From ``soft'' particle simulations to macroscopic constitutive relations

The goal is to determine the constitutive behavior of granular packings under various deformations (isotropic and anisotropic) from particle simulations. For this we consider deformations, stress, structure and the contact forces as the basis. In a previous study [6,7] we investigated using DEM, the evolution of the coordination number (and the packing structure) and pressure as functions of the volume fraction for a polydisperse granular packing of spheres under isotropic compression. Here we focus on anisotropic deformation by implementing the triaxial test setup in a similar way. We study the effect of polydispersity changing the width of the particle size distribution. We find that an increase in polydispersity leads to a decrease in pressure at constant volume fraction whereas the macroscopic friction angle seems to increase with polydispersity. Furthermore, we performed triaxial test simulations with soft friction which is characterized by a small tangential contact stiffness. Our main observation is that using the same initial packing configuration with different friction coefficients does not lead to an obvious trend in simulation results.