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 very simple model, in which spherical beads break into smaller spherical fragments with some loss of volume, enables us to perform a 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, and rupture criteria are defined in terms of maximum of contact forces. A dimensionless parameter, κ s , is defined, which combines the influence of particle strength and contact stiffness. κ s expresses the characteristic contact deflection at rupture, and model materials range from stiff-fragile (large κ s ) to soft-strong (small κ s ). Two initial packing densities were also tested. 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 back kinetic energy 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. Impact of the parameters on energy efficiency is also presented.
Keywords: Collective models, Elasticity, Energy efficiency, Granular modeling, Materials properties