Die eingereichte Dissertation beschäftigt sich mit der messtechnischen Erfassung sowie der Modellierung von Haftkräften zwischen rauen Oberflächen. Dabei wurden durch Variation von Flüssigkeiten sowie dem Nutzen beschichteter Oberflächen verschiedene Benetzungseigenschaften eingestellt und untersucht. Zusätzlich wurden neben dem Kontaktwinkel der untersuchten Systeme die freien Ober- und Grenzflächenenergien bestimmt und mit den Kräften korreliert. Es zeigte sich, dass Haftkräfte auf rauen Oberflächen stets über mehrere Größenordnungen verteilt vorliegen. Die Beschreibung der ermittelten Verteilungen ist dabei entweder durch statistischer Funktionen oder zumindest teils auch durch eine im Rahmen der Arbeit entwickelten Modellierung möglich. Weiterhin zeigte sich, dass eine Unterteilung in verschiedene Haftmechanismen (durch Kapillarbrücken oder van der Waals- sowie polare Wechselwirkungen) vorgenommen werden kann. Kapillarbrücken bilden dabei die größten Kräfte aus. Sie entstehen auf Grund nanoskaliger Blasen (Nanobubbles), welche vor allem auf schlecht benetzenden Oberflächen existieren.

This thesis is devoted to the study of some homogenization problems with applications in lubrication theory. It consists of an introduction, five research papers (I–V) and a complementary appendix.Homogenization is a mathematical theory for studying differential equations with rapidly oscillating coefficients. Many important problems in physics with one or several microscopic scales give rise to this kind of equations, whence the need for methods that enable an efficient treatment of such problems. To this end several mathematical techniques have been devised. The main homogenization method used in this thesis is called multiscale convergence. It is a notion of weak convergence in  Lp spaces which is designed to take oscillations into account. In paper II we extend some previously obtained results in multiscale convergence that enable us to homogenize a nonlinear problem with a finite number of microscopic scales. The main idea in the proof is closely related to a decomposition of vector fields due to Hermann Weyl. The Weyl decomposition is further explored in paper III.Lubrication theory is devoted to the study of fluid flows in thin domains. More generally, tribology is the science of bodies in relative motion interacting through a mechanical contact. An important aspect of tribology is to explain the principles of friction, lubrication and wear. The mathematical foundations of lubrication theory are given by the Navier–Stokes equation which describes the motion of a viscous fluid. In thin domains several simplifications are possible, as shown in the introduction of this thesis. The resulting equation is named after Osborne Reynolds and is much simpler to analyze than the Navier--Stokes equation.The Reynolds equation is widely used by engineers today. For extremely thin films, it is well-known that the surface micro-topography is an important factor in hydrodynamic performance. Hence it is important to understand the influence of surface roughness with small characteristic wavelengths upon the solution of the Reynolds equation. Since the 1980s such problems have been increasingly studied by homogenization theory. The idea is to replace the original equation with a homogenized equation where the roughness effects are “averaged out”. One problem consists of finding an algorithm for computing the solution of the homogenized equation. Another problem consists of showing, on introducing the appropriate mathematical definitions, that the homogenized equation is the correct method of averaging. Papers I, II, IV and V investigate the effects of surface roughness by homogenization techniques in various situations of hydrodynamic lubrication. To compare the homogenized solution with the solution of the deterministic Reynolds equation, some numerical examples are also included. / Godkänd; 2011; 20110408 (johfab); DISPUTATION Ämnesområde: Matematik/Mathematics Opponent: Professor Guy Bayada, Institut National des Sciences Appliquées de Lyon (INSA-LYON), Lyon, France, Ordförande: Professor Lars-Erik Persson, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Tid: Tisdag den 7 juni 2011, kl 10.00 Plats: D2214/15, Luleå tekniska universitet

