Le contrôle non destructif (CND) a pour but de détecter et de caractériser d’éventuels défauts présents dans des pièces mécaniques. Les techniques ultrasonores actuelles utilisent des capteurs multiéléments associés à des chaînes d’instrumentations et d’acquisitions de données multi capteurs en parallèles. Compte tenu de la masse de données à traiter, l’analyse de ces dernières est généralement effectuée hors ligne. Des travaux en cours, au Commissariat à l’Energie Atomique (CEA), consistent à développer et évaluer différentes méthodes d’imageries avancées, basées sur la focalisation synthétique. Les algorithmes de calculs induits nécessitent d’importantes opérations itératives sur un grand volume de données, issues d’acquisition multiéléments. Ceci implique des temps de calculs important, imposant un traitement en différé. Les contraintes industrielles de caractérisation de pièces mécaniques in situ imposent de réaliser la reconstruction d’images lors de la mesure et en temps réel. Ceci implique d’embarquer dans l’appareil de mesure, toute l’architecture de calcul sur les données acquises des capteurs. Le travail de thèse a donc consisté à étudier une famille d’algorithmes de focalisation synthétique pour une implantation temps réel sur un instrument de mesure permettant de réaliser l’acquisition de données. Nous avons également étudié une architecture dédiée à la reconstruction d’images par la méthode de Focalisation en Tout Point (FTP). Ce travail a été réalisé dans le cadre d’une collaboration avec l’équipe ACCIS de l’institut d’Electronique Fondamentale, Université de Paris Sud. Pour ce faire, notre démarche s’est inspirée de la thématique de recherche d’Adéquation Algorithme Architecture (A3). Notre méthodologie, est basée sur une approche expérimentale consistant dans un premier temps en une décomposition de l’algorithme étudié en un ensemble de blocs fonctionnels (calculs/transferts). Cela nous a permis de réaliser l’extraction des blocs pertinents de calculs à paralléliser et qui ont une incidence majeure sur les temps de traitement. Nous avons orienté notre stratégie de développement vers une conception flot de donnée. Ce type de modélisation permet de favoriser les flux de données et de réduire les flux de contrôles au sein de l’architecture matérielle. Cette dernière repose sur une plateforme multi-FPGA. La conception et l’évaluation de telles architectures ne peuvent se faire sans la mise en place d’outils logiciels d’aide à la validation tout au long du processus de la conception à l’implantation. Ces outils faisant partie intégrante de notre méthodologie. Les modèles architecturaux des briques de calculs ont été validés au niveau fonctionnel puis expérimental, grâce à la chaîne d’outils développée. Cela inclus un environnement de simulation nous permettant de valider sur tables les briques partielles de calculs ainsi que le contrôle associé. Enfin, cela a nécessité la conception d’outils de génération automatique de vecteurs de tests, à partir de données de synthèses (issues de l’outil simulation CIVA développé par le CEA) et de données expérimentales (à partir de l’appareil d’acquisition de la société M2M-NDT). Enfin, l’architecture développée au cours de ce travail de thèse permet la reconstruction d’images d’une résolution de 128x128 pixels, à plus de 10 images/sec. Ceci est suffisant pour le diagnostic de pièces mécaniques en temps réel. L’augmentation du nombre d’éléments capteurs ultrasonores (128 éléments) permet des configurations topologiques plus évoluées (sous forme d’une matrice 2D), ouvrant ainsi des perspectives vers la reconstruction 3D (d’un volume d’une pièce). Ce travail s’est soldé par une mise en œuvre validée sur l’instrument de mesure développé par la société M2M-NDT. / Non-destructive Evaluation (NDE) regroups a set of methods used to detect and characterize potential defects in mechanical parts. Current techniques uses ultrasonic phased array sensors associated with instrumentation channels and multi-sensor data acquisition in parallel. Given the amount of data to be processed, the analysis of the latter is usually done offline. Ongoing work at the French “Commissariat à l’Energie Atomique” (CEA), consist to develop and evaluate different methods of advanced imaging based on synthetic focusing. The Algorithms induced require extensive iterative operations on a large volume of data from phased array acquisition. This involves important time for calculations and implies offline processing. However, the industrial constraint requires performing image reconstruction in real time. This involves the implementation in the measuring device, the entire computing architecture on acquired sensor data. The thesis has been to study a synthetic focusing algorithm for a real-time implementation in a measuring instrument used to perform ultrasonic data acquisition. We especially studied an image reconstruction algorithm called Total Focusing Method (TFM). This work was conducted as part of collaboration with the French Institute of Fundamental Electronics Institute team of the University of Paris Sud. To do this, our approach is inspired by research theme called Algorithm Architecture Adequation (A3). Our methodology is based on an experimental approach in the first instance by a decomposition of the studied algorithm as a set of functional blocks. This allowed us to perform the extraction of the relevant blocks to parallelize computations that have a major impact on the processing time. We focused our development strategy to design a stream of data. This type of modeling can facilitate the flow of data and reduce the flow of control within the hardware architecture. This is based on a multi- FPGA platform. The design and evaluation of such architectures cannot be done without the introduction of software tools to aid in the validation throughout the process from design to implementation. These tools are an integral part of our methodology. Architectural models bricks calculations were validated functional and experimental level, thanks to the tool chain developed. This includes a simulation environment allows us to validate partial calculation blocks and the control associated. Finally, it required the design of tools for automatic generation of test vectors, from data summaries (from CIVA simulation tool developed by CEA) and experimental data (from the device to acquisition of M2M –NDT society). Finally, the architecture developed in this work allows the reconstruction of images with a resolution of 128x128 pixels at more than 10 frames / sec. This is sufficient for the diagnosis of mechanical parts in real time. The increase of ultrasonic sensor elements (128 elements) allows more advanced topological configurations (as a 2D matrix) and providing opportunities to 3D reconstruction (volume of a room). This work has resulted in implementation of validated measurement instrument developed by M2M -NDT.

