Structural health monitoring (SHM) is concerned with the continuous, long-term assessment of structural integrity. One commonly investigated SHM technique uses guided ultrasonic waves, which travel through the structure and interact with damage. Measured signals are then analyzed in software for detection, estimation, and characterization of damage. One common configuration for such a system uses a spatially-distributed array of fixed piezoelectric transducers, which is inexpensive and can cover large areas. Typically, one or more sets of prerecorded baseline signals are measured when the structure is in a known state, with imaging methods operating on differences between follow-up measurements and these baselines. Presented here is a new class of SHM spatially-distributed array algorithms that rely on sparse reconstruction. For this problem, damage over a region of interest (ROI) is considered to be sparse. Two different techniques are demonstrated here. The first, which relies on sparse reconstruction, uses an a priori assumption of scattering behavior to generate a redundant dictionary where each column corresponds to a pixel in the ROI. The second method extends this concept by using multidimensional models for each pixel, with each pixel corresponding to a "block" in the dictionary matrix; this method does not require advance knowledge of scattering behavior. Analysis and experimental results presented demonstrate the validity of the sparsity assumption. Experiments show that images generated with sparse methods are superior to those created with delay-and-sum methods; the techniques here are shown to be tolerant of propagation model mismatch. The block-sparse method described here also allows the extraction of scattering patterns, which can be used for damage characterization.

[pt] Espectroscopia de ressonância plasmônica de superfície (SPR) é uma técnica óptica amplamente utilizada para monitorizar as alterações físicas ou químicas que ocorrem em uma interface metal - dielétrico. A medição simultânea da espessura e do índice de refração de filmes finos orgânicos, adsorvidos ou depositados sobre a superfície plana de um metal, requer duas medições independentes seguindo uma metodologia designada na literatura como método de duas cores ou método de dois meios. Na primeira, as duas medições são realizadas utilizando diferentes comprimentos de onda da radiação eletromagnética interagindo com a amostra. Na segunda, o índice de refração do meio externo (gás, líquido) é alterado entre as duas medições. Enquanto o primeiro método implica no conhecimento da função de dispersão da fase orgânica, o segundo só produz resultados precisos quando as moléculas orgânicas não interagem quimicamente com o fluido externo. Ambos os métodos apresentam dificuldades quando são aplicados à caracterização de materiais luminescentes orgânicos, os quais são na maior parte do tempo altamente reativos à umidade e ao contato com solventes orgânicos. Neste trabalho foi montado um espectrômetro de SPR automatizado. Primeiramente, ele foi testado na caracterização de amostras feitas no laboratório em termos do valor absoluto, e da homogeneidade das constantes ópticas da deposição metálica que suporta a onda de plasma. Nós demonstramos que medições precisas de constantes ópticas permitem a determinação do índice de refração de filmes finos orgânicos luminescentes, evaporados termicamente utilizando o método de substrato com dois metais. Este método, que até onde sabemos é apenas teorizado na literatura, foi aplicado a uma amostra encapsulada com um filme fino de Alq3 comercial. Além disso, a interface metal/Alq3 foi exposta a ar, e a degradação foi monitorada em tempo real, indicando uma diminuição progressiva do ângulo de ressonância da amostra. / [en] Surface Plasmon Resonance Spectroscopy (SPR) is an optical technique widely used to monitor the physical or chemical changes occurring at a metal-dielectric interface. The simultaneous measurement of the thickness and the index of refraction of organic thin films adsorbed or deposited on the metal flat surface require two independent measurements following a methodology commonly named in literature as Two-Colors Method or Two-Medium Method. In the first one, the two measurements are performed using different wavelength of the electromagnetic radiation interacting with the sample. In the second one the index of refraction of the external medium (gas, liquid) is changed between the two measurements.While the first method implies the knowledge of the dispersion function of the organic layer, the second one gives accurate results only when the organic molecules don t interact chemically with the external fluid. Both of these methods present difficulties when applied to the characterization of luminescent organic materials, most of the time highly reactive to humidity and to the contact with organic solvents. In this work an automated SPR spectrometer was assembled and first tested on the characterization of home-made samples in terms of the absolute value and homogeneity of the optical constants of the metal deposition supporting the plasma wave. We demonstrate that accurate measurements of such optical constants allow the determination of the index of refraction of thermally evaporated luminescent organic thin films using a Two-Metal Substrate Method. This method, to our knowledge only theorized up to now in literature, has been applied to an encapsulated sample containing a thin film of commercial Alq3. Further, the degradation of the metal/Alq3 interface exposed to air has been real time monitored indicating a progressive drop in the angle of resonance of the sample.

