Constitutive modeling of 3-D stress induced phase transformation in polycrystalline NiTi SMA
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A thermomechanical description of the martenstitic phase transformation and the associated shape memory effect in polycrystalline NiTi shape memory alloys (SMAs) is presented. The Kuhn-Tucker optimality conditions, constraints on the evolution equations for transformation strain and the form of transformation function are obtained naturally through the principle of maximum transformation dissipation. Various transformation functions are investigated and a generalized Drucker-Prager type transformation function is proposed. Numerical results of the model based on different transformation functions are compared with experimental results to determine their accuracy to predict SMA characteristics like tension-compression asymmetry, negative volumetric transformation strain and pressure dependence.