The yielding of concentrated cohesive suspensions can be deformation rate dependent

TL;DR

This paper investigates how the flow and yielding behavior of concentrated cohesive suspensions depend on deformation rate, revealing diverse flow responses and challenges in characterizing their flow curves.

Contribution

It demonstrates the deformation-rate dependence of suspension yielding and highlights the complexities in testing methods affecting reproducibility.

Findings

Flow behavior varies with deformation rate.

Different testing protocols yield different flow responses.

Flow curves can be highly irreproducible if not tested properly.

Abstract

The yielding of concentrated cohesive suspensions can be deformation-rate dependent. One consquence of this is that a single suspension can present in one several different ways, depending upon how it is tested, or more generally, how it is caused to flow. We have seen variously Herschel-Bulkley flow, highly non-monotonic flow curves and highly erratic or chaotic yield, all in one suspension. In controlled-rate testing one sees a systematic effect of deformation rate. In controlled stress testing, matters are more subtle. Whereas step-stress creep testing will elicit reproducible behaviour, any attempt to determine a flow curve by, e.g. stepping up or sweeping stress at an inappropriate rate can lead to highly irreproducible behaviour.