Shape memory heat engines

Abstract

The mechanical shape memory effect associated with a thermoelastic martensitic transformation can be used to convert heat directly into mechanical work. Laboratory simulation of two types of heat engine cycles (Stirling and Ericsson) has been performed to measure the amount of work available per cycle in a Ni-45 at% Ti alloy. Tensile deformations at ambient temperature induced martensite, while a subsequent increase in temperature, caused a reversion to the parent phase during which a load was carried through the strain recovery, i.e. work was accomplished. The amount of heat necessary to carry the engines through a cycle was estimated from calorimeter measurements and the work performed per cycle. The measured efficiency of the system tested reached a maximum of 1.4% which was well below the theoretical (Carnot) maximum efficiency of 35.6%.