Défense publique de thèse de Mlle Florence Scheyvaerts
Titre : Multiscale modelling of ductile fracture in heterogeneous metallic alloys
Lundi 30 mars 2009 à 16h30
Auditoire BARB94
Place Sainte-Barbe
Louvain-la-Neuve
Accès Louvain-la-Neuve Biéreau
Parking 11
The development of new heterogeneous metallic materials with high
resistance, such as multiphase steels, a/b Ti-alloys, or Al-alloys
involving precipitate free zones, is often impeded by the lack of
understanding and control of the damage and fracture mechanisms. The
objective of the thesis has been to develop a multiscale modelling
strategy in order to unravel the relationships between the
micromechanisms of ductile fracture and the microstructure of
heterogeneous alloys. The present work also contributes to enhancing
the predictive capabilities of ductile fracture models regarding
structural integrity assessment.
More precisely, we have developed new extensions of a
Gurson-type constitutive model describing the growth and coalescence of
spheroidal voids, possibly not oriented parallel to the main loading
direction. These extensions are essentially (i) a description of the
void rotation and deformation under shear, (ii) a generalization of the
Thomason criterion for the onset of coalescence accounting for the
localization plane orientation, (iii) a new geometrical model for the
internal necking process. The full model has been implemented in a
home-made finite element code and validated towards finite element
unit-cell calculations.
Based on this model, we have investigated the influence of the
microstructural features of homogeneous metallic materials on the
different fracture mechanics parameters characterizing the fracture
resistance such as JIc, CTOD, CTOA, plastic zone size, and JR. The
multiscale modelling tool developed has been also applied to
heterogeneous alloys with a specific focus on 7xxx aluminium alloys
involving precipitate free zones along the grain boundaries and
displaying a competition between transgranular and intergranular
fracture modes. The study has contributed to a better understanding of
the effect of the microstructural features, flow properties of the
grain, and loading conditions on the preferential fracture mode,
fracture strain tearing resistance, and crack path.
Membres du jury :
Promoteur: Monsieur Th. PARDOEN (IMAP)
Promoteur: Monsieur P.R. ONCK (University of Groningen)
Monsieur Y. BRECHET (INP Grenoble)
Monsieur J.W. HUTCHINSON (Harvard University)
Monsieur J.-B. LEBLOND (Université Paris VI)
Monsieur L. DELANNAY (MEMA)
Monsieur I. DOGHRI (MEMA)
Président: Monsieur C. BAILLY (POLY)
Monsieur A. LALOUX, représentant le Doyen, présidera de la cérémonie.