Magnetorheological fluids (MRF) are suspensions of magnetizable particles in a carrier liquid. When a magnetic field is applied, the fluid reversibly stiffens within a few milliseconds as a result of the magnetic interactions between the particles.
The shear stress which is characteristic of the stiffening increases continuously with the magnetic flux density by a factor of up to about 100. This strong stiffening effect of the MRF can be used for numerous technologies such as adaptive dampers, controllable clutches and brakes, haptic actuators and switchable surface stiffening.
The particles in the MRF usually consist of carbonyl iron. Mineral oils or synthetic oils (polyalphaolefins) as well as silicone oils usually serve as carrier liquids, but other carrier liquids are also possible depending on requirements. Additives prevent the particles from settling.
Numerous MRF formulations have already been developed at the Center Smart Materials and Adaptive Systems and can be adapted to special requirements if required. Production takes place in batches of up to 2 litres.
For the determination of the rheological properties of MRF at different temperatures and shear rates depending on the magnetic field, appropriate measuring methods are available. Further application-relevant information about the MRF can also be obtained by generating the desired effect in an application-related demonstrator such as a damper or a clutch.