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Deterioration of bridge decks is an ongoing problem faced by transportation agencies across the country. In past decades, Non-Destructive Evaluation (NDE) techniques, capable of detecting various deteriorations types, e.g., cracking, delamination and reinforcing steel corrosion, have emerged. These techniques generate large amounts of data representing different underlying physics, (decibels for ground penetrating radar and volts for half-cell potential), making data interpretation and comparison difficult for bridge owners and practitioners. The deterioration threshold, or the transition between healthy and deteriorated areas, is essential in understanding NDE data. However, this threshold is determined empirically in former research and engineering practice. In the present research, a probability-based method is proposed to identify deterioration thresholds for specified confidence levels. NDE data measuring different underlying physics are transformed into a binary format by threshold values to compare and combine multiple NDE techniques for bridge deck assessment. The finite element method is also implemented to correlate bridge deck surface stresses with deteriorations measured by NDE techniques, and to study the causes on concrete bridge deck degradation. The general methodology developed in this study will be demonstrated on three bridges, i.e., Virginia, New Jersey and New York Pilot Bridges, which were studied under Federal Highway Administration (FHWA)'s Long-Term Bridge Performance (LTBP) Program. / Ph. D.

A sample of aberrant self-promoters (ASPs) was identified through their pattern of answers on a 179-item questionnaire. A group of comparison participants who did not exhibit the ASP pattern was also identified. The participants viewed a videotape of a lecture and rated the lecturer's performance. Half of the participants were told that they were required to provide face-to-face feedback to the lecturer (the accountability condition); the other half were not given these instructions (non-accountability condition). Also, half of the participants were told that there may be an opportunity for them to appear on a training video for graduate student instructors (opportunity for personal recognition condition); the other half were not told of this opportunity (no opportunity condition). This study attempted to identify the roles of aberrant self-promotion, accountability, and opportunity for personal recognition in rater accuracy and rater leniency. / Master of Science

Regenerative medicine involves formation of tissue or organ for replacement of a wounded or dysfunctional tissue. Healthy cells extracted from the patient are expanded and are seeded on a three-dimensional biodegradable scaffold. The structure is then placed in a bioreactor and is provided with nutrients for the cells, which proliferate and migrate throughout the scaffold to eventually form a desired to tissue that can be transplanted into the patient's body.  Inability to monitor this complex process of regeneration in real-time makes control and optimization of this process extremely difficult. Histology, the gold standard used for tissue structural assessment, is a static technique that only provides "snapshots" of the progress and requires the specimen to be sacrificed. This inefficiency severely limits our understanding of the biological processes associated with tissue growth during the in vitro pre-conditioning phase. Optical Coherence Tomography (OCT) enables imaging of cross sectional structure in biological tissues by measuring the echo time delay of backreflected light. OCT has recently emerged as an important method to assess the structures of physiological, pathological as well as tissue engineered blood vessels. The goal of the present study is to develop an imaging system for non-destructive monitoring of blood vessels maturing within a bioreactor. Non-destructive structural imaging of tissue-engineered blood vessels cultured in a novel bioreactor was performed using free-space and catheter-based OCT imaging, while monitoring of the endothelium development was performed using a fluorescence imaging system that utilizes a commercial OCT catheter. The project included execution of three specific aims. Firstly, we developed OCT instrumentation to determine geometrical and optical properties of porcine and human skin in real-time. The purpose of the second aim was to assess structural development of tissue-engineered blood vessels maturing in a bioreactor. We constructed a novel quartz-based bioreactor that will permit free space and catheter-based OCT imaging of vascular grafts. The grafts were made of biodegradable PCL-collagen and seeded with multipotent mesenchymal cells. We imaged the maturing grafts over 30 days to assess changes in graft wall thickness. We also monitored change in optical properties of the grafts based on free-space OCT scanning.   Finally, in order to visualize the proliferation of endothelial cells and development of the endothelium, we developed an imaging system that utilizes a commercial OCT catheter for single-cell-level imaging of the growing endothelium of a tissue-engineered blood vessel. We have developed two modules of an imaging system for non-destructive monitoring of maturing bioengineered vascular grafts. The first module provides the ability to non-destructively examine the structure of the grafts while the second module can track the progress of endothelialization. As both modules use the same endoscope for imaging, when operated in sequence, they will produce high-resolution, three-dimensional, structural details of the graft and two-dimensional spatial distribution of ECs on the lumen. This non-destructive, multi-modality imaging can be potentially used to monitor and assess the development of luminal bioengineered constructs such as colon or trachea. / Ph. D.