The purpose of this thesis is non-destructive determination of residual stress state in the multi-pass welded steel plates by Magnetic Barkhausen Noise (MBN) technique. To control the effectiveness of the developed procedure, continuous MBN measurements on the heat affected zone and parent metal of the welded plates were performed. In the experimental part, various steel plates were welded with different number of weld passes. Various series of samples were prepared for residual stress and for angular deflection measurements. Microstructural investigation and hardness measurements were also conducted. The results were discussed to evaluate the effectiveness of MBN measurements to monitor the changes in the residual stress state in the welded components as a function of weld pass number.

The objective of this thesis is to design and implement a rapid, reconfigurable and portable reader for wirelessly interrogating inductively coupled passive sensors. While the current method of impedance analyzer is sensitive and an accurate, the instruments used are bulky and slow, substantially hampering in-field testing and interrogation of sensors. Current methods cannot provide a quantifiable measure on minimum necessary read-speeds and instrument accuracy desirable for rapid sensing applications. This work summarizes the design and hardware implementation of two reader methods that address the aforementioned requirements. Both reader methods are based on a reflectometer approach: Swept-frequency Reflectometer Reader and Switched-frequency Interrogation Technique (SWIFT). The first method is a much faster alternative to in-lab and in-field testing for structural health monitoring, and is intended as an immediate replacement for the impedance analyzer method. Switched-frequency Interrogation is specifically designed to satisfy the need for rapid and accurate reading, potentially for in-motion sensing applications. This method provides a way of empirically relating minimum necessary read-time required for desired read-ranges. It also facilitates quantification of uncertainty in measurements, which is very critical in determining instrument accuracy in-field. The system design and implementation of both methods are described in detail and experimental results are presented to benchmark the performance of the readers. Issues of instrument reliability and practical limitations are also discussed, with potential solutions. Both methods are intended as universal techniques for wirelessly interrogating coupled passive sensors, not limited to their current form of implementation. / text

