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Free decay test in Shear mode, Magnetorheological gel / elastomer, vibration control, damping applications

This paper presents the development of a simple free decay test apparatus that can be a cost effective alternative to the popular expensive dynamical mechanical analyzers useful for characterization of the dynamic characteristics of soft magnetic composite gels in the presence of variable magnetic field. This apparatus also addresses the common difficulty faced in dynamical mechanical analyzers to conduct the characteristics of deformation dependent mechanical characteristics especially for large deformations, sometimes to the order of 100% that may be necessary for highly compliant polymeric materials. In addition, this apparatus can easily be fitted or modified to facilitate the application of magnetic field. The apparatus is designed to test thin sheet specimens of the magnetic gels in the shear mode at room temperature. As an example, magnetic composite gels prepared with micron sized polarizable particles (carbonyl iron particles) interspersed in a polymer matrix gel are used to show the effectiveness of the apparatus. The compliance of this magnetic gel can be varied under the influence of an external magnetic field. Deviations from the linear material behavior can be captured using the appropriate equations that relate the linear assumptions made. Such deviations can then be used in determining the large deformation dependent characteristics of the gel specimen. Thus, it is demonstrated that the apparatus is a cost effective and useful tool for purposes of testing soft and compliant magnetic composite gels used for damping applications.