Dissertations / Theses on the topic 'Solid contact'

Aquesta tesi aporta un avanç en la construcció d'elèctrodes de contacte sòlid (SCE) basats en materials nanoestructurats de carboni. Es verifica per una banda, la possibilitat d'utilització dels nanotubs de carboni de capa Simple (SWCNTs) per a la determinació d'ions en mostres reals complexes com és la saba vegetal. Addicionalment, es porta a terme la utilització del grafè modificat químicament com a element transductor en els elèctrodes d'estat sòlid determinant el seu mecanisme de transducció i com a prova del seu funcionament es duen a terme dos elèctrodes, per una banda un elèctrode selectiu d'ions (ISE) per a la determinació de calci, i per una altra part un aptasensor per a la determinació selectiva de Staphylococcus aureus.
Esta tesis aporta un avance en la construcción de electrodos de contacto sólido (SCE) basados en materiales nanoestructurados de carbono. Se verifica por una parte, la posibilidad de utilización de los nanotubos de carbono de capa simple (SWCNTs) para la determinación de iones en muestras reales complejas como es la savia vegetal. Adicionalmente, se lleva a cabo la utilización del grafeno modificado químicamente como elemento transductor en los electrodos de estado sólido determinando su mecanismo de transducción y como prueba de su funcionamiento se llevan a cabo dos electrodos, por una parte un electrodo selectivo de iones (ISE) para la determinación de calcio, y por otra parte, un aptasensor para la determinación selectiva de Staphylococcus aureus.
This thesis provides a breakthrough in the construction of solid contact electrode (SCE) based on nanostructured carbon materials. It is checked the possibility of using single walled carbon nanotubes (SWCNTs) for the determination of ions in real complex samples such as plant sap. Additionally, the use of chemically modified graphene is performed as a transducer in solid state electrodes to determine the transduction mechanism. As a proof of concept two electrodes have been developed, in one hand, an ion-selective electrode (ISE) for the determination of calcium, and on the other one, an aptasensor for the selective detection of Staphylococcus aureus.

The tangential contact stiffness for ground Ti-6Al-4V surfaces is measured to linearly decrease with the application of tangential load. At the beginning of the application of tangential load, for ground surfaces, the ratio of the tangential contact stiffness to the normal contact stiffness is seen to be approximately half the Mindlin ratio. This is consistent with many other published experimental studies. Measurements of normal contact stiffness for ground surfaces conform to a model that posits a linear relationship between normal contact stiffness and normal load. An equivalent surface roughness parameter is defined for two surfaces in contact; and the normal contact stiffness for ground surfaces is observed to be inversely proportional to this parameter. Single asperity models were constructed to simulate the effect of different frictional laws and plasticity on the tangential displacement of an asperity contact. Further, multi-asperity modelling showed the effect of different normal load distributions on the tangential behaviour of interfaces. In addition, normal contact stiffness was modelled for a grid of asperities taking into account asperity interactions. A receding contact problem for which the required form of the distributed dislocations is bounded-bounded was solved. Then, a fundamental 2D frictional receding contact problem involving a homogeneous linear elastic infinite layer pressed by a line load onto a half-plane of the same material was analysed. This was done by the insertion of preformed distributed dislocations (or eigenstrains), which take into account the correct form of the separation of the interface at points away from the area of loading, along with corrective bounded-bounded distributions. The general method of solution was further refined and adapted to solve three other receding contact problems. The solutions demonstrated the robustness and applicability of this new procedure.

Les composites Cu-Cr sont couramment utilisés comme matériaux de contact électrique pour ampoules à vide des disjoncteurs de moyenne tension. Pourtant très répandu, le frittage en phase solide de ces matériaux a été relativement peu étudié. L’optimisation du procédé passe par la compréhension des mécanismes de frittage. Cette étude est focalisée sur deux aspects importants du frittage : les processus d’oxydo-réduction liés aux oxydes de surfaces des poudres et la compétition entre mécanismes de densification et de gonflement au cours du frittage.L’oxydo-réduction a été étudiée par analyse thermogravimétrique couplée à différentes techniques de spectroscopie d’abord sur les matériaux purs puis sur les composites. Des analyses des interfaces par des coupes réalisées au FIB ont permis de préciser la localisation de l’oxyde dans les matériaux frittés. Un transfert d’oxygène a lieu entre les poudres de cuivre et de chrome. L’intensité de ce transfert dépend de la nature réductrice de l’atmosphère utilisée.La densification a été analysée par dilatométrie sur les matériaux purs et sur les composites. Ces analyses ont été appuyées par des observations microstructurales, notamment par tomographie des rayons X. L’effet des paramètres du procédé (atmosphère, vitesse de chauffage, poudres…) a été étudié. Les résultats montrent le lien entre la désoxydation des poudres de cuivre et le frittage. Un phénomène de gonflement du cuivre seul s’explique par le dégazage du cuivre à haute température lors de la fermeture des pores. Ce gonflement n’a pas lieu dans les composites Cu-Cr car le chrome retarde la fermeture des pores et piège les gaz émis par le cuivre en formant l’oxyde Cr2O3. L’atmosphère de frittage, la morphologie et la taille des poudres de chrome influent sur la densification. Le frittage sous vide permet de réduire la porosité. Une morphologie sphérique des particules de chrome limite l’effet inhibiteur de celui-ci sur la densification. Pour de faibles tailles de particules, le chrome participe à la densification, ce qui permet de mieux densifier le matériau. Ces résultats ouvrent des voies d’optimisation du procédé de frittage des matériaux.Les matériaux élaborés ont été testés dans leurs conditions d’utilisation, c'est-à-dire lors de coupures sur court-circuit en ampoule à vide. Ces essais ont montré l’intérêt de réduire la quantité d’oxyde de chrome et ont permis de déterminer l’effet des impuretés rencontrées usuellement sur les poudres de cuivre et de chrome
Cu-Cr composites are commonly used as contact materials for medium voltage circuit breakers vacuum bottles. Solid state sintering process of Cu-Cr composites is widespread but has been relatively little studied. Optimizing the process requires understanding the sintering mechanisms. This study was focused on two important aspects of sintering: the redox reactions associated to oxides on the powder surface and the competition between densification and swelling mechanisms during sintering.The redox reactions were studied by thermogravimetric analysis coupled to various spectroscopic techniques, first on isolated Cu and Cr, then on Cu-Cr composites. Interfaces analyses obtained by FIB clarified the location of the oxide inside the sintered materials. Oxygen transfer takes place between copper and chromium powders. This phenomenon strongly depends on the reducing character of the sintering atmosphere.Densification was analyzed by dilatometry on Cu, Cr and Cu-Cr composites. This analysis was supported by microstructural observations, including X-ray tomography .The effect of process parameters (atmosphere, heating rate, powders ...) was studied. The results show the relationship between sintering and copper oxide reduction. The swelling phenomenon of copper compacts is explained by high temperature degassing of copper during pore closure. This swelling does not occur in Cu-Cr composites as chromium delays pore closing and entraps the gases released by copper. Sintering atmosphere, chromium morphology and chromium particle size affect densification. Vacuum sintering reduces porosity. Chromium particles with spherical shape limit its inhibiting effect on densification. For small particle sizes, chromium participates to densification, leading to better densification of the material. These results open the route for optimizing the sintering of Cu-Cr composites.Cu-Cr composites were tested for short circuit performance in vacuum interrupters. The result of these tests showed the importance of reducing the chromium oxide amount. The effect of impurities commonly encountered on the powders copper and chromium powders was also determined

Chaque fois que se produit un mouvement relatif entre deux systèmes, avec une interface à contact sec, le contact frottant induit des vibrations. La dynamique locale au contact (ruptures et la génération d'ondes) se couple avec la dynamique du système, donnant origine à des vibrations et affectant le comportement frictionnel macroscopique du système. Dans cette thèse, afin de développer une approche globale pour l'investigation des phénomènes multi-physiques, l'énergie a été utilisée comme une caractéristique physique universelle du couplage. La formulation de un bilan énergétique mécanique est utilisé pour identifier deux termes dissipatifs différents, i.e. la dissipation par amortissement matériel/système et la dissipation au contact. Les flux d'énergie, provenant des surfaces en contact et dus aux vibrations induites par frottement, excitent la réponse dynamique du système et, vice versa, l'influence de la réponse dynamique du système sur la dissipation d'énergie locale à l'interface de contact affecte les phénomènes tribologiques connexes. Dans cette thèse, les vibrations induites par le frottement ont été analysées en utilisant: l'approche par éléments finis pour étudier, par l'analyse des flux d'énergie, le couplage entre le contact et la dynamique du système; l'approche expérimentale pour valider les résultats numériques et observer l'influence des phénomènes pas encore inclus dans les modèles numériques; une approche avec une modèle à paramètres concentrés pour évaluer rapidement les effets des paramètres du système. L'analyse numérique par le modèle éléments finis 2D permet une répartition de l’énergie introduite dans le système mécanique entre les deux termes dissipatifs (amortissement matériau et contact), au cours de la réponse transitoire aussi bien en conditions stables qu’instables. En particulier, les vibrations induites par frottement modifient la capacité globale du système à absorber et dissiper l’énergie; une estimation de la puissance dissipée au contact, sans prendre en compte le comportement dynamique du système (flux d’énergie par les vibrations induites par frottement) peut conduire à des erreurs significatives dans la quantification de l’énergie dissipée au contact, ce qui affecte directement plusieurs phénomènes tribologiques. Les mesures expérimentales de crissement montrent comment les mêmes modes instables sont reproduits soit expérimentalement soit numériquement, validant l’utilisation de la simulation 2D transitoires pour l’analyse des vibrations instables induites par le frottement. L’équilibre énergétique a été utilisé sur le modèle à paramétrés concentrés, pour approcher le problème de la surestimation d’instabilité, qui est caractéristique d’une analyse des valeurs propres complexes. Un nouvel indice d’instabilité (MAI) a été défini, par des considérations énergétiques, pour comparer les différents modes instables et pour sélectionner le mode qui devient effectivement instable pendant le crissement
Whenever relative motion between two system components occurs, through a dry contact interface, vibrations are induced by the frictional contact. The local dynamics at the contact (ruptures and wave generation) couples with the system dynamics, giving origin to vibrations and affecting the macroscopic frictional behavior of the system. In this thesis, in order to develop an overall approach to the investigation of the multi-physic phenomenon, the energy has been pointed out as a coupling physical characteristic among the several phenomena at the different scales. The formulation of a mechanical energy balance is used for distinguishing between two different dissipative terms, i.e. the dissipation by material/system damping and the dissipation at the contact. The energy flows coming from the frictional surfaces, by friction induced vibrations, excites the dynamic response of the system, and vice versa the influence of the system dynamic response on the local energy dissipation at the contact interface affects the related tribological phenomena. The friction-induced vibrations have been analyzed using three different approaches: the finite element approach, to investigate the coupling between the contact and system dynamics by the analysis of the energy flows; the experimental approach to validate the numerical results and observe the influence of phenomena not still included into the numerical model; a lumped parameter model approach to quickly investigate the effects of the system parameters. The numerical analysis by the 2D finite element model allowed investigating the repartition of the energy introduced into the mechanical system between the two dissipative terms (material damping and contact) during both stable and unstable friction-induced vibrations. In particular, it has been shown how the friction-induced vibrations modify the overall capacity of the system to absorb and dissipate energy; an estimation of the power dissipated at the contact, without considering the dynamic behavior of the system (energy flows by friction induced vibrations) can lead to significant error in the quantification of the dissipated energy at the contact, which affects directly several tribological phenomena. The experimental squeal measurements show how the same unstable modes are recovered both experimentally and numerically, validating the use of the 2D transient simulations for the reproduction of the unstable friction-induced vibrations. Once the energy balance formulated, it has been used on the lumped model to approach the instability over-prediction issue characteristic of the complex eigenvalue analysis. By energy considerations, a newer instability index (MAI) has been defined to compare the different unstable modes and to select the mode that becomes effectively unstable during the transient response. The Modal Absorption Index allows quantifying the capability of each mode to exchange energy with the external environment

The aim of this thesis is the development of solid contact ion selective electrodes, ISEs, where the transducer layer is made of a network of carbon nanotubes.

