Giant magnetostrictive composites (GMCs).

摘要

The limitation of magnetostrictive composites has been in their low magnetostrictive response when compared to their monolithic counterparts. In this dissertation research is presented describing the methods and analysis used to create a giant magnetostrictive composite (GMC) producing giant strains at low fields, exhibiting magnetization "jumping" and the DeltaE effect. This composite combines the giant magnetostrictive material, Terfenol-D (Tb0.3Dy0.7Fe2) in particle form, with a nonmetallic binder and is capable of producing strains (at room temperature) exceeding 1000 ppm at a nominal field of 1.5 kOe mechanically unloaded and 1200 ppm at 8 MPa preload (2.5 kOe).; Several studies leading to the high response of this composite are presented. A connectivity study shows that a [1--3] connected composite produces 50% more strain than a [0--3] composite. A resin study indicates that the lower the viscosity of the resin, the greater the magnetostrictive response; this is attributed to the removal of voids during degassing. A void study correlates the increase in voids to the decrease in strain response. A model is used to correlate analysis with experimental results within 10% accuracy and shows that an optimal volume fraction exists based on the properties of the binder. Using a Polyscience Spurr low-viscosity (60 cps) binder this volume fraction is nominally 20%; this optimum is attributed to the balance of epoxy contracting on the particle (built-in preload) and the actuation delivered by the magnetostrictive material. In addition to the connectivity, resin, void, and volume-fraction study, particle size and gradation studies are presented.; Widely dispersed (106, 212, 300 mum), narrowly dispersed (45, (90--106), (275--300) mum), and an optimized bimodal (18.7% of (45--90) mum with 81.3% of (250--300) mum) particle distributions are studied. Results show that the larger the particle size, the higher the magnetostrictive response; this is attributed to the reduction of demagnetizing effects. Results also show that the wider the distribution, the higher the magnetostrictive response and is attributed to the increase in packing density. Using a bimodal optimized distribution, both large particle response as well as superior packing is achieved resulting in a material that produces the largest magnetostriction reported for low fields.