3D numerical simulation study of quasistatic grinding process on a model granular material

We report on discrete-element method (DEM) simulations of the breakage of fragile particles under growing oedometric load, motivated by applications to clinker grinding processes in the cement industry. The use of a simplified model, in which spherical beads break into smaller spherical fragments with some loss of volume, enables us to perform a systematic parametric study and to investigate collective effects, as the transfer of load to other particles following one breakage event may entail large scale avalanches or cascades involving the rupture of many grains. Particles are attributed random strengths, chosen according to Weibull distributions of varying width, and rupture criteria are defined either in terms of contact forces or of average stresses within the grain. A dimensionless parameter, κS, is defined, which combines the influence of particle strength and contact stiffness. κS expresses the characteristic contact deflection, relative to the particle diameter, at rupture. Model materials range from stiff-fragile (large κS) to soft-strong (small κS). Initial packings also differ in solid fraction Φ0. The energy efficiency, defined as the ratio to dissipated energy of elastic energy in each grain before its breakage, is strongly correlated to the importance of the cascading effect, either through the quantity of kinetic energy released in the system, or through the capacity to capture it back in the form of elastic energy without dissipation. It ranges from 1% to 15% in the simulation, an order of magnitude compatible with the efficiency claimed in the industrial processes. Energy efficiency is mainly determined, by order of decreasing importance, by κS, Φ0, distribution width and choice of rupture criterion.