Ces dernières années, les modes de Lamb à vitesse de groupe nulle (ZGV) se sont révélés être un outil efficace pour sonder localement et précisément l'épaisseur d'un échantillon ou les propriétés mécaniques de matériaux isotropes ou anisotropes. Ce type particulier d'ondes guidées, telles de fortes résonances locales de la structure, résulte de l'interférence de deux ondes de Lamb ayant une vitesse de phase opposée et coexistant pour un couple fréquence-nombre d'ondes particulier. Les ultrasons laser ont démontré leur capacité à générer et détecter efficacement de telles résonances locales dans la gamme des MHz. En effet, la configuration tout optique, constituée d'une source laser pulsée pour générer les ondes élastiques et d'un interféromètre pour sonder le déplacement normal associé, évite tout contact avec l'échantillon, limitant ainsi l'élargissement ou la suppression de résonances. L'utilisation de modes ZGV pour suivre la fatigue des matériaux et sonder des phénomènes non linéaires reste cependant un défi et constitue le cœur des travaux de recherche présentés ici. La partie théorique porte sur la compréhension de l’effet de la fatigue mécanique sur les modes ZGV à travers l’analyse fréquence-nombre d’ondes des modes de Lamb. La partie expérimentale est consacrée à l’application de cette technique pour l'ECND et le suivi de la fatigue de plaques métalliques minces. Les modes ZGV en ultrasons laser montrent un grand potentiel pour localiser les dommages dus à la fatigue, prédire la vie en fatigue et évaluer qualitativement, voire quantitativement, les différents stades de dommages causés par la fatigue. / In recent years, zero-group-velocity (ZGV) Lamb modes have proven to be an efficient tool to probe locally and very accurately the thickness of a sample or the mechanical properties of either isotropic or anisotropic materials. This particular type of guided waves, corresponding to sharp local resonances of the structure, results of the interference of two Lamb waves having opposite phase velocity and coexisting at a couple given frequency-wavenumber. The laser ultrasonic technique has demonstrated its ability to efficiently generate and detect such local resonances within the MHz frequency range. Indeed, the all-optical setup, consisting of a pulsed laser source to generate elastic waves and of an interferometer to probe the associated normal displacement, avoids any contact with the sample, hence limiting the broadening or suppression of the resonances. Yet, the use of ZGV Lamb modes to monitor material fatigue and to probe nonlinear phenomena remains challenging and is the core of the here-reported research. The theoretical part of this PhD research deals with the understanding of the effect of mechanical fatigue on ZGV Lamb modes through the frequency-wavenumber analyzes of the Lamb waves. The experimental part of the PhD research is dedicated to the application of this technique for the nondestructive characterization and for the monitoring of mechanical and thermal fatigue of thin metal plates. Zero-group-velocity Lamb modes in laser ultrasonics shows great promises to locate fatigue damage, to predict the fatigue lifetime, and to qualitatively, and even quantitatively, assess the different stages of fatigue damage in   m- to potentially cm-thick solid plates.

