Force-spectrum-resolved micromechanics of macroscopic rheology in inertially sheared dense granular flows

Abstract

The macroscopic rheology of dense granular flows originates from heterogeneous and dynamically evolving contact networks. However, conventional binary strong–weak classifications obscure the differentiated mechanical roles of contacts across the continuous force spectrum. This study develops a force-spectrum-resolved micromechanical framework by combining two-dimensional discrete element simulations of inertial plane shear, a ten-subinterval decomposition based on the instantaneous mean normal contact force, and stress–force–fabric analysis. During shear startup, the contact network evolves from an approximately homogeneous state through localized differentiation and strong-force-chain percolation before recovering statistical spatial homogeneity. This reconstruction is accompanied by progressive force-spectrum polarization, manifested by depletion of intermediate-force contacts, accumulation near zero force, and extension of the ultra-strong tail. Increasing inertia intensifies shear dilation, network rarefaction, load concentration, and force heterogeneity, while the polarization trend remains robust under alternative partition schemes. The anisotropic response is governed jointly by force magnitude and principal-direction alignment. The lowest-force weak contacts mainly enhance contact-orientation anisotropy, whereas normal-force anisotropy arises from weak-contact reorientation and the nearly coaxial contribution of ultra-strong contacts. Tangential-force anisotropy and the increase in shear resistance are dominated by the ultra-strong tail. Stress partitioning further reveals that macroscopic rheological stability emerges from dynamic compensation between overloaded strong contacts and weak contacts possessing redundant internal shear strength. The proposed framework extends the conventional strong–weak description and provides a spectrum-resolved micromechanical basis for constitutive modeling of dense granular rheology.