DEM simulation of dense granular flows in a vane shear cell: Kinematics and rheological laws

The rheology of dense granular flows is investigated through discrete element method (DEM) simulation of a vane shear cell. From the simulation, profiles of shear stress, shear rate, and velocity are obtained, which demonstrates that the flow features in the vane shear cell are equivalent to those in the classic annular Couette cell. A novel correlation for the shear viscosity is formulated and leads to a new expression for μKT in the kinetic theory analysis. The μKT formulation is able to qualitatively capture the μ-I relation in the shear cell. A correlation length is added in the energy dissipation term to account for the effects of the particle motion correlation. A simplified correlation length model is derived based on DEM results and is compared with the literature. The modified granular kinetic energy equation is able to correctly predict the granular temperature profiles in the shear cell

Dynamics of rearrangements during inclination of granular packings: the avalanche precursor regime

International audienceThe dynamics of inclined 3D granular packings driven towards their stability limits is studied experimentally through the dynamics of rearrangements of grains at their surfaces. Two regimes are identified in that way: a regime of limited and independent rearrangements of grains at small angles and a regime of extended events, called 'precursors of avalanches', at large angles. Both regimes are characterized. The transition between the two regimes is attributed to the emergence of slidings smaller than one grain diameter at the surface of the packing with a stick-slip dynamics which reflects the emergence of long-range correlations at the approach of the avalanche. The observed superficial events are shown to depend strongly on the microscopic details of the interaction between grains. In addition to the study of precursors, we discuss the consequences of this macroscopic correlation length on the packing stability. We show in particular that the avalanche angle θa depends not only on the width of the packing but also on its length

Rheology of vibrated granular suspensions

In this work we investigate in details the flow behaviour of dense vibrated gravitational suspensions. We study the rheology in the stationary state by using a stress imposed rheometer (spectroscopy mechanics) coupled with a vibration cell, we show that applying well-controlled mechanical vibrations allows the control of the suspension viscosity by suppressing the apparent yield stress which is largely the cause of flow jamming. We show that the rheology in the stationary state is controlled by the competition between the reorganization time induced by the flow and the internal reorganization time induced by vibrations. We discuss the influence of particles size, suspending fluid viscosity and vibration parameters and demonstrate that the grains dynamics is controlled by the ratio between the lubrication stress and the granular pressure. This work evidences the major role played by the vibration induced lubrication stress on the liquefaction of vibrated granular suspensions

Rheology of vibrated granular suspensions

In this work we investigate in details the flow behaviour of dense vibrated gravitational suspensions. We study the rheology in the stationary state by using a stress imposed rheometer (spectroscopy mechanics) coupled with a vibration cell, we show that applying well-controlled mechanical vibrations allows the control of the suspension viscosity by suppressing the apparent yield stress which is largely the cause of flow jamming. We show that the rheology in the stationary state is controlled by the competition between the reorganization time induced by the flow and the internal reorganization time induced by vibrations. We discuss the influence of particles size, suspending fluid viscosity and vibration parameters and demonstrate that the grains dynamics is controlled by the ratio between the lubrication stress and the granular pressure. This work evidences the major role played by the vibration induced lubrication stress on the liquefaction of vibrated granular suspensions

How MRI can assist Rheology?

ICMRM 2019, 15th International Conference on Magnetic Resonance Microscopy, Paris, FRANCE, 18-/08/2019 - 22/08/201

Hydrophobic and raw glass beads flow behavior under different processing conditions

Controlling the powder flow by the surface properties of the particles as well as understanding their flowability under different processing dynamics are amongst the major challenges of the powder industry. Indeed, handling large quantities needs powders with good flowability, adequate compressibility and few electrostatic charges. We have performed a chemical treatment in order to obtain hydrophobic glass bead and its bulk behavior has been compared with raw glass bead. We characterized flow properties under different processing conditions. Both powders presented similar flow behavior in the free fall measurement, however hydrophobic glass bead showed lower flow behavior under flow with rotating drum. Also, hydrophobic glass bead presented negative and raw glass bead almost zero electrostatic charges

Hydrophobic and raw glass beads flow behavior under different processing conditions

Controlling the powder flow by the surface properties of the particles as well as understanding their flowability under different processing dynamics are amongst the major challenges of the powder industry. Indeed, handling large quantities needs powders with good flowability, adequate compressibility and few electrostatic charges. We have performed a chemical treatment in order to obtain hydrophobic glass bead and its bulk behavior has been compared with raw glass bead. We characterized flow properties under different processing conditions. Both powders presented similar flow behavior in the free fall measurement, however hydrophobic glass bead showed lower flow behavior under flow with rotating drum. Also, hydrophobic glass bead presented negative and raw glass bead almost zero electrostatic charges