Shear reversal response of frictional suspensions
Résumé
Lately, several studies pointed the key role of contact forces in the mechanical response of suspensions of non-Brownian rough spheres in Newtonian liquids. Both particle roughness [1] and frictional contacts [2] strongly increase the suspension viscosity. A Transition from frictionless to frictional contact between particles has been invoked to explain the discontinuous shear thickening in concentrated suspensions [3]. Recent numerical simulations [4] showed that shear reversal experiments, first proposed by Gadala-Maria and Acrivos [5], make it possible to estimate the contribution of contact forces to the viscosity. In this paper, we present the viscosity response to shear-reversal of suspensions made of either faceted sugar particles or PMMA spherical particles in a Newtonian silicon oil. In such a transient shear flow, the viscosity decreases after the shear inversion to a minimum where contacts vanish, and increases again up to the steady value as frictional contacts re-build [4,6].
The steady viscosity and the minimum viscosity were measured for both suspensions as a function of particle volume fraction with the following results. (i) Steady viscosity are larger in sugar particle suspensions than in spherical particle suspensions. (ii) Both suspensions show close values of the minimum viscosity.
We conclude from these experiments that contact forces between particles play a more important role in the steady rheological behavior of sugar particle suspensions than in spherical particle suspensions.
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[2] Gallier S. et al. (2014). JFM 757, 514–549
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[5] Gadala-Maria F. & Acrivos A. (1980). JOR 24, 799-814
[6] Lin N. Y. C. et al. (2015). PRL 115, 228304