Magnetorheological (MR) fluids, which comprise magnetically soft particles dispersed in liquids, possess rheological properties that can be rapidly and reversibly altered by the application of a magnetic field. These fluids have recently been used commercially to provide controllable resistance in exercise equipment and to generate controllable damping in shock absorbers. The commercial potential of this technology, coupled with the fascinating behavior of these materials, has motivated the development of fluids with improved stability against particle sedimentation and irreversible aggregation.
By embedding the magnetic particles not in fluids, but in viscoelastic solids, these stability problems may be eliminated. We have developed a class of such materials termed MR elastomers consisting of iron particles in natural rubber, the base polymer in most elastomeric automotive mounting components, resulting in a compound that can be mixed and molded using conventional techniques. Chemical crosslinking of the elastomer in an applied magnetic field locks in a chainlike particle structure aligned along the direction of the field. The resulting viscoelastic solid possesses stiffness and damping that is nonzero even in zero magnetic field and that increases substantially as a field is applied.
In this talk, I will present measurements of the field-dependent mechanical and magnetic properties of MR fluids and elastomers. These measurements will be compared with the predictions of analytical and numerical models that we have developed to describe them. I will also sketch some possible automotive applications of these controllable materials.