Potentiometric classical ion selective electrodes (ISEs) have been used for analytical applications since the beginning of 1900's. Determination of pH by a glass membrane ion selective electrode emerged at the beginning, being the first ISEs developed. pH glass electrode is still one the most useful and robust sensors for routine measurements both in laboratories and industries.

Throughout the years, new technologies, ideas and designs have been developed and incorporated successfully in the potentiometric fields so as to provide answers to the new society's needs. Therefore, the ion selective electrodes developed in this thesis are a step further in the progress of ISEs and must be considered as products of the scientific envisioning, growth, and interdisciplinary cooperation of many research teams over many years of continuous efforts.

The sensing part can be regarded nowadays as well developed, although it has been during only the last few years when considerable improvements have taken place in the development of new polymeric membranes, ionophores and lipophilic ions. Moreover, the understanding of the theoretical sensing mechanism has been a powerful solid backbone in the rise of ISEs.

Miniaturization of classical ISEs requires making all solid contact electrodes to avoid the intrinsic drawbacks of the inner solution. In this manner, the transduction layer has been the focus of attention for the two last decades. New solid contact transducers having the capacity to convert an ionic current into an electronic current have been emerging. Within them, conducting polymers have played an important role in the transduction of the potentiometric signal, being the most used in solid contact ion selective electrodes (SC-ISEs) up to now. However, the behaviour of conducting polymers can be further improved. For instance, their sensitivity to light one of main operational issues yet to be solved.

In the present context of searching for new materials able to transduce potentiometric signals we selected and tested carbon nanotubes (CNTs). CNTs, which were rediscovered by Ijima in 1991, display excellent electronic properties in terms of signal transduction. In addition, due to their chemical reactivity CNTs can be easily functionalized with receptors or other functional groups. In fact, depending on the type of functionalization the macroscopic and microscopic properties of CNTs can be drastically changed. This nanostructured material had not been used previously as a solid contact material in ISEs.

The main aim of this thesis is to demonstrate that CNTs can act as a clean and efficient transducer in SC-ISEs overcoming the drawbacks displayed by the previously assayed solid contact materials. The developed electrodes were used in different conditions to determine several ions in different sample types, demonstrating the capabilities of this nanostructured material.
The thesis has been structured in different chapters, each one containing the following information:

· Chapter 1 provides a short historical overview of potentiometric ISEs. The evolution from the "classical ISEs" to the SC-ISEs is briefly illustrated. Once the motivation for thesis is described, the general and specific objectives of the thesis are reported.
· Chapter 2 reports the scientific foundations of the developed electrodes. All components of the ISE, sensing layer, transducers and detection systems are introduced. Analytical performance characteristics of ISEs are also described.
· Chapter 3 corresponds to the experimental part. Reagents, protocols, procedures and instruments used in the thesis are reported.
· Chapter 4 provides the demonstration that CNTs can act as a transducer layer in SC-ISEs. The first SC-ISEs based on CNTs are characterized by electrochemical and optical techniques.
· Chapter 5 contains the experimental results that lead to the elucidation of the possible transduction mechanism of CNTs in SC-ISEs. Electrochemical impedance spectroscopy (EIS) is employed as the main characterization technique.
· Chapter 6 is composed of four sections reporting different analytical applications. In the first section, the common pH electrode is developed using a solid contact technology based on CNTs. In the second section, the development of SC-ISEs based on a new synthetic ionophore selective to choline, and CNTs as transducers is shown. In the third section, watertight and pressure-resistant SC-ISEs based on CNTs are developed and tested in aquatic research to obtain information about the gradient profiles along the depth of the lakes. In the fourth section, SC-ISEs based on CNTs are adapted for the on-line control of a denitrification catalytic process.
· Chapter 7 reports the possibilities of miniaturization of the SC-ISEs based on CNTs to reach a nanometric electrode. Potentiometric and optical characterizations are described in this section. Moreover, a discussion about the limitations of the real miniaturization in potentiometry is undertaken.
· Chapter 8 points out the conclusions of the thesis. In addition, future prospects are suggested.
· Finally, several appendices are added to complete the doctoral thesis.
El principal objetivo de esta tesis es el desarrollo de electrodos selectivos de iones de contacto sólido, ESIs-CS, utilizando como capa transductora una red compuesta de nanotubos de carbono.

Los electrodos potenciométricos selectivos de iones han sido utilizados en aplicaciones analíticas desde comienzos de 1900. La determinación de pH mediante electrodos de vidrio selectivo de iones fue el primer ESI desarrollado. Hoy en día, el electrodo de vidrio para la determinación de pH es todavía uno de los más útiles y robustos sensores utilizados en mediciones rutinarias tanto en laboratorios como en industrias.

A lo largo de los años, nuevas tecnologías, ideas y diseños han sido desarrollados e incorporados satisfactoriamente en el campo potenciométrico proporcionando soluciones a las necesidades en continua evolución de la sociedad. De esta manera, los electrodos selectivos de iones desarrollados en esta tesis son un paso más en el progreso de los ESIs y deben ser considerados como el producto de una sólida base científica, del crecimiento y de la cooperación interdisciplinaria de diversos grupos de investigación durante varios años.

La parte del sensor donde tiene lugar el reconocimiento químico y donde se genera el potencial dependiente de la muestra en estudio en los ESIs se puede considerar, en estos días, ampliamente desarrollada, aunque considerables mejoras han tenido lugar durante los últimos años, especialmente en el desarrollo de nuevas membranas poliméricas, ionóforos e iones lipofílicos. Sobretodo, el estudio y la comprensión del mecanismo teórico del sensor ha sido muy importante en el crecimiento y desarrollo de los ESIs.

El concepto de electrodos selectivos de iones de estado sólido surge como requisito vital para evitar las intrínsecas desventajas de la solución interna, en el proceso de miniaturización de los ESIs clásicos. De esta forma, la capa transductora ha sido el principal punto de atención durante dos décadas. Así, nuevos transductores de contacto sólido con la capacidad de convertir una corriente iónica en una corriente electrónica han sido desarrollados. Entre ellos, los polímeros conductores han jugado un importante papel en la transducción de la señal potenciométrica, siendo éstos los más empleados en los electrodos selectivos de iones de contacto sólido (ESIs-CS). Sin embargo el comportamiento de los polímeros conductores puede ser mejorado. Por ejemplo, la sensibilidad hacia la luz de estos materiales es un inconveniente todavía no resuelto.

En este contexto de investigación de nuevos materiales capaces de actuar como transductor de una señal potenciométrica, se han escogido y estudiado los nanotubos de carbono (NTCs) como transductores. Los NTCs fueros redescubiertos por Ijima en 1991, y muestran excelentes propiedades electrónicas en términos de traducción de señal. Además, debido a su reactividad química, los NTCs pueden ser fácilmente funcionalizados con receptores u otros grupos funcionales. De hecho, sus propiedades macroscópicas y microscópicas pueden ser afectadas drásticamente dependiendo del tipo y grado de funcionalización. Este material nanoestructurado no había sido previamente utilizado como transductor en ISEs.

El principal propósito de esta tesis es demostrar que los nanotubos de carbono pueden actuar de forma eficiente como transductor en electrodos selectivos de iones de estado sólido logrando vencer las desventajas de los transductores previamente mencionados. Los electrodos desarrollados fueron usados en diferentes condiciones para determinar distintos iones en diversos tipos de sistemas, demostrando las extraordinarias capacidades de este material nanoestructurado.


Esta tesis ha sido estructurada en capítulos que contienen la siguiente información:

· El Capítulo 1 proporciona una breve visión histórica de lo electrodos potenciométricos selectivos de iones. Se ilustra la evolución desde los "clásicos ESIs" hasta los actuales "ESIs-CS". Además se señalan en esta sección los objetivos generales y específicos.
· El Capitulo 2 contiene las bases científicas de los electrodos desarrollados. Se introducen todos los componentes que integran un ESI, tales como: capa reconocedora, capa transductora y sistema de detección. A continuación se describen los parámetros analíticos de calidad de los ESIs.

· El Capitulo 3 describe la parte experimental. Se recogen los reactivos, protocolos, procedimientos e instrumentos usados a lo largo de la tesis.
· El Capitulo 4 provee de la demostración de que los NTCs pueden actuar eficientemente como capa transductora en SC-ISEs. Se caracteriza el primer ESI-CS integrado por NTCs mediante técnicas ópticas y electroquímicas.
· El Capitulo 5 contiene los resultados experimentales que permiten la posible elucidación del mecanismo de transducción de los NTCs en los ESIs-CS. La Espectroscopia de Impedancia Electroquímica (ESI) es utilizada como la principal técnica de caracterización.
· El Capitulo 6 está integrado por cuatro secciones con diferentes aplicaciones analíticas. En la primera sección, se desarrolla un electrodo de pH que usa NTCs como nueva tecnología transductora en ESIs-CS. En la segunda sección se muestra el desarrollo de un ESI-CS integrado por un ionóforo sintético selectivo a colina, y NTCs como transductores. En la tercera sección, ESIs-CS basados en NTCs, resistentes a altas presiones y totalmente herméticos, se desarrollan y prueban en investigaciones acuáticas con la finalidad de obtener información sobre los gradientes de concentración de iones en función de la profundidad de un lago. En la cuarta sección ESIs-CS basados en NTCs se adaptan para el control on-line de un proceso catalítico de desnitrificación.
· El Capitulo 7 presenta la posibilidad de la miniaturización de los ESIs-CS basados en NTCs logrando obtener un electrodo nanométrico. Se muestran en esta sección la caracterización óptica y potentiométrica. Además, se discuten las limitaciones de la miniaturización real de los ESIs en potenciometría.
· El Capitulo 8 contiene las conclusiones de la tesis. Adicionalmente, se sugieren las perspectivas futuras del trabajo presentado.
· Finalmente, se añaden algunos apéndices como complemento de la tesis doctoral.

