Energy evolution of dense granules subjected to shear failure by discrete element method

Energy storing and dissipation are the underlying mechanisms of the macromechanical responses of granular materials subjected to shear failure, while they are difficult to measure in laboratory. We implemented a user-defined contact model considering rolling resistance to the commercial software PFC^2D, and made a calculable method to count the energy components based on the first law of thermodynamics. Then the energy storing and dissipation through the whole sample are investigated in a series of numerical biaxial compression tests by discrete element method (DEM). Four kinds of friction are adopted, i.e. sliding and rolling (S-R), sliding and non-rolling (S-NR), non-sliding and rolling (NS-R) and non-sliding and non-rolling (NS-NR). The results show that the energy is mainly dissipated in the type of sliding rather than rolling. And at a small biaxial strain, the input energy is mainly stored as elastic energy with a small portion dissipated and the dissipated energy is globally distributed through the whole sample. While a large biaxial strain is achieved, the dissipated energy gradually turns dominant and the majority of energy dissipated in a narrow zone, showing the significant localization. In addition, the main direction in which the energy is dissipated shows strong anisotropy at all loading stages.