Since the MINER Act of 2006, the minimum static load of in-situ underground mine seals has been increased from 20-psi to either 50-psi if monitoring is conducted or 120-psi if left unmonitored. These minimum strength requirements in seals must be designed, built, and maintained throughout the lifetime of the seal. Due to this, it has become necessary to assess the effectiveness of non-destructive testing (NDT) technologies to determine seal integrity, which in this case, are explored using sonic waves and tracer gases. Through both small and large scale testing, two NDT methods were evaluated on their abilities to determine integrity of the seal. A sonic wave technique to observe a change in wave velocity to identify faults within the seal material. As a NDT method, tracer gases may be used as a potential indicator of a connection between both sides of the seal material through a series of faults and cracks within the material itself. This paper reviews the history of underground mine seals and discusses the overall assessment of sonic waves and tracer gases to serve as NDT methods for estimating the integrity of these seals. / Master of Science

Tesis por compendio / La industria alimentaria, concretamente el sector poscosecha, necesita innovar en sus procesos productivos, optimizando los mismos para rentabilizar sus actividades, garantizando productos de calidad capaces de satisfacer las necesidades de los consumidores. La presente tesis doctoral se centra en evaluar el potencial de la espectroscopia VIS-NIR para la caracterización e inspección de la calidad de la fruta tanto fuera de línea como a tiempo real en procesos automatizados. En un primer lugar, la viabilidad de la técnica se estudió a nivel de laboratorio en estado estático (off-line), con el fin de conocer y optimizar las condiciones de medición. Posteriormente, se evaluó la calidad interna y externa de diferentes tipos de frutas como son caqui, nectarina y mango. En una segunda etapa, se llevó a cabo una automatización de los procesos de inspección mediante el desarrollo de nuevos prototipos in-line. Para este propósito, y con el objetivo de completar y corroborar los resultados obtenidos de manera estática, se estudió la integración de dos sondas VIS-NIR en una garra robótica capaz de manipular mangos. Finalmente, se estudió la integración de una sonda VIS-NIR a una cinta transportadora. Los resultados obtenidos a nivel estático han demostrado que la espectroscopia VIS-NIR es un método no destructivo muy prometedor para predecir la astringencia en caqui. Así mismo, ha demostrado ser una adecuada herramienta para clasificar al 100% entre variedades de nectarinas como "Big Top" y "Diamond Ray" con una apariencia externa e interna muy similar, pero con diferentes propiedades organolépticas. De manera similar, fue posible clasificar al 100% variedades como "Big Top" y "Magique" de apariencia externa y composición similar pero distinto color de pulpa., y además se desarrolló un índice de calidad interna (IQI) para evaluar la calidad de las nectarinas. Por lo que respecta a los trabajos off-line realizados con mangos de la variedad "Osteen", fue posible predecir su calidad interna mediante los índices de madurez (RPI) y de calidad (IQI) con un gran rendimiento. A su vez, los ensayos experimentales efectuados con estos mismos mangos bajo la manipulación no destructiva de una garra robótica, demostraron que los mejores modelos eran capaces de predecir tanto la firmeza mecánica, el contenido en sólidos solubles, la luminosidad de la pulpa, así como el índice RPI de las muestras en base a la información obtenida por los acelerómetros instalados en los dedos de la garra robótica. En cuanto a los ensayos realizados de manera in-line, el primer prototipo desarrollado se basó en la integración de dos sondas VIS-NIR en una garra robótica dispuesta con dos acelerómetros. El sistema desarrollado permitió alcanzar una buena estimación de la calidad del mango a través del índice RPI fusionando la información tanto de los espectros VIS-NIR como del impacto no destructivo de los acelerómetros. De este modo quedó demostrado que era posible obtener una predicción similar trabajando de forma in-line como trabajando de manera off-line para la predicción del mismo índice de calidad en mangos. El segundo prototipo in-line desarrollado se basa en la integración de una sonda VIS-NIR en una cinta transportadora para la identificación de distintas variedades y orígenes de manzanas. El prototipo desarrollado permitió registrar resultados de clasificación tan buenos como los efectuados de manera off-line con, por ejemplo, nectarina. De este modo, se puede concluir que la espectroscopia VIS-NIR permite monitorear la calidad y clasificar fruta poscosecha tanto en modo off-line como in-line. Los nuevos prototipos desarrollados aportan claras ventajas respecto a los procesos tradicionales realizados a mano, como son la reducción del tiempo de inspección, la disminución de la cantidad de residuos generados y la posibilidad de inspeccionar toda la producción, obteniendo así un análisis