基于不可逆热力学的形状记忆合金相变塑性统一本构模型研究

为了获得能够描述形状记忆NiTi合金相变和塑性行为的本构关系，基于不可逆热力学，假设两个内变量，分别推导了相变演化规律和塑性演化规律，以及NiTi合金本构模型的主控方程。将导出的本构方程写成一维的增量形式，编制FORTRAN程序，将本构模型进行了程序实现。结合单轴加载的实验曲线、非线性拟合的方法确定该本构模型的相关参数。比较实验结果，验证了该本构模型的合理性。该模型能很好地描述随着载荷不断增加，NiTi合金表现出的母相弹性、马氏体相变、马氏体弹性以及马氏体塑性流动行为，同时，对于应变率效应也能够较为理想地描述。所建立宏观唯象本构模型，参数易确定，为NiTi合金在更加苛刻、极端的环境下的工程应用打下基础。

Unified Constitutive Model for Phase Transformation and Plastic Behavior of Shape Memory Alloy Based on the Irreversible Thermodynamics

The development of constitutive relation which is able to describe the phase transition and the plasticity behavior is significant for the further application of NiTi alloy. Basing on the irreversible thermodynamics, two internal variables were assumed to characterize the phase transformation evolution and the plastic evolution respectively, then the master equation was derived. Rewritten in one dimension incremental form, the constitutive model was program implemented with FORTRAN code, in which the parameters were determined in combining with the uniaxial experiment and the nonlinear fitting. The model validation was finished from comparing the predicted results with five uniaxial tesile tests under different strain rates, that it can describe very well not only the phenomenon of parent phase transformation and martensite plastic yield, but also the strain rate effect. The phenomenological constitutive model proposed here, with easily determined parameters, laid foundations for engineering applications of NiTi alloy under more harsh and extreme terms.