The interaction of a bubble with solid surfaces, hydrophobic and hydrophilic, was investigated. When a bubble approaches towards a solid surface, a thin liquid film forms between them. The liquid in the film drains until an instability forms and film ruptures resulting in a three phase contact (TPC). Following rupture, the TPC line spreads on the solid surface. In the present study, glycerol-water solutions with varying percentages of water were used to investigate the effect of viscosity. Experiments were carried out with varying bubble size. The rupture and TPC line movement were recorded by high-speed digital video camera. The dependence of the TPC line movement on different parameters was investigated. The experimental results were compared with the existing theories for the TPC line movement. An empirical equation was developed to predict the TPC line movement. Formation or rupturing of the intervening film in case of a hydrophilic surfaces, which were glass surface cleaned by six cleaning techniques, was investigated. It was shown that a stable film forms for acid or alkali cleaning.

Nous avons étudié la dynamique de particules rigides et sphériques immergées dans un écoulement de cisaillement simple et oscillant à bas nombre de Reynolds. Les particules, au delà d’une déformation critique, se comportent de façon irréversible. La particules suivent alors un processus diffusif appelé: diffusion induite par cisaillement. Dans cette thèse, nous avons montré, par une approche numérique et expérimentale, que les collisions solides entre particules sont à l’origine de ce phénomène. Des simulations numériques ont été effectués afin d’évaluer l’importance relative des forces hydrodynamiques longues portées, des forces de lubrifications et des forces de contact. Deux expériences ont été effectuées afin de mettre en évidence l’influence des contacts solides entre particules. Nous avons étudié la dynamique de 3 particules soumises à un écoulement de cisaillement périodique. Les trajectoires des particules sont irréversibles durant le premier cycle et réversible pour les cycles suivants. En montrant que l’amplitude de l’irréversibilité est corrélée à la rugosité des particules, nous fournissons une preuve évidente que des collisions solides entre particules ont bien lieu et que ces collisions influencent la dynamique des particules. Effectuée dans une suspension homogène, le rôle des contacts a aussi été mis en évidence en montrant que l’amplitude critique de déformation dépend de la rugosité des particules. Un modèle géométrique simple qui considère des `particules effectives’ ayant un volume dépendant de l’amplitude de déformation et de la rugosité des particules, nous a permis de quantitativement reproduire les mesures expérimentales
Even at low Reynolds number, particles within a shear flow exhibit irreversible dynamics. Many theories have been put forth to explain this phenomenon, the origin of irreversibility remains unclear. An integrated program of experimental and computational studies has been performed to assess the origin of the irreversible behavior of particles. Numerical simulations were used to evaluated the relative importance of long-range hydrodynamic interactions, lubrication, and contact forces. By isolating contribution of these interactions, we have shown that neither the long-range hydrodynamic interactions nor the lubrication are responsible for irreversibility. Solid contacts between particles largely dominate this phenomenon. However, producing realistic results requires both contact interactions and lubrication. Two different experiments were performed to address the role of contacts between particles in sheared suspensions. In the first experiment, the particle trajectories are irreversible during the first cycle but reversible for the next cycles. By showing that the magnitude of irreversibility increases with the particle roughness, we provide direct evidence that contacts occur in viscous flow. Experimental particle trajectories are well captured by the numerical model. In the second experiment, performed in a homogeneous suspension, the role of solid collisions was also revealed by showing that the critical strain amplitude depends on the particle roughness. A geometrical model based on the assumption that colliding particles produce irreversibility was derived. The model successfully reproduces the measured values of the critical strain amplitude

This thesis addresses normal axisymmetric contact of dissimilar elastic solids at finite interfacial friction. It is shown that in the case of smooth and convex but otherwise arbitrary contact profiles and monotonically increasing loading a single stick-slip contour evolves being independent of loading and profile geometry. This allows developing an incremental procedure based on a reduced problem corresponding to frictional rigid flat punch indentation of an elastic half-space. The reduced problem, being independent of loading and contact region, was solved by a finite element method based on a stationary contact contour and characterized by high accuracy. Subsequently, a tailored cumulative superposition procedure was developed to resolve the original problem to determine global and local field values for two practically important geometries: flat and conical profiles with rounded edges and apices. Results are given for relations between force, depth and contact contours together with surface stress distributions and maximum von Mises effective stress, in particular to predict initiation of fracture and plastic flow. It is also observed that the presence of friction radically reduces the magnitude of the maximum surface tensile stress, thus retarding brittle fracture initiation. Hertzian fracture through indentation of flat float glass specimens by steel balls has been examined experimentally for a full load cycle. It has been observed that if the specimen survived during loading to a maximum level it frequently failed at decreasing load. It has been proposed by Johnson et al. (1973) that the underlying physical cause of Hertzian fracture initiation during load removal is that at unloading frictional tractions reverse their sign over part of the contact region. Guided by these considerations a robust computational procedure has been developed to determine global and local field values in particular at unloading at finite friction. In contrast to the situation at monotonically increasing loading, at unloading invariance properties are lost and stick-slip regions proved to be severely history dependent and in particular with an opposed frictional shear stress at the contact boundary region. This causes an increase of the maximum tensile stress at the contour under progressive unloading. It is shown that the experimental observations concerning Hertzian fracture initiation at unloading are at least in qualitative correlation with the effect friction has on the maximum surface tensile stress. A contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been further investigated analytically and numerically for a wider range of material parameters and contact geometries. With the issue of Hertzian fracture initiation in mind, results concerning the influence of the friction coefficient and compliance parameters on the absolute maximum surface tensile stress during a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. Fracture loads are measured with steel and tungsten carbide spherical indenters in contact with float glass specimens at monotonically increasing loading and during a load cycle. Computational predictions concerning the fracture loads are given based on Hertz and frictional contact theories combined with a critical stress fracture criterion. The computational results obtained for frictional contact are shown to be in better agreement with experimental findings as compared to the predictions based on the Hertz theory. The remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects on the fracture loads at monotonic loading, Weibull statistics was introduced. The predicted critical loads corresponding to 50% failure probability were found to be in close agreement with experimentally observed ones.
QC 20100729

This thesis is concerned with the bridging-dewetting mechanism of foam breakdown by spherical hydrophobic particles. The role of contact angles (of solid with surfactant solution) in foam breakdown by particles has previously been investigated using particles of ill-defined shape. As contact angle requirements are shape dependent, conclusions have often been tentative. Further, it has been assumed that the contact angles measured on flat surfaces represent those occurring on particles of similar surface molecular structure. In the work to be described, we first establish, using a Langmuir trough technique, that contact angles of particles with surfactant solutions correspond closely to those obtained conventionally on flat plates of similar surface structure. The technique is suited to the investigation of very small monodisperse particles, which do not cause curving of the interface up to the point of contact with the particle. Spherical glass particles in the size range 40 to 53µm were then hydrophobised to different extents by controlled treatment with either octadecyl trichlorosilane or perfluorodecyl trichlorosilane. Flat glass plates were treated in a similar fashion so that contact angles (both static advancing and receding) could be measured with surfactant solutions using the sessile drop technique. The hydrophobic particles were incorporated into foams produced from aqueous solutions of CTAB, AOT, SDS and SPFO. It is found that the particles exhibiting advancing contact angles less than 70 to 80° have little effect on long term stability because they are swept from the foam lamellae by the flow of interstitial liquid during film drainage. For particles which give advancing contact angles lying between 80 and 95° , however, the long term foam stability is dramatically enhanced. These particles become attached to the film interfaces and are not easily swept from the foam structure. Foam stability is enhanced because particles accumulate in the interfaces of the Plateau border regions between foam films where they act as a physical barrier slowing the drainage of liquid from the foam lamellae. Then for particles which exhibit contact angles in excess of 95° the stability falls sharply and is accounted for by the bridging-dewetting mechanism. Similarly hydrophobised thin cylindrical glass rods were incorporated into single CTAB soap films and the effect of contact angle studied in terms of the change in film lifetime and the % film rupture. Thin rods with advancing contact angles below 90° had little effect on film lifetime but any angle above 90° resulted in virtually 100% film rupture. The organosilyl coating is susceptible to hydrolysis in aqueous surfactant solution and consequently, with time, silanised particles may loose their hydrophobicity and hence also their antifoaming ability. Through a comparative study of silane coatings prepared from a variety of silanising agents we find that tri-functional silanes produce coatings which retain their hydrophobicity more effectively than other agents. This is because the tri-functional silanes produce thick polymeric coatings.

This thesis investigates a novel way to simulate cracks as an extension of the Mate- rial Point Method (MPM). Previous methods, like CRAMP (CRAcks with Material Points), often use an explicit crack representation to define the material crack. We use an implicit crack representation defined as the intersection between pieces of the original specimen created by a pre-fracture process. Material chunks are there- after forced together using massless particle constraints. The method has proven successful in tearing scenarios, and the main benefits are: (1) minor computational overhead compared to the initial MPM algorithm; (2) simple to implement and scales well in 3 dimensions; (3) gives easy and controllable setup phase for desired material failure mode. The development of the crack extension has required a fully general MPM solver that can handle arbitrarily many distinct bodies connected in the same simulation. Current collision schemes for MPM exists, however these are often focused on two-body collisions and does not scale well for additional objects due to inaccuracies in contact normal calculations. We present a method that uses an iterative pair-wise comparison scheme to resolve grid collisions that extends to any number of collision objects.

Ce travail de thèse met en évidence deux phénomènes microscopiques dissipatifs au voisinage de la ligne de contact dans les phénomènes de capillarité et d'adhésion. L'étude s'appuie sur des expériences dynamiques et des modélisations théoriques. La mesure expérimentale de quantités macroscopiques et la théorie hydrodynamique permettent d'extraire les informations dynamiques localisées au voisinage la ligne de contact. Les différents phénomènes dissipatifs localisés au voisinage de la ligne de contact ont pour origines les propriétés des substrats sur lesquels se déplace la ligne de contact. Pour une surface rigide hétérogène, nous avons développé un modèle rhéologique de la ligne de contact fondé sur l'hydrodynamique, permettant d'établir théoriquement l'évolution temporelle de la ligne de contact et de ses déformations. Une décomposition modale fondée sur la réduction de l'énergie par la théorie du chemin de réaction fournit une prédiction quantitative de la dynamique thermiquement activée de la ligne de contact, en accord avec l'expérience réalisée. Pour un substrat déformable, à partir de l'analyse de deux expériences différentes de mouillage dynamique et de l'estimation de la dissipation dans le substrat, fondée sur sa viscoélasticité, nous avons développé une compréhension générale du comportement dynamique d'une ligne de contact sur un substrat viscoélastique. Pour finir, ce modèle de dissipation viscoélastique est appliqué au cas de l'adhésion réversible, où expérimentalement nous mesurons la dynamique de pelage et de recollement sur un substrat viscoélastique. Cette extension à l'adhésion permet de relier les phénomènes interfaciaux en une compréhension générale
This thesis reveals two dissipative microscopic phenomena close to the contact line in the fields of capillarity and adhesion. The study is based on dynamic experiments and theoretical predictions. Experimental measurement of macroscopic quantities and the hydrodynamic theory give access to dynamic information located close to the contact line. The different dissipative phenomena, located close to the contact line, originate from the properties of the substrates on which the contact line moves. For a heterogeneous rigid surface, we have developed a rheological model of the contact line based on hydrodynamics, in order to theoretically establish the temporal evolution of the contact line and its deformations. A modal decomposition based on the reduction of the energy by the reaction path theory allows a quantitative prediction of the thermally activated dynamics of the contact line, in agreements with the experiment carried out. For a deformable substrate, based on the analysis of two different experiments of wetting dynamics and on the estimation of the dissipation in the substrate founded on its viscoelasticity, a general understanding of the dynamical behavior of contact lines on viscoelastic substrates is achieve. Finally, this viscoelastic model is applied to the case of weak adhesion, where experimentally we measured the peeling dynamics from a viscoelastic substrate. This extension to adhesion bridge the gap between different interfacial phenomena into a general understanding