más estandariz / The food industry, concretely the post-harvest sector, needs to innovate in their production processes, optimizing them to make their activities profitable, guaranteeing quality products capable of satisfying the needs of consumers. The present doctoral thesis focuses on evaluating the potential of visible and near infrared spectroscopy (VIS-NIR) for the characterization and inspection of fruit quality both off-line and in real time in automated processes. Firstly, the viability of the technique was studied at the laboratory level in a static mode (off-line), in order to know and optimise the measurement conditions. Subsequently, the internal and external quality of different types of fruits such as persimmon, nectarine and mango were evaluated. Secondly, an automation of the inspection processes was carried out through the development of new in-line prototypes. For this purpose, and with the aim of completing and corroborating the results obtained in a static mode, the integration of two VIS-NIR probes in a robotic gripper capable of manipulating mangoes was studied. Finally, the integration of a VIS-NIR probe to a conveyor belt was studied as an in-line monitoring tool on the inspection process of different apple varieties. The results obtained in static mode have shown that VIS-NIR spectroscopy is a very promising non-destructive method to predict the astringency in persimmon. Likewise, it has demonstrated to be an adequate tool to classify 100% between nectarine varieties such as 'Big Top' and 'Diamond Ray' with very similar external and internal appearance, but with different organoleptic properties. Similarly, it was possible to classify 100% varieties such as 'Big Top' and 'Magique' with external appearance and similar composition but different pulp colour. An internal quality index (IQI) was developed to evaluate the quality of nectarines, which can be predicted through VIS-NIR spectroscopy. Regarding the off-line work carried out with mangoes of 'Osteen' variety, it was possible to predict its internal quality through the indexes of maturity (RPI) and quality (IQI) with a high performance. Moreover, the experimental tests carried out with these same mangoes under the non-destructive manipulation of a robotic gripper, showed that the best models were able to predict both the mechanical firmness, the soluble solids content, the brightness of the pulp, as well as the RPI index of the samples based on the information obtained by the accelerometers installed on the fingers of the robotic gripper. Regarding the tests carried out in an in-line mode, the first developed prototype was based on the integration of two VIS-NIR probes in a robotic gripper fitted with two accelerometers. The developed system allowed reaching a good estimation of mango quality through the RPI index. In this way, it was demonstrated that it was possible to obtain a similar prediction working in-line as off-line mode for the prediction of the same quality index in mangoes. The second developed in-line prototype is based on the integration of a VIS-NIR probe in a conveyor belt for the identification of different varieties and origins of apples, achieving a success rate of 98% with the system. The developed prototype allowed to register classification results as good as those carried out off-line with, for example, nectarine. In this way, it can be concluded that VIS-NIR spectroscopy allows monitoring the quality and classifying post-harvest fruit in both off-line and in-line mode, being a tool that allows improving and guaranteeing the correct quality and food safety. The new developed prototypes provide clear advantages over the traditional processes performed by hand, such as the reduction of inspection time, the reduction of the amount of waste generated by destructive quality analysis and the possibility of inspecting full production, obtaining a more standardised analysis of the quality of the products. / La indústria alimentària, concretament el sector postcollita, necessita innovar en els seus processos productius, optimitzant els mateixos per a rendibilitzar les seues activitats, garantint productes de qualitat capaços de satisfer les necessitats dels consumidors. La present tesi doctoral es centra en avaluar el potencial de l'espectroscòpia visible i infraroig pròxim (VIS-NIR) per a la caracterització i la inspecció de la qualitat de la fruita tant fora de línia com a temps real en processos automatitzats. En un primer lloc, la viabilitat de la tècnica es va estudiar a nivell de laboratori en estat estàtic (off-line), a fi de conéixer i optimitzar les condicions de mesurament. Posteriorment, es va avaluar la qualitat interna i externa de diferents tipus de fruites com són caqui, nectarina i mango. En una segona etapa, es va dur a terme una automatització dels processos d'inspecció per mitjà del desenvolupament de nous prototips in-line. Per aquest propòsit, i amb l'objectiu de completar i corroborar els resultats obtinguts de manera estàtica, es va estudiar la integració de dos sondes VIS-NIR en una garra robòtica