Anisotropy of martensitic transformations in modeling of shape memory alloy polycrystals

Based on the knowledge of the ainisotropy associated with the martensitic t ransformations obtained from tension/compression experiments with oriented CuAlNi single crystals, a simple constant stress averaging approach is empl oyed to model the SMA polycrystal deformation behaviors. Only elastic and i nelastic strains due to the martensitic transformation, variant reorientati ons in the martensite phase and martensite to martensite transformations in ther momechanical loads are considered. The model starts from theoretical calculation of the stress-temperature transformation conditions and their o rientation dependence from basic crystallographic and material attributes o f the martensitic transformations. Results of the simulations of the NiTi, NiAl, and Cu-based SMA polycrystals in stress-strain tests are shown. It fo llows that SMA polycrystals, even with randomly oriented grains, typically exhibit tension/compression asymmetry of the shape of the pseudoelastic sig ma - epsilon curves in transformation strain, transformation stress, hyster esis widths, character of the pseudoelastic flow and in the slope of temper ature dependence of the transformation stresses. It is concluded that some macroscopic features of the SMA polycrystal behaviors originate directly fr om the crystallography of the undergoing MT's. The model shows clearly the crystallographic origin of these phenomena by providing a link from the cry stallographic and material attributes of martensitic transformations toward s the macroscopic sigma - epsilon - T behaviors of SMA poly-crystals. (C) 2 000 Elsevier Science Ltd. All rights reserved.