Active dry granular flows: rheology and rigidity transitions

Abstract

The constitutive relations of a dense granular flow composed of self-propelling frictional hard particles are investigated by means of DEM numerical simulations. We show that the rheology, which relates the dynamical friction $\mu$ and the volume fraction $\varphi$ to the inertial number $I$, depends on a dimensionless number $\mathcal{A}$, which compares the active force to the confining pressure. Two liquid/solid transitions -- in the Maxwell rigidity sense -- are observed. As soon as the activity is turned on, the packing becomes an `active solid' with a mean number of particle contacts larger than the isostatic value. The quasi-static values of $\mu$ and $\varphi$ decrease with $\mathcal{A}$. At a finite value of the activity ${\mathcal{A}}_t$, corresponding to the isostatic condition, a second `active rigidity transition' is observed beyond which the quasi-static values of the friction vanishes and the rheology becomes Newtonian. For $\mathcal{A}>{\mathcal{A}}_t$, we provide evidence for a highly intermittent dynamics of this 'active fluid'.

7 pages, 7 figures, final version, accepted for publication in Europhys. Lett

References in corpus (6)

• Novel type of phase transition in a system of self-driven particles
• Turning bacteria suspensions into a "superfluid"
• Towards a 'Thermodynamics' of Active Matter
• Internal states of model isotropic granular packings. I. Assembling process, geometry and contact networks
• Shearing active gels close to the isotropic-nematic transition
• Sheared active fluids: thickening, thinning and vanishing viscosity

Cited by in corpus (4)

• Rheology of dense granular flows for elongated particles
• Rheology of granular flows across the transition from soft to rigid particles
• Flow and rheology of frictional elongated grains
• Motile topological defects hinder dynamical arrest in dense liquids of active ellipsoids