capaç de manipular. Finalment, es va estudiar la integració d'una sonda VIS-NIR a una cinta transportadora. Els resultats obtinguts a nivell estàtic han demostrat que l'espectroscòpia VIS-NIR és un mètode no destructiu molt prometedor per a predir l'astringència en caqui. Així mateix, ha demostrat ser una adequada ferramenta per a classificar al 100% entre varietats de nectarines com "Big Top" i "Diamond Ray" amb una aparença externa i interna molt semblant, però amb diferents propietats organolèptiques. De manera semblant, va ser possible classificar al 100% varietats com "Big Top" i "Magique" d'aparença externa i composició semblant però distint color de polpa. Es va desenvolupar un índex de qualitat interna (IQI) per avaluar la qualitat de les nectarines. Pel que fa als treballs off-line realitzats amb mangos de la varietat "Osteen" va ser possible predir la seua qualitat interna mitjançant els índexs de maduresa (RPI) i de qualitat (IQI) amb un gran rendiment. Al mateix temps, els assajos experimentals efectuats amb estos mateixos mangos baix la manipulació no destructiva d'una garra robòtica, van demostrar que els millors models eren capaços de predir tant la fermesa mecánica, el contingut en sòlids solubles, la lluminositat de la polpa, així com l'índex RPI de les mostres basant-se en l'informació obtinguda pels acceleròmetres instal¿lats en els dits de la garra robòtica. En quant als assajos realitzats de manera in-line, el primer prototip desenvolupat es va basar en la integració de dos sondes VIS-NIR en una garra robòtica disposada amb dos acceleròmetres. El sistema desenvolupat va permetre aconseguir una bona estimació de la qualitat del mango a través de l'índex RPI fusionant l'informació tant dels espectres VIS-NIR com de l'impacte no destructiu dels acceleròmetres. D'esta manera va quedar demostrat que era possible obtindre una predicció semblant treballant de forma in-line com off-line per a la predicció del mateix índex de qualitat en mangos. El segon prototip in-line desenvolupat es va basar en la integració d'una sonda VIS-NIR en una cinta transportadora per a l'identificació de distintes varietats i orígens de pomes. El prototip desenvolupat va permetre registrar resultats de classificació tan bons com els efectuats de manera off-line. D'aquesta manera, es pot concloure que l'espectroscòpia VIS-NIR permet monitorar la qualitat i classificar fruita postcollita tant en mode off-line com in-line. Els nous prototips desenvolupats aporten clars avantatges respecte als processos tradicionals realitzats a mà, com són la reducció del temps d'inspecció, la disminució de la quantitat de residus generats pels anàlisis destructives de qualitat i la possibilitat d'inspeccionar tota la producció, obtenint així un anàlisi més estandarditz / Cortés López, V. (2018). Innovations in non-destructive techniques for fruit quality control applied to manipulation and inspection lines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/110969 / Compendio

Due to the frequent use of plastics in daily life, encountering microplastics as pollution and trace evidence in forensic investigations is a common occurrence. Nylons are a plastic class known to be strong and durable, and they are used in a variety of products. Nylon is also a popular choice among 3D printing materials, and its strength and durability lend themselves to printing tools like keys and firearms. The analysis of microplastics is typically performed using any combination of microscopy, infrared spectroscopy, Raman spectroscopy, and mass spectrometry. Nylons are known to have fluorescent impurities created during the polymer’s synthesis and processing, so this work set out to develop a method to analyze nylon microplastics non-destructively using room-temperature fluorescence spectroscopy. By analyzing impurities in the sample, fluorescence spectroscopy can provide additional information about the microplastic’s source that other non-destructive methods do not. Excitation-emission matrices, excitation and emission spectra, and synchronous fluorescence spectra were collected from pellets of four different nylons. Using these spectra, all nylons could be distinguished from one another. A trace evidence simulation was then performed with fragmented pellets and a 3D printed key, and the trace microplastics were shown to have spectra that were consistent with those of the bulk plastic. This method was then improved by applying chemometric algorithms to the fluorescence data. Fluorescence spectra, excitation spectra, and excitation-emission matrices collected from Nylon 6 and Nylon 6/12 were found to be indistinguishable by visual comparison. Using synchronous fluorescence spectra from the two nylons in conjunction with Principal Component Analysis and Common Dimension – Partial Least Squares – Discriminant Analysis, the two nylons could be fully discriminated. Overall, this work presents a powerful new method to non-destructively analyze nylon microplastics and generate more reliable conclusions about the source of the microplastic than current methods alone.

