Abstract

Magnetoactive elastomers also known as Magnetorheological elastomers (MREs) are solid analogue of the well-known magnetorheological (MR) fluids. MREs are smart composite materials made of elastomeric medium embedded with micron-sized ferromagnetic particles. Unlike MR fluids which can mainly provide variable damping, MREs can provide simultaneous variations in damping as well as stiffness properties. Moreover, MREs do not exhibit limitation of MR fluids such as sedimentation of iron particles and leakage. Hard magnetorheological elastomers (H-MREs) are MREs in which the soft magnetic particles in conventional MREs are replaced by hard micron-sized permanent magnetic particles which provide magnetic poles inside the elastomeric medium. By applying the magnetic field in the same or opposite direction of the magnetic poles, respectively, the stiffness of the H-MREs can be increased or decreased. While conventional MREs have been widely studied during the past decade, very limited studies exist to demonstrate the response behavior of H-MREs. The objectives of the present research thesis are to 1- experimentally characterize the viscoelastic properties of H-MREs under varying operating conditions and applied magnetic field, 2- develop simple phenomenological models to predict the viscoelastic response behavior of MREs, 3- explore the potential application of H-MREs in an adaptive vibration isolator. For this purpose, H-MREs with 15% volume fraction of neodymium–iron–boron (NdFeB) magnetic particles have been fabricated and then tested under oscillatory shear motion using a rotational magneto-rheometer to investigate their viscoelastic behavior under varying excitation frequency and magnetic flux density. The influence of the shear strain amplitude and driving frequency are also examined under various levels of applied magnetic field ranging from -0.2 T to 1.0 T. Moreover, field-dependent phenomenological models have been proposed to predict the variation of storage and loss moduli of H-MREs under varying excitation frequency and applied magnetic flux density. The results show that the proposed model can accurately predict the viscoelastic behavior of H-MREs under various fields and operating conditions. Finally, a tunable vibration isolator based on H-MRE is developed and the influence of applying positive and negative magnetic fields on the transmissibility of the HMRE-based isolator is investigated.