Rheology of Cohesive Granular Media*

Characterization and prediction of the `flowability' of powders are of paramount importance in many industries. However, our understanding of the flow of powders  is sparse compared to the flow of coarse granular media. The main difficulty comes from the presence of adhesive forces between the grains, preventing smooth and continuous flows. In this talk we will first present results from discrete simulations, showing that contrary to what is commonly perceived, the cohesive nature of the flow is not entirely controlled by the inter-particle adhesion, but that stiffness and inelasticity of the grains also play a significant role. We also analyzed the development of shear banding and relates it to the existence of a shear weakening branch in the rheology of cohesive grains. In a second part, I will present an experimental work in which we have developed a method for preparing a granular material with a controlled adhesion between particles. The granular material is made of spherical glass beads coated with a polyborosiloxane polymer. This material is proved to be stable in time and non-sensitive to temperature and humidity, opening many perspectives to experimentally study the flow of cohesive grains  in a controlled manner.