Development of crystal plasticity models in a thermomechanical variational framework for magnesium alloys

This thesis addresses the critical challenge of accurately modeling the complex behavior of magnesium alloys, whose highly anisotropic deformation is dominated by profuse twinning. The primary objective is to develop a thermodynamically consistent crystal plasticity model for magnesium that captures both mechanical and energy dissipation characteristics during plastic deformation, particularly twinning, and validate the model jointly by thermal-mechanical data. Experimentally, simultaneous stress, strain, and in-situ thermal measurements are employed during uniaxial testing of both single crystal and polycrystalline magnesium specimens using combined infrared thermography and digital image correlation. Key findings demonstrate that deformation mechanisms in magnesium possess distinct energetic signatures, with quantified energy dissipation providing physically-based benchmarks for model validation. Theoretically, a thermomechanically coupled crystal plasticity model incorporating slip and twinning mechanisms is developed within a variational framework, ensuring energetic consistency. The variational approach enables prediction of energy partitioning during plastic deformation, opening an additional verification channel. Model verification effort reveals that the commonly employed power-law rate dependency is unable to represent full range of thermomechanical behavior, necessitating the addition of rate-independent terms. This work advances the field by establishing a rigorous validation protocol using thermal measurements as independent verification and represents a significant idea toward truly predictive multi-physics material models.