Eulerian Rate Model for Pseudoelastic NiTi Shape Memory Alloys

A phenomenological material model for the pseudoelastic material behavior of polycrystalline NiTi is presented. It is consistently derived within the Eulerian framework using the Kirchhoff stress (weighted Cauchy stress) and the stretching tensor. Deformation–like variables such as elastic or inelastic strains are omitted. The model is based on a non–convex Helmholtz free energy function for the phases austenite and martensite, which is formulated in terms of the Kirchhoff stress, temperature, mass fraction of martensite, and a tensorial internal variable accounting for the average orientation of the martensite variants. Evolution equations for the mass fraction of martensite as well as for the average orientation of the martensite variants are derived, taking into account the restrictions imposed by thermodynamics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)