Compensation of Magnetic Force of an Electromagnet for Compression Mode Characterization of Magnetorheological Elastomers

Compression mode characterizations of magnetorheological elastomers (MREs) involve challenges associated with compensating for the magnetic force generated by electromagnets. Different series of magnetic force and flux measurements were performed in order to establish a general systematic methodology for compensating for the magnetic force. In this regard, an optimal design of a UI-shaped electromagnet was realized to facilitate measurements of the force under controlled magnetic flux density up to 1 T. Results revealed notable phase and magnitude differences between the measured static and dynamic magnetic forces, which are found to be mainly dependent on magnetic flux density and frequency. A simple and powerful compensation model was proposed to accurately predict the magnetic force for the entire range of flux density and excitation conditions considered. The proposed model is experimentally validated, and then employed to identify viscoelastic force of an isotropic MRE. Results revealed maximum errors in equivalent stiffness and damping constants of the MRE in the orders of 90% and 163%, respectively, without compensation. The proposed methodology provides a framework for accurate characterization of MREs in the compression mode.