Controlled flow of smart powders

in Physical Review E (2008), 78(6),

The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the ... [more ▼]

The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the interparticle cohesion can be tuned by a magnetic field B. We show that the rheological features of such a system can be controlled. Indeed, the granular flow can be controlled or even stopped by the magnetic field. Depending on the orientation of B, different dynamical regimes can be obtained like a "dry liquid state" forming conical droplets as well as a "layered soft state". Scaling lows are given for the flow rate outside a funnel as a function of B and for the stopping threshold of the flow as a function of the funnel output diameter D. From this analysis, it appears that the flowing properties are related to the dimensionality of the magnetic aggregates. [less ▲]

Contributions expérimentales à l'étude de la compaction des matériaux granulaires

Doctoral thesis (2007)

The influence of grain shape, friction and cohesion on granular compaction dynamics

in European Physical Journal E -- Soft Matter (2007), 22(3), 241-248

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the ... [more ▼]

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the influence of the grain shape, the friction and the cohesion between the grains. Two dimensional and three dimensional systems are analysed. And the role of dimensionality will be emphasized. Theoretical and numerical investigations provide additional informations about that phenomenon. Indeed numerical models permit us to study the influence of some parameters not easily accessible experimentally. Our results show that the above mentioned parameters have a deep impact on the compaction dynamics. Anisotropic grains lead to two different compaction regimes separated by a "burst" of the packing fraction. Friction is observed to modify how the grains are arranged in the pile. This is confirmed by numerical simulations. Cohesive forces between particles inhibit compaction and lead to extremely low values of the packing fraction. [less ▲]

Linking compaction dynamics to the flow properties of powders

in Applied Physics Letters (2006), 89(9),

The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are ... [more ▼]

The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are compared with measurements of the compaction dynamics. Strong correlations are evidenced between compaction relaxation parameters and free flow characteristics. Those correlations are given by semiempirical laws based on physical arguments. This work opens perspectives in powder technology and the knowledge on granular matter. (c) 2006 American Institute of Physics. [less ▲]

Compaction of granular materials: experiments and contact dynamics simulations

in Journal of Physics: Conference Series [=JPCS] (2006), 40

We present an original experimental study of the slow compaction dynamics for two- dimensional isotropic granular systems. Compaction dynamics is measured at three different scales : the macroscopic scale ... [more ▼]

We present an original experimental study of the slow compaction dynamics for two- dimensional isotropic granular systems. Compaction dynamics is measured at three different scales : the macroscopic scale through the normalized packing fraction ˜ ρ, the mesoscopic scale through the normalized fraction ˜ φ of domains ideally ordered in the system, and the microscopic scale through the grain mobility μ. The domains ideally ordered are found to obey a growth process dominated by the displacement of domain boundaries. We present also preliminary results of three-dimensional simulations with a model of contact dynamics. These results allow to discuss the difference between the two-dimensional and the three-dimensional cases. [less ▲]

Compaction of anisotropic granular materials: Experiments and simulations

in Physical Review E (2004), 70(5, Pt 1), 51314

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the particles size and with respect to the container diameter, we have ... [more ▼]

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the particles size and with respect to the container diameter, we have observed large variations of the asymptotic packing volume fraction. The relevant parameter is the ratio between the rod length l and the tube diameter D. Even the compaction dynamics remains unchanged for various particle lengths, and a transition between 3d and 2d ordering for grain orientations is observed for l/D= 1. A toy model for the compaction of needles on a lattice is also proposed. This toy model gives a complementary view of our experimental results and leads to behaviors similar to experimental ones. [less ▲]