Current efforts towards the identification of suitable processing parameters of shape memory alloys (SMAs) that enhance
their actuation performance, are based on semi-empirical approaches. This is largely due to a lack of models able to predict
the macro-mechanical response of SMAs as function of given composition and the temperature and time of an imposed
heat treatment. The present work aims for the development of multi-field Finite Element (FE) based models, for the NiTiHf
SMA material system, adequate to address these challenges and able to simulate materials macro-mechanical response
including transformation strain, hysteresis and transformation temperatures. Representative Volume Elements (RVEs)
with periodic geometry and boundary conditions are used to model materials microstructure. Randomly placed precipitates
are considered in the NiTiHF matrix, while eigenstrains corresponding to the lattice mismatch between the precipitates
and the matrix are introduced in order to model the residual stress and strain fields. The Hf concentration field is taken into
consideration in addition to the displacement field in order to capture the Hf diffusion process through the adoption of
Fickian diffusion law. To this end the composition of NiTiHf in the vicinity of the precipitates is computed thus resulting
in substantial SMA transformation temperature shifts. The developed framework is validated based on correlations with
Jobin K. Joy, Alexandros Solomou, Theocharis Baxevanis, and Dimitris C. Lagoudas, "Predicting the constitutive response of precipitation hardened NiTiHf," Proc. SPIE 10165, Behavior and Mechanics of Multifunctional Materials and Composites 2017, 101650F (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 26, 2017; Published: 11 April 2017); https://doi.org/10.1117/12.2263501.
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