Macroscopic modeling of NiTiHf under different loading modes: A finite difference method

High-temperature shape memory alloys have remarkably solved the limitation of conventional shape memory alloys working at low levels of temperature and stress. The focus of this study is on a semi-analytical constitutive model for high-temperature shape memory alloys to predict their mechanical behavior. The model is based on Gibbs free energy, and the equations are simplified for NiTiHf at different loading conditions. A uniaxial compression case is used to validate the model with the experimental results. Superelastic behavior and also heating and cooling at different stress levels are compared to the experimental data reported in the literature. The nonlinear equations are solved using finite difference method, which is capable to calculate the distribution of strain and phase transformation along the cross section for various loading modes. Several more case studies on pure torsion and multiaxial loading are also investigated to show the capabilities of this approach.