Thermo-Mechanical Characterization Of NiTiCu Shape Memory Alloy Under Tension, Compression And Torsion Loading Conditions

NiTiCu alloys are one of the foremost investigated shape memory alloys (SMA) because of its better performance as SMA actuators. Its advantages in front of other SMA are: lower functional fatigue, higher deformation recovery, higher transformation temperatures stability and lower hysteresis range.  Despite these advantages NiTiCu is strongly influenced by thermomechanical cycling (TMC), which generates a degradation that depends on the load and the deformation applied.

In order to characterize SMA behaviour, uniaxial tests (at constant stress with thermal cycling or isothermal tests at a certain strain level) are the more common ones to identify the degradation that a SMA suffers with TMC. These tests provide high-valuable information that allows the simplest modelization of the thermomechanical response of these materials. However, they do not provide complete information to characterize the complex behaviour of the majority of the SMA actuators because they work in different conditions than tension loads.

In this work, a complete characterization of a NiTiCu alloy (wire and tube specimens) has been done via tension, compression and torsion tests conditions. Torsion tests were done in a special home-made equipment and tube specimens were instrumented with stacked strain gauges rosettes, which permit to identify the fully strain tensor.