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.
Sci Rep. 2016 Dec 7;6:38604. 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.
颗粒介质在工业和地球物理学中具有重要意义，对材料科学构成了严峻的挑战。即使在振动流化使屈服应力不连续变得模糊的情况下，它们的响应特性也逃避了已知的软流变学模型。在这里，我们提出了一个广泛的流变学情景，其中平均应力总和包括摩擦贡献，推广了传统的 μ(I)-流变学，以及在快速流化中占主导地位的动力学碰撞项。我们的推测相当准确地描述了在振动流化叶片装置中进行的一系列广泛实验，其现象学包括速度减弱、剪切变薄、不连续变薄转变和气体剪切增稠。所采用的装置可以获得动态波动，其具有广泛的时间尺度。在缓慢密集的状态下，笼开启的频率随应力增加而增加，并相对于 μ(I)-流变学，增加了粘度的降低。在变薄和变厚两个区域，扩散系数都与剪切应力呈指数关系，在转变附近有很大的增长。
