A numerical study on transient granular flow beyond μ (I) rheology

The rheology of dense granular flows under constant shear acceleration is studied numerically in simple shear at constant pressure. We show that, in unsteady flow, the stress ratio becomes history-dependent and cannot be represented by a single steady-state μ (I) μ ( I ) curve. The deviations are governed by the interplay of imposed deformation, grain inertia, and structural relaxation. We find that this behaviour requires an extended scaling description. Based on the findings, we propose a phenomenological constitutive relation that extends the μ (I) μ ( I ) rheology to transient granular flow.