Microstructure and Rheology of Particle Suspension in a Yield Stress Fluid

4 pagesInternational audienceNumerous industrial and natural fluids, such as fresh concrete or debris flows, are made of coarse particles suspended in a yield stress fluid. Such suspensions exhibit complex rheological behaviours: elasto-plasticity, shear-thinning (non constant viscosity), normal stress differences, ... In the light of results about shear-induced microstructure in concentrated suspensions of spheres in Newtonian fluids, we experimentally addressed the role of the particle microstructure in this complex rheology. We use a model system made of non-Brownian spherical hard particles suspended in a concentrated emulsion. We associate rheological measurements to X-ray microtomography imaging techniques allowing for the determination of high resolution pair distribution functions in three dimensions. We characterize the rheological behavior and the microstructure for various shear histories (squeeze flow and rotational flow, transient and steady state, various low and high shear rates) and we relate it to their elastic and plastic properties. We show that the elastic and plastic properties of the suspensions depend strongly on shear history; in particular, for certain initial states, the materials display a strain hardening behavior. We relate all these complex properties to the observed shear-history-dependent microstructures