Functional behavior of isotropic magnetorheological gels

Magnetorheological (MR) gels are a new class of soft polymers whose properties can be controlled using a magnetic field. The functional effectiveness of these gels depends on their magnetic controllability. In this paper, an experimental investigation on the functional behavior of a particular type of magnetorheological gels under dynamic and static shear conditions in the presence of a magnetic field is studied. MR gels are prepared with micron sized polarizable carbonyl iron particles interspersed in a polymer matrix gel. The compliance of this magnetic gel can be varied under the influence of an external magnetic field. Since dynamical mechanical analysis tests are difficult to conduct in the presence of large deformations of the order of 50% and strong magnetic fields, a free decay test apparatus is designed and fabricated for obtaining the magnetic field dependent shearing response under dynamic conditions at room temperature. It is observed that a significant change in the elastic modulus occurs in the gels under a magnetic field in the range of 0.1--0.4 T. However, no significant change in the damping ratio is observed under various magnitudes of magnetic field. It is shown that the increase in shear modulus of this kind of magnetic composite gel could be as high as 59% of the zero field value for a gel prepared with 50% by weight of carbonyl iron particles.