Afin de produire de l’électricité, une éolienne doit s’orienter de manière à être face au vent. Cette rotation est assurée par un système de giration placé entre le mât et la nacelle appelé « yaw ». C’est lors de la phase de yawing que peut apparaître le phénomène de « crissement » à cause du contact frottant entre les garnitures des freins et le disque, l’effort de freinage n’étant pas relâché afin de contrôler la giration de la nacelle. Dans un objectif de réduction voire de suppression du bruit, une démarche scientifique de compréhension du phénomène comprenant un volet structure et un volet matériau a été mise en place, aucune étude sur le sujet n’ayant jamais été réalisée dans le domaine éolien. La première étape de l’étude a consisté en une caractérisation du problème en conditions réelles sur éolienne. Les données collectées complétées par une étude bibliographique élargie ont permis de définir une stratégie d’étude : de manière globale, cette recherche est basée à la fois sur une approche expérimentale et sur une approche numérique. L’accent est mis sur l’influence du matériau de friction : plusieurs matériaux ont été investigués dont l’un correspond à une « amélioration » d’une formulation industrielle initialement relativement « bruyante ». Ces matériaux sont également décrits et caractérisés en termes de propriétés mécaniques et les surfaces frottées sont observées après essai. Au final, cette étude a permis de maitriser et d’identifier certains paramètres influents tels que le rôle des garnitures, amenant de nombreux éléments de compréhension des phénomènes mis en jeu afin d’appréhender des voies d’amélioration pour la réduction du bruit. / In order to produce electricity, a wind turbine needs to be face to the wind. The system allowing its orientation is placed between the tower and the nacelle and is called ‘yaw’. Due to the contact between friction pads and disc during the rotation phases, squeal noise can occur, the braking forces being used to control the nacelle rotation. In the aim of reducing and even suppressing the noise, a scientific approach has been set up to understand the phenomena involved, including the structure and the friction material aspects, no such study has ever been carried on in the wind turbine domain. The first step has consisted in characterizing the problem in real conditions on wind turbines. The collected data and an extended bibliographic study have been used to define a strategy: globally, the study is based both on experimental investigations and numerical simulations. The influence of the friction material has been highlighted: several materials have been investigated, one of them being a “improvement” of a commercial material initially “noisy”. Those friction materials are also described and characterized regarding their mechanical properties and the rubbing surfaces have been observed after tests. In the end, that study has enable to control and identify some influent parameters as the role of the friction pads, bringing a better understanding of the phenomena involved in that squealing noise problematic in order to develop new improvement solutions to reduce noise.

Le but de cette étude est la prédiction de la durée de vie à l'initiation de la fissure d'un contact acier/aluminium sous la sollicitation de fretting fatigue. La prédiction des durées de vie a été déterminée à l'amorçage des fissures en fonction des différents chargements appliqués. Un dispositif expérimental adapté sur un banc d'essai multiaxial de fatigue a été mis au point. Des essais ont été réalisés sur un alliage d’aluminium de la série 6082T6. Les résultats obtenus montrent un abattement de la durée de vie par rapport à la fatigue classique. La modélisation par éléments finis a été menée en utilisant un code de calcul Abaqus. Les champs de contraintes et de déformations identifiés ont été utilisés sur différents critères de fatigue multiaxiale basés sur les plans critiques. Les résultats de la prédiction donne une sous estimation de la durée de vie en fretting fatigue. Ceci est dû aux forts gradients présents dans la zone de contact. La prédiction a été améliorée par couplage d’une méthode de champs moyens avec les critères de fatigue multiaxiale. Les estimations obtenues présentent une bonne corrélation avec les résultats expérimentaux. Néanmoins, la taille de la zone d'élaboration optimale semble dépendre du critère de fatigue multiaxiale utilisé et des conditions de chargement appliquées. Cette zone ne semble pas être liée directement avec la microstructure pour le matériau étudié.Dans une structure les sollicitations sont variables. La démarche ci-dessus a été couplée avec deux lois d'endommagement: loi de Miner et loi dite de la contrainte endommagée pour la prédiction avec des chargements par blocs. Les prédictions obtenues sont satisfaisantes. / The purpose of this study is to predict fretting fatigue crack nucleation of a mono contact steel/aluminum at different applied loads.An experimental device was first designed and adapted on a multiaxial fatigue apparatus. Tests were conducted aluminum alloy at constant amplitude loading under both different load levels and load ratios. As expected, the fretting fatigue life was found lower compared to uniaxial fatigue under the same loading conditions. Finite element analysis was conducted using \textit{Abaqus} software. The computed stress and strain fields were used to estimate the parameters of different multiaxial fatigue criteria based on the critical plane approach. When using stress and strain values corresponding to the material point exhibiting the maximum value of the considered parameter, we have found that, whatever the multiaxial fatigue parameter, conservative fatigue life estimates due to the severe gradients in the contact zone. An averaging method of the mechanical quantities over a given reference volume was then used to attenuate these gradients effects. The estimates show a good correlation with experimental results. However, the size of the reference volume depends on both the multiaxial fatigue criteria and on loading conditions applied. So that it could not be directly linked to the grain size for the material studied. Finally, we made an attempt to extend these criteria and the developed method to variable loadings. Fretting fatigue tests using two and four blocks loadings were performed and the previous criteria were coupled with two damage laws. The estimates we have obtained seems very promising.

