ABSTRACT

Shape memory is found in all kind of materials and is caused by very different phenomena. The best known and most used kind of shape memory materials (SMMs) are the shape memory alloys (SMAs), like Nitinol®, a nickel-titanium alloy. The SMAs recover their original shape through a reversible phase transformation between an austenitic and a martensitic crystal structure. Some ceramics also display shape memory properties, although the deformation possibilities remain limited. While SMPs have very promising characteristics compared to other SMMs, particularly their low density and high deformability, they have a few downsides. The first and largest problem with SMPs is their low mechanical properties (strength and stiffness) and the small forces they develop during recovery. SMPs generally exhibit slow recovery; the recovery can take up to a few minutes. Due to the low thermal conductivity of the SMPs, it can take quite a while before the bulk of polymer is above the transformation temperature to recover its original shape.