In this thesis project, an underwater 3D scanner based on structured light has been constructed and developed. Two other scanners, based on stereoscopy and a line-swept laser, were also tested. The target application is to examine objects inside the water filled reactor vessel of nuclear power plants. Structured light systems (SLS) use a projector to illuminate the surface of the scanned object, and a camera to capture the surfaces' reflection. By projecting a series of specific line-patterns, the pixel columns of the digital projector can be identified off the scanned surface. 3D points can then be triangulated using ray-plane intersection. These points form the basis the final 3D model. To construct an accurate 3D model of the scanned surface, both the projector and the camera need to be calibrated. In the implemented 3D scanner, this was done using the Camera Calibration Toolbox for Matlab. The codebase of this scanner comes from the Matlab implementation by Lanman & Taubin at Brown University. The code has been modified and extended to meet the needs of this project. An examination of the effects of the underwater environment has been performed, both theoretically and experimentally. The performance of the scanner has been analyzed, and different 3D model visualization methods have been tested. In the constructed scanner, a small pico projector was used together with a high pixel count DSLR camera. Because these are both consumer level products, the cost of this system is just a fraction of commercial counterparts, which uses professional components. Yet, thanks to the use of a high pixel count camera, the measurement resolution of the scanner is comparable to the high-end of industrial structured light scanners.

I detta examinationsarbetesrapport för högskoleingenjörsexamen inom Elektronik, presenteras en utredning för att svara på vad som skulle vara den mest generiska pulsgeneratorn för ultraljudstestning inom det klassiska intervallet 0.5 till 15 MHz. Det presenteras flera variabler i teorin, som påverkar en testsignal och varför det inte går att beräkna vad en generisk pulsgenerator bör åstadkomma. Denna rapport presenterar vilka pulsgeneratorer det finns och vad de mer högpresterande pulsgeneratorerna beskrivna i vetenskapliga forskningsresultat har presterat. Samt vilka tekniker som finns och varför vissa tekniker inte är lämpliga. Vid slutet av denna examinationsarbetesrapport presenteras, med hjälp av några antaganden om vad en generisk pulsgenerator behöver prestera, dras en slutsats om vilken av de föreslagna pulsgeneratorerna som är mest generisk. / This bachelor thesis, is a trial in answering what would be a generic pulse generator for ultrasonic testing in the classic test range of 0.5 to 15 MHz. It also goes through multiple variables that affects a test signal and why it really isn't possible to precalculate what a generical pulse generators should achive, in the theory chapter. This thesis also goes through what different types of pulse generators there is and what some of the more high performance pulse generators proposed in scientific articles have achieved and what techniques that have been used and why some techniques are not suitable. In the end of this thesis there is a trial with some assumptions about what a generical pulse generator should achieve, to come to a conclusion about which pulse generator from the proposed ones would be the best generical pulse generator to go with.

