A finite-deformation-based constitutive model for high-temperature shape-memory alloys

In this work, we develop a coupled thermo-mechanical, isotropic-plasticity, finite-deformation-based constitutive model for high-temperature shape memory alloys (HTSMAs). This constitutive model is capable of describing austenite-martensite phase transformations, rate-dependent plasticity (creep) in the austenitic phase,and also transformation-induced plasticity (TRIP) due to phase transformations between the austenitic and martensitic phase. The constitutive model was also implemented into a commercially-available finite-element program through a user-material subroutine interface. By using suitably valued material parameters in the constitutive model, we show that the output obtained from our finite-element simulations are able to accurately match the experimental strain-temperature cycling data for a ternary high-temperature shape memory alloy (Ti-Ni-Pd) under various applied stresses. We also show through finite-element simulations that for particular boundary-value problems of practical/engineering significance, the usage of a finite-strain-based constitutive theory gives vastly different results when compared to using a small-strain-based constitutive theory.