Experimental and numerical study on the mechanical properties of NiTi-SMA bars

This paper presents an experimental investigation that aims to study the mechanical properties of NiTi shape memory alloy (SMA) bars, with a particular emphasis on comprehensively evaluating their superelastic properties and energy dissipation capabilities. The study examines the influence of thermal treatment processes, loading rates, pre-training, and loading amplitudes on crucial parameters such as residual strain, energy dissipation capacity, initial stiffness, and equivalent viscous damping ratio of SMA bars. Additionally, the microstructure of the SMA bars' cross-sections, both prior to and following thermal treatment, is examined using scanning electron microscopy. The existing Graesser constitutive model is improved, and its validity is verified through numerical fitting. The findings demonstrate that SMA bars with a direct working section of 10 mm exhibit favorable superelastic properties after undergoing heat treatment at 350 degrees C for 35 min. It is recommended that the loading rate of SMA should not exceed 0.15 % per second, and appropriate pre-training measures should be implemented in practical engineering applications. Microstructural analysis reveals distinct dimples and intergranular fracture marks in the cross-sections of heat-treated SMA bars, indicating a high level of material toughness. Moreover, the improved Graesser constitutive model accurately calculates the mechanical characteristics of SMA bars and effectively describes their residual strain behavior. The research outcomes of this study provide valuable theoretical and technical insights for the practical application of shape memory alloy bars in engineering contexts.