Superior low-cycle fatigue performance of iron-based SMA for seismic damping application

This study reveals the superior low-cycle fatigue performance of iron-based shape memory alloy (Fe-SMA) for seismic damping application, catering to the need for more durable, resilient, and perhaps fatigue-free structural systems in seismic active regions. The study commences with material tests examining both the macroscopic and microscopic properties of Fe-SMA under monotonic and cyclic loading, followed by calibration of combined hardening parameters to facilitate numerical modelling. A Fe-SMA shear damper specimen is tested, and its behavior is compared with its mild steel counterpart. Among other findings, the study revealed good ductility of Fe-SMA with a fracture strain of up to 55% under monotonic loading. The fatigue life of Fe-SMA is from 4007 to 83 when the strain amplitude increases from ±1% to ±9%, and the values could be 10 times that of common structural steel. The cyclic strain-life relationships of Fe-SMA can be readily presented by the conventional Basquin-Coffin-Manson relationship. Both kinematic and isotropic hardening characteristics of Fe-SMA are observed, and a combined kinematic/isotropic hardening model with calibrated parameters is shown to adequately capture the hysteretic behavior of the material. The subsequent damper tests provide further evidence of its superior fatigue performance, where a fatigue life of 173 cycles is observed for the Fe-SMA damper under a constant rotational angle of 4%, in contrast to 16 cycles for its normal steel counterpart. The unique phase transformation characteristic of Fe-SMA could also affect the fatigue failure mode, where different crack patterns are observed for the dampers with the different materials.