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.
Cu-Al-Mn (CAM) shape memory alloys (SMA) are cost effective, have a high low-cycle fatigue life and superelastic limit, and a wide temperature application range compared to other types of SMAs. These characteristics of CAM SMAs have resulted in an increased research interest in their use in civil engineering applications, particularly as reinforcement in concrete structures, and dampers in steel structures. However, these applications could require machining of the CAM SMA bars for connecting with other structural elements. This study presents the methods and results of the first systematic research on the machinability of CAM SMAs. The key machinability characteristics of CAM SMAs, such as chip formation, cutting temperature, tool wear, workpiece surface roughness and diameter deviation were studied and compared with conventional NiTi SMAs, and commonly used steel: mild steel (MS) and 304 stainless steel (SS). Effects of a wide range of cutting parameters, such as cutting speed ranging from 15 to 120 m/min, feed rate ranging from 0.1 to 0.2 mm/rev, and depth of cut ranging from 0.5 to 1.5 mm, were investigated. The results from this study demonstrated that the tool wear from machining CAM SMAs was close to that of SS and slightly higher than that from machining MS but much lower than of that from machining NiTi SMAs. In all the cases considered here, the tool wear from machining CAM SMAs was found to be 0.6 to 1.8 times that from machining SS, 0.8 to 2.4 times that from machining MS, and 1/7 to 1/21 times that from machining NiTi SMAs. After a continuous machining test with a total cutting length of 4.5 m, the nose wear of machining CAM SMAs was found to be 1.6 times that of machining MS, and the average flank wear of machining CAM SMAs was found to be three times that of machining MS; the diameter deviation (relative diameter difference with the first sample) of CAM SMAs was only 10 mm larger than that of MS.
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