A constitutive model for sheared dense suspensions of rough particles

Abstract

In a concentrated suspension, particles come into contact due to the presence of asperities on their surfaces. As a result, the contact forces and interparticle friction become one of the important factors governing the rheology of rigid particle suspensions at high concentrations. We show that a load-dependent friction model can be used to reproduce the experimentally observed shear thickening [ST—continuous and discontinuous (DST)] behavior with an increase in the asperity size. Increasing the particle surface roughness size leads to a decrease in the critical shear rate above which shear-thickening takes place, a reduction in the critical volume fraction for DST and an increase in the viscosity jump across non-shear-thickened to shear-thickened regime. In this paper, we propose a constitutive model to quantify the effect of increasing the roughness size on the rheology of dense ST suspensions as well as on the critical shear rate for ST and the critical volume fraction for DST. We fit this model to our simulation data for stress controlled shear flow of dense rough particle suspensions. Once the fitting is complete, these equations are used to predict exact volume fractions and shear stress values for transitions between three regimes on the shear stress-shear rate flow state diagram for different roughness values. The results of this study can be used to tune the particle surface roughness for manipulating the dense suspension rheology according to different applications.

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“…At very high‐shear rates (>100 s −1 ), increasing shear stress and viscosity values were observed with increasing shear rates. It is likely that this shear thickening behavior resulted from particles being resuspended by the applied shear and increasing particle–particle interactions (interparticle friction) at these fast shear rates 56 . The thinning‐to‐thickening inflection point in the shear stress response of these slurries was the point at which particles transition from a settled state to a resuspended state, as reported by Crawford et al 45 in a system with settled α‐cellulose particles.…”

Sheared Thick‐Film Electrode Materials Containing Silver Powders with Nanoscale Surface Asperities Improve Solar Cell Performance

“…A detailed discussion on the numerical tool and its validation can be found elsewhere. [43][44][45][46] Starting from the equations of motion and calculating the hydrodynamic forces; for a Stokes flow regime, the force balance of particles after neglecting inertia can be described by the following equation…”

“…Further details on the numerical implementation and the procedure to calculate the stresslets can be found in the cited literature. [43][44][45] Numerical simulations were performed for a surface roughness of up to 2% of the particle diameter. The simulations shown in Figure 7 reproduce the shear-thinning behavior observed for the experimental systems.…”

A unifying mechanism to explain the rate dependent rheological behavior in non-Brownian suspensions: One curve to unify them all

“…These surface asperities not only lead to inter-particle contacts, but also dictate the friction in interesting ways. Hence, efforts on investigating the influence of particle roughness on dense suspension rheology have gained much traction in the recent years [5,[19][20][21].…”

“…Here a is the radius of the smaller particle. For this particular particle size distribution, the dry close packing fraction (φ RCP ) is 0.66 [21]. We use φ RCP to normalize the volume fraction (φ) values in this study.…”