假设NiTi单晶在相变过程中具有层状的微观结构及理想的界面连续条件, 推导出各相微观量与宏观量之间的关系, 及相变驱动力的表达式, 建立了单晶相变的控制方程, 从而得到单晶的本构模型. 以此为基础, 利用Tayloy假设, 建立了NiTi多晶的本构模型. 通过控制应变进行加载, 数值模拟了恒温条件下具有{111}织构的NiTi合金的力学响应, 得到的应力-应变曲线与实验结果吻合较好. 利用模拟结果讨论了拉伸与压缩的不对称性、软化和温度对NiTi合金变形的影响.

Shape memory alloys (SMAs) are new functional material featured by the excellent properties including shape memory effect and superelasticity. NiTi SMAs have some important implications in avitation, medical device,etc. The main objective of this work is to derive a simple Taylor model for NiTi polycrystal.By the assumption of laminated microstructure and perfect interfacial relationship for NiTi single crystal transformation, microscopic strain for each phase can be transformed to overall strain of respective volume element, and expression of phase transformation driving force is derived, then control equation of phase transformation is constructed. Based on the single crystal model, the NiTi polycrystal constitutive model is constructed by Taylor assumption. The model is used to simulate the mechanical response of NiTi polycrystal alloys with strong {111} texture, the results are in agreement with those observed experimentally. The predicted result of NiTi alloy with strong texture shows asymmetry of tension and compression. Simulation results behave softening as the free energy function is non-convex during phase transformation. Transformation stress level rises as temperature is raised.