title: S-shaped flow curves of shear thickening suspensions: direct observation of frictional rheology.
abstract: We study the rheological behavior of concentrated granular suspensions of simple spherical particles. Under controlled stress, the system exhibits an 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 S-shaped shear thickening is then due to the discontinuous formation of a frictional force network between particles upon increasing the stress.
authors.affiliation: Van der Waals-Zeeman Institute, IoP, Science Park 904, Amsterdam, Netherlands.
authors.forename: Zhongcheng
authors.initials: Z
authors.lastname: Pan
authors.affiliation: Van der Waals-Zeeman Institute, IoP, Science Park 904, Amsterdam, Netherlands.
authors.forename: Henri
authors.initials: H
authors.lastname: de Cagny
authors.affiliation: Van der Waals-Zeeman Institute, IoP, Science Park 904, Amsterdam, Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Weber
authors.affiliation: Van der Waals-Zeeman Institute, IoP, Science Park 904, Amsterdam, Netherlands.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bonn