Thermomechanical Models for NiTi Shape Memory Alloys and Their Applications

Optimal design of SMA structures must be based on a deep knowledge of the material properties. As the SMA structures increase in complexity (stents, textiles, microdevices), modeling becomes increasingly involved. Macroscopic models of shape memory alloys are being developed with the ultimate aim to effectively simulate thermomechanical response of a constitutive material element. Computational robustness, stability, adaptability and reasonable computational time with respect to the modeling goal becomes however an issue which seems to play an ever increasing role. For instance, the non-proportional mechanical loading seems to be one of the most challenging issues for models of shape set wire structures as stents or textiles made of wires. Based on systematic experimental research of behavior of NiTi wires in uniaxial tension and tension-torsion tests, we discuss several weak aspects of the existing phenomenological models and describe here a SMA material model optimized for simulation of NiTi wire structures where combination of tension, torsion and bending strains dominate.