Este estudo avaliou os efeitos de pastilhas efervescentes na superfície de liga de cobalto cromo (Co-Cr) e resina termopolimerizável, simulando um período de até 5 anos de imersão, como também analisar sua ação antimicrobiana. A partir de uma matriz metálica, padrões de cera circulares (12 x 3 mm) foram obtidos e fundidos em liga de Co-Cr (DeguDent®). As amostras foram imersas em: Polident 3 minutes® (P3M), Steradent® (St), Polident for Partials® (PP), Efferdent® (Ef), Corega Tabs® (CT), Nitradine® (Ni), Fixodent® (Fi) e Kukident® (K). Foi avaliada a resistência à corrosão (Ecorr, Ipass) (n=5) por meio do Potenciostato/Galvanostato. Foram realizadas análises qualitativas complementares com Microscópio Eletrônico de Varredura (MEV) e Espectrometria de Energia Dispersiva de Raios-X (EDS). Após o ensaio de corrosão, cada disco metálico foi incluído em mufla preparada por matrizes circulares de cera (20 x 5 mm), incorporando-o à resina acrílica termopolimerizável (Clássico Ltda®). Os grupos das 4 pastilhas que apresentaram a menor taxa de corrosão e da água destilada (controle) (n=9) foram analisados quanto à rugosidade da superfície metálica e da resina acrílica (Sa, &micro;m) por meio de microscopia confocal a laser. Foram avaliadas a alteração de cor (&Delta;E) da resina por meio de espectrocolorímetro no início e após a simulação de ½, 1, 2, 3, 4 e 5 anos e alteração de massa (g), no início e final, em balança de alta precisão. Para avaliação antimicrobiana, por meio da contagem de Unidades Formadoras de Colônia (UFC/mL), os espécimes mistos foram contaminados com biofilme misto composto por: S. mutans (Sm), S. aureus (Sa), C. albicans (Ca) e C. glabrata (Cg) e, posteriormente, imersos nas soluções higienizadoras, onde foram semeados em meios específicos para contagem das UFC. De acordo com os resultados obtidos (&alpha;=0,05), P3M causou a menor taxa de corrosão e Ni, o menor potencial de corrosão. Com o MEV, verificou-se evidenciação da microestrutura da liga metálica. Quanto à rugosidade superficial do metal, CT (p=0,009) e Ni (p=0,036) causaram aumento na rugosidade em relação ao tempo (Friedman). Na resina, houve aumento da rugosidade após 5 anos (p<0,01). Entre as soluções (Kruskal-Wallis), não houve diferença para ambos os materiais. Não houve diferença na cor da resina acrílica, tanto em relação às soluções (Kruskal Wallis) quanto aos tempos (Friedman). Não foram observadas alterações de massa (Kruskal-Wallis). Quanto à ação antimicrobiana (Kruskal-Wallis), Ni propiciou redução de UFC de Sm (p=0,001). Conclui-se que, embora todas as pastilhas efervescentes não tenham alterado a superfície do metal e da resina acrílica de maneira significativa, nenhuma apresentou ação antimicrobiana contra os microrganismos avaliados do biofilme misto; somente Ni reduziu a quantidade de S. mutans / The aim of this study were: to evaluate the effects of denture cleansers on the surface of cobalt chromium (Co-Cr) and heat-polymerized acrylic resin, simulating a period until 5 years of immersion, as well as to analyze its antimicrobial action. From a metal matrix, disc-shaped wax patterns (12 x 3 mm) were made and later were casting in Co-Cr alloy (DeguDent&trade;). The specimes were immersed in: Polident 3 minutes&trade; (P3M), Steradent&trade; (St), Polident for Partials&trade; (PP), Efferdent&trade; (Ef), Corega Tabs&trade; (CT), Nitradine&trade; (Ni), Fixodent&trade; (Fi) and Kukident&trade; (K). The corrosion resistance (Ecorr, Ipass) (n = 5) was evaluated by Potentiostat / Galvanostat. Further qualitative analyzes were performed with scanning electronic microscopy (SEM) and energy dispersive x-ray spectrometry (EDS). After the corrosion test, each metal disk was included in heat-cured acrylic resin (Clássico Ltda&trade;) using moulds previously prepared from circular wax matrices (20 x 5 mm). The four dentures cleansers with the lowest corrosive potential were analyzed for surface roughness of the metal and acrylic resin (Sa, &micro;m) by laser confocal microscopy. The color change (&Delta;E) of the resin was evaluated by means of a spectrocolorimeter at the beginning and after the simulation of ½, 1, 2, 3, 4 and 5 years and mass change (g), at the beginning and end, in high-precision balance. For antimicrobial evaluation, the mixed specimens (n = 9) were contaminated with multispecies biofilm [S. mutans (Sm), S. aureus (Sa), C. albicans (Ca) and C. glabrata (Cg)] and subsquently immersed in denture cleansers, where they were seeded in specific CFU / mL media. According to the results obtained (&alpha;=0.05), there was a significant difference: P3M presented the lowest corrosion rate and Ni, the lowest corrosion potential. According to SEM, the tablets effervescent provided evidence of the microstructure of the alloy. As for the surface roughness in the metal surface, CT (p = 0.009) and Ni (p = 0.036) showed increase in roughness in relation to time (Friedman). At the resin surface, the roughness growed after 5 years. Among the solutions (Kruskal-Wallis), there was no difference for both materials. There was no difference in the color of the acrylic resin (&delta;E), both for solution (Kruskal-Wallis), and for time (Friedman). Differences in weight weren\'t observed (Kruskal-Wallis). In antimicrobial action (Kruskal-Wallis), Ni group showed significant reduction for Sm (p=0.001). It\'s concluded that, although all the denture cleansers didn\'t significantly changed the surface of the metal and acrylic resin, none showed antimicrobial action against the evaluated microorganisms of the mixed biofilm; only Ni reduced the amount of S. mutans

