Cyclic Tensile Tests and Mechanical Property Degradation Analysis on NiTi Shape Memory Alloy Bars

Structures can obtain good self-centering performance by using superelastic NiTi alloy bars. However， due to the mechanical property degradation of NiTi alloy bars， the self-centering and energy dissipation capacity of the structure will be degraded. Therefore， it is necessary to further study the mechanical property stability of NiTi shape memory alloy bars. In this paper， the constant amplitude cyclic tensile tests were carried out on four Ti-50.8%Ni bars after different heat treatments. The effects of the number of cycles and heat treatment conditions on the hysteresis curve morphology， phase transition stress， elastic modulus， residual strain， and energy dissipation capacity of these bars were studied. The degradation of mechanical properties of different bar specimens was compared and analyzed according to the test results. The results showed that the elastic modulus and ultimate stress of NiTi alloy bars changed little in constant amplitude cyclic tensile tests， while the phase transition stress， deformation recovery rate， and equivalent damping ratio degraded significantly. The positive phase transition stress of martensite exhibited a greater reduction compared to the inverse phase transition stress， and the stress degradation of the NiTi alloy bars with better superelasticity was more obvious. Furthermore， both excessively high and low heat treatment temperatures led to superelastic deterioration of NiTi alloy bars， and their energy dissipation capacity was greatly reduced under cyclic loading.