Unified Constitutive Model and Numerical Implementation of NiTi Alloy Involving Phase Transformation and Plasticity

Abstract

In order to actually describe the mechanical behavior of phase transformation and plasticity for NiTi shape memory alloy (SMA), the master equations which based on irreversible thermodynamics theory was derived by assuming two internal variables to characterize phase transformation evolution and plastic evolution. Thus a unified constitutive model was developed by summarizing master equations of phase transformation and plasticity in the loading process of NiTi alloy. Adopting semi-implicit stress integration algorithm to update inelastic strain increment, the phenomenological-based constitutive model was numerically implemented with FORTRAN code. The numerical simulation results were in good agreement with experimental data so that the proposed model validation was conducted. The results show that the proposed model not only can describe well the different deformation stages of NiTi alloy, but also the constitutive behaviors subjected to different strain rates. And it provides the basis for the practical application of NiTi alloy in the condition of impact and high speed cutting.

Keywords

• shape memory alloy
• phase transformation and plastic behavior
• constitutive model
• semi-implicit stress integration algorithm