Low-cycle fatigue behavior of Cu-Al-Mn superelastic alloys at different temperatures

Superelastic alloy (SEA) bars are widely used in structures subjected to moderate and strong earthquakes. Compared with conventional nickel-titanium (NiTi) SEAs, Cu-Al-Mn (CAM) SEAs has received increasing attention recently due to their cost-effectiveness and easier machinability. The authors' previous research showed that despite their lower strength and limitations in the maximum length, the CAM SEAs have comparable superelastic strain recovery, a wider temperature range, and superior strain rate stability compared to NiTi SEAs. However, the previous research was limited to a few specimens and only conducted to a few hundred cycles without considering the full deterioration in the material properties. Besides, the existing research on CAM SEA was only limited to small sample sizes at room temperature, while the fatigue performance of large diameter CAM SEAs under low and high temperatures relevant for civil engineering structures has not been reported. To fill this knowledge gap, low-cycle fatigue performance of 20 mm diameter CAM SEAs was studied at room temperature 25 degrees C, low temperature, -40 degrees C, and high temperature, 50 degrees C. Both single crystal and polycrystal CAM SEAs were investigated to determine their feasibility as concrete reinforcement under repeated high strain loading cycles expected during an earthquake. Strain cycles up to 50 000 have been applied at a tensile strain amplitude of 5%. Variations in the superelastic properties were observed and analyzed, including the stress-strain curves, elastic modulus, transformation stresses, damping ratio and recovery strain. Stable hysteresis has been observed for cycles exceeding tens of thousands at all temperatures demonstrating the suitability of CAM SEAs for seismic applications in civil engineering structures.