Thermodynamics-based constitutive model for deformation twinning

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A thermodynamics-based constitutive model, which accounts for both crystallographic slip and deformation twinning, is developed for a single crystal of hcp metals within the framework of finite crystal plasticity. While the volume fractions of stress-free twin deformations are introduced as internal variables, the free-energy involves the bulk energy of separate phases and the surface energy at twin interfaces, which are introduced as functions of the internal variables, in addition to the standard hardening-related energy in crystal plasticity framework. After the formulation is described in detail, a series of numerical examples is presented to verify the performance of the proposed model in predicting the deformation twinning, the successive deformation process and the twinning-induced stress responses. The results are studied with reference to the theoretical consequences and the experimental results reported in the literature.