Development of pre-magnetized magnetorheological elastomer for bidirectionally variable stiffness applications

Magnetorheological elastomers (MREs) are materials that leverage magnetic forces among ferromagnetic particles to induce variable stiffness and damping under external magnetic fields. However, conventional MREs have limitations in achieving reduced stiffness when exposed to an external magnetic field. In response to the need for rapid and bidirectional changes in stiffness, this research proposes a novel approach—pre-magnetized MREs—using permanently magnetized ferromagnetic particles instead of an external permanent magnet for magnetic bias. The pre-magnetized MRE, fabricated with silica-coated neodymium alloy particles and silicone elastomer, undergoes a comprehensive investigation of design parameters, including silicone resin selection, particle thickness, size, and weight ratio. The study explores the directional effects of pre-magnetization through simulations, considering forces among magnetized particles and the hyperelasticity of the elastomer. Experimental investigations involve measuring shear moduli for different shear strains under varying magnetization directions. The results highlight the impact of resin type, particle size, and weight ratio on the magnetorheological (MR) effect. Additionally, an application testbed is developed to assess bi-directional changes in stiffness for various core materials. The study reveals a correlation between MR effect/response time and the magnetic permeabilities of core materials, along with the attraction and repulsion forces between the core and magnetized particles. Observations indicate that the MR effect for different core materials ranges from 0.08% to 0.25%, with response times measured at 40 and 46 ms for forward and reverse currents, respectively. The findings contribute valuable insights into optimizing the design and performance of pre-magnetized MREs for enhanced bi-directional stiffness control in engineering applications.