PhD opportunities

Characterization of GraIn Structure generated by L-PBF process at Track scale through Experiment And thermo-Metallurgical-Mechanical Modelling

Thesis proposal

Area of expertiseMécanique numérique et Matériaux
Doctoral SchoolSFA - Sciences Fondamentales et Appliquées
SupervisorBELLET Michel
Co-supervisorGANDIN Charles-André
Research unitCentre de Mise en Forme des Matériaux
KeywordsGrain structure, Anisotropic plasticity, Thermo-metallurgical-mechanical modelling, Laser powder bed fusion
AbstractThe proposed research tasks related to numerical and experimental sides are summarized as below:
Numerical simulations:
- Thermo-metallurgical-mechanical modelling of L-PBF deposition at track scale (CEMEF) → grain structure with inherent residual stress.
- Study the influence of local deformations on the intragranular texture→ distribution of different crystal orientation within one grain.
- Study the effect of grain structure on hot cracking.
- Representative volume element (RVE) traction relaxation simulations with anisotropic elastic-visco-plastic mechanical behavior laws by both crystal plasticity [3] and Hill48 anisotropic plasticity [4] (LMS, CEMEF) → average RVE behavior for part scale modelling.
- Understand the generated residual stress at grain level and its influence on traction tests at part scale.
Thermohydraulics and metallurgical simulations, and following RVE mechanical response (Chen, 2018[5], Camus et al, 2022[6], Zhang et al. 2022[7])

Experiments:
- Track printing by L-PBF (a third partner)
- Characterization of residual stress and crystal orientation distribution within the grains (LMS, CEMEF)
- Traction relaxation tests of AMed specimen (CEMEF or LMS): RVE level or standard specimen

EBSD and HR-DIC using novel laser-SEM setup (LMS, Ecole Polytechnique)
Expected results:
- Novel coupling work between the growth of grain structure and anisotropic mechanical behavior during solidification at melt pool level.
- Explain the reason of intragranular texture.
- Understand the effect of grain structure on hot cracking during LPBF process
- Study the inherent residual stress by both experiment and numerical simulations at grain level.
- Propose an anisotropic material law for part scale modelling by considering the effect of residual stress for L-PBF process simulation.
With the method of level-set, CEMEF has developed the meso-scale model for ceramics [5] and for metals [8], in which the powder bed may be assumed as a continuum. The melt pool development and resulting track shape can consequently be simulated by several deposited tracks. Furthermore, a thermomechanical analysis at the scale of the track during solidification was also demonstrated [5]. The prediction of the grain structure is also coupled with the prediction of the heat flow deduced from the meso-scale model [9, 10], which is now applied to L-PBF at part scale showing relevant trends for morphology and crystallographic textures of the grain structure [6].

GISTEAMMM is a twin project with the ANR-JCJC GRAMME at CEMEF, which is coordinated by Dr. Zhang. GRAMME aims to develop an efficient and relevant coupling strategy in LPBF process modelling between microstructure development and anisotropic mechanical behavior at part scale during and after construction. The collaborator in LMS, Ecole Polytechnique, is Dr. Upadhyay. He has recently obtained a project GAMME financed by ERC Starting Grant.
ProfileEngineer/Master student in the field of computational mechanics, or applied mathematics. Strong knowledge of finite element method, solid mechanics and programming (C++) skills, and good English level. Basic knowledge of metallurgy is also required.
FundingContrat de recherche