Improved Constitutive Modeling for Phase Transformation of Shape Memory Alloys

This work presented new developments in the constitutive modeling of shape memory alloys (SMAs). As an increasing number of experimental results are being published, it is becoming increasingly difficult to describe complicated SMA behaviors using conventional models. To overcome the shortcomings of existing models, this research proposed two major improvements to the assumed phase transformation function. A more flexible function called logistic sigmoid function has been introduced into the phase transformation function. This improvement affords a better fit to the typical SMA stress-strain relationship. Moreover, a cyclic effect has been considered while developing the new model. The new model is proposed by connecting accumulated strain with the critical phase transformation constants of SMAs. Both improvements were first validated at the material level. Thereafter, structural level validation and application were conducted. Accuracy enhancement may be expected by adopting these new models in SMA-related simulations.