The nonmonotonic shearthinning flow of two strongly cohesive concentrated suspensions
Abstract
The behaviour in simple shear of two concentrated and strongly cohesive mineral suspensions showing highly nonmonotonic flow curves is described. Two rheometric test modes were employed, controlled stress and controlled shearrate. In controlled stress mode the materials showed runaway flow above a yield stress, which, for one of the suspensions, varied substantially in value and seemingly at random from one run to the next, such that the up flowcurve appeared to be quite irreproducible. The downcurve was not though, as neither was the curve obtained in controlled rate mode, which turned out to be triplevalued in the region where runaway flow was seen in controlled rising stress. For this first suspension, the total stress could be decomposed into three parts to a good approximation: a viscous component proportional to a plastic viscosity, a constant isostatic contribution, and a third shearrate dependent contribution associated with the particulate network which decreased with increasing shearrate raised to the 7/10th power. In the case of the second suspension, the stress could be decomposed along similar lines, although the strainrate softening of the solidphase stress was found to be logarithmic and the irreducible isostatic stress was small. The flow curves are discussed in the light of recent simulations and they conform to a very simple but general rule for nonmonotonic behaviour in cohesive suspensions and emulsions, namely that it is caused by strainrate softening of the solid phase stress.
 Publication:

arXiv eprints
 Pub Date:
 May 2014
 arXiv:
 arXiv:1406.0091
 Bibcode:
 2014arXiv1406.0091B
 Keywords:

 Condensed Matter  Soft Condensed Matter;
 Condensed Matter  Materials Science
 EPrint:
 Revised and corrected version accepted by J. nonNewtonian Fluid Mech., this version 24 pages, 9 Figs inc. graphical abstract