What do materials made of solid, nonBrownian particles, such as granular media, have in common with materials made of soft, spherical objects, such as foams and emulsions? I am interested in several aspects of the rheology of each of these materials. On the granular side, after some work on the statics of such media a few years ago (elasticity of compressed granular media, 2D stress propagation), I am now interested in understanding the origin of the threshold in dense granular flows and the origin of delay before flow onset. Concerning foams and emulsions, I work on rheological models of these systems which undergo large elastic deformations before they yield (plastic flow). I also work on the precise structure of 2D foams and on the origin of static dilatancy in 2D and 3D foams, which is their tendency to raise their liquid fraction when deformed. At the junction between hard and soft particles, Pierre Rognon and I are developing a new numerical method, named Soft Dynamics, which describes each pairwise particle interaction with a limited degrees of freedom, such as the surface deflections and the liquid gap between surfaces. It shows that there exists an optimal approach or separation strategy for two particles and that in a granular paste, the typical gap determines the timescale for rearrangements and should therefore be included in rheological models of granular media. Under imposed shear and normal stress, this timescale appears in the form of a delay before flow onset. 

Modèles théoriques et simulations par la méthode de simulation Soft Dynamics pour sonder différentes questions d'élasticité et de rhéologie des systèmes encombrés. Suspensions: lubrication and repulsion (J. Fluid Mech. 2011) (HAL) Creep delay before flow (Phys. Rev. E 2010) (arXiv  Ref HAL) SoftDynamics simulations (2) T1 process (Eur. Phys. J. E 2009) (HAL) SoftDynamics simulations (1) Optimal approach of two particles (Eur. Phys. J. E 2008) (HAL) Twoparticle argument for threshold in dense granular flows (unpublished, 2008) (HAL) Interpolating between grain inertia and fluid viscosity (unpublished, 2008) (HAL) Elasticity of compressed granular medium (Europhys. Lett. 2004) (HAL) Twodimensional stress propagation (unpublished, 2002) (arxiv) (for publications on other topics, see here) 