A microstructural analysis of shear thickening

We investigate the possible microstructural underpinnings of shear thickening of dense suspensions with particular focus on simple particle structures. As a model, we consider a suspension of soft frictional disks (without lubrication or stress activated friction) at densities below shear jamming that exhibits contact driven thickening at low shear rate and overlap driven thinning at high rate. We find that the thickening flow exhibits several instances of distinct microstructure when compared with the thinning. In particular, the pair correlation function has sharp peaks at distances corresponding to particle chains, the heights of which are constant with rate, while during thinning these peaks decrease and broaden. From a statistical analysis of a range of microstrucrual patterns, we also find that straight particle chains and equilateral triangles tend to increase with rate during thickening but decreases during thinning. We try to link the presence of these structures and their capacity to percolate and transmit stresses to the toggling of the system between high and low shear stress states that occur during thickening.