Cyclic behavior of iron-based shape memory alloy bars for high-performance seismic devices

As a new member of the shape memory alloy (SMA) material family, iron-based SMAs (Fe-SMAs) show great potential in seismic applications due to their favorable properties. The thermomechanical behavior of Fe-SMAs has been extensively studied over the past decades. However, the relevant research regarding the use of Fe-SMAs in the community of earthquake engineering is still in an early stage, particularly on their mechanical behavior under cyclic tension-compression loadings. This study conducted a systematic experimental investigation of the cyclic behavior of Fe-SMA bars with a buckling-restrained device, which was cyclically tested under tension-compression loadings. The cyclic properties, such as hysteretic response, recovery capability, fatigue behavior, and fracture behavior were evaluated with varying strain amplitudes and different loading protocols. Test results show that satisfactory hysteretic loops with excellent deformation capability are obtained under cyclic tension-compression loadings. Fe-SMA bars exhibit acceptably stable behavior under multistage loadings. Moreover, they possess unique inherent properties, including moderate shape memory effect, high "post-yield " stiffness, and excellent fatigue behavior, thereby providing a promising solution to develop high-performance seismic devices. These properties are conducive to limit peak drifts, mitigate residual drifts of structures, and withstand long-duration ground motions and strong repeated aftershocks.