Modeling and experimental investigation of shear-induced particle percolation in diluted binary mixtures.

A polydispersed mixture of granular materials composed of different-sized particles segregates whenever it undergoes external actions such as shear. Predicting and controlling segregation pose a challenging problem of industrial interest. One of the most frequent and important causes of segregation is interparticle percolation that occurs when small particles fall down through the voids between large particles as a result of local shear in the presence of a gravitational field. In this paper, we present a theoretical model to predict the percolation velocity in sheared systems, and we validate it experimentally. The experiments were carried out in simple shear conditions. This type of flow was achieved in a shear box which allowed the quantitative study of particle percolation under constant shear conditions. The granular material inside the box was a binary mixture of cohesionless spheres differing only in size. The experiments allowed us to quantify the percolation speed for different size ratios and different shear rates. The collected data confirmed the validity of the proposed theoretical model; the latter can be implemented in a continuum framework to simulate more complex phenomena and geometries.