Development of the stick-slip friction model for discrete elements modeling

The object of the research is an intergranular friction model for use in discrete-element modeling of the mechanical behavior of granular materials under static and dynamic conditions. As in this approach grains are modeled by independent elements interacting through contact forces, the selection of contact force models, and in particular for the tangential component (friction), represents the most important task in obtaining the most realistic macroscopic behavior. There are many friction models that work well in dynamic regimes, but fail to model mechanical behavior in static or quasi-static regimes. In this work, an intergranular friction model is proposed based on Coulomb's regularized friction model, which takes into account the stick-slip phenomenon that appears at low sliding speeds at the contact. Three different examples are designed and modeled in order to demonstrate the robustness of the model in different situations including static, quasi-static and dynamic regimes. The first is a basic example consisting of the translational motion of a grain on a planar surface with a relatively low constant velocity. This example allowed to capture the stick-slip phenomenon. The second represents a grain subjected to its own weight and supported essentially by frictional forces. This example shows that the model works well in both quasi-static and static regimes. The third example consists of a grain sliding on a plate and subjected to accelerated motion. It showed the effect of friction velocity on the occurrence of stick-slip, as well as the evolution of friction force with sliding velocity. The obtained results demonstrated that the model effectively captures shear behavior in the different regimes. It could therefore be used in discrete element modeling of granular materials under both static and dynamic conditions. As in this work, the model is formulated in 2D, it would be interesting to develop a general 3D formulation so that it can be easily applied in 3D modeling.