Cyclic actuation of Ni-Mn-Ga composites

Planar (2-2) and fibular (1-3) composites were fabricated by embedding single crystal Ni49.9Mn29.1Ga21.0 in a polyurethane resin. Magnetic and mechanical testing was performed on all samples. Mechanical testing showed the twin boundary yield stress to be 1.0 and 0.3 MPa for the monolithic and composites, respectively. Magnetic testing was performed to determine the magnetic field induced strain as a function of increasing compressive preloads (from 0 to 2.0 MPa). Actuation strains without an external preload are 4.9% for the monolithic and 1.0% for the composite samples. The composite samples show considerable cyclic strain without the application of a compressive loading, unlike the monolithic material. A rule of mixture model is presented to predict the strain output of the composite samples under a magnetic field and explain the reduced twin boundary yield stress. (C) 2006 American Institute of Physics.