Analyse par éléments finis du sertissage de capsules d'étanchéité

Des capsules métalliques, avec joint intégré, sont couramment utilisées dans l'industrie alimentaire pour assurer l'étanchéité des bouteilles de verre par sertissage. La performance de l'assemblage est mesurée par la pression de fuite. Dans cette thèse, la simulation par éléments finis du sertissage d'une capsule sur une bouteille de verre est réalisée pour obtenir la distribution des forces exercées sur le joint en fonction de la pression interne. La simulation du sertissage est réalisée à l'aide du logiciel de calcul par éléments finis Ansys®. L'analyse tridimensionnelle tient compte du comportement élasto-plastique de la capsule métallique, du comportement hyperélastique du joint polymère, et des phénomènes de contact entre les outillages rigides et la capsule. Des mesures réalisées en laboratoire pour caractériser le comportement du joint en fonction de la pression de fuite ont été combinées aux résultats numériques de la simulation pour prédire la pression de fuite d'un assemblage donné. La comparaison entre la géométrie finale de l'assemblage serti et la simulation est très acceptable. De plus la prédiction de la pression de fuite d'un assemblage est d'un accord raisonnable avec l'expérimentation

Through-Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam-Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

In this study, the integrity of electron beam- (EB-) welded CA6NM—a grade of 13% Cr-4% Ni martensitic stainless steel—was assessed through the entire joint thickness of 90 mm after postweld heat treatment (PWHT). The joints were characterized by examining the microstructure, residual stresses, global mechanical properties (static tensile, Charpy impact, and bend), and local properties (yield strength and strain at fracture) in the metallurgically modified regions of the EB welds. The applied PWHT tempered the "fresh" martensite present in the microstructure after welding, which reduced sufficiently the hardness (<280 HV) and residual stresses (<100 MPa) to meet the requirements for hydroelectric turbine assemblies. Also, the properties of the EB joints after PWHT passed the minimum acceptance criteria specified in ASME sections VIII and IX. Specifically, measurement of the global tensile properties indicated that the tensile strengths of the EB welds in the transverse and longitudinal directions were on the same order as that of the base metal (BM). Evaluation of the local tensile properties using a digital image correlation (DIC) methodology showed higher local yield strengths in the fusion zone (FZ) and heat-affected zone (HAZ) of 727 MPa and 740 MPa, respectively, relative to the BM value of 663 MPa. Also, the average impact energies for the FZ and HAZ were 63 J and 148 J, respectively, and attributed to the different failure mechanisms in the HAZ (dimples) versus the FZ (quasi-cleavage consisting of facets and dimples). This study shows that the application of PWHT plays an important role in improving the weld quality and performance of EB-welded CA6NM and provides the essential data for validating the design and manufacturing process for next-generation hydroelectric turbine products

Investigation of pressing process forlarge and thick blades of Francis turbines

Hot pressing process is very popular for thin plates in metal forming, such as in automotive construction. However, the process mechanism for very thick plates of high strength steel at hot temperature needs to be investigated. The process is characterized by thermo-mechanical behaviors, three-dimensional unsteady deformation and high nonlinearity. In this paper, the model of the process for manufacturing large and thick blades of Francis turbine is proposed. The process analysis is based on finite element method under ANSYS/LS-DYNA platform to get better understanding of the process. The whole process consists of the pressing forming of a blade from a flat blank, the springback after the forming and the cooling of the blade from hot temperature to room temperature. Investigation of the stress evolution is performed

Reassessment of cell to module gains and losses: Accounting for the current boost specific to cells located on the edges

The power produced by a photovoltaic module is not simply the sum of the powers of its constituents cells. The difference stems from a number of so-called “cell-to-module” (CTM) gain or loss mechanisms. These are getting more and more attention as improvements in cell efficiency are becoming harder to achieve. This work focuses on two CTM mechanisms: the gain due to the recapture of light hitting the apparent backsheet in the “empty” spaces around the cells and the loss from the serial connection of “mismatched” cells i.e. with different maximum power points. In general, for insulation purposes, the spaces on the edges of modules are larger than the spacing between cells. This study reveals that, when reflective backsheets are used, these “edge spaces” provide an additional current boost to the cells placed at the edges that can lead to a 0.5% gain in the output power of modules (with 60 or 72 cells). This location-dependent current boost adds to the usual variations in cell characteristics dictated by the binning size and results in larger “cell-to-cell mismatch losses”. However, the simulations reveal that for short-circuit current bin size smaller than 5%, this additional mismatch loss is lower than 0.05%. All considered, this study demonstrates that the spaces at the edges of PV modules have a significant impact on the cell to module ratios (≈+0.5%abs or ≈16% of the CTM gains) when reflective backsheets are used

αB Crystallin Is Apically Secreted within Exosomes by Polarized Human Retinal Pigment Epithelium and Provides Neuroprotection to Adjacent Cells

