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Influence de l'orientation des hydrures sur les modes de déformation, d'endommagement et de rupture du Zircaloy-4 hydruré.

Abstract : In pressurized water reactors of nuclear power plants, fuel pellets are contained in cladding tubes, made of Zirconium alloy, for instance Zircaloy-4. During their life in the primary water of the reactor (155 bars, 300°C), cladding tubes are oxidized and consequently hydrided. A part of the hydrogen given off precipitates as Zirconium hydrides in the bulk material and embrittles the material. This embitterment depends on many parameters, among which hydrogen content and orientation of hydrides with respect to the applied stress. This investigation is devoted to the influence of the orientation of hydrides with respect to the applied stress on strain, damage and failure mechanisms. Macroscopic and SEM in-situ ring tensile tests are performed on cladding tube material (unirradiated cold worked stress-relieved Zircaloy-4) hydrided with about 200 and 500wppm hydrogen, and with different main hydrides orientation: either parallel or perpendicular to the circumferential tensile direction. We get the mechanical response of the material as a function of hydride orientation and hydrogen content and we investigate the deformation, damage and failure mechanisms. In both cases, digital image correlation techniques are used to estimate local and global strain distributions. Neither the tensile stress-strain response nor the global and local strain modes are significantly affected by hydrogen content or hydride orientation, but the failure modes are strongly modified. Indeed, only 200wppm radial hydrides embrittles Zy-4: sample fail in the elastic domain at about 350MPa before strain bands could develop; whereas in other cases sample reach at least 750MPa before necking and final failure, in ductile or brittle mode. To model this particular heterogeneous material behaviour, a non-coupled damage approach which takes into account the anisotropic distribution of the hydrides is proposed. Its parameters are identified from the macroscopic strain field measurements and a quantitative characterization of hydrides orientation by means of images analysis. The results for the 200wppm-content are in agreement with experimental observations.
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https://pastel.archives-ouvertes.fr/pastel-00002307
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Submitted on : Thursday, July 29, 2010 - 10:43:01 AM
Last modification on : Wednesday, October 14, 2020 - 3:52:13 AM
Long-term archiving on: : Thursday, November 4, 2010 - 10:20:53 AM

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  • HAL Id : pastel-00002307, version 1

Citation

Aude Racine. Influence de l'orientation des hydrures sur les modes de déformation, d'endommagement et de rupture du Zircaloy-4 hydruré.. Sciences de l'ingénieur [physics]. Ecole Polytechnique X, 2005. Français. ⟨pastel-00002307⟩

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