TR - 2015 - 06 DEM - PM Contact Model with Multi - Step Tangential Contact Displacement History

We provide a brief overview of the Discrete Element Method (DEM) for modeling large frictional contact problems in granular flow dynamics and quasi-static geomechanics applications. In terms of contact, DEM can be divided into two approaches: the Constraint Method (CM) or rigid-body approach, and the Penalty Method (PM) or soft-body approach. We give a detailed presentation of a DEM-PM contact model that includes multi-time-step tangential contact displacement history. We compare results from direct shear simulations performed with Chrono using this contact model to results from identical simulations using contact models that include either no tangential contact displacement history or only single-time-step tangential contact displacement history. We show that neither of the latter two models are able to accurately model the direct shear test. In particular, the ratio of shear stress to normal stress during direct shear simulations is under-predicted by a factor of about ten when the true tangential contact displacement history model is not used. The new multi-step tangential contact displacement history model we have implemented in Chrono was validated using direct shear simulations of small randomly packed specimens of 1, 800 and 5, 000 identical spheres. The shear-displacement curves obtained from Chrono were compared against physical direct shear experiments performed on identical glass spheres as well as against results obtained from LIGGGHTS, an open-source DEM code that specializes in granular simulations. These comparisons show that the tangential contact displacement history model currently implemented in Chrono is (1) comparable to the model implemented in LIGGGHTS, and (2) capable of accurately reproducing results from physical tests typical of the field of geomechanics. In the appendices, we provide the details of the DEM-PM contact models currently implemented in Chrono, as well as some alternative contact models found in the literature.