Die zerstörungsfreie Ultraschallprüfung von akustisch anisotropen Werkstoffen stellt auch heute noch eine Herausforderung dar. Die Gefügestruktur in solchen Materialien beeinflusst die Wellenausbreitung derart, dass es zum einen zu starken Streuungen durch die großflächigen Korngrenzen und zum anderen, aufgrund der akustischen Anisotropie, zu einer Richtungsabhängigkeit der Schallgeschwindigkeiten kommt. In den vergangenen Jahren wurden bereits Lösungsansätze zur mathematischen Modellierung der Schallausbreitung in anisotropen Materialien vorgestellt. Diese basieren in der Regel auf FEM- bzw. FIT- Algorithmen, die durch die Diskretisierung des gesamten Volumens einen hohen Rechenaufwand erfordern und in der täglichen Prüfpraxis aufgrund ihrer Komplexität bei der Parametrierung nur bedingt einsetzbar sind. Aus diesem Grund wird hier ein Ansatz zur Schallfeldberechnung gewählt, der auf die praktische Anwendung von Gruppenstrahler-Prüfköpfen zugeschnitten ist. Während sich andere Verfahren auf einzelne Wellenanteile und monofrequente Lösungen beschränken, um den Rechenaufwand zu reduzieren, können mit diesem Ansatz die reale Signalform des Prüfkopfes sowie alle auftretenden Wellenanteile in homogenen transversalisotropen Medien berücksichtigt werden. Durch entsprechende Optimierungen im Berechnungsalgorithmus lässt sich das gesamte vierdimensionale Schallfeld eines Gruppenstrahler-Prüfkopfes im Halbraum in kürzester Zeit berechnen. Die analytische Lösung der Wellengleichung für den Halbraum in Form einer Greenschen Funktion wird dabei in eine Gleichung umgeformt, die hier als vierdimensionale Punktrichtwirkung bezeichnet wird. Dieser Modellansatz ermöglicht es, die Parameter eines Gruppenstrahlersystems in der praktischen Anwendung zu überprüfen und durch iterative Rechnungen zu optimieren. Mit Hilfe einer einfach zu handhabenden Visualisierungstechnik ist es möglich diesen Modellansatz mit realen Schallfeldmessungen zu vergleichen. Dazu werden mit elektrodynamischen Sonden die einzelnen Komponenten des dreidimensionalen Vektors der Teilchenverschiebung an der Oberfläche von Festkörpern abgetastet. Die an den Messpunkten ermittelten Zeitfunktionen des Verschiebungsvektors werden dann dem berechneten Zeitverlauf der Wellenausbreitung gegenübergestellt. Die berechneten und gemessenen Schallfelder stimmen in der Phasenlage und im Amplitudenverlauf gut überein. Die Ergebnisse zeigen, dass mit dem verwendeten Rechenmodell alle in der Realität auftretenden Wellenanteile vollständig berücksichtigt werden und dreidimensionale Problemstellungen aus der Praxis mit diesem Modell korrekt berechnet werden können. / The non-destructive ultrasonic testing of acoustic anisotropic materials is an important challenge. The texture of these materials causes a strong scattering of the sound wave by the extensive grain boundaries and a direction dependent sound velocity by the acoustic anisotropy. Several approaches for the modelling of the sound propagation in anisotropic materials were presented in the last years. These approaches are normally based on FEM or FIT algorithms using a discretisation of the complete volume. Their calculation needs extensive time and a very complex parameterisation. Thus these algorithms are not suitable in practice of ultrasonic testing. In this work an approach is presented that is optimised for the application of phased array transducers. The new approach considers the real frequency spectrum of the transducer as well as all occurring wave modes in homogeneous transversely isotropic media, whereas other approaches are limited to solutions for single wave modes and single frequencies to reduce the calculation effort. The appropriate optimisations of the mathematical algorithm allow the fast calculation of the complete four-dimensional transient wave field of a phased array transducer in the half-space. The Green’s functions are derived by an analytical solution of the elastodynamic wave equation for the half-space. These functions will be transformed into an equation which will be referred to in this work as four-dimensional directivity pattern. This approach allows the verification of the parameters of a phased array system and their optimisation by iterative calculations in the practical application. To get accurate results in these calculations, the experimental verification of the applied mathematical model for the wave propagation is an essential task. The technique presented in this work applies electrodynamic probes, which provides a simple use. The probes can detect the particle displacement at a solid surface in all three spatial directions. The measured time-functions of the wave field will be compared with the calculated time-functions. They show a good accordance in the phase and the amplitude. This confirms that the applied mathematical model considers completely all in practice occurring wave modes. The results further show that three-dimensional problems in practice can be calculated correctly with this model.

Das Ziel der Arbeit bestand darin, die aus der Literatur bekannten Zusammenhänge zwischen Korrosionsaktivität von Stahl im Beton und einer galvanostatischen Pulsmessung, welche unter Laborbedingungen gute Ergebnisse liefern, auf Messungen an realen Bauwerken anzuwenden. Dazu wurden zunächst Untersuchungen an 13 Jahre alten Prüfkörpern durchgeführt und ausgewertet. Die abgeleiteten Zusammenhänge konnten anschließend an realen Bauteilen verifiziert werden. Somit stellt die galvanostatische Pulsmessung eine hilfreiche zerstörungsfreie Prüfmethode zur Interpretation des Korrosionszustandes dar. Die neuen Erkenntnisse lassen eine bessere Einschätzung des Korrosionsverhaltens in Stahlbetonbauwerken zu, als es die Potentialmessung erlaubt.

