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We present a method to predict how grain size distribution (gsd) evolves during confined comminution. We describe particle breakage as a probabilistic phenomenon considering the single particle strength and the pdf of interparticle contact forces from DEM simulations. Our results show a good agreement with published experimental data.

Using the Contact Dynamics method in discrete simulations, this paper aims at studying the influence of the size polydispersity on the force transmission properties of 3D granular media. We focus on the micromechanical origin of the so-called “cushioning effect” that prevents the breakage of largest particles in confined comminution process. The samples are composed of nearly 104 spherical particles who’s size distribution follows a power law with different size span (ratio between the extreme sizes). To increase the representativity of our packings we use a fully periodic cell to overcome boundary influence on results. We study frictionless packing at isotropic equilibrium. We show that increasing the size span leads to an efficient space filling but also to an increased heterogeneous force network. To explain the cushioning we then investigate the role of each size class in force transmission.

We use numerical simulations to investigate force and stress transmission in cohesive granular media covering a wide class of materials encountered in nature and industrial processing. The cohesion results either from capillary bridges between particles or from the presence of a solid binding matrix filling fully or partially the interstitial space. The liquid bonding is treated by implementing a capillary force law within a debonding distance between particles and simulated by the discrete element method. The solid binding matrix is treated by means of the Lattice Element Method (LEM) based on a lattice-type discretization of the particles and matrix. Our data indicate that the exponential fall-off of strong compressive forces is a generic feature of both cohesive and noncohesive granular media both for liquid and solid bonding. The tensile forces exhibit a similar decreasing exponential distribution, suggesting that this form basically reflects granular disorder. This is consistent with the finding that not only the contact forces but also the stress components in the bulk of the particles and matrix, accessible from LEM simulations in the case of solid bonding, show an exponential fall-off. We also find that the distribution of weak compressive forces is sensitive to packing anisotropy, particle shape and particle size distribution. In the case of wet packings, we analyze the self-equilibrated forces induced by liquid bonds and show that the positive and negative particle pressures form a bi-percolating structure.