Dry granular rheology microstructure with rotational constraints

Dense granular material requires a critical minimum ratio of applied shear stress and pressure to induce flow. Friction between particles causes this critical stress ratio to increase. Frictional constraints beyond sliding friction can lead to an increase in the critical stress ratio. Sliding, rolling and twisting friction are included in particle-based, discrete element simulations in bulk-like stress-controlled shear flows. These simulations show that by increasing the rolling and twisting friction coefficients the stress ratio can double. Furthermore, these constraints cause a larger decrease in the volume fraction and coordination number in the flowing state. However, the functional form of the μ(I) rheology is largely unchanged by these additional constraints. The normal stress differences and fabric tensor are used to further characterize the three-dimensional microstructure and stress states of these flowing granular systems.