X-ray computed tomography is a technique that has been successfully utilized to characterize internal microstructure of asphalt mixtures. The city of Linköping (Sweden) developed an action plan to reduce noise; accordingly KTH and VTI developed a method to determine air void content in porous asphalt using x-ray computed tomography and an image processing software called ImageJ. The present study is a continuation of the previously mentioned work and focuses on the investigation of aggregate structure in porous asphalt by x-ray computed tomography. First the previously proposed method to estimate air void content was validated. Then, the assessment of aggregate structure including qualitative and quantitative analysis was completed. Qualitative evaluation was performed to determine the quality of slices in regard to establishing challenging areas, and the extent of beam hardening present in the X-ray images. This evaluation produced quality slices for each sample in Y-direction to work as a reference to establish general threshold ranges and image enhancement procedures, as well as identifying the interface between the top and bottom layer of the porous asphalt. The quantitative analysis consisted of analysing aggregate structures in the porous asphalt and developing a method to estimate the aggregate size distribution in porous asphalt layers. The gradation curves from the quantification of aggregate size distribution in all directions (X, Y, Z) were compared to the gradation curves from laboratory sieving tests previously performed on the drilled asphalt cores. To determine the accuracy of the method a perimeter analysis was performed to evaluate the suggested method to measure the aggregates. The results obtained indicate that to quantify the aggregates in porous asphalt, enhancement of the images is needed, as well as morphological operations to deal with beam hardening and overlapping stones due to unsuccessful separation of aggregates when thresholding. This further indicates that ImageJ Fiji is more suitable for complex cases, such as cases where aggregates and mastic are hard to distinguish from each other, rather than the original ImageJ software. This is due to the extended plugins available in ImageJ Fiji, where more options of for example filtering and enhancing of images are available. The results also suggest that the proposed method is a suitable method to determine the aggregate size distribution in porous asphalt pavements, as it allows to quantify the aggregate distribution and produces realistic results with slight inaccuracies due to the analysis being performed in 2D. Future development will be focused on automizing the determination of air void structure and aggregate size distribution, but also on the development of procedures to determine other relevant parameters such as mastic and binder content to establish a complete methodology to investigate the internal structure of a porous asphalt pavement, as well as 3D analysis to determine these parameters.

The thesis explores the complex area between preservation of museum collections, and the need to allow access to the collections and the artefacts for researchers. The focus is on archaeological collections, and inorganic materials in particular. The aim is to illustrate the problems, as well as the opportunities, of archaeological scientific analysis when combined with museological sciences such as materiality and material culture studies, theories of object biographies, the concept of objects as actors, and the issue of silent objects. Exploring the exchange between the museological and the natural sciences to promote enhanced usage of collection artefacts, and to explore whether there are real barriers or if they are perceived due to a lack of mutual understanding. Methodologically it is a text based analysis of the research situation internationally and nationally in Sweden, with a case study comprised of observation of a research team that at the same time were making archaeometallurgical analyses of bronze age objects, and interviews with a small group connected to the areas of interest for this thesis. The sources have consisted of the material generated by the case study, as well as the text material used to provide the necessary background. By using text analysis, Actor-network theory, observation, and interviews, the discussions can revolve around the theoretical perspectives of materiality, object biography and silent objects, with the premise that sample analyses could bring back some context to an artefact. The findings indicate that the museum sector and other disciplines would greatly benefit from closer collaborations with each other and work more interdisciplinary. Museum collections harbour artefacts that could enrich the collective disciplines with their informative values, and with a mass of sampled and analysed context-less artefacts, new and fascinating patterns could emerge, leading to new discoveries. The findings also show that, in archaeology, this is already in motion, and the hope is that this develops on a larger scale in the museum sector as well. / Den här uppsatsen undersöker det snåriga område mellan museers plikt att bevara samlingarna samt behovet att tillåta åtkomst för forskare till samlingarna och föremålen. Fokus ligger på arkeologiska samlingar, och oorganiskt material i synnerhet. Syftet är att belysa problemen, samt de möjligheter som arkeologisk vetenskaplig analys har att ge i kombination med museivetenskapliga begrepp såsom materialitet och materiell kultur, teorier om objektbiografi, objekt som aktörer och ”tysta” föremål. Uppsatsen utforskar utbyten mellan musei- och naturvetenskap som främjar ökad användning av föremål i samlingar, och undersöker om det finns verkliga hinder i utbytet eller om de endast är upplevda på grund av en bristande ömsesidig förståelse. Metodologiskt är det en textbaserad analys av forskningsläget internationellt och nationellt i Sverige, med en fallstudie bestående av observation av en forskargrupp som samtidigt gjorde arkeometallurgiska analyser av bronsåldersföremål, och intervjuer med en liten grupp personer med koppling till intresseområdena för denna uppsats. Källorna består av det material som genererats av fallstudien, samt den litteratur som gett den nödvändiga bakgrunden. Genom att använda textanalys, Actor-network theory, observation och intervjuer, kretsar diskussionerna runt teoretiska perspektiv som materialitet och materiell kultur, objektbiografi och ”tysta” föremål utifrån förutsättningen att analys kan återföra lite av en artefakts kontext. Resultaten visar på att museisektorn och andra discipliner i hög grad skulle tjäna på ett närmare samarbete och att arbeta mer tvärvetenskapligt. Museisamlingar inhyser föremål som skulle kunna berika de samlade disciplinerna med sina informativa värden, och med en mängd provtagningar och analyser av kontextlösa föremål kan nya och fascinerande mönster framträda, vilket i sin tur kan leda till nya upptäckter. Resultaten visar också att detta redan är satt i rörelse inom åtminstone arkeologin, men förhoppningen är att detta även kan ske i större skala inom museisektorn.

Le principe du contrôle non destructif par Flux de Fuite Magnétique (FFM) consiste à magnétiser une pièce à contrôler par un champ magnétique intense et à détecter à l’aide d’un capteur magnétique les fuites des lignes de champ qui résultent de la présence d’un défaut dans la pièce. Les méthodes de contrôle FFM sont très employées notamment lors du processus de fabrication des tubes ferromagnétiques par la société Vallourec, le leader mondial des fabricants de tube. Dans le but d’améliorer les performances des systèmes de contrôle installés en usine, le CEA LIST et le centre de recherches de Vallourec (VRA) collaborent pour développer des outils de simulation rapides dédiés au contrôle virtuel des tubes ferromagnétiques. Le système expérimental existant concerne plus particulièrement la détection des défauts longitudinaux. Le problème de modélisation se pose en termes de modélisation d’un système électromagnétique à géométrie complexe en régime magnétostatique non-linéaire. Les courants de Foucault induits par le mouvement relatif entre la pièce et le circuit magnétique sont négligés. Dans ce contexte, une approche semi-analytique reposant sur le formalisme des équations intégrales (EI) a été choisie. Les travaux effectués dans cette thèse ont pour but de traiter des géométries complexes 3D mais limitées dans une première étape aux matériaux linéaires. Toutefois, le caractère non-linéaire de la relation liant l’induction magnétique et le champ magnétique dans un matériau ferromagnétique doit être envisageable lors du choix de la formulation du problème. Après une étude des paramètres influents du système expérimental existant, menée par des simulations par éléments finis, nous avons considéré deux stratégies de modélisation. La première consiste à proposer un schéma de résolution qui combine un module de calcul 2D et un module d’extension du 2D vers le 3D. Le manque de généralisation de cette première approche simplifiée nous a conduits à proposer une deuxième stratégie qui résout le problème complet de magnétostatique 3D. La formulation par équations intégrales porte sur une quantité scalaire auxiliaire : la densité surfacique de charges magnétiques. Afin de pouvoir résoudre à terme un problème 3D non-linéaire, le schéma numérique proposé considère deux hypothèses : la pièce ferromagnétique est divisée en un ensemble de cellules hexaédriques dans lesquelles la perméabilité magnétique est constante et les inconnues du problème, les densités surfaciques de charge sur les faces de chaque cellule sont projetées sur des fonctions de base d’ordre 0. Le calcul numérique des intégrales singulières s’effectue de manière analytique. Plusieurs résultats de simulation confirment la validité du modèle numérique présenté. Même si le modèle présente encore aujourd’hui quelques limitations notamment sur le manque de précision des calculs en présence de défaut, celui-ci donne satisfaction en absence de défaut. Diverses configurations géométriques ont été traitées grâce à l’emploi du mailleur libre Gmsh. Le travail réalisé débouche sur un modèle 3D linéaire intégrable dans un procédé itératif pour effectuer une simulation en régime non-linéaire. Les inconvénients liés au formalisme des équations intégrales sont aujourd’hui contournables grâce aux méthodes de compression de matrices. Ce modèle est un bon candidat pour servir d’outil de simulation pour le contrôle virtuel des matériaux plans ou cylindriques par flux de fuite. / The principle of Non Destructive Testing (NDT) by using magnetic flux leakage (MFL) consists to magnetize a magnetic component to be inspected by a strong magnetic field and to detect with a magnetic sensor the magnetic flux lines which are leaking from part due to a defect. MFL methods are usually used during the process of manufacture of ferromagnetic pipes by our partner, the Vallourec Group, the leader in the world in manufacturing of pipes. To improve NDT systems in manufacturing plants, the CEA-LIST and the research center of Vallourec are working together to develop fast simulation tools dedicated to virtual testing of ferromagnetic pipes. The main experimental system concerns the detection of longitudinal defect. The modeling problem is to solve an electromagnetism problem with a complex geometry in the magneto-static nonlinear regime. Eddy currents induced by the motion of the pipe with respect to the magnetizing system are neglected.In this context, a semi-analytical approach based on integral equations (IE) has been chosen. The goal of some works which have been carried out in this PHD thesis is to address 3D complex geometries but, in first a step, limited to the linear regime. However, the non-linear behavior of the relationship which links the magnetic flux density and the magnetic field inside a ferromagnetic material must be considered when choosing the 3D formulation of the problem.After a study about influent parameters of the experimental system, carried out by using finite elements computations, we have considered two strategies for modeling. The first one has consisted to build up a strategy which consists to join the 2D numerical model, existing in the laboratory to an extension model from 2D to 3D. This approach was a priori quite simple but the lack of generality of this approach leads us to suggest another strategy which results in solving the complete 3D magneto-static problem. This formulation is based the integral equation formalism implying an auxiliary scalar quantity: the magnetic surface charge density. In order to be able to solve a nonlinear problem in the future, the chosen numerical scheme we have adopted is based on two hypothesis: the ferromagnetic part is firstly divided into a finite number of small hexahedral cells in which the relative magnetic permeability is supposed to be constant and secondly, the unknowns of the problem, the surface charge densities on the facets of each cell are expanded by using basis functions of zero order. Thanks to this limitation, the singular integrals can be analytically computed. Some simulation results confirm the validity of the implemented numerical model. This model presents some limitations at the moment in the cases of a workpiece with a defect but it can provide quite good results without any defect. Several geometries have been addressed by using Gmsh, free meshing software. Moreover, the final numerical model can be included into an iterative process to deal with non-linear cases. The limitations due to the EI formalism can be overcome today by using some compression matrix methods. Presently, this model is a good candidate for virtual NDT for cylindrical and planar geometries by magnetic flux leakage.