Shape memory materials

Materials which may be randomly deformed and then return to a predefined geometry following an external stimulus are termed "shape memory" materials. Most examples are thermally controlled and include shape memory allows (SMA) and shape memory polymers (SMP). The latter are often in foam form thus allowing a three dimensional shape memory geometry. The basic principle of the two are however completely different. SMAs may be cold deformed in the martensitic state on on heating (austenitic) return to their original shape. For a shape memory polyer, it is the glass transition temperature of the materials which determines the state. SMA are mechanically harder when hot whereas SMP are softer at elevated temperatures.

Magnetoactive elastomers MAE also have magnetic shape memory properties. The advantage of MAEs lies in the lack of continuous energy consumption in cases where the field is generated by permanent magnets