The creep behaviour of a field-responsive fluid

Many particulate suspensions show a dramatic but reversible increase in flow resistance when subjected to an external magnetic or electric field, with the material often modeled as having a field-induced yield stress y. Creep tests on a suspension of carbonyl iron particles dispersed in oil under a constant magnetic field reveal that the material will undergo deformation over a prolonged period, even if the applied shear stress is considerably smaller than y. This indicates that the rheological behaviour is more complex than can be captured by the current simple constitutive formulations.