Mechanical and Electrical Properties of an Electrorheological Fluid

Abstract

Adaptive structures contain parts whose properties may be tuned so as to suit some purpose. Certain fluids change viscosity when subjected to an electrical field. This paper concerns the behaviour of such an electrorheological fluid, ERF, which may be characterized as visco-plastic with some elasticity present. The stress response to a prescribed strain is studied in tests. Various models for describing the observed behaviour are analyzed. Results show that modelling the ERF as a Bingham fluid gives a rather close fit for low field strength. A solid mechanics model which displays yielding with kinematic strain hardening is preferred for high field strength as it then describes the observed amplitude and frequency dependence quite well. Relevant constants for investigated models are listed as functions of the field strength. The electrical behaviour is essential in designing parts for on-line response of structures, in order to control vibrations. Results show that a damper containing ERF responds to applied voltage as a capacitor whose leak resistance depends on voltage whereas its capacity does not. AC as well as DC fields are treated. When subjected to harmonic displacement the force response of the damper contains superharmonics owing to the non-linearity of the ERF. In AC powered dampers, intermodulation frequencies between field and displacement are identified.