Yielding and flow in aggregated particulate suspensions

TL;DR

This paper tests a simple constitutive model for cohesive particulate gels' compressional strength, highlighting the importance of wall adhesion and elastic-plastic duality in understanding gel consolidation.

Contribution

It introduces a combined elastic and wall debonding model to better describe the consolidation behavior of cohesive particulate gels.

Findings

Wall adhesion significantly affects gel consolidation.

Elastic-plastic duality arises from concentration-dependent modulus.

A simple combined model can approximate consolidation equilibrium.

Abstract

A simple and popular constitutive model used to describe the compressional strength of a consolidating strongly cohesive particulate gel is tested further with new experimental data. Strong cohesive particulate gels have variously been described as being ratchet (poro) elastic, on the one hand, and as having a yield stress in compression, on the other, to the point where same groups of workers have used both descriptions at one time or another. The dichotomy is real though as such gels do show a hitherto somewhat puzzling elastic-plastic duality. This can be explained in part by the strong concentration dependence of the modulus since this leads to irreversible volumetric strain-hardening, in effect, the ratchet; but only in small part. The real problem seems to be that, until very recently, most work on consolidation has neglected what what Michaels and Bolger told us to do over 50 years ago, viz. to take into wall adhesion into account, most cohesive particulate gels being adhesive too. Since wall adhesive failure is plastic in character, the simplest non-linear elastic model of compressive strength can be combined with the simplest possible model of wall debonding to produce a approximate complete constitutive description. Examples of the use of such a description in detailed modelling of consolidation equilibrium can be found in refs 10-12. Consolidation dynamics with wall adhesion is a substantial modelling challenge remaining to be tackled.