Topological Reconfiguration in Sheared Granular Assemblies: Non-Dissipative Mechanism and Its Irreversible Characteristics

Abstract

Granular materials exhibit pronounced macroscopic irreversible deformations during shearing, which mainly contributes to frictional sliding dissipation in the conventional thermodynamic frameworks. This study aims to investigate the non-dissipative microscopic mechanisms governing macroscopic irreversibility of granular materials. Using DEM, a series of biaxial shear and reverse loading simulations are conducted on dense granular assemblies with different friction coefficients. The results show that continuous topological reconfiguration occurs through the transformation from lower-order to higher-order meso-loops, eventually reaching a statistical steady state at the critical state. Accompanying this topological evolution, elastic energy at contact level is continuously stored and released, providing a persistent non-dissipative energy exchange that sustains continuous shear alongside primary frictional dissipation. Based on the reverse loading analysis, topological reconfiguration is intrinsically irrecoverable, causing part of the free energy to remain locked within the reconfigured contact network as irrecoverable free energy. Meanwhile, another portion of the recoverable free energy is irreversibly dissipated through friction during unloading. Together, these two components constitute the irreversible free energy. The evolution of irreversible free energy with interparticle friction is consistent with those of the critical frictional dissipation and macroscopic volumetric strain, indicating that the macroscopic irreversible deformation of granular assemblies is governed not only by frictional dissipation but also by the irreversible evolution of free energy.