Impact Damping in NiMnGa/Polymer Composites

Abstract

Impact damping of Ni–Mn–Ga ferromagnetic shape memory alloy/polyurethane composites was studied by instrumented impact tests. By polymerizing the composite under a magnetic field, the martensitic Ni–Mn–Ga particles were spatially aligned in chains parallel to the field direction with the preferable crystallographic orientation of the martensitic twin variants. The rectangular prismatic samples with faces cut parallel and perpendicular to the particles chains in these composites appeared to be highly mechanically and magnetically anisotropic. The samples impacted parallel to the particles chains, have shown a considerably bigger damping capacity than the matrix material. The tests have also shown that the impact behavior is different for the first impact than for the consecutive ones. This is attributed to the stress-induced movement of the twin boundaries resulting in twin variant conversion. A corresponding rotation of the magnetic anisotropy of the samples is confirmed by measuring the magnetization curves.