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Proceedings Paper

Transverse acoustic actuation of Ni-Mn-Ga single crystals
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Paper Abstract

This paper describes a novel approach for the actuation of a Ni-Mn-Ga single crystal in the martensite phase using transverse acoustic waves. The acoustic waves, generated by piezoelectric stacks, produce shear stress levels high enough to induce twin boundary motion in the Ni-Mn-Ga crystal. By using repeated asymmetric pulses, the crystal can be made to transform reversibly from one of two variants to the other. The resulting engineering shear strain as the crystal transforms is theoretically as high as 12%. Two experimental apparatuses were developed that are able to produce actuation through this acoustic mechanism. In the first, two 33-mode piezoelectric stacks are mounted at a 45 deg angle to the base of a single Ni-Mn-Ga crystal. This geometry allows the longitudinal motion of each stack to be converted into transverse motion of the Ni-Mn-Ga crystal. In experiments using this apparatus, we were able to obtain 7.7% engineering shear strain over the length of the Ni-Mn-Ga crystal, and about 10.6% engineering shear strain over that portion of the crystal that exhibited twin boundary motion, close to the theoretical maximum. Some portions of the crystal appeared to be inactive, due to locking of incompatible twin systems. In the second apparatus, a single 15-mode piezoelectric stack was used to generate shear waves directly. In preliminary testing, we were able to achieve only about 1.9% engineering shear strain, probably due to incomplete conditioning of the Ni-Mn-Ga crystal to improve twin boundary motion.

Paper Details

Date Published: 6 April 2006
PDF: 12 pages
Proc. SPIE 6170, Smart Structures and Materials 2006: Active Materials: Behavior and Mechanics, 61702D (6 April 2006); doi: 10.1117/12.658957
Show Author Affiliations
Jesse M. Simon, Massachusetts Institute of Technology (United States)
Steven R. Hall, Massachusetts Institute of Technology (United States)


Published in SPIE Proceedings Vol. 6170:
Smart Structures and Materials 2006: Active Materials: Behavior and Mechanics
William D. Armstrong, Editor(s)

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