Modeling of rate dependency of mechanical behavior of superelastic NiTi alloy under cyclic loading

Abstract

In this paper, the susceptibility of NiTi arch wires to the strain rates during cyclic loading is investigated. To experimentally predict such effects, orthodontic specimens are submitted to cyclic loading with various strain rates of 5 × 10−3 s−1, 10−3 s−1, 5 × 10−4 s−1, and 10−4 s−1 under an imposed strain of 7.6%. Throughout cyclic loading, a significant degradation on the mechanical behavior is observed (the critical stress for the start and the end of the martensite transformation, the residual strain, and the dissipated energy evolving). This development of all properties becomes more significant with a higher strain rate. Indeed, the number of nucleated domains rises with an increasing applied strain rate, which is due to the coupling between the transfer of locally released heat and the temperature dependence of the transformation critical stress. In order to reproduce such behavior of NiTi arch wires, a model is developed to take into account the thermomechanical coupling. Finally, numerical simulation based on the proposed constitutive model is performed in our work, and good correlations with the experimental data are observed.