Evolution of particle size and shape towards a steady state: Insights from FDEM simulations of crushable granular materials

We add the recent advances in particle shape representation, particle breakage modeling, and fragmental particle size and shape acquisition to the combined finite and discrete element method (FDEM). The granular material is modeled as an assembly of crushable and irregularly shaped polyhedral particles. The particle breakage is simulated by the breakable cohesive interface elements (CIEs) embedded between any pairs of tetrahedrons in the finite element discretization of individual particles. Without calibrating the model parameters to a particular kind of granular material, the FDEM simulation results are qualitatively in good agreement with laboratory tests and DEM simulations, which indicates that the FDEM approach has revealed the primary mechanisms of crushable granular materials. Particle breakage occurs mostly by the major splitting due to tensile crack propagation or by shearing off the local asperities. We analyze the evolutions of particle size distribution and particle shape in the particle breakage process. From the FDEM simulations and other experimental results, we believe that granular soils may reach a steady state when compressed to sufficiently high stress levels or sheared to very large strains. When arriving steady state, the particle breakage is almost ceased and the particle size and shape distributions stay almost unchanged.