Polymeric coating research requires advanced spectroscopic techniques to perform more efficient and detailed analysis in order to improve knowledge on the component distribution and the degradation of functional groups in the coating. In this work, the advanced non-destructive Step-scan Photoacoustic (SSPA) FTIR and Confocal Raman Microscopy (CRM) techniques were developed and applied to the component distribution studies and degradation studies of polyester/melamine based coil coating. The results show that both techniques are very suitable to carry out both qualitative and quantitative analyses. The degradation of polyester/melamine coil coating exposed in various environmental conditions were studied in detail using the advanced SSPA-FTIR and CRM techniques; the results clearly show that the coating degradation is highly dependent on the weathering conditions. Acid rain was also found to significantly affect the coating durability. Moreover, different pigments incorporated into the coating formulation were also found to have a major impact on the coating durability. With the help of the powerful CRM component distribution analysis function, melamine enriched zones that were very likely to arise from the melamine self-condensation during the curing process of coil coating were clearly observed in the coatings. This finding confirms the hypothesis developed over 20 years in the coil coating research field. Moreover, the durability of the melamine enriched zones was also investigated in this work.

This thesis comprises studies of size effects in the plasticity of metals and ceramics at length scales of the order of micrometres and includes both experimental work and theoretical development. Experimental results are presented for foil flexure (nickel and copper)and nanoindentation (ceramics and hard metals).These studies were conducted because existing data does not cover a range broad enough or with sufficient precision to test various theories. With the developed bending technique more accurate data is obtained covering a wide range of strain, especially around the key region of the elastic-plastic transition. Moreover, the interaction between grain and thickness size effect is successfully studied by varying the ratio of grain size over thickness of the foils. After carefully calibrating the indenters, the macroscopic indentation yield strength for ceramics and high strength metals is determined in a direct way by using spherical nanoindentation. The magnitude of size effect is significantly different between metals and ceramics. By comparing the Berkovich and spherical indentation size effect, the results implies that the contact size, a, is the most fundamental length scale in the indentation size effect, independent of the indenter shape. The indentation strength is found to be inversely scaled with the square root of a. The slip-distance theory (based on (Conrad et al, 1967)) with an effective length scale reconciling intrinsic and extrinsic size effects appears able to account for the size effects in all contexts, without requiring strain gradient plasticity theory or an implicit characteristic length.

