Elucidation of the role of cohesion in the macroscopic behaviour of coarse particulate systems using DEM

Abstract

Ignoring the effect of cohesion between particles in Discrete Element Method (DEM) may incur in errors in the predictions of bulk properties. In this research work, we investigated the role of the cohesion force on macroscopic and microscopic characteristics of monodisperse and bidisperse iron ore granule systems, specifically on the angle of repose and coordination number of the assemblies. In order to simulate the cohesion between particles, a combination of the Hertz contact force and the pull-off force as predicted by the JKR model was employed. The monodisperse systems were made of particles whose sizes ranged between 3 and 10 mm. In order to analyse the effect of bidispersity on the characteristics of the particle assemblies, combinations of 10 mm particles with smaller particles (from 3 to 7 mm) were considered. The results showed that similarly to the rolling friction force, the cohesion force caused a considerable increase in the angle of repose, for the whole particle size range here studied. More importantly by increasing particle size, the rate at which the angle of repose increased as a result of the cohesion force, decreased significantly. This influence became more outstanding by increasing the value of the rolling friction coefficient, signifying the interplay between rolling friction force and cohesion force. In contrast to the case of non-cohesive particles, the effect of particle size on the angle of repose was independent of the rolling friction force in the presence of cohesion force and led to a decrease in the angle of repose for the entire range of rolling friction coefficient values. An empirical analysis of the obtained angles of repose confirmed the strong dependency of the angles on the Bond number and the rolling friction coefficient for cohesive particles. In addition, the coordination number of all studied systems was influenced by both parameters, as the value of coordination number increased by increasing cohesion force but decreased by increasing rolling friction force.