Theoretical and experimental efficiency of the conversion of heat into mechanical energy using shape‐memeory alloys

The efficiency of the conversion of heat into mechanical energy of shape‐memory alloys has been obtained from experimental data and compared with the theoretical efficiency. Using a specially constructed torsion apparatus, the work produced by both the one‐way and two‐way‐memory effects was measured. The theoretical efficiency was computed from the heat capacity and the enthalpy of the martensitic transformation, obtained from the same alloys by calorimetry. For NiTi based alloys a theoretical efficiency of up to 13% was found compared with 1–6% from measurements, depending on how the work was computed. For CuZnAl based alloys a theoretical efficiency of 3.4% was found, compared with 0–3% from measurements. The lower measured efficiencies are explained in terms of a nonideal martensitic transformation associated with the shape‐memory effect.