Electro-rheological and Magnetorheological Fluid based Dampers

Electro-Rheological fluids (ERF) and Magneto-Rheological fluids (MRF) are characterized by a colloidal suspension of electrically/magnetically semi-conductive particle in an insulating carrier fluid. Silicone oil is commercially used as the carrier fluid having carbonaceous particles in suspension. The particle size is typically of the order of microns. The ERF exhibit a dramatic change in viscosity upon application of external electric field due to the polarization of the suspended particles between the electrodes. The gap between the electrodes is of the order of millimeters. In MRF a drastic change in viscosity occurs due to the application of a magnetic field. The rapid and reversible phenomenon of change in viscosity against electric field was first observed by Winslow in 1949 and often referred to as ‘Winslow effect'. The flow behaviour of ERF is generally modelled as Bingham fluid, in which the shear stress , upon application of an electric field E , is given by

and

(36.1)

here, is the shear strain rate, is the plastic viscosity and is the yield stress induced by the electric field with α close to 2 for a moderate value of E . ERF are commonly used for vibration isolation.