Rolling contact fatigue is a problem encountered with many machine elements.In the current report a numerical study has been performed in order to predictthe crack path and crack propagation cycles of a surface initiated rolling contactfatigue crack. The implementation of the contact problem is based on theasperity point load mechanism for rolling contact fatigue. The practical studiedproblem is gear contact. Different loading types and models are studied andcompared to an experimental spall profile. Good agreement has been observedconsidering short crack lengths with a distributed loading model using normalloads on the asperity and for the cylindrical contact and a tangential load on theasperity. Several different crack propagation criteria have been implemented inorder to verify the validity of the dominant mode I crack propagation assumption.Some general characteristics of rolling contact fatigue cracks have beenhighlighted. A quantitative parameter study of the implemented model hasbeen performed.
Utmattning med rullande kontakter är ett ofta förekommande problem för många maskinelement. I den aktuella rapporten utfördes en numerisk studieför att förutsäga sprickvägen hos utmattningssprickor som initierats i ytan vidrullande kontakter. Implementeringen av kontaktproblemet bygger på asperitpunktlastmekanismen för rullande kontakter. Studien av kontaktproblemetär tillämpad till kugghjul. Olika belastningstyper och modeller studeradesoch jämfördes med profilen hos en experimentell spall. Bra överensstämmelseobserverades för korta spricklängder när en modell med fördelad belastninganvänds för en belastningstyp där en normalbelastning agerar på asperiten ochvid cylindriska kontakten och en tangentialbelastning införs på asperiten. Olikakriterier för spricktillväxt implementerades för att verifiera giltigheten av antagandetatt mode I spricktillväxt är dominant. Några generella kännetecken avutmattningssprickor med rullande kontakter framhävdes. En kvantitativ parameterstudie för den implementerade modellen utfördes.

Esta Tesis Doctoral aporta una visión del diseño, construcción y operación de electrodos de contacto sólido selectivos de iones (SC-ISEs) basados en nanotubos de carbono de pared múltiple (MWCNTs). Se logra incorporar con éxito MWCNTs como elemento transductor ion-electrón en SC-ISEs. Adicionalmente, se desarrollan nuevos materiales híbridos para la determinación de iones, donde el receptor se encuentra anclado tanto de forma covalente como no covalentes a los MWCNTs. Y finalmente, se introduce una nueva matriz polimérica basada en poli vinil butiral como alternativa a las matrices convencionales basadas en cloruro de polivinilo.
This Doctoral Thesis intends to provide an insight into the design, construction and operation of solid contact ion-selective electrodes (SC-ISEs) based on multi-walled carbon nanotubes (MWCNTs). MWCNTs are used as effective ion-to-electron transducers for SC-ISEs. Additionally, new hybrid materials with the receptor covalent and non-covalent linked to the MWCNTs have been developed for determination of ions. And finally, new polymeric matrix based on poly vinyl butyral is introduced as an alternative to conventional matrixes based on poly(vinyl chloride).

Mon projet de thèse a été réalisé en partenariat avec l'entreprise BioMérieux, qui produit des milieux de culture à base de gel d'agar coulés dans des boîtes de Pétri à destination du secteur biomédical. Ces gels, remplis d'eau à 95 %, sont susceptibles d'en relâcher par évaporation ou sous l'effet d'une perturbation externe. Le gel se contracte et peut se détacher des parois de la boite lors de la production ou lors de leur incubation. Ma thèse a consisté à identifier les paramètres clefs qui influent sur la contraction de ces milieux de culture aussi bien au niveau de la composition du gel que des propriétés de surface des parois de la boîte de Pétri. Ce travail expérimental m'a permis d'associer un panel de techniques originales comme la rhéologie à force normale contrôlée, une centrifugeuse, l'interférométrie ou encore la méthode flot optique. J'ai ainsi mis à jour les moteurs du détachement du gel des parois des boîtes et identifier des solutions concrètes pour y remédier
My PhD work was carried out in partnership with the company BioMérieux, a leader int he production of agar-based culture media, cast in Petri disches and used in microbioly. Being mainly composed of water (>95 % wt.), agar gels are naturally prone to solvent-loss by evaporation either at rest or under an external perturbation. As a result, the gel shrinks and detaches from the sidewall fo dish. The goal of my PhD work was to identify the key paramters driving the gel detachment, in relation with both the gel chemical composition, as well as the dish surface properties. This expzrimental word has allowed me to use a wide array of thecniques such as normal force controlled rheology, intererometric observations, or optical flow analysis applied to the gel deformation. I succesfully unravelled the driving forces that lead to the gel detachment from the sidewall of the dish and proposed concrete solutions to be implemented on a commercial scale to prevent il

The measurement of the work of adhesion is of significant technical interest in a variety of applications, ranging from a basic understanding of material behavior to the practical aspects associated with making strong, durable adhesive bonds. The objective of this thesis is to investigate a novel technique using an elastica loop to measure the work of adhesion between solid materials. Considering the range and resolution of the measured parameters, a specially designed apparatus with a precise displacement control system, an analytical balance, an optical system, and a computer control and data acquisition interface is constructed. An elastica loop made of poly(dimethylsiloxane) [PDMS] is attached directly to a stepper motor in the apparatus. To perform the measurement, the loop is brought into contact with various substrates as controlled by the computer interface, and information including the contact patterns, contact lengths, and contact forces is obtained. Experimental results indicate that due to anticlastic bending, the contact first occurs at the edges of the loop, and then spreads across the width as the displacement continues to increase. The patterns observed show that the loop is eventually flattened in the contact region and the effect of anticlastic bending of the loop is reduced. Compared to the contact diameters observed in the classical JKR tests, the contact length obtained using this elastica loop technique is, in general, larger, which provides potential for applications of this technique in measuring interfacial energies between solid materials with high moduli. The contact procedure is also simulated to investigate the anticlastic bending effect using finite element analysis with ABAQUS. The numerical simulation is conducted using a special geometrically nonlinear, elastic, contact mechanics algorithm with appropriate displacement increments. Comparisons of the numerical simulation results, experimental data, and the analytical solution are made.
Master of Science

Les composites thermoplastiques préimprégnés suscitent un intérêt croissant pour l'industrie automobile grâce à leurs excellentes propriétés mécaniques et leur procédé de fabrication rapide. Dans ce contexte, la modélisation et la simulation numérique des procédées de mise en forme de pièces composites à géométries complexes sont nécessaires pour prédire et optimiser les pratiques de fabrication. Cette thèse est consacrée à la modélisation et à la simulation du comportement de consolidation des composites thermoplastiques préimprégnés lors du processus de mise en forme. Un nouvel élément solide-coque prismatique à sept nœuds est proposé: six situés aux sommets et le septième situé au centre. Le champ de cisaillement transverse est supposé afin de réprimer le verrouillage de cisaillement transversal. La méthode de déformation renforcée supposée par addition d'un DOF de déplacement supplémentaire depuis le nœud central et un schéma d'intégration réduit sont combinées offrant un champ de déformation linéaire le long de la direction d'épaisseur pour contourner le verrouillage. De plus, une procédure de stabilisation de sablier est employée afin de corriger le défaut de rang de l'élément pour le pincement. Cet élément utilise un modèle de relaxation viscoélastique pour modéliser le comportement tridimensionnel de composites thermoplastiques préimprégnés avec effet de consolidation. Un modèle de contact intime est également utilisé pour prédire l'évolution de la consolidation et la microstructure du vide présente au sein du préimprégné. A l’aide d’une loi hyperélastique, plusieurs simulations ont été conduites en combinant le nouvel élément fini et les modèles de consolidation. La comparaison des résultats de simulation avec les essais expérimentaux montre l'efficacité de l’élément solide-coque face aux problèmes de déformations dans le plan et en flexion, mais également pour l'analyse du comportement de consolidation. De plus, le degré de contact intime fournit le degré de consolidation par conditions de procédé appliqué, ce qui est essentiel pour l'apparition de défauts dans la pièce finale de composite
As the pre-impregnated thermoplastic composites have recently attached increasing interest in the automotive industry for their excellent mechanical properties and their rapid cycle manufacturing process, modelling and numerical simulations of forming processes for composites parts with complex geometry is necessary to predict and optimize manufacturing practices. This thesis is devoted to modelling and simulation of the consolidation behavior during thermoplastic prepreg composites forming process. A new seven-node prismatic solid-shell element is proposed: six located at the apexes and the seventh sited at the center. A shear stain field is assumed to subdue transverse shear locking, the enhanced assumed strain method by addition of an extra displacement DOF from the central node and a reduced integration scheme are combined offering a linear varying strain field along the thickness direction to circumvent thickness locking, and an hourglass stabilization procedure is employed in order to correct the element’s rank deficiency for pinching. This element permits the modelling of three-dimensional constitutive behavior of thermoplastic prepreg with the consolidation effect, which is modelled by a viscoelastic relaxation model. An intimate contact model is employed to predict the evolution of the consolidation which permits the microstructure prediction of void presented through the prepreg. Within a hyperelastic framework, several simulation tests are launched by combining the new developed finite element and the consolidation models. The comparison with conventional shell element and experimental results shows the efficiency of the proposed solid-shell element not only dealing with the in-plan deformation and bending deformation problems, but also in analyzation of the consolidation behavior, and the degree of intimate contact provides the level of consolidation by applied process conditions, which is essential for the appearance of defects in final composite part

Les résistances thermiques d'interface sont la conséquence d'une discontinuité structurale entre deux matériaux. Des exemples peuvent être trouvés dans des délaminages au sein de composites laminés ou dans les applications de soudage où on cherche à avoir des assemblages parfaits entre deux matériaux. Ces discontinuités structurales peuvent être caractérisées en utilisant la thermographie infrarouge stimulée. La profondeur et la résistance de contact d'un défaut dans un matériau peuvent être identifiées en utilisant des méthodes basées sur la transformation De Laplace en temps pour les cas ou le transfert de chaleur peut être considéré comme unidirectionnel (défauts très étendus). Il est proposé ici d'étendre les méthodes précédentes aux cas où le transfert de chaleur ne peut être considéré comme uni-directionnel. Dans ce but, une transformation de Fourier spatiale est appliquée à la transformée De Laplace en temps du signal produit par une camera infrarouge. Grâce à l'emploi des quadripôles thermiques 2D et 3D, une solution explicite du problème peut être trouvée. Un développement asymptotique (méthode des perturbations) permet la construction d'une solution approchée, très commode pour l'inversion. Dans le cas où la résistance d'interface est continument non uniforme, une relation explicite entre la transformée De Laplace-Fourier du contraste et la transformée de Fourier de la distribution de la résistance peut être trouvée dans le cadre d'un transfert 2D. L’inversion de cette relation fournit un algorithme explicite très commode qui permet d'estimer le profil de résistance. Des exemples numériques et expérimentaux ont été présentés: ils montrent la robustesse des techniques d'inversion développées

Return collectors are predominant organs for rubber-tyred subways to operatesince they ensure both the track circuit shunt and the traction current return. Po- sitioned at the interface between the track and the rolling stock, they are subjected to the disruptions linked to the train movement and the track irregularities. One of the most critical steps is the crossing of a switch nose.This study aims at determining the collector position during this crossing by means of a quasi-static analysis of the system. Two approaches are investigated. The first one brings into play a rigid contact and geometrical angles. It enables to model the crossing until the contact with the crossing nose. The diving capability of the collector is also taken into account. The second one is a standard  approach of the contact. A slight penetration is considered, which allows to grasp the contact with  the crossing nose. The second advantage  is to prepare the ground for a complete dynamical analysis. Both approaches are then implemented on Matlab to solve the equations. Finally the study of the switch crossing in nominal conditionsand a parametric analysis are achieved for a specified switch.

Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the absence of a robust sealant. A leakage computational model has been developed and refined in conjunction with leakage experiments and material characterization tests at Oak Ridge National Laboratory to predict leakage in a single interface metal-metal compressive seal assembly as well as multi-interface mica compressive seal assemblies. The composite model is applied as a predictive tool for assessing how certain parameters (i.e., temperature, applied compressive stress, surface finish, and elastic thermo physical properties) affect seal leakage rates.

Les Vibrations Induites par Frottement (FIV) sont un phénomène complexe qui surgit chaque fois deux surfaces subissent un glissement relatif. Pendant les dernières décennies, une quantité significative de œuvres expérimentales et numériques a traité des Vibrations Induites par Frottement, tandis que la simulation de l'excitation dynamique de contacts frictionnels a été toujours un vrai défi dans beaucoup de domaines de recherche industrielles. Dans ce cadre de recherche, ce travail est adressé à l'analyse des Vibrations Induites par Frottement, en développant des analyses en même temps expérimentales et numériques ; on propose une nouvelle approche numérique pour reproduire l'excitation dynamique locale du contact et son effet sur la réponse vibrationnel du système, sans augmentation significative des coûts de calcul. Le système mécanique, l'objet de l'analyse, est composé par deux poutres en acier en contact frictionnel dans un mouvement relatif ; la dynamique simple du système tient compte de la distinction entre la réponse de dynamique du système et l'excitation à haut débit venant du contact. Une campagne expérimentale paramétrique a été conduite pour analyser les effets de trois paramètres de contact principaux (la vitesse de glissement, la charge normale et la rugosité superficielle) sur la réponse du système vibrationnel, c'est-à-dire sur les vibrations induites. En parallèle, un modèle numérique a été mis en œuvre pour reproduire l'excitation dynamique locale du contact et son effet sur la réponse vibrationnel du système. Une nouvelle loi de friction a été présentée dans le modèle, proposant l'utilisation d'un terme provoquant une perturbation dans le coefficient de frottement pour simuler les effets de l'excitation au contact. Les inclusions de l'excitation dynamique locale, en raison des phénomènes de contact, par le terme de perturbation du coefficient de frottement, permettent de reproduire correctement les Vibrations Induites par Frottement sans présenter une représentation de la topographie superficielle réelle, qui a besoin d'un grand nombre d'éléments, économisant donc le temps de calcul. Des signaux différents pour le terme provoquant la perturbation ont été testés pour simuler correctement les vibrations mesurées. L'évolution du terme provoquant la perturbation récupérée par une méthode inverse a surligné les contributions spectrales différentes de l'excitation locale du contact. La comparaison entre les Vibrations Induites par Frottement mesurées et ceux simulés numériquement a montré une bonne corrélation, validant la loi de frottement proposée. Finalement, l'effet d'un changement de rugosité e de vitesse de glissement a été aussi simulé numériquement et corrélé avec les résultats expérimentaux
Friction-Induced Vibrations (FIV) are a complex phenomenon which arises each time two surfaces undergo relative sliding. During the last decades, a significant amount of experimental and numerical works dealt with Friction-Induced Vibrations, while the simulation of the dynamic excitation from frictional contacts has always been a real challenge to face in many industrial research areas. In this research framework, this work is addressed to the investigation of the Friction-Induced Vibrations, carrying on at the same time experimental and numerical analyses; a new numerical approach is proposed to reproduce the local dynamic excitation from the contact and its effect on the vibrational response of the system, without significant increase of the computational time costs. The mechanical system, object of the investigation, is composed by two steel beams in frictional contact during relative motion; the simple dynamics of the system allows for distinguishing between the dynamics response of the system and the broadband excitation coming from the contact. A parametrical experimental campaign has been conducted to analyse the effects of three main contact parameters (the relative sliding velocity, the normal load and the surface roughness) on the system vibrational response, i.e. on the induced vibrations. In parallel, a numerical model has been implemented to reproduce the local dynamic excitation from the contact and its effect on the vibrational response of the system. A new friction law has been introduced in the model, proposing the use of a perturbative term in the friction coefficient in order to simulate the effects of the contact excitation. The inclusions of the local dynamic excitation, due to the contact phenomena, by the perturbation term of the friction coefficient allows to correctly reproduce the Friction-Induced Vibrations without introducing a representation of the real surface topography, which usually needs a large number of elements, saving then computational time. Different signals for the perturbative term have been tested to simulate correctly the measured vibrations. The evolution of the perturbative term recovered by an inverse method allowed for highlighting the different spectral contributions of the local excitation coming from the contact. The comparison between the measured Friction-Induced Vibrations and the ones simulated numerically showed good correlation, validating the proposed friction law. Finally, the effect in a change of the sliding velocity and surface roughness have been simulated numerically too and correlated with experimental results

Cette thèse traite de la modélisation du frittage à l’échelle du Volume Élémentaire Représentatif de la pastille de matériau. L’objectif est de développer des outils numériquesde compréhension des phénomènes physiques mis en jeu lors du frittage. Le domaine d’application ciblé est la fabrication du combustible nucléaire. Une approche multi-Échelle a été mise en oeuvre. Dans un premier temps une modélisation à l’échelle d’un empilement, basée sur la méthode des Éléments Discrets, a été adoptée. Différentes études utilisant cette approche ont été proposées dans la littérature ces dernières années. Tous ces travaux utilisent une méthode discrète explicite. Si certains résultats ont pu être validés expérimentalement,une des limites vient de l’utilisation des méthodes explicites dontle pas de temps critique est très petit. Afin d’augmenter le pas de temps, la masse des particules y est augmentée artificiellement de plusieurs ordres de grandeur. Or,il a été démontré que cette pratique conduit, dans certains cas, à une diminution du réarrangement des particules au sein de l’empilement. Dans cette thèse, une méthode Éléments Discrets implicite appelée Dynamique des Contacts a été adaptée au frittage. Elle permet l’utilisation d’un pas de temps très supérieur à celui des méthodes discrètes explicites et ne nécessite pas d’augmenter artificiellement la massedes particules. La comparaison entre la Dynamique des Contacts et la Méthode des Éléments Discrets explicite montre que notre approche conduit à une représentation plus fidèle du réarrangement. Une validation expérimentale par Microtomographie X ainsi qu’une étude paramétrique sur le frittage des poudres bidispersés sont également présentées pour montrer les possibilités de l’approche discrète appliquée au frittage.La seconde partie est consacrée à une modélisation à l’échelle de deux particules parla méthode des Éléments Finis. Ce modèle repose sur une approche mécanique et vise à représenter de façon plus précise le comportement de deux particules en contact. Les diffusions au joint de grains, en surface et en volume peuvent être représentées. Pour le moment, seules les diffusions en surface et au joint de grains ont été étudiées. Si certaines optimisations restent nécessaires pour que le code soit fonctionnel, plusieurs aspects apparaissent déjà déterminants, comme la courbure de la surface à proximité du joint de grains. A l’avenir, le modèle Dynamique des Contacts du frittage pourra être complété etamélioré grâce aux éléments apportés par le modèle mécanique à l’échelle du grain
This thesis deals with the simulation of the sintering of nuclear fuel on a pellet scale. The goal is to develop numerical tools which can contribute to a better understandingof the physical phenomena involved in the sintering process. Hence, a multi scale approach is proposed. First of all, a Discrete Element model is introduced. It aims at modeling the motion of particles on a Representative Elementary Volume scale using an original Discrete Element Method. The latter is a Non Smooth Method called Contact Dynamics. Recently, there have been numerous papers about the simulation of sintering using Discrete Element Method. As far as we know, all these papers use smooth methods. Different studies show that the results match well experimental data. However, some limits come from the fact that smooth methods use an explicit scheme which needsvery small time steps. In order to obtain an acceptable time step, the mass of particles have to be dramatically increased. The Non Smooth Contact Dynamics uses an implicit scheme, thus time steps can be much larger without scaling up the mass of particles. The comparison between smooth and non smooth approaches shows thatour method leads to a more realistic representation of rearrangement. An experimental validation using synchrotron X-Ray microtomography is then presented, followedby a parametric study on the sintering of bimodal powders that aims at showing the capacity of this model.The second part presents a mechanical model on the sub-Granular scale, using a Finite Element method. This targets a better understanding of the behavior of twograins in contact. The model is currently being developped but the first results already show that some parameters like the shape of the surface of the neck are very sensitive.In the future, the Non smooth Contact Dynamics model of sintering may be improvedusing the results obtained by the sub-Granular scale mechanical model

The growing need for fast sampling of explosives in high throughput areas has increased the demand for improved technology for the trace detection of illicit compounds. Detection of the volatiles associated with the presence of the illicit compounds offer a different approach for sensitive trace detection of these compounds without increasing the false positive alarm rate. This study evaluated the performance of non-contact sampling and detection systems using statistical analysis through the construction of Receiver Operating Characteristic (ROC) curves in real-world scenarios for the detection of volatiles in the headspace of smokeless powder, used as the model system for generalizing explosives detection. A novel sorbent coated disk coined planar solid phase microextraction (PSPME) was previously used for rapid, non-contact sampling of the headspace containers. The limits of detection for the PSPME coupled to IMS detection was determined to be 0.5-24 ng for vapor sampling of volatile chemical compounds associated with illicit compounds and demonstrated an extraction efficiency of three times greater than other commercially available substrates, retaining >50% of the analyte after 30 minutes sampling of an analyte spike in comparison to a non-detect for the unmodified filters. Both static and dynamic PSPME sampling was used coupled with two ion mobility spectrometer (IMS) detection systems in which 10-500 mg quantities of smokeless powders were detected within 5-10 minutes of static sampling and 1 minute of dynamic sampling time in 1-45 L closed systems, resulting in faster sampling and analysis times in comparison to conventional solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis. Similar real-world scenarios were sampled in low and high clutter environments with zero false positive rates. Excellent PSPME-IMS detection of the volatile analytes were visualized from the ROC curves, resulting with areas under the curves (AUC) of 0.85-1.0 and 0.81-1.0 for portable and bench-top IMS systems, respectively. Construction of ROC curves were also developed for SPME-GC-MS resulting with AUC of 0.95-1.0, comparable with PSPME-IMS detection. The PSPME-IMS technique provides less false positive results for non-contact vapor sampling, cutting the cost and providing an effective sampling and detection needed in high-throughput scenarios, resulting in similar performance in comparison to well-established techniques with the added advantage of fast detection in the field.

