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Page de résumé pour ULgetd-05272011-115424

Auteur : Koeune, Roxane
E-mail de l'auteur : R.Koeune@ulg.ac.be
URN : ULgetd-05272011-115424
Langue : Anglais/English
Titre : Semi-solid constitutive modeling for the numerical simulation of thixoforming processes.
Intitulé du diplôme : Doctorat en sciences de l'ingénieur
Département : FSA - Département d'aérospatiale et de mécanique
Jury :
Nom : Titre :
Agelet de Saracibar, Carlos Membre du jury/Committee Member
Atkinson, Helen Membre du jury/Committee Member
Favier, Véronique Membre du jury/Committee Member
Lecomte-Beckers, Jacqueline Membre du jury/Committee Member
Rassili, Ahmed Membre du jury/Committee Member
Habraken, Anne-Marie Président du jury/Committee Chair
Ponthot, Jean-Philippe Promoteur/Director
Mots-clés :
  • finite element method/méthode des éléments finis
  • arbitrary Lagrangian-Eulerian formalism/formalisme Aribtraire Lagrangien-Eulérien
  • liquid fraction /fraction liquide
  • thixotropy/thixotropie
  • thermomechanical coupling/couplage thermomécanique
Date de soutenance : 2011-06-14
Type d'accès : Public/Internet
Résumé :

Semi-solid thixoforming processes rely on a material microstructure

made of globular solid grains more or less connected to each other,

thus developing a solid skeleton deforming into a liquid phase.

During processing, the material structure changes with the

processing history due to the agglomeration of the particles and the

breaking of the grains bonds. This particular evolutive

microstructure makes semi-solid materials behave as solids at rest

and as liquids during shearing, which causes a decrease of the

viscosity and of the resistance to

deformation while shearing.

Thixoforming of aluminum and magnesium alloys is state of the art

and a growing number of serial production lines are in operation all

over the world. But there are only few applications of semi-solid

processing of higher melting point alloys such as steel. This can

partly be attributed to the high forming temperature combined with

the intense high temperature corrosion that requires new technical

solutions. However the semi-solid forming of steels reveals high

potential to reduce material as well as energy consumption compared

to conventional process technologies, such as casting and forging.

Simulation techniques exhibit a great potential to acquire a good

understanding of the semi-solid material process. Therefore, this

work deals with the development of an appropriate constitutive model

for semi-solid thixoforming of

steel.

The constitutive law should be able to simulate the complex rheology

of semi-solid materials, under both steady-state and transient

conditions. For example, the peak of viscosity at start of a fast

loading should be reproduced. The use of a finite yield stress is

appropriate because a vertical billet does not collapse under its

own weight unless the liquid fraction is too high. Furthermore, this

choice along with a non-rigid solid formalism allows predicting the

residual stresses after cooling down

to room temperature.

Several one-phase material modeling have been proposed and are

compared. Thermo-mechanical modeling using a

thermo-elasto-viscoplastic constitutive law has been developed. The

basic idea is to extend the classical isotropic hardening and

viscosity laws to the non solid state by considering two non-dimensional internal parameters. The first internal

parameter is the liquid fraction and depends on the temperature

only. The second one is a structural parameter that characterizes

the degree of structural build up in the microstructure. Those

internal parameters can depend on each other. The internal

parameters act on the the viscosity law and on the yield surface

evolution law. Different formulations of viscosity and hardening

laws have been proposed and are compared to each other. In all

cases, the semi-solid state is treated as a particular case, and the

constitutive modeling remains valid over the whole range of

temperature, starting from room temperature to above the liquidus.

These models are tested and illustrated by mean of several

representative numerical applications.

Autre version : http://orbi.ulg.ac.be/
Fichiers :
Nom du fichier Taille Temps de chargement évalué (HH:MI:SS)
Modem 56K ADSL
[Public/Internet] PhD_RKoeune.pdf 4.35 Mb 00:10:21 00:00:23

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