Fabrication of biased-magnetorheological elastomers (B-MRE) based on magnetized ferromagnetic particles

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Magnetorheological elastomers (MREs), like MR fluids, exploit magnetic forces between ferromagnetic particles to produce a material with instantaneously adjustable properties of stiffness and damping with external magnetic fields. In MREs, the particles are a part of a structured elastomer matrix, and an external magnetic field is applied to achieve an instantaneous change of stiffness due to magnetic forces between particles. A drawback of conventional MREs is its inability of softening (reduce stiffness) under an external field. Many engineering applications need an instant change of its stiffness in both directions, which requires a magnetic bias embedded in the MRE. One way is the use of a permanent magnet (PM) for pre-straining a base elastomer matrix, but its mechanical design can be bulky due to the size of PM. In this paper, we address a fabrication process of the biased-magnetorheological elastomers (B-MREs) and their mechanical properties. The B-MREs consist of magnetized ferromagnetic particles as fillers and an elastomer as a binder. The magnetization of ferromagnetic particles embedded in the elastomer matrix eliminates a need for the use of the PM and can achieve the desired pre-strain in the B-MRE. The experiment results related with the mechanical properties after magnetization were presented. Also, different MRE thickness and weight ratios of the ferromagnetic particles mixed with the base elastomer were compared in both normal and shear modes.