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This work consists of an experimental study of the microscale physical phenomena occurring during the growth of a single bubble attached to the heater at nucleate boiling. The experiment is performed with water at normal conditions by using the state-of-the-art high-speed (4000 frames per second) and microscopic-scale optical diagnostics. The boiling surface consists of an indium-tin oxide (ITO) film deposited on the transparent MgF2 porthole. The ITO heating is performed locally with an infrared (IR) laser directed from below. We study the liquid microlayer that can form between the heater and the bubble. Simultaneous and synchronous measurements of the microlayer profile, macroscopic bubble shape and wall temperature are obtained by the white-light interferometry, sidewise shadowgraphy and IR thermography, respectively. The wall heat ux is reconstructed using the wall temperature distribution. A new feature in the microlayer shape has been detected: a bump in the microlayer profile that appears at the initial stage of the bubble growth. A simple theory that allows us to explain the bump is presented. The bump is explained by the fast bubble growth accompanied by the bubble edge deceleration and as an interplay of viscous and capillary forces acting in the microlayer during its formation. We also describe a 2D numerical simulation of microlayer dynamics that shows both a dewetting ridge evidenced in earlier numerical simulations near the contact line and a bump farther away. A good agreement is found between the simulated and experimental microlayer profiles in the bump region. We show that the dewetting is accelerated by evaporation, which leads to the formation of a large dewetting ridge at the initial stages of bubble growth. Our results also show that the microlayer thinning in time is due to its evaporation. The measured thermal resistance at the liquid-vapor interface is a few times larger than its theoretical value and seems to grow in time, which suggests the water weak contamination as its cause.; Ce travail consiste en une étude expérimentale des phénomènes physiques à micro-échelle se produisant lors de la croissance d'une seule bulle attachée à la paroi chauffante en régime d'ébullition nucléée. L'expérience est réalisée avec de l'eau à pression atmosphérique en utilisant des diagnostics optiques rapides (4000 images par seconde) et à l'échelle microscopique. La surface d'ébullition est constituée d'un film d'oxyde d'indium et d'étain (ITO) déposée sur une fenêtre transparente en MgF2. La bulle est déclenchée par un chauffage local avec un laser infrarouge (IR). Nous étudions la dynamique et le transfert de chaleur d'une microcouche liquide qui peut se former entre la paroi et la bulle. Des mesures simultanées et synchronisées du profil de la microcouche, de la forme macroscopique de la bulle et de la température de la paroi sont obtenues respectivement par interférométrie en lumière blanche, par ombroscopie latérale et par thermographie IR. Le flux de chaleur de la paroi est reconstruit en utilisant la distribution de la température de la paroi. Une nouvelle caractéristique de la forme de la microcouche a été détectée : une bosse dans le profil de la microcouche qui apparaît au stade initial de la croissance de la bulle. Une théorie simple qui nous permet d'expliquer cette bosse est présentée. La bosse est expliquée par la croissance rapide des bulles et par l'interaction des forces visqueuses et capillaires agissant dans la microcouche pendant sa formation. Nous décrivons également une simulation numérique 2D de la dynamique de la microcouche qui montre un bourrelet de démouillage mis en évidence dans les simulations numériques précédentes près de la ligne de contact et une bosse plus éloignée. Un bon accord est trouvé entre les profils de microcouche simulés et expérimentaux dans la région de la bosse. Nous montrons que le démouillage est accéléré par l'évaporation, ce qui entraîne la formation d'un large bourrelet aux premiers stades de la croissance des bulles. Nos résultats montrent que l'amincissement de la microcouche dans le temps est dû à son évaporation. La résistance thermique mesurée à l'interface liquide-vapeur est plusieurs fois plus grande que sa valeur théorique et semble grossir dans le temps, ce qui est expliqué par une faible contamination de l'eau.

Thanks to the excellent specific stiffness and strength, as well as lower costs, the sandwich structures with composites skins, such as glass fiber reinforced polymer (GFRP)-balsa and carbon fiber reinforced polymer (CFRP)-honeycomb sandwich panels, have attracted more and more attention in marine and aviation industries. Generally, the skins of sandwich structures mainly take the bending load, while the core carries the transverse shear stresses. The objectives of this thesis are to characterize the moisture effects on bending behaviors and damage mechanisms of GFRP-balsa and CFRP-honeycomb sandwich structures under 4-point bending experimentally and numerically, with the help of Acoustic Emission (AE) and InfraRed Thermography (IRT). Firstly, by the preliminary Hsu-Nielsen tests, a new strategy of rapid determination of AE wave propagation velocity in any direction is firstly proposed for most usually used composite sandwich structures, based on the measurements of velocity in only one direction in the composite skin. And then, a new methodology is proposed to predict the elastic modulus of the skin of the wet sandwich structure based on the relationships between Moisture Content (MC), AE wave velocity and elastic modulus. Finally, static 4-point bending tests are monitored by IRT and AE to verify the good consistency between bending stiffness reduction and elastic modulus prediction of the wet sandwich by the new proposed method. A damage characterization approach coupling characteristics of AE amplitude, peak frequency and duration via K-means clustering algorithm is also developed to identify the damage sequence and classify damage modes of sandwich structures under bending loading. In order to predict the bending behaviors of the sandwich structures, numerical models in Abaqus have been developed by introducing the variation of material parameters of the skin due to moisture absorption, such as the elastic modulus, strength and fracture energy. It is demonstrated that the tested bending stiffness, strength and damage evolution process can be correctly simulated by the numerical models. In addition, the damage localizations by numerical models have a good concordance with the observations by IRT and AE. Consequently, the accuracy of the numerical models and the feasibility of AE and IRT to identify damage mechanisms of sandwich structures have been demonstrated. The results lay a critical foundation for the future dialogue between experimental and numerical analysis of sandwich structures.; Grâce à leurs propriétés spécifiques exceptionnelles aussi bien en rigidité qu’en résistance, à leurs faibles coûts, les structures sandwichs avec les peaux en composites stratifiés, telles que les panneaux en fibres de verre (GFRP)-balsa et en fibres de carbone (CFRP)-nid d'abeille, sont de plus en plus utilisées dans les industries maritimes et aéronautiques. Ce type de structures sont en général conçu pour supporter la charge de flexion, dont les peaux sont principalement sollicitées en traction et en compression due au moment fléchissant, tandis que l'âme est soumise à des contraintes de cisaillement transverses dues à l’effort tranchant. Les objectifs de cette thèse sont de caractériser expérimentalement et numériquement les effets de l'humidité sur les comportements de flexion et les mécanismes d'endommagement des structures sandwichs en fibres de verre-balsa et en fibres de carbone-nid d'abeille sous flexion 4 points, à l'aide de l'Emission Acoustique (EA) et de la Thermographie InfraRouge (TIR). Tout d'abord, grâce aux essais préliminaires de Hsu-Nielsen, une nouvelle méthode de détermination rapide de la vitesse de propagation des ondes acoustiques dans toutes les directions a été proposée pour les structures sandwichs les plus couramment utilisées. Elle est basée sur des mesures de la vitesse dans la peau composite dans une seule direction. Ensuite, une nouvelle méthodologie est proposée pour prédire le module d'élasticité de la peau d’une structure sandwich humide basée sur les relations entre la teneur en humidité, la vitesse des ondes acoustiques et le module d'élasticité. Enfin, des essais de flexion statique 4 points suivis par TIR et EA ont permis de vérifier la bonne cohérence entre la réduction de la rigidité en flexion et la prédiction du module élastique du sandwich humide obtenu par la nouvelle méthode proposée. A l’aide de la technique EA, une approche de caractérisation des endommagements couplant les caractéristiques d'amplitude, de durée et de pic fréquentiel via l’algorithme K-means est également développée pour identifier la séquence des endommagements et classer les modes d’endommagement des structures sandwiches en flexion. Afin de prédire le comportement en flexion des composites sandwiches, les essais réalisés sont aussi modélisés numériquement par Abaqus en introduisant la variation des propriétés mécaniques en fonction de l’humidité absorbée, telles le module d'élasticité, la résistance et l'énergie de rupture. Il est démontré que la rigidité et la résistance en flexion, ainsi que le processus d'évolution des endommagements des structures sandwiches testées peuvent être correctement simulés par les modèles numériques développés. En plus, les localisations des endommagements obtenue grâce aux modèles numériques concordent bien avec les observations faites par la TIR et l’EA. Par conséquent, la fiabilité du modèle numérique et la faisabilité de la TIR et de l'EA pour identifier les mécanismes d'endommagement des structures sandwichs ont été démontrées. Les résultats obtenus dans ce travail fournissent une base essentielle pour un futur dialogue entre l'analyse expérimentale et numérique des structures sandwichs.

