Numerical Simulations of Temperature-Driven NiTi SMA Actuators

One of the main challenges in numerical simulations of SMA actuators is to accurately capture the material behaviors not only at a constant temperature but in a broad temperature range usually corresponding to actuator cycles. In this contribution, we present a constitutive model tailored for nonproportional multi-axial loading of NiTi SMA capturing both martensite and R-phase transformations and covering also temperature evolution of material parameters. It allows to properly capture the material behaviors from low-temperature pseudoplastic to high-temperature superelastic regime, and thus, it is suitable for reliable simulations of SMA components driven by altering temperature. We will demonstrate the model performance on two examples:  1) numerical simulations of the mechanical response of a NiTi SMA helical spring subjected to thermal cycling at a constant applied force; results will be compared with dedicated experiments and, 2) numerical simulations of NiTiFe tube coupling, which represents probably the most successful non-medical SMA application.