  The work presents a thermomechanical model for polycrystalline NiTi-based
shape memory alloys developed within the framework of generalized standard
solids, which is able to cover loading-mode dependent localization of the
martensitic transformation. The key point is the introduction of a novel
austenite-martensite interaction term responsible for strain-softening of the
material. Mathematical properties of the model are analyzed and a suitable
regularization and a time-discrete approximation for numerical implementation
to the finite-element method are proposed. Model performance is illustrated on
two numerical simulations: tension of a superelastic NiTi ribbon and bending of
a superelastic NiTi tube.
