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No description available.

A new approach is developed for evaluating the mixing properties of binary solutions at high pressure. This involves solving Poisson's equation throughout three-dimensional cubic lattices, consistent with Thomas-Fermi-Dirac (TFD) theory. Zero temperature calculations are carried out for a variety of compositions and crystal structures in 3 pressure groups relevant to Jovian planetary interiors. Pseudopotentials based on the two-component-plasma model (with a uniform electron background) are fitted to the solid-state results, and are then used in liquid-state calculations using hard-sphere perturbation theory. TFD results for H-He solutions find critical temperatures (above which all compositions are soluble) to be ∿ 0, 500, and 1500°K at pressures of 10, 100, and 1000 Mbar, respectively. These temperatures are much lower than those obtained using free electron perturbation theory, where T(crit) ∿ 10,000°K at 10 Mbar. Thus, unlike the perturbation theory results, the TFD results predict that helium should be soluble in metallic hydrogen in the deep interiors of both Jupiter and Saturn, and our calculations give an indication of the degree of model-dependence in computing high pressure mixing properties. In addition, TFD calculations for H-C and H-O solutions find phase separation temperatures to be≲ 10⁴ °K for pressures ≲ 10³ Mbar. These temperatures are considerably lower than those found assuming a uniform electron distribution (where T(crit) ≳ 10⁵ °K), and suggest that H-C and H-O solutions should also be miscible in the metallic zones of Jupiter and Saturn.

Les viroles en acier microallié 18MND5, destinées aux générateurs de vapeur, présentent une composition hétérogène à plusieurs échelles. Un écart au procédé de fabrication ou une teneur en hydrogène excessive, peuvent conduire à la formation des Décohésions Dues à l’Hydrogène. Ces DDH résultent de la désorption de l’hydrogène interne lors du refroidissement jusqu’à température ambiante. La pression interne n’étant pas mesurables expérimentalement, une modélisation du phénomène est requise. Afin de préciser les mécanismes sous-jacents, il est proposé un scénario de formation de ces défauts s’appuyant conjointement sur une expertise et la modélisation des processus de diffusion-désorption-propagation. Les observations ont révélé une corrélation entre les DDH, les zones ségrégées et les amas de MnS (sites préférentiels d’initiation). Un modèle de diffusion dans un milieu hétérogène a été proposé afin d’évaluer la pression interne associée. La pression maximale excède ainsi 8600 bar en considérant une loi d’Abel-Noble optimisée du gaz réel. Le couplage de ce modèle avec la mécanique de la rupture a permis de quantifier l’évolution des paramètres relatifs à la propagation (pression interne, taille finale, vitesse, …). Un scénario de formation des DDH industriel a ainsi pu être formulé sur la base d’une étude paramétrique. Bien que les simulations préliminaires corroborent le retour d’expérience, le modèle raffiné et la prise en compte du gonflement de la DDH semblent sous-estimer la cinétique. Le caractère multi-fissuré des amas de MnS (homogénéisation des propriétés mécaniques) associé à un critère de rupture à l’échelle locale permettrait d’ajuster ce modèle. / Heat generators are manufactured from ingots of 18MND5 (A508cl3) low alloy steel and present composition heterogeneities at different scales. Under specific conditions (non-respect of guidelines or high initial content of H), Hydrogen Induced Cracks (HIC) may result from diffusion-desorption of internal hydrogen during cooling down to room temperature. Since neither hydrogen redistribution nor its internal pressure within cavities could be measured by experimental techniques, quantitative investigation is based on the modelling of related physical phenomena. A scenario of HIC formation, based on industrial feedback and modelling, has been proposed. A correlation between these defects, segregated areas and clusters of MnS (preferred initiation sites) has been revealed by expertise of HIC. A model of diffusion in heterogeneous alloys has then been proposed to assess the maximal pressure of H2 in such HIC. Simulation has shown that internal pressures above 860MPa are reached by considering an optimized Abel-Noble real gas behavior. The previous model has then been coupled to a failure mechanics procedure to characterize and quantify the crack growth parameters. Based on a parametric study, a scenario of HIC formation during the cooling has been proposed regarding process. Although results from preliminary simulations matched with feedback, the refined model based on the pressure induced elastic deformation of HIC has been developed but provided an underestimated kinetic of crack growth. Consequently, the multi-cracked nature of MnS clusters (homogenization of mechanical properties) and the updated local failure criterion appear to be a viable path to adjust predictions.