In this thesis, several aspects of GPR data processing for RC bridge decks are studied. First, autofocusing techniques are proposed to replace the previous expensive and unreliable human visual inspections during the iterative migration process for the estimation of the velocity/dielectric permittivity distribution from GPR data. Second, F-K filtering with dip relaxation is proposed for interference removal that is important for both imaging and the performance of post-processing techniques including autofocusing techniques and CS-based migration studied in this thesis. The targeted interferes here are direct waves and cross rebar reflections. The introduced dip relaxation is for accommodating surface roughness and medium inhomogeneity. Third, the newly developed CS-based migration is modified and evaluated on GPR data from RC bridge decks. A more accurate model by accounting for impulse waveform distortion that leads to less modeling errors is proposed. The impact of the selection of the regularization parameter on the comparative amplitude reservation and the imaging performance is also investigated, and an approach to preserve the comparative amplitude information while still maintaining a clear image is proposed. Moreover, the potential of initially sampling the time-spatial data with uniform sampling rates lower than that required by traditional migration methods is evaluated.

Les exigences de qualité des produits ainsi que des normes environnementales et énergétiques de plus en plus drastiques nécessitent le développement de technologies de fonctionnalisation de surface en particulier celles qui s’appuient sur les procédés de revêtement par dépôt de couches minces. Le contrôle de la qualité de surface revêtue présente un enjeu industriel d’envergure. En effet, il n’existe pas à l’heure actuelle de technique d’inspection non destructive qui allie à la fois rapidité, fiabilité et flexibilité pour le contrôle de l’uniformité de revêtement. Pour répondre à cette problématique, ce travail de thèse porte sur le développement d’une technique d’inspection basée sur la thermographie active. Après étude expérimentale et numérique de la réponse thermique de surfaces bicouches, nous proposons une première méthodologie d’exploitation des mesures issues d’une excitation ponctuelle (laser) et surfacique (flash(s)). L’approche mise en place s’appuie sur l’implantation d’un algorithme des moindres carrés partiels (PLS NIPALS). Celui-ci a été testé sur plusieurs matériaux conducteurs et non conducteurs et dans différentes configurations expérimentales puis comparé à la méthode de contrôle conventionnelle par courants de Foucault (pour les matériaux conducteurs). La méthode développée permet d’extraire la signature thermique intrinsèque de l’hétérogénéité d’épaisseur du revêtement. Une deuxième approche a été explorée, elle s’appuie sur la mise en œuvre des nouveaux outils que nous offre le « Deep Learning ». Les premiers résultats obtenus semblent prometteurs. L’ensemble des résultats ouvre le champ vers une exploitation industrielle de la thermographie infrarouge pour le contrôle non destructif de revêtement. / Product quality requirements as well as increasingly drastic environmental and energy standards require the development of surface functionalization technologies, particularly those based on thin film coating processes. The quality control of coated surface presents an important industrial challenge. Indeed, actually there is any non-destructive inspection technique that combines speed, reliability and flexibility for coating uniformity inspection. To respond this challenge, this work focuses on the development of an inspection technique based on active thermography. After experimental and numerical studies of thermal responses of bilayer surfaces, we propose firstly a measurement methodology based on a point (laser) and surface excitation (flash (s)). The approach is based on the implementation of a partial least squares algorithm (PLS-NIPALS). It was tested on several conductive and non-conductive materials and in various experimental configurations and compared to the conventional eddy current control method (for conductive materials). The developed method makes it possible to extract the intrinsic thermal signature of the coating thickness heterogeneity. A second approach has been explored, based on the classification algorithm based on Deep Learning tool. The first results seem promising. The overall results open the opportunity to an industrial exploitation of infrared thermography for non-destructive coating testing.

This study develops a reliable intelligent non-destructive evaluation (NDE) expert system for carbon-carbon (C/C) composites based on thermography, ultrasonic, computed tomography and post processing by means of fuzzy expert system technique. Data features and NDE expert knowledge are seamlessly combined in the intelligent system to provide the best possible diagnosis of the potential defects and problems. As a result, this research help ensure C/C composites' integrity and reliability. Four types of orthotropic aerospace composite material groups, which include 2-D pitched based commercial aircraft disc brakes and asmolds, 3-D PAN based C/C composites, and carbon fiber reinforced plastic (CFRP) panels, were tested. Based on the performance testing results of thermography, air-coupled ultrasonic, and x-ray computed tomography, the testing data pattern corresponding to feature and quantification of defects were found. This NDE knowledge databases were transformed to fuzzy logic expert system models. The models succeefully classified and indicated the defect's size and distribution and the intelligent systems perform NDE better than human operators. These fuzzy expert systems not only eliminate human errors in defect detection but also function as NDE experts. In addition, fuzzy expert systems improve the defect detection by incorporating fuzzy expert rules to remove noises and to measure defect size more accurately. In the future, the expert system model could be continuously updated and modified to quantify the size and distribution of defects. The systems developed here can be adapted and applied to build an intelligent NDE expert system for better quality control as well as automatic defect and porosity detection in C/C composite production process.

Cette étude s’inscrit dans le cadre de l’inspection en service des soudures des réacteurs nucléaires de génération IV, en vue de contribuer à la démonstration de sûreté. La structure anisotrope et hétérogène des soudures multipasses en acier inoxydable austénitique rend leur contrôle ultrasonore difficile. Ainsi, afin d'interpréter correctement les signaux mesurés et de caractériser les défauts potentiels, une description de la soudure est utilisée. Elle constitue la connaissance a priori introduite dans la méthode de l'Energie Topologique. L’étude réalisée se décline en deux temps : le développement de la méthode en milieu borné et sa comparaison avec le Matched Field Processing, puis son application au cas de soudures réelles. L'extension de la méthode de l'Energie Topologique aux milieux bornés isotropes et homogènes vise à tirer parti des réflexions multiples. Plusieurs solutions du problème numérique de propagation, obtenues pour différentes conditions aux frontières, sont judicieusement associées afin de sélectionner les échos de diffraction porteurs d'information. Selon le type de défaut à imager des énergies topologiques spécifiques sont définies. La technique est introduite analytiquement avant d'être validée numériquement puis expérimentalement.Dans un second temps, la méthode est appliquée au milieu complexe de la soudure. La procédure est testée expérimentalement sur des soudures réelles afin d'évaluer les performances en localisation. Cependant, en raison de la variabilité de la structure, la qualité de l'image peut se dégrader selon les cas d'étude. La possibilité de générer des sources arbitraires permet de pallier en grande partie cette difficulté. / The present study has been done as part of the in-service inspection of weld structure belonging to generation IV nuclear reactors. It aims at checking both the safety and integrity of these components. The anisotropic and heterogeneous structure of austenitic stainless steel welds disturbs the ultrasonic non destructive testing. Thus, a weld description model is necessary to properly analyze the ultrasonic measured signals and to characterize potential flaws. The weld model makes a priori knowledge up in the Topological Energy method. The study is divided into two parts: development of the method in a bounded medium and comparison with the Matched Field Processing method, and then its application to real weld structures.The work firstly focuses on expanding the Topological Energy method to isotropic and homogeneous bounded medium to take advantage of multiple reflections between the flaw and edges. For that, different conditions are numerically applied to boundaries. By adding up these conditions it becomes possible to select the appropriate scattering signal. Modified topological energies are defined according to the type of analyzed flaws. The approach is analytically demonstrated before being validated firstly from synthetical data and then from experimental data.The second part deals with the application of the method to the complex weld structure. The process is experimentally tested on welds in order to evaluate efficiency of flaws localization. However, the image's quality can be deteriorated because of variability of the structure. By generating arbitrary ultrasonic source this difficulty is mostly overcame.

Structural Health Monitoring (SHM) techniques are widely used in a number of Non – destructive Evaluation (NDE) applications. There is a need to develop effective techniques for SHM, so that the safety and integrity of the structures can be improved. Two most widely used SHM methods for plates and rods use either the spectrum of the impedances or monitor the propagation of lamb waves. Piezoelectric wafer – active sensors (PWAS) were used for excitation and sensing. In this study, surface response to excitation (SuRE) and Lamb wave propagation was monitored to estimate the integrity of the round objects including the pipes, tubes and cutting tools. SuRE obtained the frequency response by applying sweep sine wave to surface. The envelope of the received signal was used to detect the arrival of lamb waves to the sensor. Both approaches detect the structural defects of the pipes and tubes and the wear of the cutting tool.

