An experimental approach to the thermomechanical characterization of a NiTiCu shape memory alloy using strain gauges

In this work, a characterization of a NiTiCu (Ti44.6Ni5Cu (at.%)) shape memory alloy (tube specimens) has been done via tension, compression and torsion tests conditions. Torsion tests were done in a special homemade equipment, which is based on an instrumented dividing head with a specifically designed thermal chamber. This configuration is able to measure torque and twist angle with isothermal tests at different temperatures as well as to apply thermal cycles with a fixed twist angle. Moreover, tube specimens were instrumented with stacked strain gauges rosettes in order to obtain the strain tensor. Strain gauges were also used to calibrate the equipment and to identify the real stress state in torsion tests. The results have shown differences between the shear modulus measured on torsion tests and the shear modulus calculated from the measurements at tension and compression tests due to the tension/compression asymmetry and a non-constant strain ratio value. Thermal cycling tests at different values of fixed twist angles not only have led to characterize the evolution of torque as a function of the temperature but also to understand the different interacting mechanisms in torsion tests.