Design of crushable particles in DEM based on single grain compression

Abstract

Grain crushing controls the response in shear of granular materials and has an impact on the collapse mechanism of geo-structures. To simulate the effects of grain crushing on the macroscopic response, the Discrete Element Method (DEM) appears to be a viable option considering its proven capability of capturing key aspects of the response of granular materials. One of the approaches to simulate particle crushing via DEM consists in creating a particle by assembling smaller sub-particles ‘bonded’ together by adhesion forces. When the force at the contact between two sub-particles exceeds the adhesion, the bonding is broken irreversibly. A critical aspect in this approach is the characterization of i) the ‘random’ distribution of the adhesion between the sub-particles, and ii) the initial rotation angle of the particles being assembled initially. The tensile strength of a single grain, as measured experimentally by diametral compression between flat platens, typically follows the Weibull distribution. This is proposed to be the criterion to validate any probabilistic distribution selected for the adhesion and the initial rotation angle. The effect of a normal distribution of adhesion and initial rotation on compressive strength was investigated by compressing either a regular ‘cylindrical’ particle or an irregular particle. It is shown that a normal probabilistic distribution of both the adhesion and the rotation angle returns a Weibull distribution of the compressive strength. It is also shown that the rotation angle plays a very critical role and this should be taken into account when initially assembling the ‘crushable’ particles. The rotation angle relocates the contact points, which in turn control the stress at which the particle breaks.