Directional plastic flow and fabric dependencies in granular materials

The constitutive modelling of granular materials both at the microstructural level and the continuum level is well established. Much recent effort has been devoted to the theoretical mechanics and computer simulations of granular media through discrete element modelling (DEM). The current study uses DEM to obtain theoretical insights and extract constitutive information such as the nature of the yield and plastic flow behaviour of granular materials. In particular, we look at the influence of granular fabric on the plastic deformation response under a number of conditions. As such, a representative element volume (REV) of a granular material idealized as a numerical DEM sample is subjected to different loading paths to reach the same stress states, but with different fabrics, on the plastic failure surface. At this stage, directional stress probes of equal magnitudes are applied, so that the strain response envelopes thus obtained represent characteristics of the increment of plastic strain, i.e. the nature of the flow rule. The discussion then focuses on the relationship between fabric, stress state, loading path, direction of the plastic strain increment, and whether this direction can be considered unique or not.