Dalloz, Alexandre (2007) Study of the damage induced by the shear cutting process in dual phase steels for automotive application. PhD thesis Sciences et génie des matériaux, MAT- Centre des Matériaux P.M. Fourt, ENSMP p.193.
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Abstract
In order to optimize the metallurgical quality of future dual phase steels, the present study aims at a better understanding of the formation of the cut edge damage induced by shearing.
Observations and characterizations revealed the existence of a highly deformed area in the vicinity of the cut edges. This region of 200 µm is defined as the cutting affected zone. In addition to deformation, its microstructure presents voids, initiated at ferrite-martensite boundaries.
The formation of this zone during the cutting process was studied through two complementary approaches: first, the use of an especially designed testing device that allows precise interruption of the cutting process, then, the simulation of the process by finite elements methods. The damage and the fracture of the sheets appeared to be controlled by the voids formation at the phases boundaries and thus by the stress triaxiality ratio.
The study of the cut edge behaviour under loading showed the rapid initiation of small cracks in the cutting affected zone. The direct impact of these cracks on the sheets ductility was also highlighted.
Finally, two heat treatments that limit the ductility loss induced by cutting were proposed: one by the formation of a third phase during cooling and the other by offering better mechanical properties around phases boundaries.
| Item Type: | PhD Thesis (PhD) |
|---|---|
| Thesis Supervisor: | Gourgues, Anne-Françoise and Pineau, André |
| Date: | 11 December 2007 |
| Board of examiners: | Andrieu, Eric and Klöcker, Helmut and Pardoen, Thomas and Besson, Jacques and Sturel, Thierry and Gourgues, Anne-Françoise and Pineau, André |
| Ecole Doctorale: | ED 432 ECOLE DOCTORALE SCIENCES DES METIERS DE L'INGENIEUR |
| Discipline: | Sciences et génie des matériaux |
| Collection (Fonds): | ENSMP |
| Institution: | ENSMP |
| Department: | MAT- Centre des Matériaux P.M. Fourt |
| Subjects: | 4. Materials Science, Mechanics and Mechanical Engineering |
| Uncontrolled Keywords: | High strengh steel, Formability, Cut, Mechanical properties, Finite element method, Acier dual phase, Endommagement, Découpe, Application automobile, Acier très haute résistance |
Table of content
Introduction
1ère partie MISE EN EVIDENCE DE L'IMPACT DU PROCEDE DE DECOUPE SUR LE COMPORTEMENT DES ACIERS DUAL PHASE
1. Description du procédé de découpe à la cisaille
2. Présentation des six nuances de l'étude préliminaire
3. Impact du procédé de découpe
4. Présentation de la nuance retenue
2ème partie COMPREHENSION DES MECANISMES MIS EN JEU AU COURS DE LA DECOUPE A LA CISAILLE DES TOLES EN ACIER DUAL PHASE
1. Avant propos : rupture ductile à faible taux de triaxialité des contraintes
2. Modélisation du procédé de découpe : état de l'art
3. Approche expérimentale et simulation numérique
4. Description des mécanismes intervenant au cours de la découpe
3ème partie COMPORTEMENT DE LA ZONE AFFECTEE PAR LA DECOUPE LORS DES SOLLICITATIONS DE MISE EN FORME
1. Le mécanisme d'amorçage des fissures dans les bords découpés
2. Mécanique des petites fissures
4ème partie TRAITEMENTS THERMIQUES PERMETTANT D'AMELIORER LE COMPORTEMENT A LA DECOUPE DES ACIERS DUAL PHASE
1. Influence de la microstructure sur le comportement des DP
2. Métallurgie de la nuance B85
3. Impact des paramètres du traitement de recuit sur le comportement en découpe
4. Impact des traitements de revenu à basse température sur le comportement de la nuance B85
Conclusions et perspectives
Annexes
| ID Code: | 3490 |
|---|---|
| Deposited By: | Odile ADAM |
| Deposited On: | 31 March 2008 |
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