Electrorheological controllable smart fluid derives from their ability to provide simple, quiet, rapid response and interfaces between electronic controls and mechanical systems.
Under the influence of electric field particles, the solid phase tends to form chains and columns along the direction of an applied electrical field. This result in enhanced shear stress and such fluid exhibits increased resistance to flow. Apparent viscosity increases as well as elastic modulus, the increased stiffness is observed, the transition has been described as liquid-solid.
Electrorheological fluid characteristics
The dynamic viscosity of rheological fluid depends on dynamic viscosity of the base liquid, the volume fraction of solid particles, the amount and type of additives used to control particle settling and the shear rate at which viscosity is measured. The waterbased fluids have a higher particle volume fraction than the other oil-based fluids.
The additives in fluid cause the viscosity to increase rapidly when shear rate decreases.
Apparent viscosity of the rheological fluid becomes lower when shear rate increases until it eventually reaches a steady state value. This phenomena is called 'a shear thinning" character.
For oil-based fluids, the apparent viscosity reaches a steady state value at a relatively low shear rate in a few hundred of second.
For the water-based fluids, the apparent viscosity starts higher at low shear rate and continues to drop over a much longer range of shear rate. In this case, an asymptotic, steady state value will not be reached until the shear rate increases up to several thousand or even ten thousand second.
At these high rates, the water-based fluid will actually have lower apparent viscosity han the oil-based fluid.
Electrorheological fluid devices in average application have power requirements of about 50 W. The difference is in applied voltage and current requirement electrorheological fluid devices require high voltage 2–5 kV and low current 1–10 mA power supply.
Smart fluids have a great potential to modernize automotive industry.
The electrorheological fluid must be a user friendly engineering material, the fluid should have a high boiling point and low freezing point, it should not be abrasive or attack common engineering materials; it should have a long storage and working life; it should show a minimal tendency to settle out, it can be used with ordinary rubber seals, it must be non toxic and safe to use.
ECO Brake-By-Wire an electrorheological fluid brake system can control considerably more mechanical power than the electrical power used to control the effect, it acts as a power amplifier. The electrorheological fluid which can be transformed from the fluid state into the solid state in milliseconds, by applying an electric field to generate braking torque causing the vehicle to slow down or stop.