Award Date

August 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

Woosoon Yim

Second Committee Member

Kwang Kim

Third Committee Member

Mohamed Trabia

Fourth Committee Member

Jaeyun Moon

Fifth Committee Member

Sahjendra Singh

Number of Pages

126

Abstract

Magnetorheological elastomers (MREs) utilize magnetic forces between ferromagnetic particles to cause variable stiffness properties and damping with external magnetic fields. In the MREs, the particles are embedded in a cured elastomer matrix, and an external magnetic field makes the stiffness change due to induced magnetic forces among particles. A disadvantage of the conventional MREs is that they cannot be softened (reduced stiffness) under an external magnetic field. Considering that there are many engineering applications where fast changes of stiffness in both directions (stiffening and softening) are required, embedding magnetically biased particles in the MRE can provide potential solutions. In this research, a pre-magnetized MRE is proposed using permanently magnetized ferromagnetic particles instead of the external permanent magnet for the magnetic bias. The pre-magnetized MRE was fabricated with silica-coated neodymium alloy particles and silicone elastomer. In this work, various parameters in the design and fabrication of the pre-magnetized MRE are studied to improve the MR effect. The design parameters include silicon resin selection (Ecoflex 00-30 and 00-50), thickness, sizes of the neodymium alloy particles, and the weight ratio of the particles. MR effects by the direction of the pre-magnetizations were also studied. Simulations were performed to predict MR effect by the material variables. The simulations used forces among the magnetized particles and the hyperelasticity of the elastomer. In the experiment, shear moduli were measured for different shear strains under different magnetization directions, and their associated MR effects were compared. It has been found that the resin type, size, and weight ratio of ferromagnetic particles affect the MR effect. The application testbed with the pre-magnetized MRE has been developed, and various types of core materials were tested experimentally for effective bi-directional changes of their stiffness. The MR effects and corresponding response times of the applications were studied and compared. According to the results, the MR effect and its response time are also related to the magnetic permeabilities of the core materials in addition to the attraction and repulsion forces between the core and magnetized particles. The MR effects for different core materials were observed to be approximately 0.08~0.25%. The response times of the applications were found by measuring a rise time of the MR effect for the step input are 40ms and 46 ms each by forward and reverse currents in the coil.

Keywords

Bi-directional stiffness change; Magnetorheological elastomer; Pre-magnetized magnetorheological elastomer; Variable stiffness application

Disciplines

Mechanical Engineering

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/


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