Simulation of initial formation and growth of martensitic band in NiTi micro-tube under tension

Previous experiments have shown that the distinct features of macro-martensitic band nucleation and propagation in micro-tube under tension are in three stages: the initiation and propagation of a single helical band → self-merging → propagation of the cylindrical band. In this paper, the martensitic formation and helical band propagation in the tube at different temperatures are modeled. The free energy function of the tube is formulated by introducing an equivalent method to calculate the stress and strain disturbances in the helical martensitic domain, and the phase transformation criterion is derived based on thermodynamics. The simulations successfully capture the main features of nucleation, pattern evolution and variation of front velocity of the helical martensitic band in the tube. The analytical results and the comparison with experiments are also discussed in this paper.