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.

Uncovering Instabilities in the Spatiotemporal Dynamics of a Shear-Thickening Cornstarch Suspension

“…Although supported by both simulations [18] and experiments [19,20], this model provides only a zero-dimensional picture that ignores the spatial and dynamical aspects of the transition. In particular, the prediction of hysteresis associated with S-shaped flow curves hints at an instability that should involve the separation of the system into shear bands oriented along the vorticity direction of the flow and referred to as vorticity bands in the literature [21].…”

“…In the specific case of hard non-Brownian particles, stress balance across the interface between bands prevents the existence of steady vorticity bands [20,22]. This could explain the large temporal fluctuations that are ubiquitously observed in shear-thickening systems [19,20,[23][24][25].…”

Localized transient jamming in discontinuous shear thickening

“…An increase in viscosity, η, above a material dependent critical shear stress is commonly observed in dense colloidal and granular suspensions [1][2][3][4][5][6][7]. This increase can be abrupt if the volume fraction (φ = V particle /V total ) approaches the jamming fraction, φ J , and is known as discontinuous shear thickening (DST), while at lower concentrations the increase is gradual and termed continuous shear thickening (CST) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”

Drop formation in shear-thickening granular suspensions

“…Such small Stokes numbers for the onset of thickening are also found in other shear thickening systems; this is surprising since if the thickening were due to a viscous-to-inertial transition, one would expect the Stokes number to be of order unity. One interpretation of these small Stokes numbers is that they result from short-range interactions between particles that give the onset of thickening [20,[34][35][36][37].…”