Rolling resistance effect for sheared granular materials in the inertial regime

Abstract

In DEM simulations contact mechanics between particles is considered with simple models. A majority of the DEM studies includes a spring and dashpot or springs with two different rigidities during impact and rebound, respectively. These models specify the required contact forces in the normal and tangential directions. The contact forces also produce corresponding rotational resistance with respect to the particle’s center. Most models do not consider additional contact couples. Iwashita and Oda were the first to include the locally generated couples at the contact surface, i.e. rolling resistance. They found that without such consideration, the high void ratio in the shear band observed in tri-axial tests of granular materials could not be reproduced. In a later study it was found that without rolling resistance, the simulated shear forces could not match the experimental tests in an annular shear cell. Paradoxically, rolling resistance appears to have negligible effect in two-sphere collisions. In this study, we examine the reason for the dependence of the global shear stress on the rolling resistance. It is found that rolling resistance promotes internal structure by increasing the contact duration. This effect is negligible under low solid fraction, consistent with the pairwise collision case, but its effect increases rapidly when solid fraction reaches a threshold.