Biointerfaces bridge across inorganic and biological substances within a watercontaining environment. It is related to health care, environmental engineering and bioenergy generation. However, there is a lack of fundamental understanding of bonding and stability of biointerfaces, due to limited capabilities of experimental techniques. The research project employs molecular dynamics (MD) as the basic methodology to study selected biointerfaces, involving five carbon surfaces (amorphous carbon surface, basal graphite surface, basal graphite surface doped with hydrogen and hydroxyl groups, basal graphite surface with Stone-Wales defects, and edge graphite surface). The selected molecules are: a small alpha-helix and a beta-sheet peptide, each with 16 amino acids; and a mid-sized peptide (amyloid peptide). The systematic study of the molecular adsorption on carbon surfaces has shown that it is a very complex process, which depends on several factors such as the molecular structure, the hydropathy of the peptide molecule, the charge and defects of the substrate surface, and the orientation of the molecule upon adsorption. It is clear that the amino acids which face the surface initiate the adsorption process and influence subsequent stages of adsorption. The considered carbon surfaces have different levels of reactivity for the molecule adsorption. The amorphous and charged surfaces tend to stabilise the beta sheet secondary structure. The interaction between the amyloid peptide and the carbon surfaces seems to depend on its molecular orientation, as well as the nature of the carbon surface: it was clearly attracted to the hydrophobic basal surface of graphitic carbon but pushed away from the hydrophilic charge-doped surface in one of the orientations (the second), but the opposite is true for another orientation (the third). Details of the structural change were shown in the Ramachandran plot. The energy change of the system mainly comes from the configurational variation, and electrostatic interactions are more prominent than the others. Water molecules tend to accumulate above a hydrophobic surface, forming a dense water layer, with an estimated distance of 2.9 Å from the carbon surface, whereas they distribute relatively evenly on hydrophilic surfaces.

Carbon based materials such as CNTs and graphene have been widely studied over the last few years. The outstanding electrical and mechanical properties of these materials attracted researchers to find ways to grow and use them in nano-devices. Among the different techniques, PECVD is a relatively simple and low temperature process. It facilitates the growth of CNTs and graphene on particular sites of the substrate. The objective of this research project was to study the growth of CNTs and graphene using PECVD system and to employ them in renewable energy devices. Excimer laser processed materials were also the focus for flexible material for fuel cells and other applications to show the way to a one step manufacturing process that lends itself to large area and low cost processing using standard tools.In the growth of CNTs, the roll of a buffer layer and catalyst materials were studied in depth. Different metals were tested for best results in optimising nanotube growth for the selected applications. The role of the buffer layer in the formation of nanoparticles and their surface adhesion was studied. Different materials were used as a catalyst and analysed for best performance in the PECVD system. Growth parameters such as temperature, pressure, gas flow rate and plasma power were studied during the growth of CNTs in the PECVD system. The growth of graphene has been conducted in two ways: firstly, by the traditional mechanical exfoliation technique (with the help of Manchester University) and second by PECVD techniques.Polymer materials are promising flexible substrates for electronic and energy devices. An excimer laser was used to transform thin metallic films into nanoparticles which could play the role of the catalyst in proton exchange membrane fuel cells. In this study experiments have been conducted into a single step process to convert the poly ethylene naphthalate (PEN) surface to a robust mesoporous carbon material that conducts electrons, whilst depositing the catalyst. Such a technique has been developed for the first time in this work. Laser modification here produced a conical carbon structure and dense arrays of well defined catalysts.A prototype fuel cell was designed and crafted to employ the laser processed PEN as a proton exchange membrane. Some experiments were conducted regarding the transport of protons through laser processed PEN and the conventionally used fuel cell electrolyte, Nafion. It has been observed that the hydrophilic property of Nafion allowed proton transport across this material. It was also observed that PEN is not a good membrane for protonic transport. This material does not have free sites for vehicle transport. The catalytic activity of laser ablated Ni nanoparticles on PEN substrate was studied in temperature programme reaction (TPR) and it was observed that the metallic nanoparticles had some activity at higher temperature. Both Ni and Pt nanoparticles were tested as catalysts on the standard Nafion electrolyte. It was observed that Pt is active for the hydrogen combustion reaction and Ni has less activity for this purpose.It was not expected in this work that efficient hydrogen transport through the polymer would occur, but that future modification of the internal chemistry of PEN can be developed.