Cela fait environ soixante ans que l'on s'intéresse à la compréhension et à la modélisation du comportement Elastohydrodynamique (EHD) des joints à lèvres. Cependant, on peut considérer que, jusqu'à présent, leur modélisation n'a pas été totalement et rigoureusement traitée. En effet, même si de nombreuses études ont été consacrées à cette modélisation, plusieurs questions ont été soulevées et font toujours l'objet de controverses entre les chercheurs, à savoir l'impact sur les performances des joints à lèvre de l'effet des surfaces texturées de l'arbre, de la loi adoptée pour le comportement mécanique des joints à lèvre, de la démarche utilisée pour l'élaboration de la matrice de compliance (matrice de souplesse), de l'importance de supposer l'arbre lisse ou rugueux, ainsi que la valeur du rapport entre la largeur du contact et la longueur d'onde du défaut suivant la direction circonférentielle de la lèvre.Dans cette thèse, nous avons tenté d'apporter de façon rigoureuse des réponses claires et précises à toutes ces questions en élaborant et en validant un outil de simulation EHD complet pour les joints à lèvre qui tienne compte de presque tous les paramètres, à savoir une loi de comportement du matériau du joint précise, une matrice de souplesse rigoureusement validée et un arbre qui peut être lisse, rugueux et/ou texturé. De plus, un second modèle analytique est proposé. Il traite le comportement vibratoire du "squeeze film", en tenant compte de la non linéarité des caractéristiques intrinsèques du joint et du film. / It's about sixty years that we are interested in understanding and modeling the Elastohydrodynamic behavior (EHD) of rotary lip seals. However, we can consider that, until now, their modeling has not been accurately treated. Even though many studies have been devoted to this model, several questions have been raised and are still the subject of controversy among researchers, namely the parameters influencing on the rotary lip seals performance, such as: the shaft surface textured, the law adopted for the mechanical behavior of lip seals, the approach used to develop the matrix of compliance, the importance of assuming the smooth or rough shaft, and finally the ratio between the width of contact and the wavelength according the circumferential direction of the lip roughness.The main goal of this thesis is to answer rigorously these questions by developing and validating a numerical tool for EHD rotary lip seals modeling, that takes into account: the lip law behavior, the compliance matrix rigorously validated by assuming smooth shaft case, or rough and textured shaft case. In addition, an analytical approach is proposed, models the vibratory behavior of the "squeeze film". This implies a nonlinear comportment that is taken into account.

I det här arbetet har tätningsmetoder för aluminiumhus undersökts. Arbetet avgränsades mot fordonsindustrin och statiska packningar. Examensarbetet tar upp flänskonstruktionens inver-kan på tätheten och packningen, packningstyper, ytjämnhetens inverkan på packningsmateri-al, porositet, relativ materialkostnad och fästelement.Arbetet grundar sig på en litteraturstudie och intervjuer med berörda personer på företaget. Även praktiska prover genomfördes på ett urval av material från leverantörer där material exponerades för olika kemikalier och därefter dragprovades.Materialet som insamlats genom intervjuer och litteraturstudien vittnar om att många paramet-rar påverkar vilka tätningsmetoder som är möjliga att använda. Det är inte bara materialval som det behövs tas hänsyn till. Faktorer som flänskonstruktioner, materialkostnader, ytdefek-ter, fästelement samt porositet har en stor påverkan. De praktiska proverna vittnar om att olika kemikalier har olika stor inverkan på materialens mekaniska egenskaper och svullnad.Slutligen föreslås ett par packningsmaterial som är lämpliga för företaget att använda i deras produkter. / In this work sealing methods for aluminum housing have been investigated. The work was delimited to the automotive industry and static gaskets. The thesis brings up how the flange impacts on the sealing capability and the gasket, sealing types, the surface impact on gasket materials, porosity, relative material cost and fasteners.The work is based on a literature study and interviews with concerned people at the company. Practical samples were carried out on a number of materials from suppliers and the materials where exposed to different chemicals and then tensile tested.The materials that were collected through interviews and the literature study testify that many parameters influence the possible sealing methods. It’s not just the material itself that needs to be taken into account. Factors like flange design, material cost, surface defects, fasteners and porosity have a great impact. The practical sample testifies that different chemicals have dif-ferent impact on the mechanical properties and swelling of the material.Finally, a couple of sealing materials are suggested that are suitable for the company to use in their products.

Cette étude concerne le transport de particules colloïdales en milieu poreux. Les colloïdes (particules de taille caractéristique inférieure au micron) se rencontrent dans de nombreux domaines de la vie quotidienne (encre, cosmétiques, ...), de la biologie (bactéries, virus, protozoaires, ...) et de l’ingénierie (filtration, hydrologie, génie civil, génie pétrolier, ...). De par leur taille et leur nature, l’étude de ces systèmes nécessite de s’intéresser aux interactions qui peuvent exister entre les particules elles mêmes mais aussi avec le milieu environnant. On cite particulièrement le cas d’écoulements dans des aquifères qui concernent le transport de contaminants d’origine biologique (bactéries, virus), d’origine chimique (hydrocarbures, polluants) ou d’origine minérale (argiles, métaux, ...). Dans chacun des cas cités, il est nécessaire de s’intéresser au transport et dépôt/décollement des particules pour mieux comprendre et modéliser les mécanismes mis en jeu. Une première partie du travail est consacrée à la mise en place et à la résolution d’un modèle macroscopique de dépôt de particules. La comparaison des résultats numériques avec des données expérimentales de la littérature a permis d’établir les relations existantes entre le facteur de retard et la force ionique d’une part et le nombre de Péclet d’autre part. La seconde partie du travail concerne l’étude, à l’échelle microscopique, du transport de particules colloïdales en présence de rugosités de surface (obstacle ou cavité). Les résultats mettent en évidence le rôle joué par ces rugosités de surface sur l’adsorption et désorption de particules sous l’influence des forces hydrodynamiques et des interactions physico-chimiques. / This study deals with the transport of colloidal particles in porous media. Colloids (particles with a characteristic size smaller than one micron) are found in daily life (ink, cosmetics ...) and in many fields of science and technology such as biology (bacteria, viruses, protozoa ...) and engineering (filtration, hydrology, civil engineering, petroleum engineering ...). Because of their size and nature, the study of these systems needs to focus on interactions that may exist between the particles themselves but also with the surrounding environment. This is particularly true in the case of transport of colloids in porous media where the particles characteristic dimension size is close to that of the porous medium. We mention especially the case of flow in aquifers that may affect the transport of contaminants of a biological origin (bacteria, viruses), chemical origin (hydrocarbons, pollutants) or minerals (clay, metals ...). In each case cited above, it is necessary to consider particles transport in porous media and their deposition/release to better understand and model the involved mechanisms. The first part of this work is devoted to the development and resolution of a macroscopic model of particle deposition. Comparison of numerical results with experimental data in the literature has established the existing relationships between a delay factor and both ionic strength and the Peclet number. The second part of the study deals with the study, at the microscopic level, of a colloidal particle transport taking into account DLVO forces for smooth and rough pore surfaces. Our results highlight the role played by surface roughness on the adsorption and desorption of particles under the influence of ionic strength and flow rate.

Afin de mieux comprendre les mécanismes liés à l’érosion du sol sous l’effet du vent, le transport de particules solides dans un écoulement de couche limite turbulente à l’échelle d’une soufflerie est étudié à l’aide de simulations numériques. La présence d’une ou plusieurs collines Gaussiennes au sol permet d’étudier les effets de la topographie sur le transport, le dépôt et la réémission de particules solides. L’écoulement du fluide porteur est résolu par la Simulation des Grandes Échelles (SGE). Des modèles de paroi pour la vitesse du fluide sont implémentés afin de mieux représenter l’écoulement proche d’une colline. Le mouvement des particules est pris en compte par un suivi Lagrangien. Des modèles d’envol et de rebond sont développés et utilisés pour prendre en compte l’émission et l’impact au sol des particules. Dans la première partie, l’écoulement au-dessus de collines transversales est simulé et validé par des comparaisons avec différentes expériences. Selon Oke [1988], l’écoulement dans la canopée urbaine peut être schématiquement caractérisé par différents régimes en fonction du positionnement relatif des obstacles. Ce concept est appliqué au cas des dunes, assimilées à des collines dans notre étude. L’accent est mis sur la zone de recirculation (ZR) formée derrière ces collines. Les variations de la ZR sont examinées en fonction de différents paramètres dont la configuration des collines et le nombre de Reynolds. De plus, une étude portant sur la sous couche rugueuse est effectuée de façon à déterminer l’effet de la rugosité due à la couche de particules solides au sol. La seconde partie du travail porte sur la simulation des particules au-dessus des collines. L’objectif est l’amélioration des modélisations concernant l’envol, le rebond et le couplage entre le fluide et les particules. Un premier travail de validation est réalisé en utilisant le modèle complet de transport des particules solides. En particulier, l’évolution du flux d’émission des particules, estimé par le modèle d’envol, en fonction du nombre de Shields, donne des résultats comparables aux modèles classiques de saltation et aux expériences de la littérature. Au-dessus des collines, le transport des particules solides est étudié par des profils de concentration et de vitesse moyenne. Pour analyser les résultats, deux cartographies sont réalisées. La première donne l’intensité des événements locaux et instantanés qui seraient à l’origine de l’évacuation des particules piégées au sein de la ZR. La seconde montre la distribution des particules déposées au sol. Ces résultats permettent d’identifier des zones sujettes à l’érosion et à l’accumulation autour des collines. Enfin, les flux des particules piégées et déposées à l’intérieur de la ZR sont quantifiés et comparés aux flux des particules émises en amont. Ces flux, bien que faibles par rapport au flux entrant, contribueraient aux migrations des dunes et à l’avancée des déserts. / The transport of solid particles inside a laboratory-scale turbulent boundary-layer is studied by numerical simulations, to obtain a better understanding of the mechanisms associated with wind erosion of soil. The presence of one or several Gaussian hills allows a study of the topographic effects on the transport, deposition and re-emission of solid particles. The carrier fluid motion is resolved in a Large Eddy Simulation (LES). Wall models are implemented to better account for the effects of turbulent flow near the terrain. Particle trajectories are calculated using a Lagrangian tracking. Take-off and rebound models are developed in order to take into account particle emissions and impacts at the wall. In the first part, the flow over transversal Gaussian hills is simulated and validated by comparison with different experiments. According to Oke [1988], the flow inside an urban canopy can be schematically characterised into different flow regimes depending on the relative localisation of the obstacles at the ground. This concept is applied to the case of sand dunes, assimilated to 2D hills in this study. The focus is on the recirculation zone (RZ) on the lee side, which has the characteristic of increasing the residence time and the interaction fluid/particle in general, particle trapping and deposition in particular. The variations of RZ with different hill geometries and Reynolds numbers are examined. A study on the roughness sublayer is conducted in order to determine the roughness effects due to the layer of solid particles on the wall. The second part of the work is devoted to the simulation of solid particle transport over the Gaussian hills. The objective is to improve the modelling of particle take-off, rebound and the two-way coupling between the fluid and the particle. A first work of validation is conducted by using the complete model of solid particle transport developed in this thesis. In particular, the evolution of particle emission flux predicted by the take-off model is in accordance with classical saltation models and experiments from the literature. Over the Gaussian hills, analysis of particle transport is conducted using concentration and mean velocity fields. Two mappings are realised. The first indicates the intensity of the local and instantaneous flow structures that arguably regulate the re-entrainment of particles trapped inside the RZ. The second shows the accumulation of particles on the wall. These results highlight zones prone to wind erosion and particle deposition around the hills. Last but not least, the fluxes of particle trapping and deposition inside the RZ are quantified and compared to the incoming flux from upstream. These fluxes, albeit relatively weak in comparison to the incoming one, contribute potentially to dune migrations and desertification.

La mise en oeuvre de matériaux acoustiques est une méthode efficace et très utilisée pour réduire le bruit le long de sa propagation. Les propriétés acoustiques de nouvelles structures sandwich multifonctionnelles et de matériaux absorbants poreux sont étudiées dans la thèse. Les principales contributions de la thèse sont les suivantes: Les panneaux sandwich ont généralement d'excellentes propriétés mécaniques et un bon indice de perte en transmission sonore (STL), mais aucune capacité d'absorption acoustique. De nouvelles structures sandwich multifonctionnelles sont développées en intégrant des microperforations et des matériaux absorbants poreux aux panneaux sandwich ondulés et en nid d’abeilles conventionnels, structurellement efficaces pour obtenir de bons STL et de bonnes absorptions en basses fréquences. Le coefficient d'absorption acoustique (SAC) et la perte en transmission (STL) des panneaux sandwich ondulés sont évalués numériquement et expérimentalement en basse fréquence pour différentes configurations de perforations. Les modèles éléments finis (EF) sont construits en tenant compte des interactions vibro-acoustiques sur les structures et des dissipations d'énergie, visqueuse et thermique, à l'intérieur des perforations. La validité des calculs FE est vérifiée par des mesures expérimentales avec les échantillons testés obtenus par fabrication additive. Par rapport aux panneaux sandwich ondulés classiques sans perforation, les panneaux sandwich perforés (PCSPs) avec des perforations dans leur plaque avant présentent non seulement un SAC plus élevé aux basses fréquences, mais aussi un meilleur STL, qui en est la conséquence directe. L'élargissement des courbes des indices d’absorption et de transmission doit être attribué à la résonance acoustique induite par les micro-perforations. Il est également constaté que les PCSPs avec des perforations dans les plaques avant et les parois internes onduleés ont les fréquences de résonance les plus basses de tous les PCSPs. En outre, les performances acoustiques des panneaux sandwich en nid d'abeilles avec une plaque avant microperforée sont également examinées. Un modèle analytique est présenté avec l'hypothèse que les déplacements des deux plaques sont identiques aux fréquences inférieures à la fréquence de résonance des plaques. Le modèle analytique est ensuite validé par des modèles d'éléments finis et des résultats expérimentaux existants. Contrairement aux panneaux sandwich en nid d'abeilles classiques qui sont de piètres absorbeurs de bruit, les sandwichs en nid d'abeilles perforés (PHSPs) conduisent à un SAC élevé aux basses fréquences, ce qui entraîne en conséquence un incrément dans le STL basse fréquence. Les influences de la configuration du noyau sont étudiées en comparant les PHSPs avec différentes configurations de noyaux en nids d'abeilles. […] / Implementation of acoustic materials is an effective and popular noise reduction method during propagation. Acoustic properties of novel multifunctional sandwich structures and porous absorbing materials are studied in the dissertation. The main contributions of the dissertation are given as, Sandwich panels generally have excellent mechanical properties and good sound transmission loss (STL), but no sound absorption ability. Novel multifunctional sandwich structures are developed by integrating micro perforations and porous absorbing materials to the conventional structurally-efficient corrugated and honeycomb sandwich panels to achieve good SAC and STL at low frequencies. Low frequency sound absorption and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations are evaluated both numerically and experimentally. Finite element (FE) models are constructed with considerations of acousticstructure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich panels without perforation, the perforated corrugated sandwich panels (PCSPs) with perforations in its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The enlargement of SAC and STL should be attributed to the acoustical resonance induced by the micro perforations. It is also found that the PCSPs with perforations in both the face plates and corrugated cores have the lowest resonance frequencies of all the PCSPs. Besides, the acoustic properties of honeycomb sandwich panels with microperforated faceplate are also explored. An analytical model is presented with the assumption that displacements of the two faceplates are identical at frequencies below the faceplate resonance frequency. The analytical model is subsequently verified by finite element models and existing experimental results. Unlike classical honeycomb sandwich panels which are poor sound absorbers, perforated honeycomb sandwiches (PHSPs) lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Influences of core configuration are investigated by comparing PHSPs with different honeycomb core configurations. In order to enlarge the SAC bandwidth of perforated sandwich panels, porous absorbing materials are added to the cores of novel perforated sandwich panels. FE models are set up to estimate the SAC and STL of perforated sandwich panels with porous materials. Results show that perforated sandwich panels with porous material can provide SAC with broader bandwidth and lower resonance frequency than that without porous materials. Whereas the peak values in the SAC and STL curves are reduced due to the weakened acoustical resonance by the porous materials. […]

