Cyclic Behaviors under Thermal and Loading-unloading Conditions in TiNiCu Shape Memory Alloy. Influence of Strains on Cyclic Behaviors under the Constant Heating and Cooling Temperature.

Abstract

Use of a heat engine of which the working elements consists of a shape memory alloy is a useful method for direct conversion of power from low grade heat. The authors have proposed a reciprocating heat engine using shape memory alloy wires. However, in order to undertake reliable engineering designs and optimum material selection, it is imperative that the cyclic behaviors of the shape memory alloy are well understood. In this paper, the cyclic behaviors of Ti-41.7 at% Ni-8.5 at% Cu are investigated experimentally. Experiments are carried out by repeating the combination of the thermal cycle and the loading-unloading cycle under the constant heating and cooling temperature. The results show that the transformation temperatures of Mf and As almost do not vary with the number of cycles, but Ms and Af temperatures increase gradually with cycles when the number of cycles is greater than about 500. It is also noted that two-way strain and irrecoverable strain increase proportionately with the increase in maximum strain. Furthermore, from results of deformation stress in the martensitic phase, the plastic deformation is recognized in the strain range of boyond 4%.