Vibration damping in Ni-Mn-Ga-polymer composites

Abstract

Martensitic Ni-Mn-Ga single crystals evidence twin boundaries that can be displaced by applying a mechanical stress. Twin boundary motion is a form of plastic deformation. Thus, Ni-Mn-Ga alloys are very good candidates for passive vibration damping, because relatively large amounts of energy can be dissipated in this way. However, research in to the damping properties of this material has been limited for several reasons. Twin boundaries only occur in specific crystal directions, limiting the performance of polycrystals in energy absorption. Single crystals of these alloys are difficult to grow, making them impractical for large-scale commercial applications. Single crystals are also brittle and tend to crack under tension. By orienting small particles of Ni-Mn-Ga in a polymer matrix these problems are ameliorated. Polymer composites respond better to tensile stresses than do the single crystals as has been shown for terfenol composites. Further, martensitic Ni-Mn-Ga has a strong magnetic anisotropy, so in the martensitic state the magnetic moment is strongly coupled to the c-axis. This allows the particles to be oriented in the polymer matrix as it is cured. Here we describe the effects of Ni-Mn-Ga alloy composition, the fraction of alloy in the matrix, and the particle size on the vibration damping capacity of the composite. The relation between the stress and strain in the composite under dynamic conditions is reported, as well as the variability of the loss tangent as a function of frequency for several composites.