**Abstract**

The propagation of short cracks in FCC metals is strongly influenced by microstructures, in particular associated with the linear defects of the crystals, i.e. dislocations.

In this work, a new coupling between two methods at the mesoscale is proposed to investigate the interaction of moving cracks with three-dimensional dislocation microstructures. First, crack propagation is predicted by a phase field model. In this approach, cracks are described by some continuous damage field that evolves so as to minimize the total free energy, including stored elastic energy and surface energy associated with the crack. Second, dislocation microstructures are handled by a Dislocation Dynamics (DD) model that describes plastic deformation by the movement of dislocations under external loading.

To couple both models, the DCM (Discrete-Continuous Model) approach is used, where dislocations are described by continuous fields (eigenstrain or Nye tensor) in an elastic solver. Fast Fourier Transform (FFT) based solvers are used for their computational efficiency. Particular discretization schemes have been adopted to minimize the smoothing of dislocation cores, usually performed in MDC approaches. The different schemes are carefully analyzed with respect to the quality of the predicted fields. In addition, the resulting model is implemented using efficient parallelization solutions.

Thanks to this new coupling, we have been able to study the elastic shielding on crack propagation according to the nature of the slip systems and the dislocations density. We have also been able to investigate phenomena and ingredients rarely accounted for, such as dislocation cross slips close to the crack front or the influence of the number of sources. This mesoscale method constitutes a breakthrough for the thorough analysis of physical mechanisms controlling the early stages of fracture in metallic materials.

**Keywords :** Crack, Plasticity, Multiphysics modelling, Dislocation Dynamics, Phase Field

Phd Candidate:

**Luis Eon**

Jury:

Stéphane Berbenni – Directeur de Recherche CNRS, LEM3, Metz – Rapporteur

Samuel Forest – Directeur de Recherche CNRS, CDM, Evry – Rapporteur

Véronique Doquet – Directrice de Recherche CNRS, LMS, Palaiseau – Examinatrice

Lionel Gélébart – Ingénieur-chercheur HdR, CEA/DEN, Gif-sur-Yvette – Examinateur

Rénald Brenner – Directeur de Recherche CNRS, D’Alembert, Paris – Examinateur

Yoann Guilhem – Maître de conférences, LMPS, Gif-sur-Yvette – Examinateur

Riccardo Gatti – Chargé de Recherche CNRS, LEM, Châtillon – Encadrant de thèse

Benoît Appolaire – Professeur des Universités, IJL, Nancy – Directeur de thèse

**Tuesday 14th June 2022, 10h00**

Salle Contensou, ONERA, 29 Avenue de la Division Leclerc,92320, Chatillôn