Shear Strength of Assemblies of Frictionless Particles

Whether a granular assembly of frictionless particles has shear strength is a very interesting but not well-understood question. This study addressed this question using discrete element method (DEM) simulations along with an energy-based analysis. It is shown that the use of artificial damping in DEM simulations leads to a frictionless assembly exhibiting normal quasi-static shear behavior, with the overall angle of friction at the critical state being nonzero. However, when this artificial damping is absent, the frictionless assembly cannot achieve a quasi-static state but rather exhibits a stress oscillating state, with all particles in vibration, and the shear strength is expected to be zero. From an energy perspective, it is shown that the artificial damping used in DEM simulations plays the sole role in energy dissipation for the frictionless assembly and that it facilitates the establishment of a quasi-static state from which shear strength is mobilized. Therefore, the nonzero angle of shear resistance reported in the literature for frictionless granular assemblies under quasi-static shear should be regarded as a false rather than a true strength parameter.