The thermal dependence of the mechanical behavior, coupled with the numerous thermomechanical couplings present in elastomers, implies that the use of field methods to investigate the thermomechanical response of elastomers gives lot of information on physical phenomena which occurs in the material. The aim of this PhD thesis is to develop a method using both infrared thermography and digital image correlation to extract all information possible during mechanical testing of elastomeric materials., La dépendance du comportement mécanique à la température, couplée aux nombreux couplages thermomécaniques présents dans les élastomères, implique que l'utilisation conjointe de méthodes de champs pour caractériser la thermomécanique des élastomères offre d'innombrables informations sur les phénomènes physiques apparaissant dans le matériau. L'objet de cet thèse est de développer une méthode utilisant à la fois la thermographie infrarouge et la corrélation d'images numériques pour tirer le maximum d'informations possible lors d'essai mécaniques hétérogènes sur des matériaux élastomères.

International audience; The phase diagram is an essential tool in material sciences for the synthesis and the understanding of materials behaviorand macroscopic properties. Many experimental techniques exist for the determination of a binary system phase diagram but they are all time-consuming. The IRT method (infrared thermography) allows the fast establishment of a preliminary phase diagram in order to accelerate the screening step often preceding new materials development. In this work, we are presenting the used method and the obtained results for a complex binary system of fatty acids. Our results are compared to literature data, DSC measurements and to results obtained with a thermodynamic model.; Le diagramme de phases, outil primordial en sciences des matériaux, sert à la synthèse, la compréhension des comportements et des propriétés macroscopiques des matériaux. De nombreuses techniques expérimentales existent pour déterminer un diagramme de phases d’un système binaire mais elles sont chronophages. La méthode IRT (Thermographie InfraRouge) permet d’établir rapidement un diagramme de phase préliminaire pour accélérer l’étape de "screening", qui précède souvent le développement d’un nouveau matériau. Dans ce travail, nous présentons la méthode utilisée et les résultats obtenus pour les diagrammes de phases de systèmes binaires de complexité croissante (transitions eutectique, péritectique etc.). Nos résultats sont comparés aux résultats obtenus dans la littérature, par mesure de calorimétrie différentielle à balayage (DSC) et grâce à un modèle thermodynamique.

The building sector has a major role to play in the mitigation of greenhouse gas emissions. Indeed, residential and non-residential buildings account for 40% total energy consumption in the European union. In addition, given that 80% of building energy demand come from heating, thermal insulation is a domain with great potential for energy savings.The estimation of the thermal performance of a building usually relies on theoretical calculations. When in situ measurements are performed, the results often show some discrepancies with predictions: this is the so-called “performance gap”. Thus, it is important to distinguish the contribution of each element of the building envelope to the overall energy losses. In particular, “thermal bridges” (insulation irregularities) generate locally additional heat losses. They may also alter the thermal comfort of inhabitants as well as lead to mould growth issues.This thesis proposes several methods for the in situ estimation of heat losses in a building wall or in a thermal bridge. The methodology consists in applying an artificial thermal load to the wall and to analyze its transient response. This “active” approach is usually faster and less sensitive to weather conditions than standard steady-state methods. In practice, the indoor air is heated, and both the temperature and heat flux are measured on the wall surface. An inverse method then estimates the thermal resistance of the wall by fitting a model (direct model) to these transient measurements. The well-posedness of the inverse problem is assessed thanks to several mathematical tools. Some model reduction steps are required for the parameters of the direct model to be estimable with the desired uncertainty.In the case of a homogeneous wall, temperatures and heat fluxes are measured with contact sensors at one specific location. For a non-homogeneous wall or a thermal bridge, these local contact measurements are extrapolated to the rest of the wall thanks to infrared thermography and the quantification of the total heat transfer coefficient. For this purpose, several methods were developed to measure this coefficient in situ. Thanks to this extrapolation procedure, the inverse method can estimate the thermal resistance (or thermal transmittance) of an equivalent homogeneous wall having the same behavior as the real wall.The methods developed were validated on four experimental campaigns. Measurements were carried out in laboratory, in a climate chamber, and in situ. Different types of wall (heavyweight internally insulated wall, lightweight insulated wall) were tested. Several types of material-related thermal bridges were also investigated (mainly high-conductive materials in insulation systems). The results were compared to reference values obtained from steady-state measurements. Indeed, several methods for the characterization of thermal bridges in steady-state were compared: some are inspired from the literature, others are original., Le secteur du bâtiment a un rôle majeur à jouer dans la réduction des émissions de gazes à effet de serre. En effet, les bâtiments (résidentiels et non-résidentiels) représentent 40% de la consommation d’énergie totale en Europe. De plus, étant donné que 80% des besoins énergétiques des bâtiments proviennent du chauffage, l’isolation thermique représente un grand potentiel d’économies d’énergie. L’estimation des performances thermiques d’un bâtiment repose la plupart du temps sur des calculs théoriques. Quand des mesures de terrain son réalisées, les résultats montrent souvent des écarts par rapport aux prédictions. Ainsi, il est important de pouvoir distinguer les contributions de chaque élément de l’enveloppe du bâtiment aux déperditions totales. En particulier, les « ponts thermiques » (irrégularités et défauts dans l’isolation), génèrent localement des pertes supplémentaires. De plus, ils peuvent altérer le confort des habitants et engendrer de problèmes de développement de moisissures. Cette thèse propose plusieurs méthodes permettant de mesurer sur le terrain les déperditions thermiques à travers une paroi de bâtiment ou un pont thermique. La méthode consiste à chauffer artificiellement le mur et à analyser sa réponse transitoire à cette sollicitation. Cette approche, dite « active », est en général plus rapide et moins sensible aux conditions météorologiques que les méthodes en régime stationnaire habituelles. En pratique, l’air intérieur est chauffé, et la température et le flux thermique sont tous les deux mesurés à la surface du mur. Une méthode inverse estime ensuite la résistance thermique de la paroi en calant un modèle sur ces mesures (modèle direct). Le caractère bien-posé du problème inverse est évalué grâce à divers outils mathématiques. Des étapes de réduction de modèle sont nécessaires pour que les paramètres inconnus du modèle direct utilisé puissent être estimés avec une incertitude correcte.Dans le cas d’une paroi courante homogène, les températures et les flux sont mesurés à un endroit spécifique, supposé représentatif de l’ensemble du mur. Pour une paroi non-homogène ou un pont thermique, ces mesures locales par contact sont extrapolées au reste du mur grâce des mesures infrarouges et à la quantification du coefficient d’échange total en surface. A ces fins, plusieurs méthodes ont été développées pour mesurer ce coefficient sur le terrain. Grâce à cette procédure d’extrapolation, les méthodes inverses peuvent estimer la résistance (ou la transmittance) thermique d’un mur homogène équivalent ayant le même comportement que le mur réel.Les méthodes développées ont été validées sur quatre campagnes expérimentales. Des mesures ont été réalisées en laboratoire, en chambre climatique, puis en conditions réelles. Différents types de parois (mur porteur isolé par l’intérieur, paroi légère) ont été testés. Plusieurs types de ponts thermiques intégrés ont également été étudiés. Les résultats ont été comparés à des valeurs de référence obtenues grâce à des mesures en régime stationnaire. En effet, plusieurs méthodes pour la caractérisation des ponts thermiques en régime permanent ont été comparées : certaines proviennent de la littérature, d’autres ont été développées pendant cette thèse.

The latest technological improvements in low-cost infrared cameras have brought new opportunities for long-term infrastructures monitoring. The accurate measurement of surfaces' temperatures is facing the lack of knowledge of radiatives properties of the scene. By using multi-sensors instrumentation, the measurement model can be refined to get a better estimate of the temperature. To overcome a lack of sensors instrumentation, it is shown that online and free available climatic data can be used. Then, Bayesian methods to estimate simultaneously the emissivity and temperature have been developed and compared to literature's methods. A radiative exchange simulator of 3D scenes have been developed to compare those different methods on numerical data. This software uses the hardware acceleration as well as a GPGPU approach to reduce the computation time. As a consequence, obtained numerical results emphasized an advanced use of multi-spectral infrared thermography for the monitoring of structures. This simultaneous estimation enables to have an estimate of the temperature by infrared thermography with a known uncertainty.; L'utilisation de caméras infrarouges bas coûts pour la surveillance long-terme d'infrastructures est prometteuse grâce aux dernières avancées technologiques du domaine. Une mesure précise de la température des surfaces observées in-situ se heurte au manque de connaissance des propriétés radiatives de la scène. L'utilisation d'une instrumentation multi-capteurs permet d'affiner le modèle de mesure afin d'obtenir une estimation plus précise de la température. A contrario, il est montré qu'il est toujours possible d'exploiter des données climatiques en ligne pour pallier un manque de capteur. Des méthodes bayésiennes d'estimation conjointe d'émissivité et de température sont ensuite développées et comparées aux méthodes de la littérature. Un simulateur d'échanges radiatifs diffus de scènes 3D a été implémenté afin de tester ces différentes méthodes. Ce logiciel utilise l'accélération matérielle de la machine pour réduire les temps de calcul. Les résultats numériques obtenus mettent en perspective une utilisation avancée de la thermographie infrarouge multi-spectrale pour la surveillance de structures. Cette estimation conjointe permet alors d'obtenir un estimé de la température par thermographie infrarouge avec une incertitude connue.

International audience; Fire-induced decomposition of composite materials involves complex and coupled multi-physics phenomena experienced for instance in standard tests (cone calorimeter, FAR 25.856(b):2003 and ISO 2685:1998(e)). It is proposed to address this issue in a simplified laboratory facility using a gas burner embedded with coupled measurement techniques to assess all desired physical quantities. A focus is given in this study on non-intrusive (no coating required) DIC and infra-red thermography measurements. Displacement and temperature of the unexposed surface were accurately measured as a function of time to investigate the 3D fire behaviour of a composite laminate used in the aircraft industry. Those complementary measurements offer relevant and correlated information to identify the damage mechanisms.

Simultaneous measurement of kinematic and thermal full fields are very important for thermomechanical procedures. Silicon-based cameras are widely used to perform real-time observation of the kinematic fields, mainly thanks to digital image correlation. Moreover, they are known to be as well sensitive in the near-infrared spectral range, thus the acquirement of thermal fields using silicon-based cameras is possible. However, there are two main problems for the silicon-based camera to obtain simultaneously kinematic and thermal fields. One is that in the near-infrared spectral range, a small temperature variation will lead to a large modification in the image gray level, which easily leads to poor quality images. Another is that digital image correlation needs a heterogeneous and contrasting surface, while the near-infrared thermography needs a homogeneous and constant surface. In this thesis, an innovative technique was proposed to automatically adjust the exposure time of the camera to obtain kinematically and thermally exploitable images whatever the temperature evolution occurs on the surface of the observed object. This technique was validated by different experiments, including blackbody heating experiments and realistic specimen heating experiments. Radiometric models of blackbody and specimen surfaces ware calibrated respectively. Based on the radiometric models, thermal fields have been reconstructed on the kinematically and thermally exploitable images. High temperature tube ballooning experiment is conducted to perform both kinematic and thermal fields. Global digital image correlation was performed to obtain kinematic fields. To perform near-infrared thermography on the specimen surface, radiometric model is calibrated based on portions of the brightest pixels. In this case 20% of the brightest pixels are used to perform radiometric model calibration. Based on the radiometric model using 20% of the brightest pixels, the thermal fields are reconstructed. Combined with the known coordinates of kinematic fields by digital image correlation, the thermal fields at the same coordinates as kinematic fields can be obtained., La mesure simultanée des champs cinématiques et thermiques est très importante pour les procédures thermomécaniques. Les caméras à base de silicium sont largement utilisées pour l'observation en temps réel des champs cinématiques, principalement grâce à la corrélation d'images numériques. De plus, ils sont aussi connus pour sa sensibilité dans le spectre du proche infrarouge, ce qui permet d’acquérir des champs thermiques à l’aide d’une caméra à base de silicium. Cependant, pour la caméra à base de silicium, il y a deux problèmes principaux d’obtenir simultanément des champs cinématiques et thermiques. D’abord, dans le spectre du proche infrarouge, une petite variation de température entraînera une modification importante du niveau de gris de l'image, ce qui entraînera facilement une mauvaise qualité des images. Deuxième, la corrélation d’images numériques nécessite une surface hétérogène et contrastée, tandis que la thermographie dans le proche infrarouge nécessite une surface homogène et constante. Dans cette thèse, une technique innovante a été proposée pour ajuster automatiquement le temps d'exposition de la caméra afin d'obtenir des images exploitables pour l’analyse cinématique et thermique, quel que soit l'évolution de température à la surface de l'objet observé. Cette technique a été validée par expériences différentes, notamment des expériences de chauffage d’un corps noir et des expériences de chauffage d’un échantillon réel. Les modèles radiométriques du corps noir et de la surface des échantillons calibrent respectivement. Basé sur les modèles radiométriques, des champs thermiques ont été reconstruits sur les images exploitables pour l’analyse cinématique et thermique. L'expérience à haute température est réalisée pour le ballonnement des tubes où les champs cinématiques et thermiques sont observés. La corrélation d'images numériques a été effectuée globalement afin d'obtenir des champs cinématiques. Pour effectuer la thermographie du proche infrarouge sur la surface de l’échantillon, le modèle radiométrique est étalonné selon une partie des pixels les plus brillants. Dans ce cas, 20% des pixels les plus brillants sont utilisés pour effectuer l'étalonnage des modèles radiométriques. Basée sur le modèle en utilisant 20% des pixels plus brillants, les champs thermiques sont reconstruits. Combiné avec les coordonnées connues du champ cinématique par corrélation d'images numériques, le champ thermique et le champ cinématique dans les mêmes coordonnées peut être obtenu.

International audience; The characterization and visualization of the radiated electromagnetic field is a way to diagnose and check microwaves sources, in particular in the space industry. Beyond the traditional 3D scanning of the radiating element, infrared thermography is an alternative way that may give key results in a reduced time, since a few seconds are sufficient to obtain the emitted field map even for a complex multi-cells antenna. This method, called EMIR (ElectroMagnetic InfraRed) has been developed and used for years at ONERA. We have recently extended this technique to the magnetic field, which will lead to a complete characterization of the near field structure. We illustrate this feature in the particular cases of antennas for space application and for a High Impedance Surface (HIS), a metamaterial structure that could be used to reduce the coupling between antennas confined in compact structures (typically size constraints of the spatial components).

The latest technological improvements in low-cost infrared cameras have brought new opportunities for long-term infrastructures monitoring. The accurate measurement of surfaces' temperatures is facing the lack of knowledge of radiatives properties of the scene. By using multi-sensors instrumentation, the measurement model can be refined to get a better estimate of the temperature. To overcome a lack of sensors instrumentation, it is shown that online and free available climatic data can be used. Then, Bayesian methods to estimate simultaneously the emissivity and temperature have been developed and compared to literature's methods. A radiative exchange simulator of 3D scenes have been developed to compare those different methods on numerical data. This software uses the hardware acceleration as well as a GPGPU approach to reduce the computation time. As a consequence, obtained numerical results emphasized an advanced use of multi-spectral infrared thermography for the monitoring of structures. This simultaneous estimation enables to have an estimate of the temperature by infrared thermography with a known uncertainty., L'utilisation de caméras infrarouges bas coûts pour la surveillance long-terme d'infrastructures est prometteuse grâce aux dernières avancées technologiques du domaine. Une mesure précise de la température des surfaces observées in-situ se heurte au manque de connaissance des propriétés radiatives de la scène. L'utilisation d'une instrumentation multi-capteurs permet d'affiner le modèle de mesure afin d'obtenir une estimation plus précise de la température. A contrario, il est montré qu'il est toujours possible d'exploiter des données climatiques en ligne pour pallier un manque de capteur. Des méthodes bayésiennes d'estimation conjointe d'émissivité et de température sont ensuite développées et comparées aux méthodes de la littérature. Un simulateur d'échanges radiatifs diffus de scènes 3D a été implémenté afin de tester ces différentes méthodes. Ce logiciel utilise l'accélération matérielle de la machine pour réduire les temps de calcul. Les résultats numériques obtenus mettent en perspective une utilisation avancée de la thermographie infrarouge multi-spectrale pour la surveillance de structures. Cette estimation conjointe permet alors d'obtenir un estimé de la température par thermographie infrarouge avec une incertitude connue.

Freezing is a limiting factor for plant life, as it can cause damage on living tissues and embolism formation in xylem conduits. Ice formation in plant tissues is usually detected by exotherm analysis or infra-red thermography, whereas freeze-thaw induced embolism is measured through loss of hydraulic conductivity (PLC). We used a nondestructive method based on ultrasonic acoustic emissions (UE) generated by the freezing xylem. However, the exact source(s) of UE has not been identified up to now, especially in angiosperm species, in which xylem tissues are composed of several diverse cell types. We report recent advances on how UE detection could enable insights into: We report recent advances on how UE detection could inform on: (i) Ice nucleation and propagation (Charrier et al., 2015), (ii) Presence of ice within xylem (Charrier et al., 2014a), (iii) Loss of hydraulic conductivity after a freeze-thaw cycle (Charrier et al., 2014b), (iv) Damages generated on living cells (Kasuga et al., 2015). Results indicate that cavitation events are generated at the ice front leading to UE. Species-specific cavitation thresholds are thus reached during freezing due to the temperature-dependent decrease of ice water potential, while bubble expansion (embolism) and the resulting PLC occur during thawing. Contrarily to drought-induced embolism, UE analysis during freeze-thaw cycles can allow to split between cavitation and embolism stages: on freezing and thawing, respectively. Ultrasonic emission analysis enabled new insights into the complex process of xylem freezing and might be used to monitor ice propagation in a whole plant in natura in relation with stress intensities and physiology (Charrier et al., 2017).

International audience; With the increase of the use of composite materials, various experimental methodologies have been proposed to characterise the matrix crack density evolution in cross-ply laminates for quasi-static loadings. These methodologies cannot easily be extended to intermediate or high strain rate loadings as they rely on interrupted tests. In this work, a new approach is considered relying on the use of passive infrared thermography to capture the transverse cracking appearance. The objective of this study is twofold. On one hand confirm that the classically used assumption that the crack propagation is instantaneous from side to side in the specimen remains valid with the loading rate increase. On the other hand, study the influence of the loading rate increase on the crack density evolution with respect to the applied load.

International audience; With the increase of the use of composite materials, various experimental methodologies have been proposed to characterise the matrix crack density evolution in cross-ply laminates for quasi-static loadings. These methodologies cannot easily be extended to intermediate or high strain rate loadings as they rely on interrupted tests. In this work, a new approach is considered relying on the use of passive infrared thermography to capture the transverse cracking appearance. The objective of this study is twofold. On one hand confirm that the classically used assumption that the crack propagation is instantaneous from side to side in the specimen remains valid with the loading rate increase. On the other hand, study the influence of the loading rate increase on the crack density evolution with respect to the applied load.

This Ph.D. dissertation thesis addresses the conditions and mechanisms that lead superelastic NiTi wires to fail under cyclic mechanical loads. NiTi shape memory alloys exhibit functional thermomechanical properties (superelasticity, shape memory effect, thermal actuation) due to martensitic phase transformations caused by a change of the applied stress and temperature. These phase transformations are though as fully reversible damage-free processes, however, when NiTi is subjected to repetitive stress-induced phase transformations its fatigue performance drops drastically in comparison to non-transforming NiTi. Most of fatigue S-N curves reporting this drop were measured on straight NiTi wires in which martensitic transformations proceed heterogeneously through nucleation and propagation of shear bands. Moreover, from our experience fatigue testing straight wire samples results in undesired failure inside the testing machine clamps. Hence, the reported stress-strain values in S-N curves are not necessarily representative of the critical mechanical conditions that lead the material to failure. With the aim of better characterize the fatigue performance of NiTi wires, we started by carrying out a series of pull-pull fatigue tests using hourglass-shaped samples. This sample geometry allowed us to confine all martensitic transformation and related material fatigue processes into a well-defined gauge volume. The samples’ characterization was performed by combining several experimental and analysis techniques such as Digital Image Correlation, Infrared Thermography, Synchrotron-source X-ray diffraction, Optical Microscopy, Scanning Electron Microscopy and Finite Element Analysis. A special attention was paid to the High Cycle Fatigue (HCF) performance of NiTi in which the material shows elastic behavior and/or an intermediate phase transformation (so-called R-phase). The results from HCF tests allowed us to distinguish crack nucleation and crack propagation stages during the total life of our NiTi samples. In order to get a better understanding of the mechanisms that lead to crack nucleation, we applied the nonconventional Self-Heating fatigue assessment method, which has shown efficiency in the case of aluminum and steel alloys. This method correlates the temperature elevation of a sample subjected to different cyclic load amplitudes with energy dissipating mechanisms that contribute to accumulating local damage in the material. The Self-Heating method was performed using full-field thermal measurements of cyclically loaded NiTi hourglass-shaped samples., Ce travail de thèse aborde les conditions et les mécanismes qui conduisent des fils superélastiques de NiTi à la rupture sous chargement mécanique cyclique. Les alliages à mémoire de forme du type NiTi présentent des propriétés thermomécaniques fonctionnelles comme la superélasticité et l’effet de mémoire de forme simple et double, lesquels sont générées grâce aux transformations de phase martensitiques provoquées soit par un changement de la contrainte ou de la température. Ces transformations de phase sont en principe des processus totalement réversibles et sans endommagement. Cependant, lorsque le NiTi est soumis à des transformations de phase induites par des contraintes cycliques, la performance en fatigue de l’alliage chute considérablement par rapport au NiTi non-transformant. La plupart des courbes S-N de fatigue rapportant cette chute ont été mesurées sur des fils NiTi a section constante dans lesquels les transformations martensitiques se développent de façon hétérogene par nucléation et propagation de bandes de cisaillement. De plus, d'après notre expérience, des essais de fatigue sur des échantillons de fils à section constante entrainent la rupture à l'intérieur des mors de la machine d'essai. Par conséquent, les valeurs de contrainte-déformation rapportées dans les courbes S-N ne sont pas nécessairement représentatives des conditions mécaniques critiques qui conduisent le matériau à la rupture. Dans le but de mieux caractériser les performances en fatigue des fils NiTi, nous avons effectué une série de tests de fatigue en traction-traction, tout en utilisant des échantillons sous forme ≪ diabolo ≫. La géométrie de ces échantillons nous a permis de confiner tous les processus de transformation martensitique et de fatigue dans un volume utile bien défini. La caractérisation du comportement thermomécanique de ces échantillons a été réalisée en combinant plusieurs techniques expérimentales et d'analyse telles que la corrélation d'image numérique(DIC), la thermographie infrarouge, la diffraction des rayons X à source synchrotron, la microscopie optique, la microscopie électronique à balayage et l'analyse par éléments finis. Une attention particulière à été portée à la performance de NiTi dans le régime à grand nombre de cycles (HCF) dans laquelle le matériau présente un comportement élastique ou une transformation de phase intermédiaire (appelée R-phase). Les résultats des tests de fatigue nous ont permis de distinguer les étapes de nucléation et de propagation des fissures pendant la durée de vie totale de nos échantillons. Afin de mieux comprendre les mécanismes qui conduisent à la nucléation des fissures, nous avons appliqué la méthode de l’auto-échauffement, qui a démontré son efficacité dans la prédiction de fatigue dans les cas des alliages d'aluminium et des alliages d'acier. Cette méthode corrèle l'élévation de température d'un échantillon soumis à différentes amplitudes de charge cyclique avec des mécanismes de dissipation d'énergie. Ces mécanismes dissipatifs sont après associés à l’accumulation d’endommagement locale dans le matériau. La méthode d'autoéchauffement a été réalisée en utilisant des mesures de champs thermiques des d'échantillons de NiTi sous forme diabolo pendant de chargement cyclique.

National audience; A hybrid non-destructive testing (NDT) approach has been developed for structural composites damage monitoring using several NDT techniques. Three nondestructive techniques (acoustic emission, infrared thermography and digital image correlation) were used simultaneously, in-situ and in real time to assess damage in an aeronautical carbon/epoxy composite material under tensile fatigue loading. A data fusion processing was developed to combine the results of the used NDT techniques in order to optimize the structural health diagnosis of the material and to predict its residual life.; Une approche multi-technique non destructive pour le monitoring de l’état de santé des matériaux composites structuraux et le pronostic de leur durée de vie résiduelle est ici proposée. Trois techniques non destructives (émission acoustique, thermographie infrarouge et corrélation d'images numérique) sont utilisées simultanément, in-situ et en temps réel. La méthodologie est appliquée à un matériau composite carbone-époxy aéronautique soumis à un chargement de fatigue par blocs de traction. Un post-traitement par fusion de données a été développé pour combiner les résultats obtenus par les trois techniques afin d’optimiser le diagnostic de l’état de santé du matériau et d’estimer sa durée de vie résiduelle.

Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices (solar cells, LEDs, touch screens), transparent film heaters (TFHs) and electromagnetic (EM) applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely-used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO’s lack of flexibility and the relatively high manufacturing costs have prompted search into alternative materials. With their outstanding physical properties, silver nanowire (AgNW)-based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution-based processing, and compatibility with large area deposition techniques. First cost estimates are lower for AgNW based technology compared to current ITO fabrication processes. Unlike ITO, AgNW are indeed directly compatible with solution processes, never requiring vacuum conditions. Moreover, due to very large aspect ratio of the NWs, smaller quantities of raw materials are needed to reach industrial performance criteria.The present thesis aims at investigating important physical assets of AgNW networks – unexplored (or not explored enough) so far – in order to increase the robustness, reliability, and industrial compatibility of such technology. This thesis work investigates first optimization methods to decrease the electrical resistance of AgNW networks. In situ electrical measurements performed during thermal ramp annealing and/or chemical treatments provided useful information regarding the activation process at the NW-NW junctions. At the scale of the entire network, our ability to distinguish NW areas taking part in the electrical conduction from inactive areas is a critical issue. In the case where the network density is close to the percolation threshold, a discontinuous activation process of efficient percolating pathways through the network was evidenced, giving rise to a geometrical quantized percolation phenomenon. More generally, the influence of several parameters (networks density, applied voltage, optimization level) on the electrical and thermal homogeneity and stability of AgNW networks is investigated via a dual approach combining electrical mapping techniques and simulations. A thermal runaway process leading to a vertical crack and associated to electrical failure at high voltage could be visually evidenced via in situ electrical mapping of AgNW networks during voltage plateaus. Moreover many efforts using Matlab and Comsol softwares were devoted to construct reliable models able to fit with experimental results. Due to the increasing demand for portable and wearable electronics, preliminary tests were also conducted to investigate the stretching capability of AgNW networks when transferred to elastomeric substrates. Finally, integrations of AgNW networks in several devices were performed. Specifically, studies were conducted to understand the mechanisms leading to failure in AgNW-based transparent film heaters, and to improve their overall stability. Preliminary investigations of the benefits of incorporating of AgNW networks into electromagnetic devices such as antennas and EM shielding devices are also discussed at the end of the manuscript., L’intérêt pour les électrodes transparentes (TEs) concerne un large spectre de domaines technologiques, tels que les dispositifs optoélectroniques (cellules solaires, LEDs, écrans tactiles), les films chauffants transparents, ou les applications électromagnétiques. Les TEs de nouvelle génération auront à combiner à la fois un très haut niveau de conduction électrique, de transparence optique, mais aussi de flexibilité mécanique. L’oxyde d’Indium dopé Etain (ITO) domine actuellement le marché des matériaux transparents conducteurs (TCMs). Cependant, la rareté de l’Indium, combinée à ses faibles performances en flexion mécaniques et ses coûts de fabrication élevés ont orienté les recherches vers des TCMs alternatifs. Les réseaux percolants de nanofils métalliques, en particulier les nanofils d’argent (AgNWs), se sont imposés comme l’une des alternatives les plus sérieuses à l’ITO, en raison de leurs propriétés physiques très attractives. Ces réseaux interconnectés offrent également la possibilité d’utiliser des méthodes de synthèse en voie chimique et d’impression à bas coût, sur de grandes surfaces. De manière générale, les premières estimations concernant les coûts de fabrication sont inférieures à celles de l’ITO. De plus, grâce au très haut facteur de forme des nanofils et à la nature percolante des réseaux, les besoins en quantité de matières premières nécessaires pour atteindre un haut niveau de performance sont moindres.Ce travail de thèse s’intéresse à l’étude des propriétés physiques fondamentales – inexplorées ou non encore suffisamment étudiées – des réseaux d’AgNWs, afin d’améliorer la robustesse, la fiabilité et la compatibilité de ce type d’électrodes avec les critères de performance industriels. La première partie est consacrée à l’étude des méthodes d’optimisation utilisées pour diminuer au mieux la résistance électrique des électrodes. Les mesures électriques in situ effectuées au court d’un recuit thermique et/ou après traitement chimique fournissent de précieuses informations concernant les mécanismes d’activation au niveau des jonctions entre nanofils. A l’échelle du réseau, notre capacité à distinguer les zones qui participent efficacement à la conduction électrique de celles qui seraient potentiellement inactives est un défi majeur. Pour les réseaux dont la densité en nanofils est proche du seuil de percolation, un processus d’activation discontinu de chemins efficaces de percolation à travers le réseau a pu être mis en évidence. De manière générale, l’influence de plusieurs paramètres (densité du réseau, tension, niveau d’optimisation) sur l’homogénéité et la stabilité électrique et thermique des électrodes a été étudiée, à l’aide de techniques de cartographie électrique et de simulations. A tension élevée, un processus d’emballement thermique conduisant à la formation d’une fissure physique à travers un réseau d’AgNWs soumis à des plateaux de tension croissants a pu être détecté visuellement. Des modèles de simulation via les logiciels Matlab et Comsol ont aussi été construits afin de confirmer, voire anticiper, les phénomènes observés expérimentalement. Par ailleurs, encouragés par la demande croissante pour les dispositifs électroniques portatifs en toute circonstance, des tests préliminaires ont été conduit pour évaluer le comportement des réseaux d’AgNWs sous contrainte d’étirement mécanique lorsqu’ils sont transférés sur des substrats élastiques. Ce travail de thèse a également donné lieu à l’intégration de réseaux d’AgNWs dans des dispositifs. Des études ont été menées afin d’améliorer la stabilité des films chauffants transparents à base d’AgNWs et de mieux appréhender les mécanismes favorisant l’émergence de défauts. L’utilisation des réseaux d’AgNWs pour des applications électromagnétiques (antennes, blindage) a également fait l’objet de tentatives préliminaires dont les résultats sont commentés à la fin du manuscrit.

International audience; The comparison and ranking of advanced data processing techniques of thermographic nondestructive testing (NDT) seems decisive for end users who are required to optimize their NDT tools. This is a difficult task, which explains why there are so few articles dealing with this challenge. Furthermore, these works are often incomplete, since the choice of metrics is too limited and/or inappropriate to an accurate, unbiased ranking. Most of them are based on the number of detected discontinuities among a series of discontinuities of various sizes and depths, and the only assessed metric is the contrast-to-noise ratio of the discontinuity signatures. This observation justifies the need for a more thorough comparison, based on the evaluation of several unbiased parameters. In this article, three metrics are considered: not only the contrast-to-noise ratio, but also the sharpness of the discontinuity edges and the accuracy of the identified characteristic dimension of the discontinuity using the contrast full-width at half-maximum. They are assessed for a trio of thermal images of a composite sample with 12 embedded calibrated discontinuities, provided by four different pulse thermographic NDT data processing techniques: thermographic signal reconstruction polynomial coefficient (PC-TSR) technique, pulse phase thermography (PPT), principal component thermography (PCT), and higher order statistics (HOS). The relative comparison of the relevance of each of these techniques is then based on 432 discontinuity signatures (4 techniques × 3 images × 12 discontinuities ×3 metrics). In order to simplify the final ranking procedure, it is also shown that this high number of data can be drastically reduced to four numbers.; La comparaison et le classement entre les différentes méthodes de post-traitement appliquées à des données de contrôle non-destructif (CND) par thermographie IR sont un élément décisif pour les utilisateurs afin d'optimiser les outils de CND. La tâche n'est pas simple, ce qui explique le peu d'articles qui lui sont dédiés. Les rares travaux sur le sujet sont souvent incomplets, les critères de comparaison se limitant souvent au rapport signal sur bruit des signatures thermiques des discontinuités. Le but de l'article est donc de proposer une méthode d'évaluation approfondie, basée sur trois paramètres objectifs : le rapport signal sur bruit, mais aussi la netteté des bords des défauts et la précision sur l'estimation de leurs dimensions caractéristiques (qui repose sur le calcul du contraste à mi-hauteur et du contraste maximal). Ces indicateurs sont évalués pour des trios de cartographies thermiques obtenus pour un échantillon composite contenant 12 défauts calibrés à partir de quatre techniques de post-traitement : le traitement polynomial TSR ; la thermographie de phase pulsée ; la décomposition en composantes principales ; les ordres élevés. La comparaison entre chacune de ces techniques est donc basée sur 432 signatures de défauts (4 techniques x 3 cartographies x 12 défauts x 3 indicateurs). Dans le but de simplifier la procédure ce classement final, il est également montré que ce nombre conséquents de données peut se réduire à l'analyse de quatre indicateurs.

National audience; Ces travaux abordent la question du Contrôle Non Destructif (CND) par Thermographie InfraRouge (TIR) des réparations par collage structural de stratifiés carbone-époxyde. Les difficultés d’investigation de ce type d’assemblage proviennent du faible contraste de propriétés thermiques entre les différents éléments constitutifs de la réparation. Pour remédier à ce problème, une approche originale visant à modifier les propriétés thermique du joint de colle structural a été mise en œuvre numériquement par le biais d’un modèle par Eléments Finis (EF). La pertinence du comportement thermique identifié a ensuite été validée expérimentalement sur une réparation comportant des défauts de collage représentatif de cas réels.

This PhD work intends to contribute to the characterization of structural bonded repair quality of primary composite structures using InfraRed Thermography (IRT). Generally, in this case, the parent structure and the repair patch are both made of carbon-epoxy and are linked together by an epoxy adhesive. Such repair configuration then leads to a weak property contrast between the parts of the repaired assembly. Therefore, the non-destructive analysis of the bonding quality remains dificult and represents the very challenging issue of this study. In this way, a new specific Non Destructive Testing (NDT) procedure has been firstly developed that allows physically consistent numerical model of the thermal problem and a good correlation with experimental data. Additionally, it is proposed to use relevant additives that modify the thermal properties of the glue joint in order to improve the detection of bond defects.

International audience; A hybrid non-destructive testing (NDT) approach has been developed to characterize composites damage using simultaneously bulk and guidedultrasonic waves, acoustic emission, and passive and active infrared thermography. Combining multiple NDT techniques makes it possible to optimize the diagnosis of a material’s structural health.

Cette étude s'inscrit dans une approche originale basée sur des techniques d'imagerie quantitatives comme la thermographie infrarouge pour étudier l'endommagement sous chargement de fretting. Le premier objectif était de développer une méthode de construction rapide de carte de fretting basée sur l'analyse du signale thermique au cours d'essais de fretting. Un deuxième objectif était de déterminer les sources de chaleurs accompagnant le fretting pour une meilleure compréhension des mécanismes d'endommagement. Ce travail a souligné le grand potentiel de la thermographie infrarouge pour l'étude de c'est phénomènes.; This study is part of an original approach based on quantitative imaging techniques, such as Infrared Thermography, to study the damage under fretting loadings. The main objective was the establishment of new experimental method for a rapid determination of crack initiation conditions under fretting loadings, based on the analysis of the thermal signal. One other objective was the determination of the different heat sources in order to assess a local analysis of the fretting damage. This work underlined the great potential of Infrared Thermography to study this damage.

The main objective of our dissertation is to analyze the mechanical behavior of two-dimensional composite granular materials through the granular textures. Thermoelatic stress analysis experiments and molecular dynamics simulations are used for this purpose. The composite granular systems are prepared from polyoxymethylene (POM) and high-density polyethylene (HDPE) cylinders with a stiffness ratio of about 4 between them. Different configurations in terms of ratios of diameter size and ratio of particle numbers are systematically investigated. Experimental and numerical results are good correlated at the macroscopic scale. In particular the strong network, which is here characterized by hydrostatic stresses higher than the mean value, consists of less than 50% of all particles, and exhibits an exponential decay whatever the type of particles considered for the analysis (soft, stiff, or both types). In addition, the contact distributions between stiff particles (POM-POM contacts) is anisotropic with an effort to arrange parallel to the direction of the external applied load, whereas the other types of contacts just act to sustain the granular system in equilibrium., L'objectif de la thèse est d'analyser le comportement mécanique de matériaux granulaires composites bidimensionels en terme de textures granulaires en utilisant deux approches : étude expérimentale par "thermoelastic stress analysis" et étude numérique par dynamique moléculaire. Les systèmes granulaires composites sont préparés à l'aide de cylindres en polyoxyméthylène (POM) et polyéthylène haute densité (PEHD), présentant un rapport de rigidité de 4 entre eux. Différents rapports de diamètres et de nombres de particules sont considérés. Les résultats expérimentaux et numériques sont en bon accord à l'échelle macroscopique. En particulier, le réseau fort (qui est ici caractérisé par des contraintes hydrostatiques supérieures à la valeur moyenne) contient moins de 50% des particules, et présente une distribution décroissance exponentielle quel que soit le type de particules considéré pour l'analyse (particules souples, particules rigides, toutes les particules). De plus, la distribution des contacts entre particules rigides (contacts POM-POM) est anisotrope et tend à s'organiser dans le sens de la direction du chargement extérieur appliqué, tandis que les autres types de contact agissent principalement pour maintenir le système en équilibre.

Remote-sensing techniques are changing the way of investigating the Earth and its surface processing. Among these, rock fall from vertical cliffs are very frequent and difficult to be investigated because they frequently occur from inaccessible places. At this regard, terrestrial remote-sensing techniques represent a great opportunity for investigating inaccessible cliffs from a remote position. In this paper, a new approach for the investigation of rock cliff and the prioritization of rock fall hazard based on data collected by remote-sensing techniques has been developed and applied to a real coastal cliff located in the southern part of Italy. By the herein presented approach, data derived from a survey performed by the combination of terrestrial laser scanner, ground-based SAR interferometry and infrared thermography are used in order to identify both predisposing factors (mapping of discontinuities) and state of activity indicators of rock instabilities. Hence, a prioritizations map of the cliff in terms of stability interventions is achieved that can be easily used by local authorities in charge of land management.

Improving the adaptation of poultry to heat stress by selection requires having measures that are easy to obtain and that are heritable. Internal body temperature is used to quantify heat stress but is long to obtain and lacks precision. We tested the possibility of infrared thermography to record body temperature (BT) in two commercial lines of laying hens between 28 and 72 wk, submitted cyclically to periods at neutral or high ambient temperatures (19.6°C and 28.4°C, resp.). Mean BT were estimated for the wing, comb and shank areas (N=4465-4481 in line A, 7279-7311 in line B, depending on the trait). During hot periods, mean BT increased by 29.5-32.6% on the wing, by 20.6-22.5% on the shank and by 28.9-29.8% on the comb. Heritability of the mean BT was estimated in both lines. It was very low for the wing (0.03) consistently with the fact that wing BT is mainly linked to environmental temperature and to feather coverage. Heritability of the shank and the comb BT was also low but significantly different from zero (0.08-0.14), which indicates that the capacity of animals to dissipate heat is partly under genetic control. Heritability of the shank BT was the most consistent between the two lines, probably reflecting a higher precision of the measure of this part, the easiest to distinguish from environment. Using infrared thermography in chicken experimentation seems promising but a higher degree of precision is required in order to increase the heritability of these traits.

Therapeutic ultrasound has become a topic of growing interest in ophthalmology. High intensity focused ultrasound (HIFU) for the treatment of glaucoma and ultrasound (US) drug delivery are the two main areas of research in this field. This work addresses these domains in two separate parts: transscleral ultrasound drug delivery (USDD), and infrared (IR) field characterization of an ophthalmic HIFU device for glaucoma treatment. The sclera is a promising pathway for ocular drug delivery, since transscleral administration can address both the anterior and posterior segments of the eye. Due to the low permeability however, efficient drug delivery is challenging. In this study, HIFU was investigated as a potential modality for an enhanced transscleral drug delivery (in vitro). Among US effects, cavitation was shown to be the major contributor to an enhanced USDD. A pulsed US protocol designed to maximum cavitation activity may therefore be a viable method for enhancing ocular drug delivery. In the second part, a new method of ultrasonic field characterization was developed for a multi-element HIFU device. This system is designed and produced for glaucoma treatment by Eyetechcare Company (Rillieux-la-Pape, France). The traditional hydrophone method for field characterization was prohibitively slow on an industrial scale. An alternative modality for rapid qualitative assessment of the intensity distribution based on infra-red (IR) thermography was developed specific to this high frequency (19-21 MHz) device with line-focus US radiators. The second part of the study was aimed to expand the application of a R&D technique for ultrasonic field characterization to an industrial scale, Les ultrasons (US) thérapeutiques sont devenus un sujet d'intérêt croissant en ophtalmologie. Les ultrasons focalisés de haute intensité (HIFU) pour le traitement du glaucome et pour la délivrance de médicaments dans l'oeil sont les deux principaux domaines de recherche dans ce domaine. Cette thèse traite des deux sujets en deux parties distinctes : l'administration de médicaments ou drug delivery par d'ultrasons (USDD) à travers la sclère et la caractérisation par rayonnement infrarouge (IR) d'un dispositif HIFU ophtalmique pour le traitement du glaucome. Bien que plus perméable que la cornée, l'administration de médicaments efficace à travers la sclère reste un réel challenge. Dans ce travail, nous avons évalué l'effet d'une propagation d'us en mode pulsé sur l'administration de médicaments à travers la sclère. Parmi les mécanismes sous-jacents, la cavitation semble être un contributeur à une USDD renforcée. L'activité maximale de cavitation sous-jacente à une émission d'ultrasons en mode pulsé peut donc être une méthodologie viable pour l'amélioration de l'administration de médicaments à travers l'oeil. Dans la deuxième partie de la thèse, une nouvelle méthode de caractérisation ultrasonore de terrain a été développée pour un dispositif HIFU multi-éléments. Ce dispositif médical développé par Eyetechcare est destiné au traitement du glaucome réfractaire (Rillieux -la-pape, France). Une alternative basée sur la thermographie par infra-rouge a été développée pour une évaluation rapide et qualitative de la distribution d'intensité émise spécifiquement par ce dispositif à haute fréquence (19-21 mhz) constitué de multiéléments à focalisation en ligne. Cette méthodologie permettra de caractériser les sondes de thérapie à l'échelle industrielle

International audience; An infrared system has been developed to monitor transport infrastructures in a stand-alone configuration. It is based on low cost infrared thermal cameras linked with a calculation unit in order to produce a corrected thermal map of the surveyed structure at a selected time step. With the inline version, the data collected feed simplified radiative models running a GPU. With the offline version, the thermal map can be corrected when data are collected under different atmospheric conditions up to foggy night conditions. A model for radiative transmission prediction is proposed and limitations are addressed. Furthermore, the results obtained by image and signal processing methods with data acquired on the transport infrastructure opened to traffic are presented. Finally, conclusions and perspectives for new implementation and new functionalities are presented and discussed.

International audience; This paper investigates thermography and shearography couplings, using feasibility trials and numerical simulations, for non-destructive control evaluations of bonding of carbon fiber-reinforced polymer plates glued over concrete structures. Those are well-known methods in non-destructive testing (NDT) applied to civil engineering, but in this context, they are seen as paired because they use the same excitation source: square-pulsed optical heating. Furthermore, because both methods are based on different properties, the detection of defects is optimised regardless of its nature or type. The combination of the methods allows the measurement of a thermal as well as a thermomechanical response from the structure at the same time. A quick review of those methods and their respective advantage and inconvenient is mentioned. An in-depth study of the interpretation of the thermal and mechanical responses is carried out in relation to the thermal excitation. Then, the thought process behind the conception of the finite element model and its limitation is discussed. The experimental setup, used for feasibility testing, is described as well as a thorough analysis of the experimental and simulated results. Finally, the pairing of both methods is discussed regarding the evaluation of the bond quality, as well as the similitude of the sample and its numerical model.

This work concerns the development of a non-contact calorimeter for two-phase flow characterization. The biphasic flow is performed under a droplet configuration inside millimetric tubings which are inserted into the isoperibolic chip. The main idea is to combine the Infrared Thermography and microfluidic tools to propose a suitable technique for accurate measurements. Microfluidics enables the use of small reaction volumes thus limiting any risk of dangerous reactions inside droplets, the Infrared tool enables to monitor the thermal signature of these flows with high accuracy. The results of this thesis show that this tool is able to estimate the thermophysical properties of non-reactive flows. Also , it is possible to characterize chemical reactions in terms of enthalpy and kinetics . Finally the latter characterization was compared to conventional techniques to demonstrate the benefits and the precision of the tool.; Ce travail porte sur le développement d’une technique de calorimétrie sans contact pour des écoulements diphasiques. Ces derniers sont réalisés sur la forme d’un train gouttes dans des tubes de taille millimétriques dans des supports isopériboliques. L’idée principale est de coupler la Thermographie Infrarouge et les outils microfluidiques pour proposer une technique adapté de mesure. L’utilisation de la microfluidique rend possible l’utilisation de très faibles volumes réactionnels limitant ainsi tout risque lié à la dangerosité des réactions réalisées au sein des gouttes, l’outil Infrarouge permet de suivre ces écoulements avec grande précision. Les résultats de ces travaux de thèse montrent que l’outil est capable d’estimer des propriétés thermo-physiques des écoulements non réactifs. Ainsi, que de caractériser de réactions chimiques en termes d’enthalpie et cinétique. Finalement cette dernière caractérisation a été comparée aux techniques classiques pour mettre en évidence la précision et les avantages de l’outil développé

International audience; A new methodology has been developed to characterize the loss of efficiency of heat exchangers due to a maldistribution of the two-phase flow. The approach consists to measure the distribution of the local heat transfer coefficients with a non-intrusive and fast measurement method, based on a periodic excitation by Joule effect and infrared thermography measurement. An analytical model of the heat transfer is used to deduce heat transfer coefficients from the amplitude of the outside tube temperature fluctuations amplitude and heat flux measurement. This method, initially developed for a cylindrical tube, has been also applied on various tube shapes, including microchannel flat tubes. As an example, the method is used to evaluate the heterogeneity of distribution of an air-water mixture in a compact heat exchanger composed of seven multiport flat tubes. The distribution of heat transfer coefficients was studied for a vertical downward header and horizontal channels and for mass flux from 29 kg.m-2.s-1 to 116 kg.m-2.s-1 and for quality from 0.10 to 0.70. Results are presented and discussed.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEE; International audience; A methodology has been developed based on periodic excitation by Joule effect and infrared thermography measurement. It has been applied to measure heat transfer coefficients of water flowing in a round tube and in a multiport-flat tube. Models were developed to deduce heat transfer coefficient from wall temperature amplitude and heat flux measurement. For the round tube and for the multiport flat tubes, Reynolds number investigated ranges respectively from 2000 to 14000 and from 800 to 10000 and heat flux from 5 W to 29 W and from 10 W to 70 W. The good agreement between experimental and theoretical results has demonstrated the reliability of the methodology. This methodology also present the advantage to require a low heat flux, is not intrusive and fluid independant.

Des analyses par thermographie pulsée conduites sur des données expérimentales et simulées sont présentées. Ces méthodes sont appliquées à des données issues d'une caméra infrarouge non refroidie équipée d'un détecteur matriciel à microbolomètres (de moindre sensibilité thermique que les caméras refroidies). Les données font l'objet de calculs pour déterminer la profondeur des défauts en s'appuyant sur l'hypothèse du milieu semi-infini. Enfin, une discussion sur l'influence des performances de ce type de caméra sur la détection potentielle de défauts non émergents est proposée vis-à-vis du domaine des matériaux de structure de chaussées.

Strengthening or retrofitting of reinforced concrete structures by externally bonded fiber-reinforced polymer (FRP) systems is now a commonly accepted and widespread technique. The use of bonding techniques, however, always requires following rigorous installation procedures. Conformance checking through an in-place auscultation of the bonded FRP systems is highly recommended. The quality control program should involve a set of appropriate inspections and tests. Because it's rapid and efficient and can be readily used in the field, active infrared thermography shows promise as a nondestructive inspection technique that can be used as a quality control check during installation.

We present a method for detection and characterization of defects (delaminations or adhesive disbonds) that can take place at the interface between the concrete substrate and the bonded FRP. This method consists in a preliminary heating of the surface to be inspected, and in the use of infrared thermography. Detection of disbonds between different layers is also possible. Theoretical and experimental analyses of adhesive disbonds are presented in this paper. The performance of the method is firstly demonstrated using laboratory specimens with calibrated defects. In the inspected samples ; debonded areas were simulated by locally replacing the epoxy resin by non-adherent polytetrafluoroethylene (PTFE) discs at the concrete-to-FRP interface or between different layers of FRP. Comparison of theoretical and experimental results have confirmed the feasibility of this technique for in situ inspection. The transfer of this innovative method into the field application was accomplished during the control of the CFRP strengthening of the Toutry viaduct. Inspection methods are described and results of IR imaging showing air voids between multiple plies or between the FRP system and concrete are presented. This results clearly demonstrate the efficiency of the innovative method.

In this dissertation, we have developed the necessary basis for the characterization of the RF output of a gyrotron. The characterization includes the phase reconstruction and Gaussian beam mode decomposition. In order to analyze the phase reconstruction in detail, we have developed an accurate field propagation method using the complete Rayleigh-Sommerfeld scalar diffraction integral (RSDI) and the Huygens-Fresnel diffraction integral (HFDI), using a fast Fourier Transform (FFT) based approach. The discretization of the two diffraction integrals is analyzed analytically and numerically. In the case of the HFDI, a condition on the distance of propagation, where aliasing and replication are completely removed, is found. It relates the distance of propagation Δz, the number of sampling points M, the grid cell size Δx and the wavelength λ as: Δz = M(Δx)2 · 1/λ. The two formalisms are also studied using a zero-padding technique, which can be used to propagate the field to any arbitrary distance. These propagation methods are then used in the Iterative Phase Retrieval Algorithm (IPRA) for phase reconstruction. The effects of several parameters on the IPRA (the number of planes, the measurement plane size, the distance of propagation, the number of sampling points and the grid cell size, the misalignment along the optical axis, etc.) are then analyzed. For the theoretical field profiles used in this dissertation, the misalignment along the optical axis in the form of a transverse shift affects the IPRA most severely. The experimental procedure to measure the beam intensity patterns using infrared (IR) thermography is explored extensively. Out of the many target materials used, Robax is the most appropriate in terms of dynamic range, temperature linearity and for the possibility to perform measurements from the front side and the back side. Further, infrared image data processing is investigated for intensity pattern enhancement. This includes various steps: Fixed Pattern Noise (FPN) correction by subtracting the background image of the target taken before the microwave irradiation, defective pixels correction, perspective correction, image pattern enhancement by filtering and denoising. Further, the intermodal decomposition of the reconstructed phase and amplitude is analyzed in detail using two methods, in order to extract the Gaussian content: Finding a set of Gaussian beam parameters and a mode content matrix which maximizes the power in the fundamental mode |C00|2. This method is commonly used by the gyrotron tube developers. Finding a set of Gaussian beam parameters and a mode content matrix which minimizes the error between the corresponding reconstructed field and the input (theoretical and/or experimental) field. It is found that, the two methods may give significantly different results. As a general rule, the second method gives more precise and more reliable results, but the solution is unfortunately not unique and depends both on the measured profile and the measurement parameters. Therefore, the concept of Gaussian content adopted by the community seems to be incomplete, and the corresponding optimized parameters should be associated to it. The definition of Gaussian content should then be reexamined, and completed by an analysis of the power coupling coefficient of the microwave beam to the transmission line (corrugated waveguide or a quasi-optical line).

This summary presents two complementary techniques, Shearography and Active Infrared Thermography, used to detect and characterize depth and width of defects (delaminations or adhesive disbonds) that can take place at the interface between the concrete substrate and the bonded FRP used for the reinforcement of concrete structures. Shearography associated to a depressure solicitation on the one hand, and step heating infrared thermography on the other hand are presented. Performances of these methods are demonstrated using data from experimental inspection of specimens containing calibrated defects. Typically, debonded areas were simulated by locally replacing the epoxy resin with non-adherent polytetrafluoroethylene (PTFE) discs at the concrete-to-FRP interface.

Welding of wood is a well-known joining procedure that offers several advantages over traditional mechanical fasteners or gluing. During welding, extensive solid-state transformation phases occur in the so-called melting zone and the heat-affected zone. The nature and the extension of such transformations are correlated to the energy input and thus to the heat generated during the process at the wood joint interface. In the present work the influence of the welding parameters and wood grain orientation on the temperature profile and distribution and final strength of welded connections was investigated. For this purpose, the characteristics of the joints were evaluated with both destructive and non-destructive techniques. Non-destructive evaluation was performed with infrared thermography, which allowed measurement of the maximal and average peak temperature, temperature profile and distribution, and rate of temperature increase. Thus, this technique can also be used to detect welding defects and to provide information on material modification during welding.

Edge Localised Mode (ELM)-induced heat loads, in particular divertor heat loads present one of the main challenges in adopting nuclear fusion as an industrial-scale energy source. At present, the type-I ELMy plasma regime is chosen as the most suitable operational scenario because of its energy confinement and steady-state capabilities, however, with the understanding that the enormous quasi-periodic heat loads deposited by the ELMs will need to be controlled in order to avoid intolerable damage to heat- bearing elements. At present, a detailed theoretical understanding, and in particular, a sufficiently reliable way of predicting ELM behaviour based on basic discharge parameters is missing. The fusion community has been expending a great deal of effort in order to improve this situation by gathering as much experimental data as possible from a range of different-sized tokamaks, in order to develop empirical scalings and refine theoretical models, with the ultimate aim of mitigating their destructive power below thresholds where they won’t affect continuous scientific exploitation of the reactors. This experimental thesis joins into this effort via the installation and commissioning of a fast infrared camera on TCV viewing the outer divertor. Near the end of the thesis, an effort of similar magnitude has been carried out with a camera on temporary loan from the MAST group, in order to image the inner divertor region as well. The cameras possess a sub-array recording capability, enabling acquisition frequencies up to 25 kHz. Both cameras were calibrated with the combination of a low- and high-temperature blackbody source with large and small radiation surfaces, respectively. By estimating the surface emissivity as 0.85 and employing a gray-body model, target surface temperatures could be inferred. The resulting images were processed to produce 1D poloidal temperature profiles serving as an input to the THEODOR (THermal Energy Onto DivertOR) 2D finite-element code, with the goal of calculating the heat fluxes impinging on plasma facing components. The VIR (Vertical InfraRed) outer divertor system images a flat, horizontal surface covered by relatively large tiles from a perpendicular viewing angle. Deposited layers, microscopic surface changes and very small dust particles cause the appearance of microscopic hot-spots in the field-of-view (FOV), leading to a substantial deviation from the assumed model of a single-temperature (the tile bulk graphite) gray body radiator. Near the middle of the thesis, nearly all tiles inside TCV have been removed for cleaning via sandblasting. With 3 of the tiles having been left untouched, this presented a good opportunity to contrast the behaviour of the cleaned and uncleaned (~12 years of operation) surfaces. It has been found that already after 10 days of operation, the temperature signal significantly exceeds what could be expected from a pure graphite surface. This, though increasing error bars of the final heat flux figures, is also beneficial in the sense that it serves as a signal amplifier – e.g. most observed ELM filaments near the main divertors carry very little energy, and were it not for this effect, they would not be visible at all. In contrast to the outer divertor, the inner divertor geometry is more complicated, as the tiles’ shape causes a gradual toroidal change in the magnetic field line attack angle from ~20 to 0 degrees, excluding toroidal averaging. Sequences recorded by this system also require a correction for mechanical vibrations, which, though also present for the vertical system, are much more pronounced, affecting the outcome of heat flux calculations to a great degree. Best results have been achieved with a method based on cross-correlations. Apart from eliminating the effects of the horizontal shaking, as the global vertical movement of the strike point leg on the target needed to be retained, the vertical shaking was either left uncorrected or parametrized in a way to remove the oscillations about the obtained vertical displacement trendline. In the process of calculating the heat flux from the temperature spatio-temporal evolution, the surfaces’ deviation from a one-temperature blackbody radiator manifests as an overshooting during transients, in both the positive and negative directions. This leads to the appearance of unphysical results (heat fluxes conducted outwards from the tiles, whilst plasma is still depositing heat on it). By introducing a simple boundary condition in THEODOR, a crude correction for this effect could be applied. The resulting tile deposited energies were cross-checked with rudimentary heat capacity calculations based on tile-installed thermocouples, yielding ~25% agreement. Two discharges, one in FWD-, the other in REV-B configuration, were selected for detailed analysis of ELM divertor heat loads. Both were heated by 3rd harmonic ECRH heating, the former exhibiting large- and the latter type-III ELMs. A dataset of various parameters such as maximum heat flux, profile width, total divertor deposited powers, ELM deposited energies and in-out power balance during and in between the ELMs, as well as the fraction of ELM energy recovered at the divertors, the rise-to-peak times and integral energy-to-peak was built up and evaluated in detail. The TCV outer divertor power loads dominate those of the inner under all circumstances – a finding that contradicts empirically established ELM characteristics from other tokamaks. The observed power imbalance is larger during the ELMs, and smaller in between. The ratio of ELM deposited energies at the inner- and outer divertors is 1:3, always in favour of the outer divertor. ELM profile broadening of a factor in the range ~1-2 has been found to occur consistently in both field directions, at both divertors. The total fraction of ELM energy recovered at the divertors (EIR/WELM) has been found to decrease with growing ELM size. The ELM pedestal energy fraction versus collisionality, the rise-to-peak time versus parallel convection time and integral rise-to- peak energy versus collisionality were compared to values from other tokamaks. With the exception of the ELM pedestal energy fraction of the “giant” ELMs in FWD-B discharge #38014, all values are in agreement with what would be extrapolated from other devices. In line with the target of predicting ELM heat loads, comparisons with 1D kinetic PIC simulations and the so-called free-streaming particle (FSP) approach (an analytical expression for the power density based on a relatively simple model) were performed. With the exception of the early rise phase, PIC simulations of type-III ELMs reproduce the experimental time evolution well. They give insight into finer details of ELM heat transport: a very fast electron heat pulse (carrying about 5% of total ELM energy), is followed by the main pulse on a slower time-scale. About 3⁄4 of the total energy is carried by the ions, of which 0.3-0.4 is deposited in the rise phase. The FSP expression, based on a collisionless approximation, provides a reasonable fit to the temporal evolution of divertor-deposited power for TCV ELMs of various sizes. In most cases, both the rise- and decay phases can be described by the single time parameter within the expression. This parameter is at least twice as large as the parallel transport time based on pedestal parameters, implying a delaying of particles near the X-point region. In contrast to other tokamaks, filamentary ELM heat deposition patterns are only occasionally recorded at the outer divertor. The observed spatial structure is consistent with a plasma release at discrete toroidal locations in the outer midplane vicinity, but as very few are visible on the IR (when compared to the Langmuir probes), the determination of quasi-mode numbers was deemed unfeasible. A crude estimation of the energy content of individual filament spirals yielded 1% of the total ELM energy in each, consistent with existing non-divertor ELM heat load predictions. Finally, a new divertor configuration, the snowflake, was recently demonstrated in TCV experimentally, and, subsequently, the creation of H-modes in it. This configuration presents many advantages, most prominently the possibility of distributing the divertor heat load to 4 (as opposed to 2 for standard single-null divertors) regions. Infrared measurements at one of these additional legs have confirmed substantial heat loading and a lack of ELM profile broadening.