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Dense non-Brownian suspensions with conservative repulsive forces between the particles are known to exhibit shear thickening, where viscosity increases with applied stress due to a change in the dominant stress mechanism. At low stress, repulsion maintains liquid films that lubricate particle interactions, while higher stress overcomes the repulsion to generate frictional contacts and leads to greater flow resistance. Here, shear-thickened suspensions are studied in stress-controlled simulations incorporating hydrodynamic, electrostatic double-layer repulsion, and frictional forces; two-dimensional monolayers are studied for monodisperse and bidisperse suspensions with size ratios δ=as/al from 1.0 to 4.0, where as and al are the small and large particle radii. Small-particle fractions ζ=ϕs/ϕ=0.25,0.50, and 0.75 are considered. Total area fractions of 0.71≤ϕ≤0.82 are studied, with the larger values at greater size ratios. Flow curves for mono- and bidisperse systems under varying stress are analyzed, along with detailed structural comparisons for different interparticle friction. We examine the approach to shear jamming, through the emergence of rigid local clusters generated by the reduction of degrees of freedom by frictional contacts. The variance of the fraction of particles in rigid clusters increases sharply near the jamming solid fraction, consistent with a second-order phase transition description of the phenomenon. The contact fabric tensor is determined to provide a measure of the structural anisotropy.
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Shear stress dependence of force networks in 3D dense suspensions
The geometric organization and force networks of 3D dense suspensions that exhibit both shear thinning and thickening have been examined as a function of varying strength of interparticle attractive interactions using lubrication flow discrete element simulations. Significant rearrangement of the geometric topology does not occur at either the local or global scale as these systems transition across the shear thinning and shear thickening regimes. In contrast, massive rearrangements in the balance of attractive, lubrication, and contact forces are observed with interesting behavior of network growth and competition. In agreement with prior work, in shear thinning regions the attractive force is dominant, however as the shear thickening region is approached there is growth of lubrication forces. Lubrication forces oppose the attraction forces, but as viscosity continues to increase under increasing shear stress, the lubrication forces are dominated by contact forces that also resist attraction. Contact forces are the dominant interactions during shear thickening and are an order of magnitude higher than their values in the shear-thinning regime. At high attractive interaction strength, contact networks can form even under shear thinning conditions, however high shear stress is still required before contact networks become the driving mechanism of shear thickening. Analysis of the contact force network during shear thickening generally indicates a uniformly spreading network that rapidly forms across empty domains; however the growth patterns exhibit structure that is significantly dependent upon the strength of interparticle interactions, indicating subtle variations in the mechanism of shear thickening.
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- Award ID(s):
- 1916879
- PAR ID:
- 10284290
- Date Published:
- Journal Name:
- Soft Matter
- ISSN:
- 1744-683X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1039/D1SM00184A
