title: Unified rheology of vibro-fluidized dry granular media: From slow dense flows to fast gas-like regimes.
abstract: Granular media take on great importance in industry and geophysics, posing a severe challenge to materials science. Their response properties elude known soft rheological models, even when the yield-stress discontinuity is blurred by vibro-fluidization. Here we propose a broad rheological scenario where average stress sums up a frictional contribution, generalizing conventional μ(I)-rheology, and a kinetic collisional term dominating at fast fluidization. Our conjecture fairly describes a wide series of experiments in a vibrofluidized vane setup, whose phenomenology includes velocity weakening, shear thinning, a discontinuous thinning transition, and gaseous shear thickening. The employed setup gives access to dynamic fluctuations, which exhibit a broad range of timescales. In the slow dense regime the frequency of cage-opening increases with stress and enhances, with respect to μ(I)-rheology, the decrease of viscosity. Diffusivity is exponential in the shear stress in both thinning and thickening regimes, with a huge growth near the transition.
authors.affiliation: Istituto dei Sistemi Complessi, CNR and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Gnoli
authors.affiliation: Istituto dei Sistemi Complessi, CNR and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2 00185 Rome, Italy.|Departamento de Física, Universidad de Extremadura, 06071 Badajoz, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lasanta
authors.affiliation: Istituto dei Sistemi Complessi, CNR and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2 00185 Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sarracino
authors.affiliation: Istituto dei Sistemi Complessi, CNR and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2 00185 Rome, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Puglisi