Investigation of dynamic properties of isotropic and anisotropic magnetorheological elastomers with a hybrid magnet shear test rig

Magnetorheological elastomers (MREs) exhibit instantaneous and reversible adaptability of stiffness and damping properties under the influence of magnetic field, which can be implemented in the development of controllable devices. The main MRE components are normally elastomeric matrix and magnetisable particles. Depending on the distribution of the particles in the matrix, MREs can be classified into isotropic and anisotropic. This work experimentally explored, compared, and modelled the dynamic characteristics of both isotropic and anisotropic MREs with different iron particle weight fractions (17%, 22%, and 32%). A novel shear test rig was designed with hybrid magnets system, i.e. permanent magnet and electromagnets, to fulfil the characterisation tasks. The involvement of the hybrid magnets effectively cuts down the maximum electric current and energy consumption of the rig. The tests were conducted under sinusoidal shear motions with excitation frequency ranging from 0.1 Hz to 2 Hz and shear strain varying from 20% to 60% to record the force-displacement hysteresis of MRE samples. Four different levels of magnetic field (0.02, 0.54, 0.77, 1.01 T) were supplied by the hybrid magnetic system and were considered in the tests to evaluate the influence of the magnetic fields. Furthermore, characterised hysteretic behaviours for both isotropic and anisotropic MRE were modelled by a strain stiffening phenomenological model with ideal accuracy under the shear excitation inputs and magnetic fields considered. (paper)