Parametric Study of Mechanical Properties of Superelastic Cu-Al-Mn SMA Alloy Bolts

Abstract To advance low-cost, large-scale superelastic components for civil engineering, this study investigates the mechanical behavior of Cu-Al-Mn shape memory alloy (SMA) bars under varied solution heat treatments. Based on these findings, superelastic Cu-based SMA bolts were designed and fabricated for structural applications. A series of experiments examined the influence of heat treatment strategy, bolt diameters of 10 and 14 mm, cyclic strain amplitude, training, and loading/unloading rates on core mechanical properties, including self-centering capacity, energy dissipation, and residual strain control. The results indicate that Cu-Al-Mn SMA bars exhibit excellent deformability. Compared to conventional isothermal treatment, cyclic temperature-ramp treatment improves heat efficiency and self-centering behavior, shortening solution time by 31.0%, increasing lower platform strength by 28.7%, and reducing residual strain by 31.9%; further, 10 mm diameter bolts enhance self-centering but slightly reduce stiffness and strength compared to 14 mm bolts. A three-cycle treatment at 500°C is optimal for 10 mm diameter bolts. With increasing strain amplitude, stiffness, yield, and platform strength gradually decline, while peak strength, energy dissipation, damping ratio, and residual strain increase. Cyclic tensile training further improves mechanical stability. After 20 training cycles, residual strains at 4%, 5%, and 6% amplitudes dropped to 0.24%, 0.99%, and 1.73%, respectively. This study offers practical guidance for the design of Cu-based SMA bolts for prefabricated beam–column connections and seismic braces, contributing to high-performance, cost-effective resilient infrastructure.