Abstract To describe the grain size dependence and rate dependence of superelastic NiTi, a constitutive model involving intrinsic material instability and thermomechanical coupling is proposed and implemented implicitly into finite element software. The material is regarded as a mixing of transformable phase and non-transformable phase. The thermodynamic driving force for martensitic transformation and the heat equilibrium equation are deduced in the framework of irreversible thermodynamics. The global thermomechanical response, i.e. stress-strain curve, and local thermomechanical response, i.e. strain and temperature profiles, are simulated. If the grain size is above 68 nm, NiTi is characterized with Luders like deformation associated with strong thermomechanical coupling. If the grain size is 42 nm and 27 nm, Luders like deformation does not take place because Considere criterion is not fulfilled. Strain localization is visible owing to the collective effect of thermomechanical coupling and temperature inhomogeneity. If the grain size is 10 nm, thermomechanical coupling is suppressed and NiTi deforms homogeneously.

中文翻译：

---

超弹性镍钛形状记忆合金晶粒尺寸相关热机械响应的建模

摘要 为了描述超弹性NiTi 的晶粒尺寸依赖性和速率依赖性，提出了一种涉及固有材料不稳定性和热机械耦合的本构模型，并将其隐含地实施到有限元软件中。该材料被认为是可转变相和不可转变相的混合物。在不可逆热力学的框架内推导出马氏体相变的热力学驱动力和热平衡方程。模拟了全局热机械响应，即应力-应变曲线，以及局部热机械响应，即应变和温度曲线。如果晶粒尺寸大于 68 nm，则 NiTi 的特征是与强热机械耦合相关的 Luders 变形。如果晶粒尺寸为 42 nm 和 27 nm，不会发生像 Luders 那样的变形，因为未满足考虑标准。由于热机械耦合和温度不均匀性的集体效应，应变局部化是可见的。如果晶粒尺寸为 10 nm，则热机械耦合受到抑制，NiTi 变形均匀。