Comparison of thermomechanical models for shape memory alloy springs

There are relatively few applications of Shape Memory Alloys (SMA) in comparison with their potential and the large amount of patents concerned with these properties. This can be partly explained by the lack of design tools able to dimension correctly SMA devices. Many studies were conducted to describe the SMA behavior, but very few works have been done considering mechanical elements, where the stress distribution is in many cases non-homogeneous, even if a great part of experimental study is made on structures such as coils or bending beams. In this paper, two methods of SMA structure calculation are featured. They are applied here to helical springs. The theoretical results obtained with these methods are compared with experimental data of a Ni-Ti SMA spring submitted to a thermomechanical loading. Superthermoelastic response is predicted from superelastic experimental data.