Investigation of Low-Cycle-Fatigue Behavior of NiTi SMA Rebar and Development of Low-Cycle-Fatigue Model

Shape memory alloys (SMAs) are smart metallic alloys that have become an attractive material for structural engineering applications owing to two distinct features: the superelasticity effect (SE), and the shape memory effect (SME). In RC structures, NiTi SMA reinforcing rebars have emerged as a suitable alternative for conventional steel rebars due to their ability to dissipate seismic energy and reduce earthquake-induced damage. Seismic application of NiTi SMAs in RC structures warrants investigating the low-cycle-fatigue (LCF) behavior of NiTi SMA bars. Furthermore, longitudinal rebar buckling in a RC column subjected to seismic loading is a common failure mode, and can accelerate the LCF failure of reinforcing rebar. However, there is a lack of research examining the LCF response of NiTi SMA rebar subjected to cyclic tension-compression loading, considering the buckling effects. To address this gap, this paper focuses on the LCF behavior of NiTi SMA rebars under cyclic tension–compression loading, and proposes LCF life prediction models considering the effects of buckling. Using numerical parametric analysis, various strengths, diameters (10, 12, and 15 mm), and slenderness ratios (5, 7, and 10) of NiTi SMA rebars were examined under different constant strain amplitudes (2%, 4%, 6%, 8% and 10%). The study incorporated the effects of buckling, and proposed total strain amplitude–based and dissipated energy–based LCF models to estimate the LCF life of NiTi SMA rebar. The comparison of the predicted LCF life and the results from numerical investigation validated the accuracy of the proposed models.