We study the rheological behavior of concentrated granular suspensions of simple spherical particles. Under controlled stress, the system exhibits an $\mathsf{S}$-shaped flow curve (stress vs shear rate) with a negative slope in between the low-viscosity Newtonian regime and the shear thickened regime. Under controlled shear rate, a discontinuous transition between the two states is observed. Stress visualization experiments with a fluorescent probe suggest that friction is at the origin of shear thickening. Stress visualization shows that the stress in the system remains homogeneous (no shear banding) if a stress is imposed that is intermediate between the high- and low-stress branches. The $\mathsf{S}$-shaped shear thickening is then due to the discontinuous formation of a frictional force network between particles upon increasing the stress.

• Received 19 December 2014
• Revised 1 May 2015

DOI:https://doi.org/10.1103/PhysRevE.92.032202