Abstract
This study evaluated the validity of a new testing method that was proposed by Bastola et al. [1] to determine a simplified process for experimentally obtaining the magnetic permeability of magnetorheological elastomers (MRE). The methodology for obtaining these values is referred to as Magnetic Circuit Analysis, in which a closed electromagnetic circuit is built from an iron core with two air gaps—one for a MRE sample, and another for a Gaussmeter probe that records changes to the circuit’s magnetic induction. An analysis was made on thirty-six isotropic, silicone rubber MREs containing different volume fractions of carbonyl iron powder (CIP) from 0 to 30%. The results were compared with theoretical values obtained from two different mixing rule models used for composites, known as the Maxwell-Garnett and Bruggeman models. It was determined that the method was effective if placement of the probe was near the inside edge of the air gap; however, there were some important parameters that were found and documented in this report. A non-magnetic mount should be made to create a specific and constant height of the air gap. The iron core should have a high saturation limit and a large induction factor—as such it can apply a larger electromagnetic force through the air gap which squeezes the sample down to the specified height of the mount—this is ideal in that it relaxes the tolerances in making uniformly thick MRE samples. Also, the MRE samples cross-sectional area should be larger than the cross-sectional area of the iron core to ensure the sample is uniformly distributed over the magnetic field of the iron core. Additionally, the electromagnetic circuit should be tested beforehand to determine the iron core’s nonlinear regions—these nonlinear regions should be avoided when performing the magnetic circuit analysis. Lastly, the probe should be rigidly mounted.