Smart materials find application in every field due to their properties that external stimuli can alter. Being one of the smart materials, Magnetorheological (MR) gels can modify their characteristics upon applying the external magnetic field. The magnetic controllability displays the effectiveness of the gels. The stiffness of these gels is tun- able under the influence of the magnetic field. This benefit allows MR gels to find application in the areas of vibration isolation, vibration control, and smart sensing. It is thus significant to study the dynamic characteristics of these gels experimentally.
To conduct the experimental study on the isotropic MR gels in the presence of the magnetic field, MR gels are fabricated by dispersing the iron filler particles. Here, two types of filler particles are used, such as magnetite (Fe3O4) nanoparticles and carbonyl iron (CI) microparticles of sizes 1.4 μm and 3.4 μm. The magnetite nanoparticles are synthesized by co-precipitation method and characterized by techniques such as Trans- mission Electron Microscopy (TEM), X-Ray Diffraction (XRD), and Vibration Sample Magnetometer (VSM), while the carbonyl iron particles are procured and characterized by VSM and Scanning Electron Microscopy (SEM). Once the MR gels are prepared with different weight percentages of filler particles, i. e., 5%, 10%, 15% and 20%, a free decay test apparatus built in-house is used to obtain the magnetic field dependent shear response of the gels under dynamic conditions at room temperature and the results are compared for varying sizes of particles. The free decay test setup is preferred over Dynamic Mechanical Analyzer (DMA) since it can accommodate the large deformations of the gels.
Further, in order to design and optimize the CI particulate MR gels, MR gels are prepared by dispersing CI microparticles of different volume percentages (10%, 20%, 30%) in a polymer gel. The effect of the magnetic field, constant stress level and the influence of the volume percentage of these microparticles on the creep response of the MR gels are investigated using the free decay test setup with few modifications in it. A simple three-parameter model is used to validate the experimental creep data. A microstructure-based model that captures the time-dependent viscoelastic behaviour is adopted and further extended to account for the surface interaction between the magnetic particles and the matrix to study the particle size effect on the properties of MR gels. The developed model is calibrated and validated using a set of experimental data. The results are compared for varying sizes of particles for different magnetic field strengths.