A thermomechanical constitutive model for superelastic SMA wire with strain-rate dependence

The recent increased use of shape memory alloys (SMAs) for civil engineering applications manifests the need for a high-fidelity constitutive model which considers the material's strong dependence on the loading rate. This paper presents an improved thermomechanical constitutive model with strain-rate dependence for predicting the uniaxial superelastic behavior of shape memory alloys. The proposed constitutive model, which is formulated within a thermomechanical framework, is comprised of three principal parts: a mechanical law, an energy balance equation, and a transformation kinetics rule. The analytical derivation of the model and experimental test results for superelastic NiTi wires are described in this paper. The prediction made by this phenomenological model shows good agreement with experimental data for superelastic NiTi wires at various loading rates. Through a comparison with experimental results, the proposed constitutive model was evaluated for several key characteristics of superelastic behavior such as reduction of hysteresis area, increase of transformation plateau, and temperature change with strain rate. The proposed constitutive model offers a useful tool for the design and simulation of superelastic SMA-based devices in civil engineering applications.