Materials Characterisation of NiTi and CuAlMn Shape Memory Alloy Bars Under Dynamic Bending

Copper-based shape memory alloy (SMA) is becoming a widely used material exhibiting comparable mechanical properties with NiTi SMA. This study presents the results form cyclic bending tests on both NiTi and copper superelastic SMA bars to assess the material characteristics. The tests were carried out on 7 mm diameter NiTi SMA bars and 12 mm diameter CuAlMn SMA bars of 125 mm in length, which were installed in a specific three-point bending rig. Dynamic bending tests with 1Hz loading rate were carried out on both NiTi and CuAlMn SMAs for 100 cycles at different strain levels (0.5%, 1%, 2% and 6%). The stress-strain curves, damping ratio, stiffness, and the evolution of these properties are presented. Overall, the damping capacity of CuAlMn is better than that of NiTi SMA while the secant stiffness of NiTi is higher, and the evolution along cyclic loading shows the stabilization. The NiTi SMA bars show higher phase transformation stress, the damping capacity increases nearly 10 times at 6% strain compared with at 1% strain which remains in its elastic deformation phase.