. Afin, oxydation sur la mesure de la déformation viscoplastique, les sections à mi-diamètre des éprouvettes ont été examinées en vue de mesurer l'épaisseur de la couche d'oxyde. Avant coupe, un nickelage électrolytique est appliqué pour protéger la couche d'oxydes lors de la préparation métallographique, La Figure B, vol.5

. La-couche-d, oxydes est facilement observée sur la figure ci-dessus, une valeur approximative de l'épaisseur peut être estimée à 25 µm. Si on suppose que l'oxydation a lieu à l'extérieur de la surface et donc augmente le diamètre de l'éprouvette, il y a un

. Après-la-pré-déformation,-la-mise-en-tonneau-de-l-'éprouvette-est-Évidente, L'objectif de cette section est d'étudier l'effet de la forme en tonneau sur la déformation viscoplastique lors de l'étape de fluage suivante. Pour cela, une mise en charge en compression a été modélisée par éléments finis (sous Zébulon [Besson et Foerch, 1997]) sur une éprouvette avec une forme issue de la mise en tonneau. Comme on s'intéresse seulement à la distribution de la contrainte

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