Dynamic characterization of isotropic and anisotropic magnetorheological elastomers in the oscillatory squeeze mode superimposed on large static pre-strain

Abstract

Characterization of magnetorheological elastomers (MREs) is a fundamental step toward designing MRE based devices for adaptive vibration control over wide frequency ranges. While the properties of MREs in the shear mode have been widely characterized, the squeeze mode properties of the MREs have been addressed in only a few studies due to many experiment design complexities. In this study, the dynamic properties of isotropic and anisotropic MREs were experimentally characterized in the compression mode under broad ranges of strain amplitude, excitation frequency and the magnetic field intensity superimposed on a large static pre-strain. The isotropic as well as anisotropic MREs samples with 30% volume fraction of iron-particles were fabricated. An electro-magnet was further designed and developed with minimal mass and field density capacity of 1T. An experimental set-up integrating the electro-magnet was designed for characterizing compression mode properties of the isotropic and anisotropic MRE samples. The experiments were designed to obtain force-deflection (stress-strain) characteristics of the samples subject to pre-strain (21%) and compression under broad ranges of strain amplitude (2.5–20%), excitation frequency (0.1–50 Hz), and magnetic flux density (0–750 mT). The measured data were analyzed to evaluate samples’ properties in terms of stress-strain characteristics, relative MR effect, storage moduli and loss factor as functions of the anisotropy, strain amplitude, strain rate and the magnetic field intensity considering the correction for the magnetic force generated between the poles of the electromagnet. Results revealed maximum increases in the storage moduli of the isotropic and anisotropic MRE specimens of 340.47% and 206.47%, respectively, which occurred under the low strain amplitude of 2.5% at frequencies of 10 and 30 Hz. The measured data obtained for 20% strain revealed maximum changes in the loss factors of 188.32% and 216.24% for the isotropic and anisotropic MREs, respectively, which occurred under excitation frequency of 0.1 Hz. The observed broad changes in the compression mode storage and loss moduli suggest unique potentials of MREs for vibration and noise control in load-bearing type applications.