Constitutive modeling and finite element approximation of B2-R-B19′ phase transformations in Nitinol polycrystals

A path-dependent constitutive model is proposed for the stress-induced phase transformation of Nitinol single crystals between austenite, rhombohedral and martensite phases. A multi-directional active set strategy is employed to resolve the path and state of the transformation. The resulting algorithm is implemented using a multi-scale finite element-based method which extends the applicability of the model to textured Nitinol polycrystals. Representative numerical simulations are included and show good agreement with experimental results.