Houssam Kharouji, PhD student in the group since November 2021, successfully defended his PhD thesis on December 5, 2024. in front of a jury composed of Dr. Forest, Dr. Upadhyay, Dr. Tanguy, Dr. Thuillier, Dr. Berbenni and Dr. Dezerald, Houssam has defended his work on the micromechanical modeling of crystal defects informed by atomistic simulation [LinkedIn].

This thesis proposes a multi-scale framework for continuously modelling core structures of crystalline defects, such as grain dislocations and boundaries, as well as their elastic interactions and associated core energies, combining atomistic and mechanical approaches of continuous media. The central idea of this study is to transform the atomic core structures of defects into continuous fields of dislocation densities, while preserving essential atomistic details. The developed approach is based on a recent micromechanical model based on dislocation field mechanics that uses the Nye dislocation density tensor, derived from atomistic data, to model short- and long mechanical fields. The method was successfully applied to compact screw dislocations in tungsten, resulting from ab initio simulations, as well as on grain boundaries in copper, simulated by molecular statics. This approach has proved to be able to reproduce the Burgers' vectors and the mechanical fields of defects, demonstrating the absence of significant loss of information at the hearts. It was possible to reproduce grain boundaries of any angle of disorientation using an equivalent density of dislocations, while capturing the continuous elastic fields. In addition, this study integrated elastic fields and dislocation densities into energy functionals based on the Nye tensor, typically used in gradient plasticity models, to evaluate their respective contribution to the total energy of the grain boundaries. We thus analysed and discussed the functional forms relevant to these energy models, exploring the physical origin of the internal length parameter inherent in these functionals, and its dependence on grain boundary types, atomistic structures, and the spatial resolution scale. This formulation allowed us to establish correlations between the atomic structures of grain boundaries and core energies, providing new insights for understanding and modelling of crystalline defects in polycrystalline materials.