Unified rheology of vibro-fluidized dry granular media: From slow dense flows to fast gas-like regimes

• Published in: Scientific reports 2016-12, Vol.6 (1), p.38604-38604, Article 38604
• Main Authors: Gnoli, Andrea, Lasanta, Antonio, Sarracino, Alessandro, Puglisi, Andrea
• Format: Article
• Language: English
• Subjects: 639/301/923/1029; 639/766/530/2803; Fluidization; Geophysics; Humanities and Social Sciences; Mechanical stimuli; Media; multidisciplinary; Rheology; Science; Shear stress; Thinning; Velocity; Viscosity
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep38604

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.