Shear thickening in highly viscous granular suspensions

Abstract

We experimentally investigate shear thickening in dense granular suspensions under oscillatory shear. Directly imaging the suspension-air interface, we observe dilation beyond a critical strain γc and the end of shear thickening as the maximum confining stress is reached and the contact line moves. Analyzing the shear profile, we extract the viscosity contributions due to hydrodynamics ηµ, dilation ηc and sedimentation ηg. While ηg governs the shear thinning regime, ηµ and ηc together determine the shear thickening behavior. As the suspending liquid's viscosity varies from 10 to 1000 cst, ηµ is found to compete with ηc and soften the discontinuous nature of shear thickening.PACS numbers:

Stress fluctuations and shear thickening in dense granular suspensions

“…The particles are first dispersed within the rheometer and sediment in the absence of any applied shear. As shear is applied, the suspension overcomes the gravitational force, it fluidizes and exhibits thinning behavior as was probed in detail in our previous study 16 .…”

“…For instance, the contribution of lubrication forces to shear thickening has been discussed extensively. Depending on the system, viscous coupling has been found to enhance 14,15 , weaken 16 or not affect shear thickening 17 .…”

Rheological Signature of Frictional Interactions in Shear Thickening Suspensions

“…Shear thickening is observed in both granular suspensions, where the particle diameter d is generally d 10 µm, and colloidal suspensions, where d 10 µm. In granular suspensions, the evidence that friction drives shear thickening is well established [8][9][10][11][12][13][14][15][16] but in colloidal suspensions shear thickening is instead commonly attributed to diverging hydrodynamic lubrication forces, which lock particles together in correlated 'hydroclusters' [17][18][19][20][21].A key difference between friction and lubrication forces lies in the stress anisotropy generated by these two types of interactions. This difference is captured by the first normal stress difference N 1 ≡ σ xx − σ zz , where σ ij is the stress tensor for a shear flow in the x direction with a gradient along z. Simulations based on hydrodynamic interactions show that shear-induced distortions of the suspension microstructure and short ranged lubrication forces drive N 1 < 0 [7,18,19,22].…”

“…Shear thickening is observed in both granular suspensions, where the particle diameter d is generally d 10 µm, and colloidal suspensions, where d 10 µm. In granular suspensions, the evidence that friction drives shear thickening is well established [8][9][10][11][12][13][14][15][16] but in colloidal suspensions shear thickening is instead commonly attributed to diverging hydrodynamic lubrication forces, which lock particles together in correlated 'hydroclusters' [17][18][19][20][21].…”

Shear Thickening Behaviour of Composite Propellant Suspension under Oscillatory Shear

“…It has also been found that particle size and volume fraction of dispersed solids affect the critical shear rate corresponding to onset of shear thickening. 16 , et. al.…”