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Modeling and Experimental Study of Simultaneous Creep and Transformation in Polycrystalline High-Temperature Shape Memory Alloys

The viscoplastic behavior in high-temperature shape memory alloys and its interaction with the transformation behavior is investigated in this work. Standard creep tests and isobaric transformation-induced tests were conducted for a TiPdNi high-temperature shape memory alloy on a uniaxial frame fitted with a custom high-temperature setup. Motivated by the experimental observations indicating simultaneous creep and phase transformation, a 1D constitutive model is presented that aims to capture the coexistence of the rate-independent transformation and the rate-dependent viscoplastic behavior. Based on continuum thermodynamics, the evolution equations for forward and reverse transformation and viscoplasticity are properly chosen. The material parameters needed for the model calibration are identified from the experimental data. The predicted material response by the proposed constitutive model is in good agreement with the experimental results.