A thermodynamic constitutive model for gradual phase transformation of SMA materials
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A thermally induced phase transformation in a Shape Memory Alloy (SMA) polycrystal occurs gradually over a range of temperatures unlike the first-order transition (at a single temperature) of a SMA monocrystal. This spread in transformation temperatures is believed to be caused by such factors as material inhomogeneities and internal stresses in the polycrystal. Taking a recently proposed thermodynamic model by Bo and Lagoudas for the Two-Way Memory Effect of SMA materials as a starting point, we extend it to account for the presence of initial heterogeneities, by introducing a statistical distribution in the Gibbs free energy function. The extended theory is then used as a basis to correlate strain recovery vs. temperature measurements from thermally induced cyclic phase transformation in untrained polycrystalline wires.
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Smart Structures and Materials 1996: Mathematics and Control in Smart Structures