| A number of thermoelastic theories have been established to interpret the phase transformation phenomena of shape memory alloy (SMA) at the single crystal level. The SMAs used in real applications are polycrystals such as NiTi microtubing in medical surgery. Recent experiments on the mechanical response of SMA in thin-walled tube configuration revealed many interesting phenomena such as the dynamic formation, self-merging and topology transition of a macroscopic deformation band. So far there is no theoretical model that can satisfactorily describe the above deformation instability and pattern evolution in polycrystalline materials. In this thesis, a continuum Ginzburg-Landau type free energy function was constructed based on the material symmetry (anisotropy) considerations of the polycrystal. The established theoretical model was implemented into FEM codes to simulate the martensitic band formation and pattern evolution under applied stress. The computational results captured many important features of the experimental observations. |
