Particle mixtures in magnetorheological elastomers (MREs) Paris R. von Lockette *a , Jennifer Kadlowec a , Jeong-Hoi Koo b a Rowan University, Glassboro, 201 Mulica Hill Rd, NJ 08028; b Miami University, 501 East High Street, Oxford, Ohio 45056 ABSTRACT Keywords: Magnetorheological elastomer, nanoparticle, tunable vibration absorber, polydimethysiloxane Magnetorheological elastomers (MREs) are state-of-the-art elastomagnetic composites comprised of magnetic particles embedded in an elastomer matrix. MREs offer enormous flexibility given that elastomers are easily molded, provide good durability, exhibit hyperelastic behavior, and can be tailored to provide desired mechanical and thermal characteristics. MRE composites combine the capabilities of traditional magnetostrictive materials with the properties of elastomers, creating a novel material capable of both highly responsive sensing and controlled actuation in real-time. This work investigates the response of MRE materials comprised of varying mixtures of 40 and 10 micron iron particles. Samples are tested in compression yielding a compressive modulus and measure of the shear stiffness via Mooney plots. Samples are also tested using a tunable vibration absorber (TVA) designed specifically for this experiment. The TVA loads the samples in oscillatory shear (10 – 100Hz) under the influence of a magnetic field. In all samples, results show increases in the material’s stiffness under the application of a magnetic field as evidenced by the frequency response function of the TVA system. Increases in stiffness of 50% at 0.15T were achieved with samples containing 30%-40 micron particles and 30%-40micron + 2%-10 micron particles. This yields a ratio of over 300%/T. The two-particle MRE appeared not to have reached saturation suggesting further stiffness enhancement was possible beyond the saturated single-particle 40 micron sample. However, this may be a result of the larger iron content. Results also suggest variation in the behavior of two- versus single-particle MRE behavior as evidenced by the shear modulus found in compression, but results are inconclusive. MRE materials made with nanoparticles of hard magnetic barium ferrite show stiffness increases of 70%/T which is comparable to MREs having larger iron particles. 1. INTRODUCTION Magnetorheological elastomers (or MREs), solid analogs of MR fluids (MRFs), are state-of-the-art elastomagnetic composites comprised of magnetic particles embedded in an elastomer matrix. A recently published definition of this class of materials states that MREs have the following characteristics: “…the particles have an asymmetric shape, preferably with a main anisotropy axis; the particles are soft ferromagnetic or small permanent magnets; and the composite has an elastic behavior, due to the matrix properties, up to a relative deformation of 10 -1 . 1 The study of MREs as a viable class of smart materials has gained increasing interest since they have recently exhibited large magnetorheological (or MR) effects in sample materials. 2 The MR effect, ∆E, is measured as the relative change in a material’s complex modulus when placed within a magnetic field, B, with respect to the modulus with no field present, e.g. 0 0 = = − = ∆ B B B E E E E (1) vonlockette@rowan.edu , 856 256 5341 , (fax) 856 256 5241 Please verify that (1) all pages are present, (2) all figures are acceptable, (3) all fonts and special characters are correct, and (4) all text and figures fit within the margin lines shown on this review document. Return to your MySPIE ToDo list and approve or disapprove this submission. 6170-30 V. 2 (p.1 of 13) / Color: No / Format: Letter / Date: 2/3/2006 10:58:26 AM SPIE USE: ____ DB Check, ____ Prod Check, Notes: