L’accident de Fukushima-Daiichi du 11 Mars 2011 a fortement marqué l'industrie nucléaire en mettant en évidence plusieurs faiblesses dans le contrôle des systèmes critiques qui assurent la sécurité des centrales nucléaires, en particulier, lors de conditions accidentelles. Cette thèse a été réalisée en collaboration avec AREVA, groupe industriel français actif dans le domaine de l'énergie, avec l’objectif de réaliser des capteurs à fibres optiques résistants aux contraintes sévères d'une centrale nucléaire et, en particulier, de surveiller la température et le niveau de l'eau à l'intérieur d’une piscine de stockage de combustible. La thèse est composée de deux parties organisées en 7 chapitres. Dans la première partie, le chapitre 1 traite des phénomènes contribuant à l'atténuation de la lumière au cours de sa propagation dans la fibre et donne un aperçu des effets des radiations sur les fibres optiques. Pour identifier la technique la plus prometteuse adaptée aux applications visées par AREVA, le chapitre 2 propose un état de l’art sur les capteurs distribués à fibres optiques existants avec une attention particulière à leur emploi dans des environnements radiatifs. La dernière partie de ce chapitre est consacrée à la description détaillée de l’OFDR qui est la technique retenue pour cette application. La deuxième partie est consacrée à la présentation des résultats obtenus et leur analyse. Le chapitre 3 présente le détail des irradiations et des traitements thermiques, les échantillons retenus et les bancs de mesure utilisés. Afin de déterminer la meilleure combinaison fibre/technique par rapport à l’application visée, une étude systématique des capteurs distribués de température et de contrainte a été réalisée. Les effets permanents des rayonnements (niveaux de dose du MGy) sont étudiés dans le chapitre 4. Le chapitre 5 illustre des mesures in situ sur les fibres résistantes aux radiations pour comprendre les effets combinés de la température et des radiations (rayons X), effets représentatifs des conditions nominales et accidentelles des piscines de stockage. Enfin, nous avons développé un prototype de capteur de niveau d’eau pour les piscines de combustible qui est décrit dans le chapitre 6. Ensuite, les principales conclusions et les perspectives de ce travail de thèse sont discutées / Fukushima-Daiichi event on March 11th, 2011, signed a turning point in nuclear industry by highlighting several weaknesses in the control of critical systems that ensure the safety in nuclear power plant (NPP) operating, particularly, in accidentals conditions. This PhD thesis has been carried out in collaboration with AREVA, the French industrial group active in the energy domain, with the aim of realizing optical fiber sensors resistant to the harsh environment constraints of a NPP and, in particular, to monitor temperature and water level several parameters inside the spent fuel pools (SFPs). It consists of two parts organized in 7 chapters. In the first part, chapter 1 deals with the phenomena contributing to the light attenuation during its propagation along the fiber and gives an overview on the radiation effects on optical fibers. To identify the most promising technique suitable for AREVA needs, in chapter 2 is reported the state-of-the-art on the distributed OFSs with particular attention to their employment in radiation environments. The last part of this chapter is devoted to the detailed description of the OFDR that is the selected sensor technique for this application. The second part is devoted to present and discuss the obtained results. Chapter 3 gives the experimental details on radiation and thermal treatments, investigated samples and used setups. In order to determine the best fiber/setup combination, a systematic study on temperature and strain distributed sensors was carried out in relation to the harsh constraints demanded from the application. The permanent radiation (MGy dose levels) effects on different fiber classes are investigated in Chapter 4. Chapter 5 illustrates in situ measurements on radiation resistant fibers to understand the combined temperature and radiation (X-rays) effects representative of the SFP nominal and accidental conditions. Simultaneously, we have developed the OFS design for its integration at SFP facility. The prototype is described and its performance is evaluated in chapter 6. Then, the main conclusion and perspective are discussed / L'incidente di Fukushima-Daiichi dell’11 marzo 2011 ha segnato un punto di svolta per l’industria nucleare, mettendo in evidenza diversi punti deboli nel controllo di sistemi critici che garantiscono la sicurezza nelle centrali, in particolare in condizioni di incidente. Questa tesi è stata condotta in collaborazione con AREVA, il gruppo industriale francese attivo nel settore dell'energia, con l'obiettivo di produrre sensori a fibra ottica resistenti alle condizioni estreme di una centrale nucleare e, in particolare, per controllare diversi parametri all'interno di una piscina di stoccaggio di combustibile nucleare, quali la temperatura e il livello dell'acqua. La tesi si compone di due parti organizzate in 7 capitoli. Nella prima parte, il capitolo 1 riguarda i fenomeni che contribuiscono all'attenuazione della luce durante la sua propagazione nella fibra e permette di comprendere gli effetti della radiazione sulle fibre ottiche. Per identificare la tecnologia più promettente per le esigenze di AREVA, nel capitolo 2 é discusso lo stato dell’arte sui sensori distribuiti con particolare attenzione alle loro performance in ambienti radiativi. L'ultima parte di questo capitolo è dedicato ad una descrizione dettagliata della tecnica OFDR che è la tecnologia scelta per questa applicazione. La seconda parte è dedicata a presentare e discutere i risultati. Il capitolo 3 fornisce i dettagli sui campioni studiati e i trattamenti effettuati su di essi e descrive il setup utilizzato. Per determinare la migliore combinazione fibra/tecnica per l’applicazione prevista, è stato eseguito uno studio sistematico sulla risposta alla radiazione dei sensori distribuiti di temperatura e strain. Glieffetti permanenti della radiazione (dosi dell’ordine del MGy) su diverse classi di fibre, resistenti e sensibili alle radiazioni, sono discussi nel capitolo 4. Il capitolo 5 riporta le misure in situ sulle fibre resistenti alla radiazione per investigare gli effetti combinati di temperatura e radiazioni (raggi X) rappresentativi delle condizioni operative e accidentali nelle piscine di stoccaggio. Infine, abbiamo sviluppato un prototipo di sensore del livello dell’acqua nelle piscine di stoccaggio che è descritto nel capitolo 6. In seguito, le principali conclusioni e le prospettive sono discusse

Lors de ce travail de thèse, nous avons effectué des recherches sur des chromophores organiques. Notre étude s’est portée sur la commutation des propriétés optiques linéaires et non linéaires via l’étude d’interrupteurs organiques multi-adressables. Notre étude s’est portée plus particulièrement sur la famille des dérivés de l’indolino-oxazolidine. Ce type de molécule présente l’avantage d’avoir deux voix de commutations distinctes par photochromisme et acidochromisme. Nous avons recherché le lien entre la structure des molécules et leurs propriétés optiques par une étude combinée originale théorie/expérience avec l’utilisation de calculs quantiques sophistiqués et par diffusion hyper-Rayleigh de la lumière. / In this work we have investigated the commutation of linear and non linear optical properties in organic multifunctional switches. Indolino-oxazolidine compounds and their derivatives were chosen as example of multifunctional systems, because they combine both acidochromic and photochromic properties. The relationships between the molecular structure of these compounds and their optical properties were established by means of high level the quantum chemical approach and hyper-Rayleigh Scattering of light approaches.

Os métodos de ondas superficiais com ênfase nas ondas Rayleigh foram utilizados como o núcleo desse trabalho de Doutorado. Inicialmente, as ondas Rayleigh foram modeladas permitindo o estudo de sensibilidade de suas curvas de dispersão sob diferentes configurações de parâmetros físicos representando diversos modelos de camadas, em que pôde ser observado parâmetros com maior e menor sensibilidade e também alguns efeitos provocados por baixas razões de Poisson. Além disso, na fase de inversão dos dados a modelagem das ondas Rayleigh foi utilizada para a construção da função objeto, que agregada ao método de mínimos quadrados, a partir do método de Levenberg-Marquardt, permitiu a implementação de um algoritmo de busca local responsável pela inversão de dados das ondas superficiais. Por se tratar de um procedimento de busca local, o algoritmo de inversão foi complementado por uma etapa de pré-inversão com a geração de um modelo inicial para que o procedimento de inversão fosse mais rápido e eficiente. Visando uma eficiência ainda maior do procedimento de inversão, principalmente em modelos de camadas com inversão de velocidades, foi implementado um algoritmo de pós-inversão baseado em um procedimento de tentativa e erro minimizando os valores relativos da raiz quadrada do erro quadrático médio (REQMr) da inversão dos dados. Mais de 50 modelos de camadas foram utilizados para testar a modelagem, a pré-inversão, inversão e pós-inversão dos dados permitindo o ajuste preciso de parâmetros matemáticos e físicos presentes nos diversos scripts implementados em Matlab. Antes de inverter os dados adquiridos em campo, os mesmos precisaram ser tratados na etapa de processamento de dados, cujo objetivo principal é a extração da curva de dispersão originada devido às ondas superficiais. Para isso, foram implementadas, também em Matlab, três metodologias de processamento com abordagens matemáticas distintas. Essas metodologias foram testadas e avaliadas com dados sintéticos e reais em que foi possível constatar as virtudes e deficiências de cada metodologia estudada, bem como as limitações provocadas pela discretização dos dados de campo. Por último, as etapas de processamento, pré-inversão, inversão e pós-inversão dos dados foram unificadas para formar um programa de tratamento de dados de ondas superficiais (Rayleigh). Ele foi utilizado em dados reais originados pelo estudo de um problema geológico na Bacia de Taubaté em que foi possível mapear os contatos geológicos ao longo dos pontos de aquisição sísmica e compará-los a um modelo inicial existente baseado em observações geomorfológicas da área de estudos, mapa geológico da região e informações geológicas globais e locais dos movimentos tectônicos na região. As informações geofísicas associadas às geológicas permitiram a geração de um perfil analítico da região de estudos com duas interpretações geológicas confirmando a suspeita de neotectônica na região em que os contatos geológicos entre os depósitos Terciários e Quaternários foram identificados e se encaixaram no modelo inicial de hemi-graben com mergulho para Sudeste. / The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical The surface wave methods to Rayleigh waves were used as the center of this Doctoral work. Initially, the Rayleigh waves were modeled, what enabled the study of the sensitivity of dispersion curves about different sets of physical parameters representing several layer models, wherein it could be observed parameters with higher and lower sensitivity and also some effects caused by low Poisson ratios. Moreover, in the data inversion step the Rayleigh modeling was used for the construction of the object function, that aggregate to the least-squares method, by Levenberg-Marquardt, allowed the implementation of a local search algorithm responsible for data inversion of the surface waves. By reason of being a local search procedure, the data inversion algorithm was complemented with a pre-inversion step wherein an initial model was generated so that the inversion procedure was faster and efficient. Seeking a more efficiency of the inversion procedure, mainly to layer models with velocities inversion, it was implemented a post-inversion algorithm based in a trial and error procedure minimizing the values of the relative Root Mean Squared Error (rRMSE) of the data inversion. More than 50 layer models were used to test the data modeling, pre-inversion, inversion and post-inversion allowing the precise fit of the mathematical and physical parameters present in the several scripts implemented in Matlab. Before to invert the field-acquired data, they need to be treated in the data processing step, whose main aim is the extraction of the dispersion curve caused due the surface waves. For this, three processing methodologies with different mathematical approaches were implemented, also in Matlab. These methodologies were tested and evaluated with synthetic and real data and it was possible to find their strengths and weaknesses, as well as the limitations caused by discretization of the field data. Lastly, the data processing, pre-inversion, inversion and post-inversion steps were unified to form a complete data treatment program of surface waves (Rayleigh). It was used to real data originated by study of a geological problem in the Bacia de Taubaté wherein it was possible to map the geologic contacts along of the seismic acquisition points. The results were compared to an existing initial model based in geomorphological observations of the study area, geological map and global and local geologic information of the tectonic movements in the region. The geophysical information associated with geological information allowed the generation of an analytical profile of the study region with two geological interpretation confirming the suspect of neotectonic movements in the region wherein the geological contacts between the quaternary and tertiary deposits were identified and they agreed with the initial model of a hemi-graben with dip to Southeast.

Nous étudions les comportements dynamiques de solutions aqueuses de dioxyde de carbone, pures ou sous forme de boissons gazeuses. Nous observons les façons dont des solutions carbonatées, initialement à l'équilibre de Henry, répondent à une perturbation, qui peut être un changement brusque de pression ou une agitation mécanique. Ces questions sont examinées expérimentalement, à l'aide de dispositifs construits pour cette étude. Ceux ci permettent de visualiser les champs de vitesse et les fronts de dissolution dans le fluide, dans des conditions variées de pression, taille et forme de système. Une partie importante est consacrée à la chemi-convection provoquée par la déstabilisation d'une couche diffuse de CO2 dissout. Nous présentons une caractérisation complète du phénomène, et une interprétation basée sur une théorie de l'instabilité de Rayleigh-Taylor correspondante. L'autre partie de notre travail concerne des systèmes fermés, dont la bouteille de champagne est l'exemple type. Nous montrons que l'agitation de la bouteille provoque une légère baisse transitoire de la pression interne, et expliquons le phénomène à l'aide d'un modèle basé sur la théorie d'Epstein-Plesset de la dynamique des bulles. / This work is about dynamical phenomena of water-carbon dioxide solutions, either pure binary mixtures or carbonated beverages. We address the general problem of how such solutions, initially at Henry's equilibrium, respond to a perturbation. The latter may be a sudden change in pressure, or mechanical shaking. These problems are investigated with the help of especially designed experimental hardware that allows us to visualize the velocity field and the concentration front inside solutions, in diverse conditions of pressure, system size and shape. An important part of the work is dedicated to chemi-convection, i.e. the fluid motion induced by destabilisation of the diffuse layer of dissolved CO2. Both experimental characterization and interpretation through a theory of the corresponding Rayleigh-Taylor instability are presented. The other part of the work is related to closed systems, representative of a bottle of champagne and of sodas in general. A key observation is that shaking produces a small transient drop of the internal pressure, which we explain through a dedicated modelbuilt on Epstein-Plesset's theory of bubble dynamics.

La convection thermique dans les objets naturels de grande taille est associée à de fortes variations de la pression, hydrostatique au premier ordre. C’est le cas pour l’atmosphère de la Terre (et d’autres planètes), les planètes gazeuses géantes, les étoiles, mais aussi l’intérieur des planètes telluriques. De part l’importance des effets de compressibilité, l’approximation de Boussinesq n’y est pas vérifiée et d’autres modèles, comportant également des approximations, sont utilisés : les modèles anélastiques. Toutefois, peu d’expériences ont été réalisées pour les vérifier. Cette thèse présente une expérience dont les paramètres ont été optimisés afin d’obtenir des effets de compressibilité importants en laboratoire. Pour ce faire, une gravité apparente forte est obtenue à l’aide d’une centrifugeuse et du xénon gazeux est utilisé, nous permettant d’atteindre un nombre de dissipation significatif. Ces expériences ont permis l’observation en laboratoire d’un gradient adiabatique de 3 K/cm et d’un exposant de 0,3 pour la loi de puissance caractérisant le transfert thermique turbulent entre le nombre de Nusselt et le nombre de Rayleigh superadiabatique.L’étude des fluctuations de pression et de température montrant que l’écoulement est quasi-geostrophique dû à la forte rotation imposée par la centrifugeuse, un modèle anélastique quasi-géostrophique est développé afin de réaliser des simulations numériques bidimensionnelles relatives à l’expérience. / In large natural objects, thermal convection is associated with large pressure differences, mainly due to hydrostatic balance. This is true in the atmosphere of the Earth (and other planets), in gas giant planets, in stars, but also in the interior of telluric planets. Boussinesq approximation is not valid owing to large compressibility effects, and other approximate models can be used to model these objects, like the anelastic approximation. However, very few experiments have been performed to assess these models. In the present PhD thesis, an experiment is shown, with parameters designed to maximize compressibility effects in a laboratory. In this perspective, an enhanced apparent gravity is obtained using a centrifuge, and Xenon gas is used, allowing us to reach a significant dissipation parameter. In our experiments, we have observed an adiabatic gradient of 3~K/cm and the power law between the superadiabatic Rayleigh number and the Nusselt number measuring the turbulent heat transfer is characterized by an exponent 0.3.Measurements of temperature and pressure fluctuations show that the flow is quasi-geostrophic as a result of the strong rotation rate of the centrifuge. An anelastic, quasi-geostrophic model has then been developed and solved numerically in the same configuration as the experiments.

Cette thèse nous a permis de produire des cartes de vitesse de groupe du mode fondamental des ondes de Rayleigh, en utilisant les séismes et les corrélations du bruit sismique ambiant. En plus de la méthode moindres carrées amortis, nous avons adapté la nouvelle méthode d’inversion, SOLA-Backus-Gilbert dans un contexte régional. À courte période, les cartes de vitesse de groupe présentent des vitesses rapides pour la croûte océanique et des vitesses lentes pour la croûte continentale. Pour les périodes intermédiaires, le bassin de Taoudeni se caractérise par de faibles vitesses par rapport au reste du craton ouest africain en raison de l’épaisseur de la couche sédimentaire. A longue périodes, les racines des dorsales Man-Leo et Reguibat sont caractérisées par des vitesses rapides, montrant une lithosphère froide et épaisse sous le craton, tandis que nous avons trouvé des vitesses de groupe lentes sous les zones de ceinture mobile panafricaine indiquant une lithosphère mince. / This thesis allowed us to produce group velocity maps of the fundamental mode of Rayleigh waves, using both earthquakes and seismic ambient noise correlation. In this study, in addition to the damped least squares method, we adapted for the very first time a new inversion method, called SOLA-Backus-Gilbert in regional context. At short periods, the group velocities maps exhibit fast velocities for the oceanic crust and slow velocities for the continental crust. For the intermediate periods, the Taoudeni Basin is characterized by low velocities compared to the rest of the west african craton due to the thickness of the sedimentary layer. Over long periods, the roots of the Man-Leo and Reguibat shields are characterized by fast velocities, showing a cold and thick lithosphere under the craton, while we found slow group velocities under the Pan-African orogenic belts zones indicating a thin lithosphere.

Le contrôle non destructif (CND) par émission acoustique (EA) est utilisé dans un grand nombre de domaines tels l’énergie nucléaire, le secteur pétrolier et gazier, le génie civil ou l’industrie mécanique afin de vérifier l’intégrité des structures sous contrainte. Selon le rapport entre la longueur d’onde et l’épaisseur de la structure, l’énergie libérée par un défaut sous contrainte peut se propager sous forme d’ondes guidées (cas des structures minces) ou sous forme d’onde de Rayleigh (cas des structures épaisses). L’analyse des signaux issus de cette méthode ultrasonore « passive » présente des difficultés liées principalement à la complexité des signaux typiquement mesurés. L’objectif de la thèse est de développer des modèles permettant la simulation d’expériences de CND par EA dans le cas des structures épaisses ou minces. Les modèles développés sont basés sur un couplage entre un modèle de source d’EA, un modèle de propagation des ondes et un modèle de capteur d’EA. Dans le cas des structures épaisses, deux modèles 2D (concernant le contrôle de pièces de surface plane et cylindrique) et un modèle 3D (surface plane) ont été développés afin de prédire le signal correspondant à l’onde de Rayleigh émise par un défaut sous contraintes. Concernant les structures minces, un modèle 2D a été développée permettant de prédire le signal correspondant aux modes guidés émis par une fissure sous contrainte. Plusieurs études paramétriques ont été menées afin de définir l’influence des différentes données d’entrée des modèles sur les signaux d’EA et ainsi aider à l’interprétation des contrôles par EA. / AE Non-destructive testing is used in many fields such as nuclear energy, oil and gas, civil engineering or mechanical engineering to check the integrity of structures under stress. Depending on the ratio of structure thickness to wavelength, the energy released by a crack under stress can propagate either as guided waves (in thin structures) or as Rayleigh wave (in thick structures). The analysis of signals resulting from this ultrasonic "passive" method is particularly difficult due to the complexity of typically measured signals. The objective of this thesis is to develop models to enable the simulation of AE testing experiments in the case of thick or thin structure. The developed models rely on the coupling between an AE source model, wave propagation models and an AE Sensor model. In the case of thick structures two 2D models (for plane and cylindrical surfaces) and a 3D model (for plane surface) have been developed to predict the signal corresponding to the Rayleigh wave emitted by a crack under stress. In the case of thin structures, a 2D model has been developed to predict the signal corresponding to the guided modes emitted by a crack under stress. Several parametric studies have been conducted to determine the influence of the different model input data on the AE signals and thus help to interpret AE testing results.

Les dépôts effectués sur substrats de silicium sont très courants notamment dans le domaine de la microélectronique. Les propriétés physiques recherchées pour ce type de structures dépendent fortement de celles de la couche. Il apparaît donc essentiel de connaître les paramètres élastiques ainsi que l’épaisseur des films considérés. De plus, la détection de certains défauts concernant la couche est souvent recherchée. L’objectif de ce travail a été de contribuer à la caractérisation de structures du type couche sur substrat. Pour cela, les ultrasons-lasers présentent de nombreux avantages puisqu’ils autorisent entre autres leur contrôle non destructif sans contact. Les ondes acoustiques de surface dans une gamme de fréquence s’étendant jusqu’à 45 MHz ont été utilisées. Nous avons développé différents modèles analytiques et les résultats expérimentaux ont aussi été comparés à certaines simulations par éléments finis. Plus particulièrement, nous avons montré qu’il était possible d’obtenir l’ensemble des paramètres élastiques du substrat et de la couche ainsi que l’épaisseur de cette dernière. Par ailleurs, nous nous sommes aussi intéressés à la détection de certains défauts en régime impulsionnel mais aussi quasi-monochromatique. Des résultats originaux concernant l’effet d’une absence de couche de forme déterminée sur le premier mode de Rayleigh ou bien encore de problèmes d’adhésion ont été présentés. Sur ce dernier point, une méthode innovante permettant de distinguer un fort niveau d’adhésion d’un faible a aussi été introduite. / Thin films deposited on silicon substrates are very common especially in microelectronic applications. The physical properties expected for these types of structures depend on the properties of the layer. Therefore, it is essential to know elastic parameters and thickness of the films considered. Furthermore, some layer defects detection is often required. The aim of this work was to contribute to the characterization of structures composed of a single layer deposited on a substrate. For this, laser ultrasonics offers many advantages since it is nondestructive and non-contact method. Surface acoustic waves excited in a frequency range up to 45 MHz are used. Analytical models have been developed and experimental results have also been compared with some finite element simulations. More specifically, we have shown that it was possible to obtain the thickness of the layer and all elastic parameters of both substrate and layer. In addition, we have been interested in the detection of various defects with a broadband and quasi-monochromatic excitation. Original results concerning the effect of a lack of layer with a specific geometry on the first Rayleigh mode or even adhesion problems were presented. Concerning this last point, an innovative method to tell difference between high and low adhesion was introduced.

