11 April 2017 Predicting the constitutive response of precipitation hardened NiTiHf
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Abstract
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 experimental results.
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Jobin K. Joy, Jobin K. Joy, Alexandros Solomou, Alexandros Solomou, Theocharis Baxevanis, Theocharis Baxevanis, Dimitris C. Lagoudas, Dimitris C. Lagoudas, } "Predicting the constitutive response of precipitation hardened NiTiHf", Proc. SPIE 10165, Behavior and Mechanics of Multifunctional Materials and Composites 2017, 101650F (11 April 2017); doi: 10.1117/12.2263501; https://doi.org/10.1117/12.2263501
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