On the Phenomenological Modeling of Electrorheological and Magnetorheological Fluid Preyield Behavior

Phenomenological constitutive models for electrorheological and magneto-rheological fluids and devices in the literature have used various approaches for the representation of the preyield regime. These include modeling the preyield regime using an elastic spring, a viscous dashpot, a Kelvin–Voigt solid, a Maxwell fluid, a three-element (Zener) solid, and a three-element fluid. This paper reviews the behavioral attributes associated with each of the above models. Then, considering the physical phenomena prior to the onset of yield, and experimental data in the preyield regime, and comparing with the behavioral attributes exhibited by the various preyield models, it is concluded that the behavior in the preyield regime is solid-like, not fluid-like, and most conveniently represented as a Kelvin–Voigt viscoelastic solid. In particular, over frequency ranges of interest, the storage modulus does not approach zero at low-frequency limits, as a fluid would exhibit. Effectively modeling the preyield behavior as a Maxwell fluid, as has been done in the literature, yielded frequency-dependent system parameters (specifically the preyield viscosity). This is the result of a viscoelastic fluid model attempting to display the viscoelastic solid-like characteristics exhibited by the test data.