Magnetorheological (MR) materials are intriguing smart materials that transform their physical characteristics in response to external magnetic fields. While MR fluids (MRFs)
are often in the spotlight due to their rapid response and field-dependent yield strength and
apparent viscosity, they grapple with issues like magnetic particle deposition and settling as well as leakage in MRF based devices. On the other hand, magnetorheological elastomers (MREs) are versatile, magnetically responsive composite materials with rubber-like qualities. By blending magnetic particles into nonmagnetic elastomeric matrices, MREs demonstrate field-dependent viscoelastic properties, such as a customizable field-dependent modulus which can not be achieved using MRFs. MREs can instantly revert to their original state when the magnetic field is withdrawn, showcasing a fascinating interplay of magnetism and material science. MREs fall into two distinct categories depending on their curing process; those formed without the influence of a magnetic field, creating isotropic MREs, and those shaped under the application of a magnetic field, yielding anisotropic MREs.
During the recent decades, the advent of finite element (FE) modeling has provided considerable benefits, by reducing the financial and time expenses forced by experimental procedures. Alongside with providing substantial accuracy, its ability to conduct parametric studies with multiple systematic parameter adjustments, ensuring greater reproducibility while simultaneously reducing the environmental impact by minimizing resource consumption and waste production are among its significant benefits. As a finite element approach, the concept of Representative Volume Element (RVE) enables predicting the material’s macroscopic behaviour from microscale modeling.
This research thesis aims at modeling the MREs’ shear behaviour under the influence of magnetic field, using the RVE concept as the modeling scheme. For this purpose, MREs with different elastomeric host matrix including silicone rubber Ecoflex 30 and Ecoflex 50 have been considered. The stress-strain characteristic of these pure silicon rubbers was first evaluated experimentally using available tensile test machine. The experimental data was then used to identify the constant parameters of the Ogden strain energy function using the least-square minimization technique. The optimized Ogden strain energy function is subsequently used in the finite element model to characterize the matrix behavior of the MREs. These, along with the mechanical and magnetic properties of Carbonyl Iron Particle (CIP), used as magnetic particles in MREs, were integrated into COMSOL Multiphysics to develop the RVE for the MREs, integrating properties of the matrix with magnetic particles. The RVE was generated in 2D and 3D configurations, for CIP volume fraction varying from 5% to 40%. Periodic Boundary Condition (PBC) was imposed on the RVE boundaries, while undergoing pure shear deformation. The results of 2D modeling suggest its ability to predict the shear deformation behaviour of isotropic MRE-RVE under varied external magnetic field. The maximum difference between theoretical and experimental shear modulus under varied magnetic field was found to be ±20%, however, the 2D model was not able to predict the MR effect at saturation with acceptable accuracy. The results from 3D modeling of isotropic MRE-RVE show a reasonably good agreement with the experiment data, with the error generally in the range of 1%- 4% for magnetic flux densities up to 0.4T. The results also suggest that the MRE-RVE with the softer silicone rubber matrix (Ecoflex 30) provides substantially higher MR effect compared with the MRE-RVE based on Ecoflex 50. Moreover, 3D isotropic MRE-RVE predicts the influence of CIP volume fraction on the shear behaviour and MR effect of MREs, comparable to experiments. All in all, the developed 3D isotropic MRE-RVE has shown the potential to accurately predict the field-dependent macroscopic mechanical properties of different MREs and thus can be used effectively to design MREs with enhanced properties without expensive experimental tests.