Effects of low cycle fatigue and inelastic buckling on the superelasticity and energy dissipation capacity of NiTi SMA rebar

Superelastic NiTi Shape Memory Alloy (SMA) rebars have emerged as compelling materials for structural engineering applications in concrete bridge piers, owing to their superior superelastic and energy dissipation properties. Incorporating NiTi SMA rebars enhances structural resilience against seismic loads by enabling effective earthquake energy dissipation while minimizing structural damage. However, under tension-compression cyclic loads, NiTi SMA rebars are subjected to strain reversals, leading to buckling and potential low cycle fatigue (LCF) failure. This study investigates the LCF behavior of NiTi SMA rebars under tension-compression cyclic loading, considering various strengths, diameters, and slenderness ratios (<i>L</i>/<i>D</i>). The findings indicate that NiTi SMA rebars with higher slenderness ratios experience accelerated LCF failure due to buckling, leading to deteriorated mechanical properties after fewer cycles compared to rebars with lower slenderness ratios. Moreover, the study reveals that total energy dissipation and residual strain of NiTi SMA rebars are influenced by strain amplitudes and slenderness ratios. Specifically, increasing the slenderness ratio and strain amplitude results in decreased total energy dissipation and increased residual strain, underscoring the significant impact of inelastic buckling on the LCF behavior of NiTi SMA rebars. Finally, equations are presented for the prediction of energy dissipation and residual strain of NiTi SMA rebars with different slenderness ratios under tension compression cyclic loading with different strain amplitudes.