Hysteretic Behavior and Ultimate Energy Dissipation Capacity of Large Diameter Bars Made of Shape Memory Alloys under Seismic Loadings

Abstract

Shape memory alloys in the form of bars are increasingly used to control structures under seismic loadings. This study investigates the hysteretic behavior and the ultimate energy dissipation capacity of large-diameter NiTi bars subjected to low- and high-cycle fatigue. Several specimens are subjected to quasi-static and to dynamic cyclic loading at different frequencies. The influence of the rate of loading on the shape of the hysteresis loops is analysed in terms of the amount of dissipated energy, equivalent viscous damping, variations of the loading/unloading stresses, and residual deformations. It is found that the log-log scale shows a linear relationship between the number of cycles to failure and the normalized amount of energy dissipated in one cycle, both for low- and for high-cycle fatigue. Based on the experimental results, a numerical model is proposed that consists of two springs with different restoring force characteristics (flag-shape and elastic-perfectly plastic) connected in series. The model can be used to characterize the hysteretic behavior of NiTi bars used as energy dissipation devices in advanced earthquake resistant structures. The model is validated with shake table tests conducted on a reinforced concrete structure equipped with 12.7 mm diameter NiTi bars as energy dissipation devices.

Advances in enhancing structural and functional fatigue resistance of superelastic NiTi shape memory alloy: A Review

“…Rotating-bending fatigue tests were conducted at 1%, 2%, 3%, 4% and 5% maximum strains in a heating chamber at 37°C. Fatigue test result at 3% to 5% maximum strains for the S400 and S450 samples showed the number of cycles to failure in the range of 2500 to 3000 (see Figure 7(a)) which was much higher than the results obtained by several researchers when conducted at room temperature (Braga et al, 2014;Goo et al, 2017;Shen et al, 2011). The differential scanning calorimetry (DSC) test during heating of S400 and S450 samples detected two-phase structures (austenite and R-phase) having different phase fractions at 37°C.…”

“…Energy dissipation is also affected by the applied frequency. Gonza´lez-Sanz et al (2019) found that the loading/ unloading stresses increased with increasing frequency while the energy dissipated in each cycle decreased; residual stress remained almost constant.…”

Shape Memory Alloys 2020

“…Recommendations about the texture effect on the shape memory effect for potential engineering applications were provided. The last contribution, by González et al [10], investigated the hysteretic behavior and the ultimate energy dissipation capacity of large-diameter NiTi bars subjected to low-and high-cycle fatigue, keeping an eye on the real-life importance of protection from seismic actions. The model was validated with tests conducted on a concrete prototype equipped with large diameter NiTi bars as energy dissipation devices.…”