The Generalized Finite Element Method (GFEM) is a numerical method based on the Partition of Unity (PU) concept and inspired on both the Partition of Unity Method (PUM) and the hp-Cloud method. According to the GFEM, the PU is provided by first-degree Lagragian interpolation functions, defined over a mesh of elements similar to the Finite Element Method (FEM) meshes. In fact, the GFEM can be considered an extension of the FEM to which enrichment functions can be applied in specific regions of the problem domain to improve the solution. This technique has been successfully employed to solve problems presenting discontinuities and singularities, like those that arise in Fracture Mechanics. However, most publications on the method are related to linear analyses. The present thesis is a contribution to the few studies of nonlinear analyses of Solid Mechanics by means of the GFEM. One of its main topics is the derivation of a segment-to-segment generalized contact element based on the mortar method. Material and kinematic nonlinear phenomena are also considered in the numerical models. An Object-Oriented design was developed for the implementation of a GFEM nonlinear analyses framework written in Python programming language. The results validated the formulation and demonstrate the gains and possible drawbacks observed for the GFEM nonlinear approach.
O Método dos Elementos Finitos Generalizados (MEFG) é um método numérico baseado no conceito de partição da unidade (PU) e inspirado no Método da Partição da Unidade (MPU) e o método das Nuvens-hp. De acordo com o MEFG, a PU é obtida por meio de funções de interpolação Lagragianas de primeiro grau, definidas sobre uma rede de elementos similar àquela do Método dos Elementos Finitos (MEF). De fato, o MEFG pode ser considerado uma extensão do MEF para a qual se pode aplicar enriquecimentos em regiões específicas do domínio, buscando melhorias na solução. Esta técnica já foi aplicada com sucesso em problemas com descontinuidades e singularidades, como os originários da Mecânica da Fratura. Apesar disso, a maioria das publicações sobre o método está relacionada a análises lineares. A presente tese é uma contribuição aos poucos estudos relacionados a análises não-lineares de Mecânica dos Sólidos por meio do MEFG. Um de seus principais tópicos é o desenvolvimento de um elemento de contato generalizado do tipo segmento a segmento baseado no método mortar. Fenômenos não lineares devidos ao material e à cinemática também são considerados nos modelos numéricos. Um projeto de orientação a objetos para a implementação de uma plataforma de análises não-lineares foi desenvolvido, escrito em linguagem de programação Python. Os resultados validam a formulação e demonstram os ganhos e possíveis desvantagens da abordagem a problemas não lineares por meio do MEFG.

The present work deals with the numerical solution of dynamic contact and fracture problems. The contact problem is a Signorini problem with or without Coulomb friction. The fracture problem uses a cohesive zone model with a prescribed crack path. These problems are characterized by a non-regular boundary condition and can be formulated with evolutionary variational inequations or differential inclusions. For the numerical solution, we combine, as usual in solid dynamics, a finite element discretization in space and time-integration schemes. For the contact problem, we begin by comparing the main methods proposed in the literature. We then focus on the so-called modified mass method recently introduced by H. Khenous, P. Laborde et Y. Renard, for which we propose a semi-explicit variant. In addition, we prove a convergence result of the space semi-discrete solutions to a continuous solution in the frictionless viscoelastic case. We also analyze the space semi-discrete and fully discrete problems in the friction Coulomb case. For the dynamic fracture problem, using a fully explicit scheme is impossible or not robust enough. Therefore, we propose time-integration schemes where the boundary condition is treated in an implicit way. Finally, we present and analyze augmented Lagrangian methods for static fracture problems

Des réacteurs avec solide en suspension (« slurry »), très répandu dans l'industrie chimique, du laboratoire à la production, offrent des bonnes capacités en transfert de matière et de chaleur. Leur flexibilité facilite le changement de la phase solide et permet une régénération en continue des catalyseurs en cas de désactivation. Cependant, ils présentent un fort rétro-mélange, et donc un désavantage pour des réactions ayant des enjeux de sélectivité et/ou de conversion poussées. L'écoulement segmenté dit de Taylor est souvent mis en œuvre dans les réacteurs micro-structurés (RMS), grâce à ses propriétés intéressantes (capacités de transfert, écoulement, piston). Cependant, l'utilisation des solides catalytiques dans ces RMS est le plus souvent résolue par immobilisation du catalyseur nuisant la flexibilité. L'écoulement « slurry Taylor » (EST) qui utilise les recirculations internes dans les segments liquides pour transporter des particules en poudre, peut potentiellement répondre à cet enjeu. L'objet de cette étude est la conception et la caractérisation de ce nouveau mode de contact gaz-liquide-solide (G-L-S) dans des tubes millimétriques horizontaux et verticaux. Des études hydrodynamiques ont révélé différents régimes d'écoulement dépendant de la vitesse et de l'orientation de l'écoulement. Pour étudier le transfert de matière L-S, une résine échangeuse d'ion a été utilisée et une première corrélation pour le nombre de Sherwood est proposée
Slurry reactors, widely encountered in chemical industry (laboratory scale up to manufactaring), offer good mass and heat transfer capacities and their high flexibility ensures the simple changeover of solid phases enables a continuous online fresh catalyst feed for fast deactivating catalysts. However slurry reactors promote a high degree of backmixing which can be a drawback for reactions with selectivity issues or when very high conversions are required. In microreaction technology, Taylor flow is often employed providing excellent heat and mass transfer and almost ideal plug flow behavior. Solid handing in these small structures is often resolved by immobilizing the solid catalyst which impinges on the flexibility. One possible solution to combine beneficial properties of Taylor flow with the operational flexibility of conventional slurry reactors is a “slurry Taylor” flow (STF) where catalyst particles are suspended and kept in motion by the internal circulations present in the liquid slugs. The focus of this work is the design and characterization of this innovative gas-liquid-solid contactor. Particles were transported in millimetric horizontal and vertical tubing without the risk of clogging. Hydrodynamic studies revealed different flow patterns depending mainly on velocity and flow orientation. Ion exchange resin particles were used to study the liquid-solid mass transfer and first correlation for the Sherwood number in STF is proposed

Engineering assemblies are very frequently subject to fretting fatigue, which is a damage process that results when very small slip displacements arise at nominally stationary frictional interfaces. Fretting accelerates the initiation and early propagation of fatigue cracks, thereby causing significant reductions in the fatigue performance of many critical engineering components. A majority of the previous research on fretting fatigue has focused on incomplete (i.e. smooth-edged) contacts, while complete (i.e. sharp-edged) contacts have received less attention. The aim of this thesis is to contribute to the theoretical understanding of complete contacts, especially when they are subject to fatigue conditions. This problem is addressed in two separate ways. First, because fretting failures almost invariably initiate from the edge of contact, a detailed understanding of the conditions in this region should enable more accurate assessments of fatigue performance to be made. Thus, an asymptotic analysis is presented, which provides an accurate description of the contact edge under many conditions. This is done by using the elasticity solution for a semi-infinite notch to represent the state of stress near the contact edge in an asymptotic sense. Attention is then placed on the fact that cyclically loaded frictional contacts tend toward a steady-state response in which less frictional slip (and energy dissipation) occurs than in the first few load cycles. To investigate this effect, a numerical sub-structuring procedure is described, which significantly reduces the number of degrees of freedom in finite element models of frictional contact. This reduced model is then used to calculate the shakedown limit, i.e. the amplitude of cyclic load above which frictional slip is guaranteed to persist in the steady state. The sensitivity of the steady-state solution to the initial residual displacement state is then investigated, and it is shown that initial conditions can have a large influence on the steady-state behaviour of complete contacts.

Les réacteurs à impact de jets, contenant ou non des phases dispersées, constituent une classe mal connue de réacteurs. Dans le cas du procédé de craquage catalytique trois phases sont mises en jeu : du gaz, des particules de catalyseur et des gouttelettes de charge pétrolière. La zone de mise en contact initiale des jets de réactifs semble particulièrement déterminante pour le rendement global de la réaction. L’objet de ce travail est donc l'étude expérimentale du comportement global des phases continues ou dispersées au cours de leur mise en contact qui s'effectue en des temps de l'ordre de quelques dizaines de millisecondes. À partir de mesures de distributions de temps de séjour sur des maquettes froides le comportement hydrodynamique de la phase continue est déterminé, l'éventuelle influence de la présence des solides étant aussi envisagée. Une étude sur l'efficacité des transferts de chaleur au cours de la mise en contact des particules et de la phase gazeuse est ensuite menée. Par ailleurs l'efficacité de la mise en contact des phases dispersées est caractérisée par l'étude des interactions entre des particules modèles, réactives ou non, et des gouttelettes d'eau. Une réaction test est mise au point et un modèle simple décrivant le comportement des phases dans le réacteur y est associé. L’existence d'une fraction de solides ne participant pas à l'impact des particules et des gouttelettes a ainsi pu être mise en évidence. Ce phénomène est quantifié par certains paramètres dont l'évolution est étudiée en fonction des conditions expérimentales. Il en ressort un certain nombre de conclusions mais aussi de possibilités d'études futures pour une meilleure connaissance des phénomènes.

