Biaxial shearing of star-shaped particles with multiellipse DEM model

Using the multiellipse-based discrete element method (DEM), we numerically study the biaxial shearing behavior of granular materials composed of star-shaped particles. These particle shapes are generated by overlapping two or three identical ellipses with a common center of mass, while varying the aspect ratio from 1 to 5. Our results reveal that the macroscopic shear strength of the system increases monotonically with particle non-convexity. In contrast, the packing fraction exhibits a non-monotonic dependence on non-convexity, initially increasing and then decreasing as non-convexity further grows. This behavior reflects variations in the local pore size due to the competition between short-range ordering and excluded volume effects. Furthermore, microscopic analysis indicates that the increase in shear strength is linked to higher contact numbers and reduced contact and inter-grain distances, corresponding to stronger interlocking at higher non-convexity.