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

Abstract

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℃, low temperature, -40℃, and high temperature, 50℃. Both single crystal and polycrystal CAM SEA 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.

Mechanical properties and constitutive models of shape memory alloy for structural engineering: A review

“…According to past experimental studies (DesRoches et al, 2004; Hong et al, 2022; Wang and Zhu, 2018), it has been shown that SMAs experience small residual strain under cyclic loading despite their good superelastic behavior. This residual strain happens when planes of densely packed atoms glide past one another; individual bonds are broken and rebuilt with fresh atoms.…”

“…Although the transformation plateau stress decreased when the temperature decreased, the elastic modulus remained constant. Hong et al (2022) examined the fatigue behavior of 20 mm Cu-Al-Mn SMA rebar at three different temperatures (240°C, 25°C, and 50°C) under a tensile strain amplitude of 5%. The results showed that the superelastic behavior of Cu-Al-Mn rebar is not sensitive to the temperature, and in all three temperatures, the superelastic behavior of rebar can be observed.…”

“…However, the maximum stress level decreased. Hong et al (2022) investigated the fatigue performance of Cu-Al-Mn SMAs at various temperatures. Figure 18 shows the stress-strain curve of Cu-SMA rebar at different cycles.…”

“…This will facilitate selecting the optimal compositions depending on their demands and to properly simulate the SMA rebar response in Finite Element (FE) packages. Several studies have been conducted on the mechanical properties and the cyclic behavior of different compositions of SMAs (DesRoches et al, 2004; Dolce and Cardone, 2001; Fang et al, 2021; Hong et al, 2022; Wang and Zhu, 2018). Although, as mentioned, the buckling fracture of rebar is one of the most common failure modes, previous studies have mainly focused on the cyclic behavior of SMA rebars under tensile loadings.…”

“…Figure14. Temperature effect on the behavior of Cu SMA: (a) Cu-Al-Be SMA(Zhang et al, 2009) and (b) Cu-Al-Mn SMA(Hong et al, 2022).…”