Abstract
Composites of Ni–Mn–Ga particles in a polyurethane matrix can be made by mixing the particles with the polymer, and allowing them to cure under a magnetic field to texture the composites. These composites show large hysteresis and mechanical losses, when subjected to a cyclic stress, that were far larger than the matrix polymer ones. The additional losses are attributed to the motion of twin boundaries in the filler particles and provide a way for obtaining mechanical energy absorption in a wide frequency range. By means of X-ray and neutron diffraction we present evidence that confirms that twins are present in the particles and that they do move when mechanically loading the composite
Highlights
Ferromagnetic shape memory alloys (FSMAs) are a kind of active materials that exhibit large plastic deformations due to mechanical stress or magnetic field induced twin boundary motion
Curing the polyurethane/FSMA slurry under a field yielded pseudo 3:1 composites that have the appropriate crystallographic texture for the twin boundaries in the particles within the composites to respond to a stress applied to them along the direction of the magnetic field used while curing the composites
The vibrating sample magnetometer measurements (VSM) measurements showed that the particles used to make the composites were successfully preconditioned to obtain mostly a single variant state
Summary
Ferromagnetic shape memory alloys (FSMAs) are a kind of active materials that exhibit large plastic deformations due to mechanical stress or magnetic field induced twin boundary motion. They are attractive because they combine the large strains associated with conventional shape memory alloys (SMAs) and bandwidth approaching that of magnetostrictive or piezoelectric materials. For off-stoichiometric, tetragonal NiMnGa a 6% strain has commonly been reported in the literature [1] and strains of up to 10% have been reported in the orthorhombic phase [2] These strains are comparable to the strains achieved in NiTi, one of the most widely used SMAs [3]. Plastic deformation has been studied as a damping mechanism because it can
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