  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.
