Force and flow transition in plowed granular media

We use plate drag to study the response of granular media to localized forcing as a function of volume fraction, $ϕ$. A bifurcation in the force and flow occurs at the onset of dilatancy, $ϕ_c.$ Below $ϕ_c$ rapid fluctuations in the drag force, $F_D,$ are observed. Above $ϕ_c$ fluctuations in $F_D$ are periodic and increase with $ϕ$. Velocity field measurements indicate that the bifurcation in $F_D$ results from the formation of stable shear bands above $ϕ_c$ which are created and destroyed periodically during drag. A friction-based model captures the dynamics for $ϕ>ϕ_c$.

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