Large magnetostrictive response of Terfenol-D resin composites (invited)

In this article we present results for magnetostrictive composites containi ng between 10% and 50% Terfenol-D (Tb0.3Dy0.7Fe2) in a nonmetallic binder. The composite consists of aligned Terfenol-D particles representative of a [1-3] fiber composite. For this study we measure the modulus of elasticity and other pertinent magnetostrictive properties. The measured stiffness val ues fall between the upper and lower bounds predicted by a rule of mixtures approximation. The magnetostriction for the composites rival that of the m onolithic at comparable magnetic field levels. A mechanically unloaded 20% volume fraction composite produces 900 ppm and a 30% volume fraction compos ite preloaded with 8 MPa produces 1000 ppm. Contrary to the belief that the greater the magnetostrictive particulate volume, the greater magnetostrict ive properties-this study shows that there is an optimal balance of epoxy a nd magnetostrictive material that will maximize magnetostriction for a mech anically unloaded specimen. For the matrix chosen in this study, the optima l volume fraction is near 20%. (C) 2000 American Institute of Physics. [S00 21-8979(00)20408-8].