Cette thèse est consacrée à l’analyse mathématique du problème du mouvement d’un nombre fini de corps rigides homogènes au sein d’un fluide visqueux incompressible homogène. Les fluides visqueux sont classés en deux catégories: les fluides newtoniens et les fluides non newtoniens. En premier lieu, nous considérons le système formé par les équations de Navier Stokes incompressible couplées aux lois de Newton pour décrire le mouvement de plusieurs disques rigides dans un fluide newtonien visqueux homogène dans l’ensemble de l’espace R^2. Nous montrons que ce problème est bien posé jusqu’à l’apparition de la première collision. Ensuite, nous éliminons tous les types de contacts pouvant survenir si le domaine fluide reste connexe à tout moment. Avec cette hypothèse, le système considéré est globalement bien posé. Dans la deuxième partie de cette thèse, nous montrons la non-unicité des solutions faibles au problème d’interaction fluide-solide 3D, dans le cas d’un fluide newtonien, après collision. Nous montrons qu’il existe des conditions initiales telles que nous pouvons étendre les solutions faibles après le temps pour lequel le contact a eu lieu de deux manières différentes. Enfin, dans la dernière partie, nous étudions le mouvement bidimensionnel d’un nombre fini de disques immergés dans une cavité remplie d’un fluide viscoélastique tel que des solutions polymériques. Les équations de Navier Stokes incompressible sont utilisées pour modéliser le solvant, dans lesquelles un tenseur de contrainte élastique supplémentaire apparaît comme un terme source. Dans cette partie, nous supposons que le tenseur de contrainte supplémentaire satisfait la loi différentielle d’Oldroyd ou sa version régularisée. Dans les deux cas, nous prouvons l’existence et l’unicité des solutions fortes locales en temps du problème considéré
This thesis is devoted to the mathematical analysis of the problem of motion of afinite number of homogeneous rigid bodies within a homogeneous incompressible viscous fluid. Viscous fluids are classified into two categories: Newtonian fluids, and non-Newtonian fluids. First, we consider the system formed by the incompressible Navier-Stokes equations coupled with Newton’s laws to describe the movement of several rigid disks within a homogeneous viscous Newtonian fluid in the whole space R^2. We show the well-posedness of this system up to the occurrence of the first collision. Then we eliminate all type of contacts that may occur if the fluid domain remains connected at any time. With this assumption, the considered system is well-posed globally in time. In the second part of this thesis, we prove the non-uniqueness of weak solutions to the fluid-rigid body interaction problem in 3D in Newtonian fluid after collision. We show that there exist some initial conditions such that we can extend weak solutions after the time for which contact has taken place by two different ways. Finally, in the last part, we study the two-dimensional motion of a finite number of disks immersed in a cavity filled with a viscoelastic fluid such as polymeric solutions. The incompressible Navier–Stokes equations are used to model the flow of the solvent, in which the elastic extra stress tensor appears as a source term. In this part, we suppose that the extra stress tensor satisfies either the Oldroyd or the regularized Oldroyd constitutive differential law. In both cases, we prove the existence and uniqueness of local-in-time strongsolutions of the considered moving-boundary problem

Le squat est un défaut de fatigue de contact apparaissant à la surface du rail et dont le mécanisme d’amorçage est mal compris. Afin de pallier ce manque, une analyse tribologique locale de la bande de roulement du rail est mise en oeuvre à proximité d’un squat naissant. Cette caractérisation révèle une anisotropie importante des couches superficielles du rail associée aux développements de Transformations Tribologiques Superficielles. Ces résultats témoignent de conditions de contact roue/rail particulières dans la zone d’étude, notamment d’un niveau d’efforts de cisaillement inhabituel pour une voie en alignement. Dans le but de valider ces observations, plusieurs essais sont effectués. D’une part les conditions de contact roue/rail dans une zone de squats sont mesurées à partir d’un train instrumenté. D’autre part, la réponse tribologique de l’acier à rail à ces conditions de contact est étudiée à travers le suivi régulier d’une zone d’essais soumise à la circulation ferroviaire. Ces essais permettent d’identifier un déséquilibre important des efforts de traction sur les bogies moteurs et des glissements locaux élevés de la roue sur le rail. Différents mécanismes d’amorçage thermo-mécaniques sont alors proposés au sein d’un schéma global de la réponse tribologique de l’acier à rail
Squats have recently become recognised as one of the major rolling contact fatigue defects in modern railway networks for which there is currently no solution other than preventive grinding operations or costly rail renewal. To better understand the entire damage mechanism of squat, A tribological and metallurgical analysis of the rolling band and the near surface layer was performed close to an incipient squat. This characterization show a significant anisotropy of the rail surface layer associated with developments of Tribological Transformation of Surface. These results reflect some specific wheel/rail contact conditions in this squat area, including an unusual level of shear forces in a straight track. In order to validate this observations, two tests were performed. On the one hand, the contact conditions in a squat area were measured from an instrumented train. On the other hand, the tribological response of the rail steel was studied through regular monitoring of a test site subjected to railway traffic. These tests allow to identify a high imbalance of the traction forces and the presence of local slips at the wheel/rail interface. Several thermomechanical initiation mechanism of squats are then given in a overall diagram of the tribological response of rail steels

Ce mémoire reporte dans une première partie les études menées sur des polymères à empreintes moléculaires (MIP) en extraction solide-liquide (SPE). La nature des interactions polymère-analyte, l’influence de la composition de la matrice de l’échantillon et la sélectivité des MIPs sont étudiés.La première application concerne l’extraction de molécules ciblées dans un extrait de plante. Deux MIPs respectivement préparés à partir de l’acide méthacrylique (MAA) et l’acide itaconique (IA) et avec respectivement la catharanthine et la vindoline comme molécule empreinte ont montré leur sélectivité sur des solutions standards puis sur un extrait de plante. Des expériences de réactivité croisée réalisées sur des molécules analogues à la molécule empreinte (alcaloïdes dimères) montrent la spécificité de reconnaissance des analytes par les MIPs. Le MIP-catharanthine est caractérisé par les isothermes de Scatchard et sa capacité est évaluée en SPE à partir de l’extrait de Catharanthus roseus. Un MIP préparé à partir de MAA avec la vinorelbine comme molécule empreinte a été appliqué à des matrices aqueuses salines pour l’extraction de la vinflunine et de son métabolite dans du plasma bovin et de l’urine. Des rendements d’extraction élevés ont été atteints grâce à une étude de l’impact des sels et au choix de solvants de lavage adaptés à la matrice. Une deuxième partie montre la simplicité d’utilisation et la sensibilité de la détection conductimétrique sans contact à couplage capacitif (C4D) lors de l’analyse du contre-ion et du principe actif dans des composés pharmaceutiques en électrophorèse capillaire (EC). La technique de la double injection a permis l’analyse simultanée des cations et des anions. La méthode EC-C4D développée est appliquée aux alcaloïdes Vinca et à différents médicaments avec des contre-ions anioniques ou cationiques
This thesis reports in a first part results obtained with molecularly imprinted polymers (MIP) during solid liquid extraction. Polymer-analyte interactions, composition of the sample matrix and selectivity of MIPs have been studied.The first application concerned the extraction of molecules in a plant extract. Two MIPs respectively prepared from the methacrylic acid (MAA) and itaconic acid ( IA) and with respectively catharanthine and vindoline as template showed their selectivity on standard solutions then on a plant extract. Experiments of cross reactivity performed with analogue of the template (dimers alkaloids) have proved the specificity of analytes recognition by the MIPs. The MIP-catharanthine is characterized by Scatchard isotherms and its capacity was estimated from the extract of Catharanthus roseus. A MIP prepared from MAA with the vinorelbine as template was applied in salt aqueous matrices for the extraction of vinflunine and its metabolite in bovine plasma and urine. High extraction recoveries were reached with a study of the impact of salts and the choice of washing solvents adapted to the matrix. The second part showed the simplicity of use and the sensibility of capacitively coupled contactless conductivity detection (C4D) for the analysis of counter-ion and active principle in pharmaceutical compounds in capillary electrophoresis (CE). The technique of double injection allowed the simultaneous analysis of cations and anions. The developed method EC-C4D was applied to Vinca alkaloids and various medicines with anionic or cationic counter-ions

La tenue des surfaces des contacts rugueux roulants est un problème crucial l’évaluation de la durée de vie des mécanismes. Cette durée de vie est conditionnée dès les premiers cycles par le rodage puis par les mécanismes de fatigue des surfaces. Le rodage est défini par le temps nécessaire à l’accommodation géométrique des surfaces rugueuses entre elles, à l’interface du contact. La charge transmise sur une faible aire de contact par rapport à l’aire apparente, crée des pressions importantes qui induisent de fortes contraintes en couche superficielle et des déformations plastiques de la microgéométrie. Cette plastification a lieu dans les tous premiers cycles puis la surface se stabilise, c’est le rodage. La répétition cyclique des sollicitations au cours du fonctionnement conduit enfin à l’endommagement du matériau et des avaries en surface telles que des micro-écailles. Après une étude bibliographique sur le contact roulant rugueux et les dispositifs expérimentaux existants, la difficulté de ce type d’analyse est mise en évidence. Elle consiste à effectuer un suivi en continu de l’évolution de l’état de surface du contact à une échelle suffisamment fine et précise. Une micromachine bi-disque a été développée afin de réaliser ce suivi quasi "in-situ" à l’échelle des rugosités permettant d’identifier les mécanismes de rodage et de dégradation. Un protocole expérimental précis permet de mesurer les surfaces antagonistes dans les premiers cycles correspondant au rodage. Les surfaces vierges mesurées sont utilisées comme paramètre d’entrée d’une simulation numérique du contact rugueux d’une sphère sur un plan. La déformée de surface numériquement obtenue à l’état stabilisé est comparée à celle mesurée expérimentalement à la fin du rodage. La très bonne superposition de ces résultats permet de valider cette méthode et les résultats numériques tels que les contraintes résiduelles et déformations plastiques. Les surfaces à l’état stabilisé obtenues, sont exploitées à travers différents critères de fatigue multiaxiaux. Les résultats numériques sont également comparés aux observations expérimentales pour déterminer le critère le plus adapté à cette analyse et permettant d’expliquer la formation de fissures et d’avaries de surfaces
The surface life of rolling rough contacts is an important problem in the evaluation of the life expectancy of a machine. This life span is conditioned by the first cycles of the running-in process and then by the surface fatigue. The running-in period is defined by the time necessary for the rough surfaces to accommodate. The real area of contact is small compared with the apparent area, hence the load creates important pressures which lead to important stresses in the superficial layer and to plastic deformation of the microgeometry. The plastic deformation takes place over the first cycles then the surface stabilizes, this is the end of running-in process. The repeated cyclic loading finally leads to material damage below the surface and to surface micropitting. After a bibliographical study on the rough rolling contact and the existing experimental test machines, the difficulty of analysing the roughness evolution is pointed out. It requires a precise, continuous monitoring of the contact surface evolution on a small enough scale. A two-disk micro-machine was developed to perform this almost "in situ" monitoring at the roughnesses scale, allowing one to identify the mechanisms of running-in and surface degradation. An accurate experimental protocol allows one to measure the opposing surfaces in the first cycles corresponding to the running-in period. The initial surfaces are used as entrance parameters for a numerical simulation of the rough contact of a sphere on a plane. The deformed surface numerically obtained in the stabilized state is compared with the measured one at the end of the running-in period. The very good agreement between these results allows one to validate this method and the numerical results such as the residual stresses and the plastic deformation. Different multiaxial fatigue criteria are applied to the numerical results obtained in the stabilized state. The results are compared to the experimental observations to determine the criterion that is the most suited for this analysis and allows one to explain the crack formation and surfaces damage

Simulation numérique d'un réacteur gaz-solide d'hydropyrolyse du charbon. Les résultats montrent que le procédé permet de fabriquer de l'acétylène à un prix compétitif. Calcul des transferts radiatifs dans un nuage de particules par un modèle à zones concentriques bidimensionnel. Modélisation du comportement thermique d'un échangeur à pluie de particules. Simulation numérique d'un écoulement d'argon chaud refroidi dans un tube cylindrique. Influence des variations des propriétés physiques.

