Investigating new symmetry classes in magnetorheological elastomers: cantilever bending behavior

Abstract

This work defines and examines four classes of magnetorheological elastomers (MREs) based upon permutations of particle alignment–magnetization pairs. Particle alignments may either be unaligned (e.g. random) or aligned. Particle magnetizations may either be soft-magnetic or hard-magnetic. Together, these designations yield four material types: A–S, U–S, A–H, and U–H. Traditional MREs comprise only the A–S and U–S classes. Samples made from 325-mesh iron and 40 µm barium hexaferrite powders cured with or without the presence of a magnetic field served as proxies for the four classes. Cantilever bending actuating tests measuring the magnetically-induced restoring force at the cantilever tip on 50 mm × 20 mm × 5 mm samples yielded ∼ 350 mN at μ0H = 0.09 T for classes A–H, A–S, and U–S while class U–H showed only ∼ 40 mN. Furthermore, while classes U–S and A–S exerted forces proportional to tip deflection, they exerted no force in the undeformed state whereas class A–H exerted a relatively constant tip force over its entire range of deformation. Beam theory calculations and models with elastic strain energy density coupled with demagnetizing effects in the magnetic energy density were used to ascertain the magnitude of the internal bending moment in the cantilever and to predict material response with good results. This work highlights the ability of the newly developed A–H MRE materials, and only that material class, to operate as remotely powered bidirectional actuators.