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Page de résumé pour ULgetd-02272007-101152

Auteur : Castagne, Sylvie
E-mail de l'auteur : sylvie.castagne@unswasia.edu.sg
URN : ULgetd-02272007-101152
Langue : Anglais/English
Titre : Finite element mesoscopic analysis of damage in microalloyed continuous casting steels at high temperature/Analyse mésoscopique par éléments finis de l’endommagement à haute température des aciers microalliés de coulée continue
Intitulé du diplôme : Doctorat en sciences de l'ingénieur
Département : FSA - Département ArGEnCo
Jury :
Nom : Titre :
Bobadilla, M. Membre du jury/Committee Member
Lecomte-Beckers, Jacqueline Membre du jury/Committee Member
Magnée, Adrien Membre du jury/Committee Member
Onck, P. Membre du jury/Committee Member
Pineau, A. Membre du jury/Committee Member
Cescotto, Serge Président du jury/Committee Chair
Habraken, Anne Promoteur/Director
Mots-clés :
  • micromechanics of materials/micromécanique des matériaux
  • non-linear finite element code Lagamine/code non-linéaire par éléments finis Lagamine
  • metal forming/formage des métaux
  • multi-scale modelling/modélisation multi-échelle
  • metallurgy/métallurgie
Date de soutenance : 2007-02-12
Type d'accès : Public/Internet
Résumé :

This thesis addresses the problem of damage at elevated temperature with a view to analysing transverse cracking during the continuous casting of microalloyed steels. Based on the results of a previous project undertaken at the University of Liège to simulate the continuous casting process at the macroscopic level, the present research aims at studying the damage growth using a finite element mesoscopic approach that models the grains structure of the material. The developments are done at the mesoscopic scale using information from both the microscopic and macroscopic levels.

In order to determine the constitutive laws governing the damage process at the mesoscopic scale, the physical mechanisms leading to the apparition of cracks during steel continuous casting are first investigated. It is acknowledged that in the studied temperature range (800 to 1200 °C), the austenitic grain boundary is a favourable place for cracks to initiate and propagate. The mechanisms of voids nucleation, growth and coalescence are established, the cavities evolving under diffusion and creep deformations.

Having identified the damage mechanisms occurring under continuous casting conditions, a numerical approach for the modelling of these phenomena at the grain scale is proposed. The mesoscopic model, which is implemented in the Lagrangian finite element code LAGAMINE developed at the University of Liège, is built on the basis of a 2D mesoscopic cell representative of the material. The finite element discretization comprises solid elements inside the grains and interface elements on the grains boundaries. An elastic-viscous-plastic law of Norton-Hoff type, which represents the thermo-mechanical behaviour of the material, is associated to the solid elements for the modelling of the grains; and a damage law accounting for cavitation and sliding is linked to the interface elements for the modelling of the damage growth at the grains boundaries. The transfer between the macroscopic and mesoscopic scales is realised by imposing the stress, strain and temperature fields, collected during the parent macroscopic simulation, as boundary conditions on the mesosopic cell.

Macroscopic experiments, analytical computations and finite element simulations, as well as literature review and microscopic analyses, are used to define the parameters of the material laws. The experimental results and the identification methodology leading to the definition of the set of parameters specific to the studied steel are described.

Finally, the influence of oscillation marks and process defects on cracks formation during the industrial process of continuous casting is analysed. The results are compared with in-situ observations and cracking risk indicators computed by the macroscopic model.

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