Les nanoparticules (NPs) organiques représentent un outil majeur d'innovation en dermatologie. L'objectif de cette thèse a été de développer et d'optimiser des procédés d'encapsulation d'un mélange de molécules odorantes appelé fragrance mix I (FMI) dans des nanoparticules (NPs) de différentes natures: NPs polymères (poly-ε-caprolactone, PCL), ou NPs lipidiques solides (SLNs) (à base de vaseline, beurre de karité, cire de candelilla, triglycérides C10-18, ou palmitate de cétyle). Ces nouveaux systèmes ont alors été évalués pour la vectorisation de ce mélange à travers un explant de peau de porc, afin de modéliser la distribution des molécules composant le FMI dans les différentes assises cutanées. En parallèle, elles ont également été appliquées en tant que promoteurs de solubilisation du FMI pour le développement d'un nouveau test de diagnostic in vitro de l'allergie aux parfums. Nos résultats montrent que: (i) les NPs polymères, principalement anioniques, sont les plus adaptées pour promouvoir la pénétration transépidermique du FMI. Au contraire, les SLNs s'agglomèrent dans le stratum corneum, conduisant à une accumulation du FMI dans cette assise ; (ii) qu'au-delà du type de vecteur utilisé, la pénétration des molécules du FMI dans les couches les plus profondes de la peau dépend de leur coefficient de partage intrinsèque ; (iii) que les nanoparticules de PCL augmentent significativement la solubilisation du FMI dans les milieux de culture conventionnels et permettent ainsi une réactivation robuste des lymphocytes T spécifiques circulant chez des patients présentant une allergie au parfums. L'ensemble de ces résultats confirme donc tout le potentiel des NPs organiques pour le développement de futures stratégies de délivrance ciblée de plusieurs actifs dans les différents compartiments cutanés. Ces nouveaux vecteurs offrent en outre une alternative prometteuse pour améliorer le diagnostic de l'eczéma de contact induit par les parfums et plus généralement par des allergènes hydrophobes
The aim of this work was to develop and optimize methods for fragrance mix I (FMI) encapsulation into nanoparticles (NPs) of two types of nanoparticles (NPs) : polymeric NPs (poly-ε-caprolactone, PCL) and solid lipid NPs (SLNs) (prepared with petrolatum, shea butter, candelilla wax, C10-18 triglycerides, or cetyl palmitate). Then, these new NPss were evaluated as vectors through a pig skin to analyze the distribution of the FMI molecules in the different skin layers. In parallel, NPs have also been applied as solubilizers for the development of a new in vitro test for the diagnosis of fragrance allergy. Our results show that (i) NPs polymers, mainly anionic NPs, are the most suitable vectors to promote trans-epidermal penetration of fragrance. On the contrary, SLNs were found in the stratum corneum, leading to an accumulation of fragrance in this layer; (ii) whatever the type of NPs, the penetration of the FMI molecules in the deeper layers of the skin depends on their intrinsic partition coefficient; (iii) PCL-NPs significantly increase the FMI solubilization in conventional culture media and, allowing a robust reactivation of circulating specific T cells in patients with allergy to fragrances. All of these results confirm the potential of organic NPs for the development of future strategies (for the skin delivery of several actives in the different skin layers). These new vectors further offer a promising alternative to improve the diagnosis of contact dermatitis induced by fragrances and more generally by hydrophobic allergens

The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.

The purpose of this thesis work was to develop a headspace solid phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS) method to detect volatile organic compounds (VOCs) in board samples and to statistically investigate potential correlation between chromatographic data and flavor data obtained from a trained panel. The developed method would hopefully serve as a complement to the already established routine analyses at Stora Enso and gain an increased understanding of which VOCs in the board influence its flavor properties. The impact of incubation time and adsorption time on the area under curve (AUC) was studied with a Design of Experiment screening using the software MODDE. The screening data showed a correlation between large AUC and low repeatability measured as relative standard deviation (RSD). The data was hard to fit to a model due to the large RSD values for the replicates, AUC for identified compounds as response gave an acceptable fit. The regression coefficients for the model showed that a longer adsorption time gave larger AUC, while incubation time had no significant impact on the response.  Instead of following up the screening with an optimization, the focus was shifted to improving the repeatability of the method, i.e. lowering the RSD. The high RSD was believed to mainly be the result of leakage of analytes and unstable temperature during adsorption, preventing the system from reaching equilibrium. Different heating options and capping options for the vial was tested. Septum in crimp cap ensured a gas tight seal for the vial, giving lower RSD values and larger AUC compared to the other alternatives, showing that there was indeed a leakage. Using oil bath ensured stable temperature during the adsorption and detection of a larger number of VOCs but created a temperature gradient in the vial due to it not being fully submerged in the oil. Oil bath gave larger AUC, but still high RSD due to the temperature gradient making the method sensitive to variance in fiber depth in the vial. The final method was performed with 2 g of board sample in a 20 ml headspace vial sealed with a crimp cap with septa. The incubation and adsorption were performed with the vial immersed in a 90-degree oil bath. 20 min incubation time was chosen based on the time it took to get a stable temperature gradient in the vial, and 20 minutes adsorption time was chosen as a good compromise between large AUC and low RSD. Compared to Stora Ensos routine analysis, the developed SPME method gave chromatograms with an improved signal-to-noise ratio for the base line and several more peaks with larger AUC. For the board sample used during method development, the SPME-method identified 34 VOCs, while the routine analysis only identified 12. The developed method was applied on 11 archived board samples of the same quality that were selected based on their original flavor properties, to get a large diversity of samples. Flavor analysis was performed by letting a trained flavor panel describe the flavor based on intensity and character of the water that had individually been in indirect contact with one of the 11 board sample for 24 h. Potential correlation between chromatographic data obtained with the developed method and the flavor experience described by the flavor panelists was statistically investigated with the multivariate analysis software SIMCA. The correlation study showed that a combination of 12 VOCs with short retention time are most likely the main source of off-flavor which of 5 could only be identified with the developed SPME method. VOCs with long retention time did not contribute to an off-flavor and might have a masking effect on flavor given by other VOCS, however not confirmed in this study. Furthermore, the age of the board samples proved to be a good indicator for prediction of the flavor intensity, whereas the total AUC of the samples was not. Possible correlation between detected VOCs in the samples and flavor character given by the flavor panel were seen, however the variation in the data and the sample set were too small, preventing from making conclusions on individual VOCs impact on the flavor experience. The developed HS-SPME-GC-MS method would serve as a complement to the already established routine analyses at Stora Enso and has slightly increased the understanding of which VOCs in the board influence the flavor properties

This thesis presents cutter swept volume generation, in-process workpiece modeling and Cutter Workpiece Engagement (CWE) algorithms for finding the instantaneous intersections between cutter and workpiece in milling. One of the steps in simulating machining operations is the accurate extraction of the intersection geometry between cutter and workpiece. This geometry is a key input to force calculations and feed rate scheduling in milling. Given that industrial machined components can have highly complex geometries, extracting intersections accurately and efficiently is challenging. Three main steps are needed to obtain the intersection geometry between cutter and workpiece. These are the Swept volume generation, in-process workpiece modeling and CWE extraction respectively. In this thesis an analytical methodology for determining the shapes of the cutter swept envelopes is developed. In this methodology, cutter surfaces performing 5-axis tool motions are decomposed into a set of characteristic circles. For obtaining these circles a concept of two-parameter-family of spheres is introduced. Considering relationships among the circles the swept envelopes are defined analytically. The implementation of methodology is simple, especially when the cutter geometries are represented by pipe surfaces. During the machining simulation the workpiece update is required to keep track of the material removal process. Several choices for workpiece updates exist. These are the solid, facetted and vector model based methodologies. For updating the workpiece surfaces represented by the solid or faceted models third party software can be used. In this thesis multi-axis milling update methodologies are developed for workpieces defined by discrete vectors with different orientations. For simplifying the intersection calculations between discrete vectors and the tool envelope the properties of canal surfaces are utilized. A typical NC cutter has different surfaces with varying geometries and during the material removal process restricted regions of these surfaces are eligible to contact the in-process workpiece. In this thesis these regions are analyzed with respect to different tool motions. Later using the results from these analyses the solid, polyhedral and vector based CWE methodologies are developed for a range of different types of cutters and multi-axis tool motions. The workpiece surfaces cover a wide range of surface geometries including sculptured surfaces.

Fenômenos multifásicos são frequentemente observados na natureza, tais como nas gotas de chuva ou neve no ar, nos vulcões e tempestades de areia, e em diversas outras situações. Na solução desses problemas que envolvem escoamentos gás-sólidos e granulares são frequentemente utilizadas duas abordagens: a contínua (formulação Euleriana-Euleriana) e a discreta (formulação Euleriana-Lagrangiana). Na abordagem discreta pode-se utilizar dois modelos para descrever o contato entre as partículas: o modelo de esfera rígida e o modelo de esfera suave. Neste trabalho é realizado um estudo detalhado dos modelos de contato, com foco na modelagem de esfera suave, que é baseada em um sistema dinâmico mola-massa-amortecedor. Por meio desse estudo, com a finalidade de aprimorar o modelo de contato não-linear, são propostas duas relações para o mecanismo de contato de partículas. Essas relações são fundamentadas em um modelo dinâmico, com não-linearidades nas partes conservativas e dissipativas, não apresentando descontinuidades entre as acelerações do início e do fim do contato. A metodologia de desenvolvimento da presente pesquisa está dividida em três partes: pesquisa bibliográfica dos modelos de contato; estudo analítico e numérico desses modelos e testes de problemas com a realização de experimentos numéricos, utilizando o código computacional MFIX (Multiphase Flow with Interphase eXchange). As novas aproximações propostas neste trabalho são analisadas e aplicadas em três diferentes problemas: de dinâmica, escoamento gás-sólido e escoamento granular. Os resultados obtidos utilizando as relações são comparados com dados disponíveis na literatura, mostrando-se adequados para os casos investigados neste trabalho.
Multiphase flow are frequently observed in nature, such as rain drops in air or snowfalls, volcanoes and sandstorms, and several other situations. For solving these problems which involve gas-solid and granular flows are often used two models: the continuous model (Eulerian-Eulerian formulation) and the discrete model (Eulerian-Lagrangian formulation). There are two main contact models used in DEM, the hard-sphere model and the soft-sphere model. In this work is carried out a detailed study of contact models, focusing on soft-sphere model, based on a dynamic system modeled as nonlinear mass-spring-damper. In order to improve the nonlinear contact model, in this study it is proposed two new approximate relations for determining the damping coefficient and duration of contact for a specific nonlinear soft-sphere contact model where the contact force is continuous at the start and end of the contact. The methodology of the development of this work is divided into three parts: literature research of the contact models; analytical and numerical study of these models and test problems with numerical experiments, using the open source code MFIX (Multiphase Flow with Interphase eXchange). The proposed relations are analyzed and applied in three different problems: dynamic problem, gas-solid flow and granular flow. All results are compared with literature data showing good agreement for these cases studied in the present work.