particle crushing will advance the fundamental understanding of energy transfer in particulate media.