The relationship between contact network and energy dissipation in granular materials

A micromechanical study of the relationship between contact force networks and energy dissipation is presented. A series of drained triaxial compression tests with different stress paths have been simulated using the discrete element method. Two existing contact force network partitioning methods have been used for analysing the energy dissipation, one based on the average contact force magnitude and the other based on the contribution of contact forces to the global deviator stress. For both methods, energy dissipation in neither the strong nor weak contact networks is negligible. When the average contact force partitioning method is used, over 70% of the energy dissipation occurs in the weak contact network, but the dissipation per sliding contact is higher in the strong contact network because the tangential contact force is higher. When the contact network is partitioned based on the contribution of forces to global deviator stress, more than 60% of the energy dissipation occurs in the strong contact network. A new normal contact force threshold for splitting energy dissipation is identified. Specifically, over 93% of energy dissipation occurs at contacts with a normal contact force below 2 times the average normal contact force. There is very small energy dissipation in contacts with higher normal contact force because there is little particle sliding.