Analyse de la rupture et évaluation de la durée de vie basée sur la fiabilité des tubes en polyéthylène pour le transport du gaz

L'objectif de la première partie de cette recherche est de mettre en relief les lois statistiques qui s'adaptent à la rupture par fatigue des canalisations de transport de gaz en polyéthylène. Les résultats indiquent qu'il est recommandé d'utiliser la distribution de Weibull à deux paramètres pour l'évaluation de la fiabilité de ces canalisations pour la phase conception vu leur l'aspect conservateur. La seconde partie est une nouvelle contribution pour l'analyse des résultats de fissuration par fatigue dans ces tubes en termes de paramètres énergétiques basés sur le travail irréversible et la vitesse de propagation. La transition de fragile à ductile est ainsi décrite par des énergies critiques obtenues pour différentes charges de fatigue. Enfin, la fiabilité et l'optimisation de la maintenance des pipes en polyéthylène sont approchées par l'étude de l'effet de la température et de la pression sur la probabilité de défaillance. Il en ressort que l'effet des incertitudes relatives à la température et au modèle de durée de vie est plus important que les fluctuations de la pression du gaz et la géométrie, alors que le remplacement groupé des tronçons usés est bien justifié à partir de la vie de service et des coûts correspondantsCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Inelastic X-ray scattering and first-principles study of electron excitations in MgB2

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)An experimental and theoretical study of electronic excitations in MgB2 covering the domain of large energy and momentum transfers is reported. Energy-loss spectra for several values of momentum transfers were measured in a polycrystalline sample by means of inelastic X-ray scattering spectroscopy. Ab initio calculations of the dielectric function as well as the energy-loss function were performed in the frame of the time-dependent local density approximation with inclusion of crystal local-field effects. We obtained very good agreement between the experimental and the theoretical energy dispersion of the peak maximum of the loss function. We found that crystal local-field effects are responsible for this agreement at large momenta. Fine structure observed in the measured spectra was interpreted in terms of strong interband transitions predicted by the calculations in the Gamma A and Gamma K directions. The theoretical dispersion of these features is in good accordance with the experimental data. Further spectral features in the measured spectra due to Mg 2s and 2p core electron excitations are also discussed. (c) 2009 Elsevier Ltd. All rights reserved.14939-4017061711SeCyT (Universidad Nacional de Cordoba, Argentina)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)University of the Basque Country [GIC07IT36607]Departamento de Educacion del Gobierno VascoSpanish Ministerio de Ciencia y Technologia (MCyT) [FIS200766711C0101]IKERBASQUE FoundationLNLS-Brazilian Synchrotron Light Laboratory/MCTFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)University of the Basque Country [GIC07IT36607]Spanish Ministerio de Ciencia y Technologia (MCyT) [FIS200766711C0101

Interaction of slow multicharged ions with solid surfaces

The present report deals with the main aspects of the interaction of slow (impact velocity typically below 1 a.u.) multicharged ions (MCI) with atomically clean solid surfaces of metals, semiconductors and insulators. It is based to a large extent on the results obtained by the authors and their affiliates within the Human Capital and Mobility Network of the European Union on ''Interaction of Slow Highly Charged Ions with Solid Surfaces'', which has been carried out during the last three years.After briefly reviewing the pertinent historical developments, the experimental and theoretical techniques applied nowadays in the held of MCI-surface interaction studies are explained in detail, discussing especially the transient formation and relaxation of ''hollow atoms'' formed in such collisions. Further on, the status of the field is exemplified by numerous results from recent studies on MCI-induced emission of slow and fast electrons (yields and energy distributions), projectile soft X-ray spectroscopy, charge-changing and energy loss of scattered and surface-channelled projectiles, MCI-induced sputtering and secondary ion emission, and coincidence measurements involving different signatures from the above processes. The presented theoretical and experimental work has greatly contributed to an improved understanding of the strongly inter-related electronic transitions taking place for MCI above, at and below a solid surface.</p