PhD opportunities

Controlled characteristics materials produced by wire + arc additive manufacturing.

Thesis proposal

Area of expertiseComputational mechanics and Materials
Doctoral SchoolSFA - Sciences Fondamentales et Appliques
SupervisorM. Charles-Andr GANDIN
Co-supervisorM. Michel BELLET
Research unitCentre for material forming
KeywordsAdditive manufacturing, arc + wire process, grain growth, thermo-mechanical evolution, multi-scale coupling, finite-element method
AbstractThe CEMEF laboratory has developed during the past years two approaches dedicated to the simulation of LBM additive manufacturing processes. A micro- approach dedicated to the simulation of track development and a macro- approach at the part scale (Figure). The two methods are part of the C++ library Cimlib developed in the laboratory in finite element approach. A level-set method has been proposed in both models in order to follow the evolution of the material/air interface also including a remeshing strategy. Indeed, these two approaches are required in order to achieve a correct estimation of the material deposition during the entire heat source movement. The solvers are parallelized in order to end simulation in a correct computing time. The numerical development done in the MACCADAM project will be part of these numerical developments to enrich current simulations. At the end, both methods should benefit from the numerical activities planned in the project at CEMEF.

At the scale of a few tracks, the numerical modelling should consider the process parameters effect. Mainly, the gas/material interaction should be considered also including the surface tension effect and Marangoni force (Figure b). This simulation should help to follow the fluid flow evolution in the liquid bath, the solidification stage and the phase change in solid state as well as mechanical evolution. At the same scale, the microstructure evolution should be considered based on the CAFE (Cellular Automaton-Finite Element) approach. This relevant method at micro-scale will provide information on grain orientation in materials after solidification. In addition, the phase transformation modelling should be coupled to the computation of thermodynamic equilibrium and diffusion kinetics (Thermo-Calc software). The comparison of simulation results with experimental observations provided by other partners should validate the modelling approach. At the end process parameters effect will be estimated considering set of simulations (effect on track geometry, microstructure, phase evolution ).
At the macro-scale (part scale), the numerical simulation will be mainly based on a thermo-mechanical approach (Figure c). This simulation will provide information on deformations and residual stress field during manufacturing process. The challenge will be to determine relevant mechanical evolution law (elasto-visco-plastic behaviour) considering the phase development and their specific properties. At the end, quantitative comparisons of deformation and stress fields should be achieved. Similarly to the previous micro-scale simulations, experimental observations are essential to validate the model considering observations developed by other partners (DRX).

The project aims consequently to engulf in a single model a set of existing numerical approaches in order to consider all the complex phenomena occurring during the solidification and cooling stages of a metallic alloy melted by arc. The numerical tool will correspond to a clear opportunity to investigate, master and optimize the arc+wire FA process. All the numerical development will also be part of the collaborative C++ library developed at CEMEF (C++ library for scientific computing). The hired student will also benefit from the numerical development introduced by other students in their research activity (remeshing strategy, parallel computing, numerical solution ).

The PhD student will benefit from lectures in material science, numerical metallurgy and heat transfer. In addition, he will receive advance teaching in scientific computing and programming in C++ language. These competences will provide opportunities to develop future activities in various R&D sectors in nuclear, automotive or metallurgical industries.
ProfileEngineer / Master student in the field of material science, mechanic or applied mathematics. Student attracted by problematic linked with the modelling and simulation of physical phenomena in forming processes.
FundingFinancement par crdits ANR