Cette thèse entre dans le cadre d’un projet de recherche intitulé Electromagnetic Characterization of new Materials for Industrial Applications up to microwave frequencies (EMINDA). Il a pour objectif principal de développer une traçabilité électromagnétique de matériaux fonctionnels afin de permettre l’adoption de ces matériaux dans les industries européennes plus particulièrement dans le domaine de l’électronique. Le projet vise dans un premier temps à développer des techniques de caractérisation électromagnétiques des matériaux à l’échelle submicronique aux fréquences micro-ondes, puis par la suite à élargir la traçabilité métrologique de ces matériaux car la métrologie des propriétés électromagnétiques des matériaux. Une technique de caractérisation électromagnétique sur des matériaux ferroélectrique (BST et PZT) en couches minces à partir d’une topologie CPW pour en déterminer leurs propriétés électromagnétiques a été développée dans cette thèse. La topologie CPW a été privilégiée dans la réalisation de ces mesures hyperfréquences, car elle est compatible avec les exigences métrologiques de traçabilité des mesures aux unités du SI. Ce travail de thèse a également pour objectif de réaliser des mesures comparatives entre laboratoires nationaux de métrologie utilisant des techniques expérimentales différentes. Ces travaux constitueront au final au niveau européen, une base de mesures des propriétés électromagnétiques de matériaux émergents dans l’industrie avec une grande précision sur les incertitudes pour des mesures allant jusqu’à 110 GHz. / This thesis is part of a Join Research Project entitled Electromagnetic Characterization of new Materials for Industrial Applications up to microwave frequencies (EMINDA). The central aim of EMINDA is to develop traceable Electromagnetic (EM) materials metrology to enable the uptake of new EM and functional materials by European industries, especially electronics and ICT related industries.The project aims initially to develop techniques for electromagnetic characterization of materials at the submicron scale to microwave frequencies, and later to extend the metrological traceability of these materials. An electromagnetic characterization technique has been developed to extract electromagnetic properties of ferroelectric thin films (BST and PZT) from a CPW topology (CoPlanar Waveguide). CPW measurements on such thin-films have been shown to be the most tractable for metrological purposes.This thesis also aims to make comparative measurements between national metrology institutes using different experimental techniques. This work will constitute at European level, a measurement base of electromagnetic properties of emerging materials in industry with high accuracy on uncertainties measurements up to 110 GHz.

Dans les industries laitières, les procédés de transformation du lait conduisent à la formation de dépôts indésirables sur les parois des équipements. En raison du manque de solutions pour minimiser ces dépôts et assurer la sécurité et qualité des transformations, des procédures de nettoyage aux impacts économiques et environnementaux conséquents sont réalisées. Redéfinir les conditions optimales de transformation en amont afin de rendre éco-efficientes les procédures de nettoyage en aval représente aujourd’hui un enjeu important. Dans ce contexte, disposer d’outils capables de discriminer l’adhésion des dépôts en fonction des conditions d’expérience est une nécessité. Or il existe peu de dispositifs adéquats. Ce travail de thèse présente une nouvelle approche de quantification de l'adhésion de dépôts laitiers par ondes ultrasonores (US). Elle est basée sur l’étude du coefficient de réflexion des ondes transversales en incidence normale à l'interface substrat/dépôt. Le développement de la technique US avec des milieux modèles a permis de vérifier son aptitude quant à la caractérisation de l’adhésion aux interfaces solide/fluide et solide/solide. Les résultats montrent que le coefficient de réflexion est corrélé avec le pouvoir collant du fluide étudié et qu’il est possible de distinguer différentes qualités d’interfaces solide/solide. Les essais de caractérisation par la technique US de différents dépôts laitiers formés sur des aciers inoxydables confirment l’aptitude du dispositif à nous renseigner sur l’adhésion. Cette thèse ouvre de nombreuses perspectives sur la caractérisation de surfaces antiadhésives ou encore l’adhésion de biofilms. / In the dairy industry, the milk processing leads to the formation of undesirable deposits. Due to the lack of solutions to minimize these deposits and to ensure the safety and quality of transformation, cleaning processes with both economic and environmental impacts are commonly performed. Setting optimal processing conditions to make eco-efficient cleaning procedures is an important issue today. The knowledge of deposits adhesion is a prerequisite for tuning innovative operating conditions of processing and for improving cleaning strategies. Unfortunately, these data are lacking because few methods of characterization of the adhesion quality exist. This thesis presents a new approach for quantifying the adhesion of whey protein fouling by ultrasonic waves. This work is based on the reflection of shear waves at normal incidence at the interface between the substrate and the deposit.In order to illustrate the potential of the US method for adhesion quantification, measurements were conducted with various models fluids deposited on different substrates. The results show that the reflection coefficient is correlated with stickiness of fluids and allows distinguishing between different solid/solid inter-faces. The US method was then applied to the characterization of the deposit adhesion on stainless steel substrates. The results show that the reflection coefficient can be also an effective indicator for evaluating the fouling deposit adhesion onto stainless steel. It could be a decisive test for rapidly assessing the interest of surfaces coatings, with regard to anti-fouling properties or to better understand interaction magnitude of biofilm on wall equipment.

