Abstract

Magnetorheological elastomers (MREs) are smart materials whose viscoelastic properties can be varied upon the application of an external magnetic field. They are solid analogue of well-known MR fluids (MRFs) in which magnetic particles are embedded in a non-magnetic elastomer matrix instead of carrier fluids. Compared with their fluid counterparts, MREs do not have problems associated with particles' sedimentation, stability and leakage often encountered in MRFs. Besides in contrast to MRF-based adaptive devices, MRE-based systems can provide field dependent variable stiffness and damping simultaneously due to viscoelastic properties of MREs. This unique behaviour of MREs enable them to be effectively utilized in the development of adaptive isolators or absorbers to supress vibrations in wide range of frequencies. The present research study aims to provide a comprehensive investigation of the material characterization and phenomenological modelling of MREs under varying dynamic loading conditions, design and development of a novel vibration and shock isolator featuring magnetorheological elastomers, design optimization of the proposed isolator to enhance its dynamic range and finally design and implementation of semi-active control strategies to mitigate vibration and shock under different external disturbances.
MREs with a 25% volume fraction of soft magnetic particles (carbonyl iron) were used to investigate variation of storage and loss moduli of MRE under varied frequencies, strain amplitudes, and magnetic field densities. Considering operation of MREs in the linear range, field dependent linear viscoelastic models based on the Kelvin–Voigt, Maxwell, Standard Linear Solid, and Generalized Maxwell models, were formulated to predict the variation of storage and loss moduli under varying driving frequency and applied magnetic flux densities. The performance of these models to capture the response behaviour of MREs under different applied frequencies and magnetic field were subsequently compared.
A semi-active MRE-based vibration isolator operating under shear mode with embedded electromagnet was then proposed. Analytical magneto-static model of the magnetic circuit of the proposed adaptive isolator was first formulated using Ampere’s law to estimate the induced magnetic flux density in the MRE region gaps versus applied current to the electromagnet. The validity of the analytical results was verified using the finite element magneto-static analysis. A multidisciplinary design optimization problem was subsequently formulated to optimize the isolator geometrical parameters as design variables to maximize its frequency bandwidth under weight, material magnetic saturation, and total volume constraints. A hybrid approach based on combination of Genetic Algorithm (GA) and gradient based Sequential Quadratic Programming (SQP) was used to accurately capture the global optimal solution for the optimization problem.
Finally, closed-loop control strategies, based on on-off sky-hook and PID, were implemented and compared to assess the capability of the proposed adaptive isolator to mitigate vibration and shock under different disturbances.