αB Crystallin is a chaperone protein with anti-apoptotic and anti-inflammatory functions and has been identified as a biomarker in age-related macular degeneration. The purpose of this study was to determine whether αB crystallin is secreted from retinal pigment epithelial (RPE) cells, the mechanism of this secretory pathway and to determine whether extracellular αB crystallin can be taken up by adjacent retinal cells and provide protection from oxidant stress. We used human RPE cells to establish that αB crystallin is secreted by a non-classical pathway that involves exosomes. Evidence for the release of exosomes by RPE and localization of αB crystallin within the exosomes was achieved by immunoblot, immunofluorescence, and electron microscopic analyses. Inhibition of lipid rafts or exosomes significantly reduced αB crystallin secretion, while inhibitors of classic secretory pathways had no effect. In highly polarized RPE monolayers, αB crystallin was selectively secreted towards the apical, photoreceptor-facing side. In support, confocal microscopy established that αB crystallin was localized predominantly in the apical compartment of RPE monolayers, where it co-localized in part with exosomal marker CD63. Severe oxidative stress resulted in barrier breakdown and release of αB crystallin to the basolateral side. In normal mouse retinal sections, αB crystallin was identified in the interphotoreceptor matrix. An increased uptake of exogenous αB crystallin and protection from apoptosis by inhibition of caspase 3 and PARP activation were observed in stressed RPE cultures. αB Crystallin was taken up by photoreceptors in mouse retinal explants exposed to oxidative stress. These results demonstrate an important role for αB crystallin in maintaining and facilitating a neuroprotective outer retinal environment and may also explain the accumulation of αB crystallin in extracellular sub-RPE deposits in the stressed microenvironment in age-related macular degeneration. Thus evidence from our studies supports a neuroprotective role for αB crystallin in ocular diseases

BPAG1a and b Associate with EB1 and EB3 and Modulate Vesicular Transport, Golgi Apparatus Structure, and Cell Migration in C2.7 Myoblasts

BPAG1a and BPAG1b (BPAG1a/b) constitute two major isoforms encoded by the dystonin (Dst) gene and show homology with MACF1a and MACF1b. These proteins are members of the plakin family, giant multi-modular proteins able to connect the intermediate filament, microtubule and microfilament cytoskeletal networks with each other and to distinct cell membrane sites. They also serve as scaffolds for signaling proteins that modulate cytoskeletal dynamics. To gain better insights into the functions of BPAG1a/b, we further characterized their C-terminal region important for their interaction with microtubules and assessed the role of these isoforms in the cytoskeletal organization of C2.7 myoblast cells. Our results show that alternative splicing does not only occur at the 5′ end of Dst and Macf1 pre-mRNAs, as previously reported, but also at their 3′ end, resulting in expression of additional four mRNA variants of BPAG1 and MACF1. These isoform-specific C-tails were able to bundle microtubules and bound to both EB1 and EB3, two microtubule plus end proteins. In the C2.7 cell line, knockdown of BPAG1a/b had no major effect on the organization of the microtubule and microfilament networks, but negatively affected endocytosis and maintenance of the Golgi apparatus structure, which became dispersed. Finally, knockdown of BPAG1a/b caused a specific decrease in the directness of cell migration, but did not impair initial cell adhesion. These data provide novel insights into the complexity of alternative splicing of Dst pre-mRNAs and into the role of BPAG1a/b in vesicular transport, Golgi apparatus structure as well as in migration in C2.7 myoblasts

Méthodologie pour la sélection d'éléments mécaniques complexes

La complexité d'un système mécanique soumis à des chargements séquentiels provoquant des déformations plastiques entraîne de grandes difficultés de conception. Ces difficultés, sous réserve de fournir un évaluation précise des énergies à dissiper pour chacun de ces chargements, peuvent être surmontées en trois temps par: 1) la définition d'une fonction objectif, 2) l'identification des variables et des liaisons du problème, et 3) l'adaptation d'un système informatisé, en l'occurrence le programme DMNC conçu à cet effet, qui utilise les résultats des calculs sur la fonction objectif, séquence après séquence, pour sélectionner les paramètres de conception adéquats. Le programme tient compte de l'évolution de la géométrie et de conditions difficiles ou impossibles à traiter sous forme de liaisons numériques. Dans ce mémoire, on se propose d'appliquer cette méthodologie à la conception d'une structure de protection (ROPS) pour tracteur agricole ou industriel subissant un renversement latéral. Le programme DMNC utilise l'information de base d'une conception initiale de la structure de protection pour bâtir un modèle par éléments finis. Ce modèle est ensuite soumis à une séquence de chargements qui simule l'historique de la série d'impacts encaissés au cours du renversement latéral. Le rôle de cette simulation est de faire absorber à la structure une quantité d'énergie donnée sous forme de déformation permanente. Au cours du processus de chargement, la matrice de rigidité de la structure est constamment remise à jour pour tenir compte des grands déplacements et les paramètres de conception sont modifiés jusqu'à ce que l'objectif "énergie absorbée" soit atteint. Le programme DMNC donne alors, pour une distribution d'énergie à absorber fournie par l'utilisateur, les paramètres de conception de la structure de protection. Il faut maintenant noter trois remarques importantes: 1°) il n'est pas présenté ici de méthode pour évaluer la distribution d'énergie réelle à absorber par impact du fait de la grande difficulté que représente son estimation, 2°) cette estimation dépasse le cadre de ce mémoire, et 3°) la distribution d'énergie utilisée pour présenter le programme DMNC n'est pas représentative d'un cas réel de renversement latéral, ce qui implique que les paramètres de conception déterminés, liés à cette distribution, n'ont pas de signification physique réelle

Solubilisation et caracterisation de macromolecules proteiques d'origine placentaire

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 81362 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc