Les tendances actuelles en lubrification visent à réduire la quantité d’huile dans les mécanismes. En conséquence l’épaisseur de film dans les zones de contact est réduite à l’échelle du nanomètre, et peu de molécules de lubrifiant assurent la séparation des surfaces. Des simulations basées sur la méthode de la Dynamique Moléculaire sont utilisées pour étudier le comportement de ces films sévèrement confinés à l’échelle des atomes. Une attention particulière est portée sur le phénomène de glissement aux parois : des lois analytiques sont formulées pour quantifier et prédire cet effet en fonction du couple surface-fluide ou des conditions opératoires locales dans un contact. Ensuite, un couplage entre les modèles moléculaires et macroscopiques est effectué. Les équations classiques de la lubrification sont modifiées pour inclure les effets de glissement quantifiés précédemment. Il est montré que l’épaisseur de film au centre d’un contact et le frottement sont modifiés de façon significative. Enfin, la problématique de réduction de la quantité de lubrifiant est poussée à ses limites jusqu’à atteindre la rupture du film et le contact direct entre solides. Une analyse à l’échelle moléculaire de ce processus permet de faire le lien entre la disposition des dernières molécules séparant les surfaces et le comportement tribologique local. / The modern trends in lubrication aim at reducing the oil quantity in tribological applications. As a consequence, the film thickness in the contact zone decreases significantly and can reach the order of magnitude of a few nanometres. Hence, the surface separation is ensured by very few lubricant molecules. Atomistic simulations based on the Molecular Dynamics method are used to analyze the local behavior of these severely confined films. A particular attention is paid to the occurrence of wall slip: predictive models and analytical laws are formulated to quantify and predict this phenomenon as a function of the surface-lubricant pair or the local operating conditions in a contact interface. Then, the coupling between Molecular Dynamics simulations and macroscopic models is explored. The classical lubrication theory is modified to include slip effects characterized previously. This approach is employed to study an entire contact featuring a nano-confined lubricant in its center, showing a severe modification of the film thickness and friction. Finally, the lubricant quantity reduction is pushed to the limits up to the occurrence of local film breakdown and direct surface contact. In this scenario, atomistic simulations allow to understand the relationship between the configuration of the last fluid molecules in the contact and the local tribological behavior.

Ce travail de thèse concerne les écoulements de fluides à seuil de contrainte autour d‘un obstacle cylindrique en milieu confiné avec une configuration d‘écoulement de Poiseuille.Expérimentalement, un banc d‘essai permettant d‘obtenir un écoulement en continu dans un circuit fermé a été mis en place. Les régimes d‘écoulement rampant, recirculant et instationnaire périodique ont été étudiés. De nouveaux résultats ont été obtenus avec un fluide newtonien et des solutions de Carbopol, polymère permettant de réaliser des fluides à seuil modèles utilisés en recherche et développement et dans l‘industrie. Une caméra rapide et un éclairage plan laser a servi pour l‘établissement d‘images qui ont ensuite été traitées par PIV. Les champs de vitesses cinématiques, les morphologies d‘écoulement et les paramètres critiques de transitions de régimes ont été déterminés.Numériquement, un modèle viscoplastique basé sur la loi de Herschel-Bulkley régularisée a été utilisé. Des résultats comme les morphologies d‘écoulement, la localisation des zones rigides, les champs de vitesses ont été obtenus. Ceci a permis de comparer les différences entre les effets liés à la nature des gels de Carbopol et la modélisation viscoplastiques. Une étude spécifique sur le glissement à l‘interface fluide-structure a également été réalisée avec l‘utilisation d‘un modèle de lubrification élasto-hydrodynamique. / The flow of yield stress fluids around a circular cylinder in a confined geometry has been investigated with a Poiseuille flow configuration.Experimentally, a test set-up was built which provides a continuous flow in a closed loop. We studied creeping, recirculating and vortex shedding flow regimes. New results has been realised with a Newtonian fluid and Carbopol solutions, models for yield stress behaviour in laboratory experiments and in industry. A high speed camera and a laser sheet have been used to perform images which are treated by PIV. Kinematic fields, flow morphologies and critical transition parameters have been determined.Numerically, a viscoplastic model based on the regularised Herschel-Bulkley law has been used. Results as flow morphologies, rigid areas and local flow parameters fields have been performed. That allowed us to compare the intrinsic effects of Carbopol solutions and the viscoplastic numerical model. A specific study on the wall slip has also been considered with an elasto-hydrodynamic lubrication model.

Um den Spritzgießprozess zu simulieren, sind korrekte Materialdaten nötig. Diese Daten umfassen Viskositätsmodelle, Wärmekapazitätskoeffizienten, Wärmeleitfähigkeitskoeffizienten, PVT-Modelle und bei reaktiven Materialien Härtungsmodelle. Bei der Spritzgießsimulation von Thermoplasten sind die Materialdaten in der Regel in den Simulationstools verfügbar. Der Anwender kann problemlos Thermoplastmaterialdaten auswählen, die bereits in die Materialdatenbank der Simulationswerkzeuge eingebettet waren, um die gesamten Phasen des Thermoplastspritzgießprozesses zu simulieren. Bei der Duroplastspritzgießsimulation sind nur begrenzt Materialdaten vorhanden und selten aus der Datenbank der Simulationswerkzeuge verfügbar, da sie nicht nur bei der Messung rheologischer und thermischer Eigenschaften, sondern auch bei der Modellierung rheologischer und kinetischer mathematischer Modelle kompliziert sind. Daher ist es notwendig, eigene Materialdaten zu generieren. Um dieses Problem zu lösen, bedarf es einer umfangreichen Wissensbasis bei der Messung von Materialeigenschaften sowie der Erstellung eines Optimierungsalgorithmus´. Um den Prozess des duroplastischen Spritzgießens exakt zu simulieren, bedarf es zudem fundierter Kenntnisse über die Formfüllungseigenschaften dieser Materialien. Die Untersuchung des Fließverhaltens von duroplastischen Spritzgießmassen im Inneren der Kavität ist jedoch nicht ausreichend beschrieben. Bisher gab es noch keine veröffentlichten Hinweise, die zeigen, wie man aus experimentellen Messdaten (thermische und rheologische Daten) für den reaktiven Spritzgießsimulationsprozess komplette Materialdaten für Duroplaste erzeugen kann. Diese Probleme führen zu einer Abhängigkeit der Anwender von der Materialdatenbank der Simulationssoftware, was zu einer Einschränkung der Anwendung der Computersimulation in der duroplastischen Spritzgießsimulation und dem Vergleich zwischen experimentellen und Simulationsergebnissen führt. Darüber hinaus stellt sich die Frage, ob es beim Füllen der Kavität ein Wandgleiten zwischen Duroplastschmelze und Wandoberfläche gibt oder nicht. Aus diesem Grund wird die Wirkung des Wandgleitens auf die Kavitätenoberfläche bei der Simulation des duroplastischen Spritzgießens immer noch vernachlässigt. Die vorliegende Arbeit konzentriert sich auf drei wichtige wissenschaftliche Ziele. Das erste ist die Innovation eines neuen technischen Verfahrens zur physikalischen Erklärung des Formfüllverhaltens von duroplastischen Spritzgießmassen. Das zweite Hauptziel ist die Entwicklung einer numerischen Methode zur Erstellung eines duroplastischen Materialdatenblattes zur Simulation der Formfüllung von duroplastischen Spritzgießmassen. Schließlich wird die Erstellung von Simulationswerkzeugen auf der Grundlage der physikalischen Gegebenheiten und des erzeugten Materialdatenblattes durchgeführt. / To simulate the injection molding process, it is necessary to set material data. The material data for an injection molding process must include a viscosity model and its fitted coefficients, heat capacity coefficients, thermal conductivity coefficients, a PVT model and its coefficients, a curing model and its coefficients (only for reactive injection molding). With thermoplastics injection molding simulation, the material data is generally available from simulation tools. Users could easily choose thermoplastics material data that was already embedded in the material data bank of simulation tools to simulate the entire phases of thermoplastics injection molding process. However, with thermosets injection molding simulation, the material data is found in limited sources and seldom available from data bank of simulation tools because of complication not only in rheological and thermal properties measurement but also in modeling rheological and cure kinetics mathematical models. Therefore, with thermoset injection molding compounds that its material data bank has not been found in data bank of simulation tools, before setting material data, it is necessary to create its own material data that simulation packages do not supply a tool. Therefore, to solve this problem, it requires an extensive knowledge base in measurements of material properties as well as optimization algorithm. In addition, to simulate exactly the thermosets injection molding compound process, it requires a profound knowledge in the mold filling characteristics of thermoset injection molding compounds. However, investigation of flow behavior of thermosets injection molding compounds inside the mold has not been adequately described. Up to now, there has not been any article that shows a complete way to create thermoset material data from measured experimental data (thermal data and rheological data) for the reactive injection molding simulation process. These problems are leading to the users ‘dependency on the material data bank of simulation tools, leading to restriction in application of computer simulation in the thermoset injection molding simulation and comparison between experimental and simulation results. Furthermore, there is still a big question related to whether there is or no slip phenomenon between thermosets melt and the wall surface during filling the cavity, for which has not yet been found an exact answer. Because of this the effect of wall slip on the cavity surface is still ignored during thermoset injection molding simulation process. This thesis focused on three key scientific goals. The first one is innovation of a new technical method to explain the mold filling behavior of thermoset injection molding compounds physically. The second key goal is developing numerical method to create thermoset material data sheet for simulation of mold filling characterizations of thermoset injection molding compounds. Finally, creating a simulation tool base on the physical technique and generated material data sheet.

<p></p><p>This doctoral dissertation takes the reader through a journey where applied shear rheology and flow-velocimetry are used to understand the mesoscopic factors that control the flow behavior of three microstructured fluids. Three individual protocols that measure relative physical and mechanical properties of the flow are developed. Each protocol aims to advance the particular transformation of novel soft materials into a commercial product converging in the demonstration of the real the chemical, physical and thermodynamical factors that could potentially drive their successful transformation. </p> <p> </p> <p>First, this dissertation introduces the use of rotational and oscillatory shear rheometry to quantify the solvent evaporation effect on the flow behavior of polymer solutions used to fabricate isoporous asymmetric membranes. Three different A-B-C triblock copolymer were evaluated: polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(4-vinylpyridine) (ISV); polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide) (ISD); and polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>tert</i>-butyl methacrylate) (ISB). The resulting evaporation-induced microstructure showed a solution viscosity and film viscoelasticity strongly dependent on the chemical structure of the triblock copolymer molecules. </p> <p> </p> <p>Furthermore, basic shear rheometry, flow birefringence, and advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE₁S) was used to replicate spherical, worm-like, and hexagonally packed micelles and lamellar structures. Interesting findings demonstrated that regular features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of experimental artifacts that appeared when measuring microstructured fluids with shear rheometry.</p> <p> </p> <p>Finally, the successful integration of shear rheometry to calculate essential parameters to be used in a cost-effective visualization technique (still in development) used to calculate the dissolution time of polymers is addressed. The use of oscillatory rheometry successfully quantify the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify formulations changes such as additive addition. The flow behavior of PVA solutions was correlated to dissolution behavior proving that the developed protocol has a high potential as a first screening tool.</p><br><p></p>