Properties of Zeolite- and Cornstarch-Based Electrorheological Fluids at High Shear Strain Rates

The mechanical and electrical properties of zeolite- and cornstarch-based ER fluids are explored using a concentric cylinder viscometer. With cylinder radius to gap size ratio on the order of 400, we achieved shear strain rates ranging from 3000 to 20,000 sec ^-1 . Two different volume fractions of zeolite and cornstarch suspensions in silicone oil were tested at a constant temperature of 30°C. The shear stresses and electric resistivity of the fluids were computed from experimental measurements as functions of shear strain rate. Although the cornstarch ER fluids indicated anomalous behavior, the zeolite ER fluids were found to be more stable under high shear strain rates and electric fields and were characterized by a Bingham viscoplastic model-like behavior. Dynamic yield stress was increased in proportion to a power of the electric field. The higher the volume fraction of dispersions, the higher the yield stress. Plastic viscosity, as defined by the Bingham model, remained unchanged with the variation of elec tric field for a fixed volume fraction. This work was motivated by the need for applications to rotor-bearing control, where for usual bearings, the shear rate is much higher than the maxima of most of the published experimental results. Moreover, for high shear rates, the validity of the Bingham model was questioned by many authors without specific experimental justification, which is attempted here for two different kinds of dispersed particles.