Diverses industries telles que l'aéronautique ou la sidérurgie s’intéressent de plus en plus aux ultrasons laser qui sont une technique de pointe utilisée pour le contrôle et l'évaluation non destructifs des matériaux. Cette méthode d’excitation et de détection des ondes ultrasonores présente comme principaux avantages d’être sans contact et adaptée à des échantillons pour lesquels la mise en œuvre de méthodes conventionnelles s'avère difficile notamment lorsqu’ils sont portés à haute température et/ou qu’ils sont de géométrie complexe.Durant cette thèse, nous nous sommes intéressés à la propagation des ondes acoustiques de surface générées par sources lasers et à l’interaction de ces ondes avec différents défauts. Les modèles analytiques de l’interaction onde-défaut étant limités à quelques cas particuliers, l’étude théorique a été menée en privilégiant une modélisation par éléments finisqui a permis d’accéder aux champs de déplacement des ondes engendrées. Les résultats expérimentaux ont d’abord permis de confirmer la pertinence des modèles analytiques et des modélisations par éléments finis. Ils ont ensuite consisté en l’étude de l’interaction onde-défaut pour différentes formes de défauts et différentes sources thermoélastiques.Les résultats de modélisation associés aux résultats expérimentaux ont en particulier mené à une méthode originale de caractérisation basée sur une conversion de mode permettant de déterminer à partir d’un seul A-scan à la fois la position et la profondeur du défaut. Des sources thermoélastiques non conventionnelles ont également été développées et leur potentiel d’applications pour le contrôle non destructif a été mis en évidence. / Industries like aeronautics or iron and steel industry are more and more interested in laser ultrasonics, which is a cutting-edge technique used in non-destructive testing and evaluation. The main advantages of this acoustic wave generation and detection method are its noncontact feature and its ability to characterize high temperature and/or geometrically complex materials for which conventional methods implementation turns out to be difficult.During this thesis, we dealt with the propagation of surface acoustic waves (SAW) generatedby laser sources and their interaction with different flaws. As analytical models describing theinteraction between SAW and flaws are limited to a few special cases, the theoretical study was preferentially led thanks to the finite element method (FEM) that gave the different waves displacement fields. Experimental results first confirmed analytical models and FEM results suitability. Then, they consisted in studying the interaction between SAW and flaws for different flaw shapes and different thermoelastic sources.FEM results combined with experimental results especially led to an original characterizationmethod based on mode conversion giving both the flaw position and depth thanks to a singleA-scan. Unusual thermoelastic sources have also been implemented and their potentialities in non destructive testing and evaluation applications have been highlighted.

Comparative studies of nondestructive evaluation methods have shown that nonlinear ultrasonic techniques are more sensitive than conventional linear methods to changes in material microstructure and the associated small-scale damage. Many of the material degradation processes such as carbonation in concrete, corrosion in metals, etc., begin at the surface. In such cases, ultrasonic Rayleigh surface waves are especially appropriate for detection and characterization of damage since their energy is concentrated in the top layer of the test object. For the civil engineering infrastructure, only a limited number of field applicable nonlinear ultrasonic techniques have been introduced. In this paper a nonlinear ultrasonic measurement technique based on the use of Rayleigh waves is developed and used to characterize carbonation in concrete samples. Wedge transducer is used for the generation and an accelerometer for detection of the fundamental and modulated ultrasonic signal components. The measurements are made by varying the input voltage and along the propagation distance. The slope of the normalized modulated amplitudes is taken as the respective nonlinearity parameter. Concrete samples with two different levels of damage are examined, and the difference of the two fundamental frequencies is used to quantify damage state.