The use of ultrasound contrast agents increases the information available for reconstruction during ultrasound imaging. Previously studied microbubbles, consisting of a gas core, are subject to limitations such as a short lifetime and a large size. Droplets with a liquid perfluorocarbon core that is stabilized by cellulose nanofibers eliminate these drawbacks, but require further investigation. By studying the frequency-dependent attenuation profile of the cellulose nanofiber coated perfluorocarbon droplets within an ultrasound field, information about the droplets as oscillators can be retrieved, enabling characterization of their physical properties. In this study, the frequency-dependent attenuation profile was experimentally acquired and compared between two concentrations, using flat transducers covering the frequency range of 1-15 MHz. The data collected in the time domain was processed and transformed into the frequency domain and the attenuation was calculated across the entire frequency range. Among the frequencies studied, the attenuation increases with frequency and covers the range of approximately 0.25-8.3 dB/cm and 0.01-3.3 dB/cm at the concentrations of 50 million droplets/ml and 10 million droplets/ml respectively. The attenuation reaches a minimum at 3 MHz within the highest concentration, compared to 4.43 MHz within the lowest. The increase of the attenuation with frequency is explained by the droplets not exhibiting large oscillations within the range covered. It is probable that the droplets do exhibit oscillations, due to a viscosity lower than that of water, but a resonance frequency is not found within the spectrum studied. This could be explained by a shell elasticity or a small droplet radius placing the resonance frequency outside of the spectrum studied, or high levels of damping broadening the resonance peak. Localizing the resonance frequency would enable characterization of these physical properties of the cellulose nanofiber shell as well as the perfluorocarbon liquid core of the droplets. The increase of the attenuation with frequency demonstrates that the droplets do not produce a maximized amount of scattering at a specific frequency within the range studied, which is observed among other oscillating particles implemented as ultrasound contrast agents. The attenuation is, however, larger than that of blood across all frequencies except for those among which the attenuation reaches its minimum. Potential errors that are affecting the results include droplet vaporization, the formation of flocs after the mechanical agitation has ceased, the experimental setup, the settings on the pulse generator, the sensitivity of the transducers and the processing code.

Today, microbubbles are one of the most commonly used ultrasound contrast agents, since their high compressibility results in a strongly scattered signal. Despite this advantage, microbubbles experience limitations by the decreased stability and large diameter. The cellulose nanofiber (CNF) stabilized perfluoropentane (PFC5) droplets have the possibility of eliminating these drawbacks. In order to examine the droplet behavior and scattering ability when exposed to ultrasound, the acoustic response of the droplets is studied and compared with that of microbubbles (MBs). Therefore, this thesis aims to design an experimental set-up and a processing method to determine the phase velocity, bulk modulus and compressibility of the CNF-coated PFC5 droplets. The experimental study of the acoustic characterization uses pulse-echo spectroscopy with an aluminum reflector and seven flat transducers covering the frequency range 0.7 to 14.1 MHz. By using fast Fourier transform, while accounting for the 2πn ambiguity, the phase velocity profiles are obtained. The dispersions within this frequency spectrum are 1391-1487 m/s and 1387-1488 m/s for the concentrations 10 ∙ 106 and 50 ∙ 106 droplets/ml, respectively. These profiles display an increasing phase velocity with frequency and a slight increase in dispersion with concentration. These results agree with theory and studies examining the phase velocity of MBs. The bulk modulus presents values between 3-4 GPa, while the compressibility is 2.7 − 3.2 ∙ 10-10 𝑃𝑎-1 within the frequency range studied. Compared to water and certain MBs, both possessing a lower bulk modulus, the droplets are less compressible. To conclude, the droplets have similar phase velocity profiles with the same dependencies on frequency and concentration as MBs, resulting in similar behavior of these droplets when exposed to ultrasound. Hence, affecting the wave similarly to MBs in terms of spreading. The droplet are, however, not as compressible. This most likely affects their oscillation and they, hence, might not have equally beneficial scattering ability. This could reduce their utilization as contrast agents. Some of the potential error sources present during the laboratory work and the development of the post-processing code were not achieving perfect optimization of the transducer alignment, vaporization of the droplets resulting in reduced concentration, possible diffraction, not optimal processing of data and inadequate correction for 2πn ambiguity.