Les propriétés mécaniques (dureté et module d’élasticité) peuvent s’étudier à différentes échelles en fonction de la composition et de la microstructure des matériaux (nombre de phases, répartition des constituants, diamètre des grains…). Dans ce travail nous étudions ces comportements aux échelles nano, micro et macroscopiques, grâce à une gamme d’appareils expérimentaux en indentation instrumentée qui permettent d’appliquer des forces variant de 1 mN à 2,5 kN et de provoquer des enfoncements mesurables de 10 nm à 3 mm. Une première partie consiste à optimiser les conditions expérimentales, dépouiller et interpréter les données en suivant une démarche métrologique rigoureuse, dans le but d’effectuer le raccordement entre les résultats obtenus aux trois échelles de mesure étudiées. Ces essais sont effectués sur des matériaux métalliques industriels mais suffisamment homogènes (aciers et alliage d’aluminium). Nous proposons par exemple une méthode alternative à celle d’Oliver et Pharr pour estimer le module d’élasticité à partir de la courbe de décharge en indentation. Cette méthodologie est ensuite appliquée à l’étude du comportement sous indentation d’un matériau composite, hautement hétérogène, utilisé pour la fabrication de semelles de freinage dans le domaine ferroviaire. Les données obtenues (répartition spatiale en surface et en volume de la dureté et des modules d’élasticité) sont destinées à être utilisées dans les modèles simulant le bruit de crissement au freinage, afin d’en atténuer les effets. / The mechanical properties (hardness and elastic modulus) can be studied at different scales as a function of the composition and microstructure of materials (number of phases, constituent distribution, grain size…). In this work, we studied this mechanical response at the nano, micro and macroscopic scales, through different instruments that allow to apply loads ranging from 20 mN up to 2 kN generating penetrations depths between 100 nm up to 2.5 mm. The first stage consisted in the improvement of the experimental conditions, developing and interpreting the experimental data, following a rigorous metrological methodology, in order to achieve the connection between the results obtained at the three studied scales. These tests were performed in metallic industrial materials, which are sufficiently homogeneous at the tested penetration depths (steels and aluminum alloy). For example, we had proposed an alternative approach to the Oliver and Pharr method to fit the unloading curve to estimate the elastic modulus. Afterwards, this methodology is applied to the study of the response obtained by indentation in a composite material, which is highly heterogeneous, used in the fabrication of brake pads in the railway industry. The obtained results (spatial distribution on the surface and through the volume of hardness and elastic modulus) are going to be valuables in the applications of models to study the squeal noise during braking, looking to reduce its effects.

Many failure theories have been postulated to predict the behaviour of glass reinforced plastics (GRP) under complex stresses. However, the efficient use of these theories for design purposes is inhibited because the experimental complex stress data needed to verify and discriminate between them is not available. This thesis presents some of the experimental data required. Uniaxial stress test results from flat laminates, and biaxial stress test results from thin-walled tubes under combined internal pressure and axial force, are presented for various damage states under both static and fatigue loading for a plane isotropic material and an orthotropic material. The data were then used to establish which failure theory provided the most acceptable prediction of the observed behaviour. For ultimate strength, the Norris Failure theory gave adequate predictions, but not for resin cracking. The most generally acceptable predictions, for both materials, were given by those theories whose equations contain a constant which is derived from complex stress data, these being the modified Marin and the strength tensor theories. For the orthotropic material, three-dimensional representations of the plane stress ultimate strength and damage failure surfaces are presented for both static and fatigue loading. However, even though a considerable number of specimens were tested, only very few failure surface sections were experimentally established. It was found for both materials that fatigue loading was more damaging than static loading, for both uniaxial and biaxial stress conditions, and that the behaviour of the materials was dependent upon the ratio of the biaxial stresses. Jointed reinforcement layers severely affect the zero-tension fatigue behaviour of the plane isotropic material, but the effect on the orthotropic material decreases with increasing fatigue life. The effect of macro-voids on crack initiation should be acknowledged if damage is used as a design criterion.