Abstract：Based on the concept that NiTi shape memory alloys (SMAs) are substantially heterogeneous and there inevitably exist residual micro-stress fields, and the superposition of the residual stress and the that induced by applied thermal-mechanical loads may cause martensitic transformation at low level of applied thermal-mechanical loads, a new transformation driving force model is proposed for an existing description for martensite variants in NiTi SMAs. The corresponding numerical algorithm is developed and the pseudoelasticity of NiTi SMAs is analyzed, and compared with experimental results and the results by Gall et al. In the proposed model the transformation driving force is considered as a continuous function of martensite volume fraction, however, the transformation as well as its rare is insignificantly small as the transformation driving force is far from its saturated magnitude. Analysis shows that the range of the transformation driving force with respect to prescribed tolerance of transformation volume fraction is much smaller that that adopted in the existing work, and vice versa, indicating higher computation accuracy. On the other hand, no assessment is needed for the occurrence of transformation and its direction in each variant a priori, which is significant in computation, especially in the case of multiaxial thermal-mechanical loading. Since the proposed approach avoids the discontinuity in the evolution of transformation driving force at the instant when transformation starts, and the additional numerical process for the identification of the variants where transformation proceeds or not, it can not only simplify the numerical process, but also enable the computation process be more stable and efficient.
2012, Vol. 33 