Modélisation du mécanisme de coalescence des grains de polymère

Dans le procédé du rotomoulage, le phénomène physique majeur lors de l’écoulement des poudres est la coalescence et densification des grains. La coalescence est la formation d’une seule particule elliptique à partir de deux particules sous l’effet de la température et des forces de tension surfacique. Nous intéressons dans cette étude en particulier au mécanisme de coalescence des grains de poudre de PVDF. Les résultats de cette étude permettent de déterminer des paramètres tel que la vitesse de la coalescence pour l’optimisation du procédé

Etude de l'endommagement de structures composites à matrice thermoplastique : application aux réservoirs de stockage hyperbare de l'hydrogène = Study of damages on thermoplastic composite structures: application for hydrogen storage vessels under high pressure

National audienceLe stockage de l'hydrogène est un verrou technologique et scientifique majeur à son utilisation comme vecteur énergétique, en remplacement des sources d'énergie traditionnelles. En effet, aujourd'hui encore, aucune solution « Haute pression » ne satisfait pleinement l'ensemble des spécifications techniques et économiques des industriels. Des progrès sont donc encore nécessaires pour améliorer les performances et la durabilité des réservoirs. Depuis 1998, le CEA travaille sur le développement de réservoirs de stockage haute pression de type IV (liner polymère renforcé d'une structuration composite). L'identification des paramètres matériaux et procédé influents ainsi que des sollicitations susceptibles de modifier les performances et la durabilité des réservoirs doit être prise en compte. En ce sens, les composites à matrice thermoplastique apparaissent comme de bons candidats en terme de durabilité et sécurité (Projet Français HYPE). Cet article présente les premiers résultats de travaux visant à développer les connaissances sur les mécanismes d'endommagement de structures composites à matrice thermoplastique (polyamide) liés à leur procédé de mise en forme (enroulement filamentaire) et leur utilisation pour le stockage hyperbare. Cette étude vise notamment à optimiser les étapes de conception numérique et de fabrication grâce à la connaissance des lois de comportement et de la durabilité du matériau. Dans un premier temps, on s'intéresse à des endommagements sous sollicitations statiques avant de s'intéresser à des sollicitations dynamiques comme l'impact

Chemorheological study of DGEBA/IPD system for Reactive Rotational Molding (RRM)

The identification of kinetic parameters controlling the crosslinking of Diglycidyl ether of bisphenol/isophorone diamine reactive system was achieved via optimization program (Inverse method) based on Fourier transform near infrared spectroscopy results. The reactivity ratio (k2/k 1) was determined using a new method based on the variation of amine conversion ratio versus epoxy conversion ratio. Gelation and vitrification of the reactive system were also analyzed. Time, temperature, transformation diagram was established to assess the rotational molding of this reactive system

The 2010 Haiti earthquake : a complex fault pattern constrained by seismologic and tectonic observations

After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N-S compressive mechanism, and not the expected left-lateral strike-slip mechanism. A first-order slip model of the mainshock shows a N264 degrees E north-dipping plane, with a major left-lateral component and a strong reverse component. As the aftershock distribution is sub-parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north-dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south-dipping faults, such the Trois-Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt

Tectonic and sedimentary architecture of the Karukera spur: A record of the Lesser Antilles fore-arc deformations since the Neogene

International audienceThe Karukéra spur is an easternmost submerged rise of the Lesser Antilles fore-arc in the Guadeloupe archipelago, culminating about 4000 m above the fore-arc basin 150 km west of the deformation front. The analysis of 3500 km 2D high-resolution multichannel seismic reflection and multibeam bathymetric data, and the study of 14 core samples, allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution. Seven seismic units (US1 to US7) are evidenced, organised into four major depositional sequences separated by erosional surfaces. Units US1 to US4 thicken to the south-southeast on the spur. The sedimentary deposits rest upon a deeply eroded metamorphic basement of the Caribbean Plate as in La Désirade Island. Sequence 1 (units US1 and US2) remains unknown in its lower part because it does not outcrop. Its upper part comprises early Miocene shallow water carbonates. Sequence S2 (Unit US3) only comprises an upper Miocene transgressive systems tract deposited into basinal environment. It is bounded by major erosional surfaces SB2 and SB3. Sequence 3 (US4 to US6) is Zanclean to Pleistocene. It is dominantly composed of shallow water, reefal deposits. Sequence 4 corresponds to recent deposits. The Karukéra spur experienced three main extensional episodes with alternations between uplift and subsidence periods. Uplifts are responsible for emersions and erosions. Subsidence severely drowned shallow water deposits. The first extensional episode led to the formation of horsts and grabens in the basement, prior to early Miocene deposits. The second extensional episode occurred during upper Miocene, in accordance with data in surrounding islands. The third tectonic episode developed since Calabrian. Noticeable is the constant reactivation of N130°–N150°, N150°–N180° and N40° trending faults since early Miocene and the neoformation of E–W trending faults since Calabrian. Our results suggest that at the latitude of Guadeloupean archipelago the Lesser Antilles subduction zone is an erosional margin because of the successive sweepings of the Santa Lucia then Tiburon Ridges

Pliocene to Pleistocene carbonate systems of the Guadeloupe archipelago, French Lesser Antilles: a land and sea study (the KaShallow project)

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