On the Importance of Displacement History in Soft-Body Contact Models

Two approaches are commonly used for handling frictional contact within the framework of the Discrete Element Method (DEM). One relies on the Complementarity Method (CM) to enforce a non-penetration condition and the Coulomb dry-friction model at the interface between two bodies in mutual contact. The second approach, called the Penalty Method (PM), invokes an elasticity argument to produce a frictional contact force that factors in the local deformation and relative motion of the bodies in contact. We give a brief presentation of a DEM-PM contact model that includes multi-time-step tangential contact displacement history. We show that its implementation in an open source simulation capability called Chrono is capable of accurately reproducing results from physical tests typical of the field of geomechanics; i.e., a direct shear tests on a mono-disperse material. Keeping track of the tangential contact displacement history emerges as a key element of the model. We show that identical simulations using contact models that include either no tangential contact displacement history or only single-time-step tangential contact displacement history are unable to accurately model the direct shear test.