Experimental Characterization of Tunable Visco Elastic Properties of Isotropic Magnetorheological Gels Subjected to Combined Magnetic and Compressive Loads

Controlling the stiffness and natural frequency of the foundation consisting of magnetorheological (MR) gel isolation can help the structure to survive the earthquake. MR gel stiffness can be varied by changing the magnetic field applied. MR gels placed in between the foundation and the super structure can isolate the structure from vibrations of the earth caused by earthquake by limiting the transfer of shear across the isolation medium thereby providing safety to human beings and their belongings. The matrix material is a polymer that belongs to the group of viscoelastic materials. Since these materials are used in dynamic or vibration control applications, their viscous properties are important to be characterized. Though standard equipment are available for characterizing polymeric materials, applying the magnetic field is not straightforward and inclusion of the set up related to applying the magnetic fields becomes quite expensive. In order to be able to accomplish this, a simple model that predicts the stiffness of the gel isolator under different magneto-mechanical loading conditions is needed. The model parameters that best suit the tests conducted on different conditions have to be evaluated. The intention of the present work is to determine these parameters of a typical MR gel and to determine the change in material properties of MR gels with respect to magnetic field and compressive load acting separately and together. The results from the experimental work prove that stiffness of MR gels can be significantly altered by modifying compressive loads as well as the magnetic field. Also, a magnetic shape retaining ability is observed because of which changing the order of application of loads (magnetic/compressive) produces significantly different responses.