La grande diversité des applications, dans tous les domaines industriels, des plus simples aux plus complexes, que ce soit pour un usage quotidienne ou pour des applications high-tech, nécessite la conception continue de systèmes d'étanchéité de plus en plus performants. Les vérins pneumatiques sont des éléments fondamentaux de l'automatisation dans des domaines industriels très variés : les dispositifs de levage, la robotique, l'aérospatial, les systèmes respiratoire, etc. Cependant, un dysfonctionnement d'étanchéité conduit à des performances plus faibles et même à des disfonctionnements. Inversement, une meilleure connaissance des phénomènes aux interfaces, permettra l’amélioration du rendement, la prolongation de la durée de vie et de la fiabilité des différentes applications pneumatiques.Ce travail de thèse est focalisé sur l'étude expérimentale et numérique des systèmes d'étanchéité par joints pneumatiques. Un banc d'essais modulable a été conçu et réalisé pour permettre l'investigation expérimentale de différents types de joints pneumatiques, pour une large gamme de conditions de fonctionnement, en termes de vitesse linéaire, pression pneumatique et solutions constructives. Il permet principalement de caractériser le frottement des joints mais aussi la visualisation des phénomènes physiques au niveau de la zone d'étanchéité et de son environnement.En parallèle, un modèle théorique ElastoHydroDynamique, incluant la prise en compte des conditions de lubrification mixte et le comportement rhéologique non-newtonien de lubrifiant (graisse) a été développé. Il est basé sur le couplage d'un logiciel de calcul non-linéaire (permettant la prise en compte du comportement mécanique hyperélastique des joints) et un modèle d'écoulement en film mince. Les comparaisons de mesures expérimentales avec les prédictions numériques ont permis de valider le modèle théorique ainsi que d'améliorer la compréhension des conditions de fonctionnement et d'alimentation de la zone d'étanchéité. / The great diversity of applications in all industrial fields, from the simplest to the most complex, whether for everyday use or for high-tech applications, requires the continuous design of increasingly efficient sealing systems. Pneumatic cylinders are fundamental elements of automation in a wide variety of industrial fields: lifting devices, robotics, aerospace, respiratory systems, etc. However, a sealing failure leads to lower performance and even malfunctions. Conversely, a better knowledge of the phenomena at the interfaces will allow the improvement of efficiency, the extension of the service life and of the reliability of the various pneumatic applications.This thesis work focuses on the experimental and numerical study of pneumatic seal systems. A modular test bench has been designed and built to allow the experimental investigation of different types of pneumatic seals, for a wide range of operating conditions, in terms of linear velocity, pneumatic pressure and constructive solutions. It mainly allows to characterize the friction of the joints but also the visualization of physical phenomena at the level of the sealing zone and its environment.In parallel, an ElastoHydroDynamic theoretical model, including the consideration of mixed lubrication conditions and the non-Newtonian rheological behaviour of lubricant (grease) has been developed. It is based on the coupling of a non-linear comercial software (allowing the modelling of the hyperelastic mechanical behaviour of the joints) and a thin film flow model. Comparisons of experimental measurements with numerical predictions validated the theoretical model and improved the understanding of the operating and supply conditions of the sealing area.

The aim of this research work is to study the inter-relationship, under controlled industrial conditions, among skin pass reductions, surface topography characterized by 2D and 3D roughness parameters, stampability and painted surface finish quality for automotive steel sheet stampings. Different surface textures obtained from cold rolling finishing have been evaluated in terms of paint appearance (rating and spectral curve) and tentatively related to roughness parameters (2D and 3D) obtained from the cold finished sheets. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research showing that there is a clear relationship between these parameters, and that further detailed studies are needed. / O foco do presente trabalho é o estudo, em condições industriais, da inter-relação entre grau de redução do passe de acabamento, topografia superficial caracterizada pelos parâmetros de rugosidade 2D e 3D, estampabilidade e aparência de pintura de chapas de aço para painéis automotivos. Diferentes texturas superficiais de chapas de aço foram analisadas em termos de aparência de pintura (rating e curvas espectrais) e tentativamente relacionadas com os parâmetros de rugosidades (2D e 3D) obtidos na chapa antes de estampar. Algumas tendências relevantes foram estabelecidas entre estes parâmetros. Os resultados presentes aqui estão de acordo com publicações recentes mostrando uma clara relação entre estes parâmetros e que trabalhos futuros ainda são necessários.