Mechanical Stability of Granular Assemblies: A Matter of Scale

Granular assemblies are prone to form self‐organized dissipative structures. The microscopic interparticle sliding, entailing frictional dissipation at contacts drives configurational changes that critically influence the mechanical stability of the system. Using the discrete element method (DEM), this study investigates the mechanical stability of granular assemblies based on a mesoscale second‐order work criterion. In dense specimen, the vanishing of the mesoscopic second‐order work exhibits a spatial localization after the stress peak, consistent with the formation of a shear band. By analyzing the evolution of stability indexes, the sub‐domain inside the shear band undergoes a fluctuating regime of stability, which governs the fluctuating stability characteristic of dense specimen at the critical state. For the loose specimen, this fluctuating stability regime maintains throughout loading up to the critical state. The shear band domain and the whole loose specimen were identified as inherent dissipative structures, governing the fluctuating stability regime, where the different loop categories composing the topology of the granular assembly share similar stability mechanisms. Furthermore, the dissipative structure exhibits a similar mean characteristic size of unstable meso‐loops at the critical state regime. The meso‐loops with sufficiently large instability influence range contribute to a loss of stability of the dissipative structures, ultimately controlling macroscopic instability of granular assembly.