Magnetostrictive Composite Material Systems Analytical/Experimental
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fMechanical and Aerospace Engineering Department, University of California, Los Angeles, California 90095-1597 [email protected] ttHughes Space and Communications Company, Los Angeles, California 90030-9009, Post Office Box 92919 [email protected] tttMechanical and Aerospace Engineering Department, University of California, Los Angeles, California 90095-1597 [email protected]
ABSTRACT Experimental and theoretical results are presented for a composite magnetostrictive material system. This material system contains Terfenol-D particles blended with a binder resin and cured in the presence of a magnetic field to form a 1-3 composite. Test data indicates that the magnetostrictive material can be preloaded in-situ with the binder matrix resulting in orientation of domains that facilitate strain responses comparable to monolithic Terfenol-D. Two constitutive equations for the monolithic material are described and a concentric cylinders model is used to predict the response of the composite structure. Experimental data obtained from the composite systems coincide with the analytical models within 10%. Particle size, resin system, and volume fraction are shown to significantly influence the response of the fabricated composite system. INTRODUCTION In the early 1960's scientists discovered that certain rare earth elements-i.e., terbium (Th) and dysprosium (Dy)--exhibited giant magnetostriction effects on the order of 10,000 microstrain [1, 2]. These large effects, however, were only present in these rare earth materials at cryogenic temperatures. A decade later notable magnetostriction effects at room temperature as high as 2000 microstrains were discovered by combining Th and Dy with magnetic transition materials [3]. Research on these magnetostrictive materials, like Terfenol-D, shows that they provide several advantages over their electro-mechanical counterparts including larger strains (in some instances) as well as freedom from depoling
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Mat. Res. Soc. Symp. Proc. Vol. 459 01997 Materials Research Society
effects and breakdown strengths. These advantages have led investigators to explore the benefits of using magnetostrictive materials in various engineering structures, for example, using Terfenol-D in active control flaps for reducing the vibrations on a rotorcraft system [4]. While investigators are exploring applications for Terfenol-D, engineering models are still predominantly based on linear piezomagnetic behavior [5]; these linear models neglect critical coupling terms which must be considered to develop accurate predictive capabilities required in structural applications-including the effect of preload (prestress), magnetic field intensity, and temperature on the mechanical response as indicated by Clark [6]. Brown [7] describes constitutive approaches for magnetostrictive materials that include magnetic body moment coupling. Carman [81 uses a higher-order series expansion in thermodynamic relations to account for specific nonlinear coupling effects while Kannan and Dasgupta [9] suggest using
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