Fiber-reinforced plastics for industrial applications face constantly increasing demands regarding efficiency, reliability, and economy. Furthermore, it was shown that fiber-reinforced plastics with tailored reinforcements are superior to metallic or monolithic materials. However, a trustworthy description of the load-specific failure behavior and damage evolution of composite structures can hardly be given, because these processes are very complex and are still not entirely understood. Among other things, several research groups have shown that material damages like fiber fracture, delamination, matrix cracking, or flaws can be discovered by analyzing the electrical properties of conductive composites, for example, carbon fiber–reinforced plastics. Furthermore, it was shown that this method could be used for structural health monitoring or nondestructive evaluation. Within this study, magnetic induction tomography, which is a new imaging approach, is introduced in the topic of nondestructive evaluation of carbon fiber–reinforced plastics. This non-contacting imaging method gains the inner spatial distribution of conductivity of a specimen and depicts material inhomogeneity, like damages, not only in two-dimensional images but also in three-dimensional images. Numerical and experimental investigations are presented, which give a first impression of the performance of this technique. It is demonstrated that magnetic induction tomography is a promising approach for nondestructive evaluation. Potentially, it can be used for fabrication quality control of conductive fiber–reinforced plastics and as a structural health monitoring system using an integrated or superficially applied magnetic induction tomography setup.

No description available.

CE-märkta stålbalkar byggdes in i två konstruktioner innan det upptäcktes att det fanns porer i hattbalkarnas svets. Den defekta svetsen innebar att byggnadernas bärförmåga inte kunde garanteras. Kunskapen kring inbyggt stål stommaterial med defekt svets är liten. Det är dessutom svårt att reparera och undersöka stålbalkarnas svets när de är inbyggda i konstruktionen. Syftet med examensarbetet är att hitta förstärkningsmetoder och därmed främja kortare hanteringstid vid händelse av att defekta stålbalkar byggs in i en konstruktion. Metoden består av litteraturstudie och intervjuer. Först granskas litteratur för att förstå problematiken med defekt svets i stål stommaterial. Därefter utförs intervjuer med personer erfarna inom stål och byggteknik. Examensarbetets resultat är ett flertal förstärkningsmetoder för inbyggda stålbalkar med defekt svets. Några av förstärkningsmetoderna är möjliga att utföra med den kunskap som finns idag medan andra behöver undersökas och värderas innan de kan implementeras. Förstärkningsmetoderna som är möjliga att utföra med dagens kunskap är: att svetsa om balken från insidan eller att placera en balk/fackverksbalk under den befintliga balken. De metoder som behöver undersökas och värderas vidare är: skruvförband genom balken, efterspänna balken med vajrar eller GWS-stag och sedan fylla den med betong, föra in en balk inne i balken och fylla balken med betong och att kolfiberförstärka svetsen. Slutsatsen är att den här studien kan ligga till grund för framtagning av åtgärder för inbyggda stålbalkar med defekt svets med mål att uppnå den dimensionerade hållfastheten och en lösning som är tidseffektiv, kostnadseffektiv och har låg klimatpåverkan. / Before the discovery of pores in the weld, CE-certified steel beams were embedded in two constructions. Since the weld was defective, the carrying capacity of the two buildings was questioned. There is a lack of knowledge about embedded steel beams with a damaged weld. It is difficult to repair and analyze the weld when the beams are embedded in the construction. The aim of the study is to find reinforcement methods for steel beams. The expectation is to shorten time in the production in case that defective steel beams are detected in the construction. The method consists of a literature study complemented by interviews. Literature is examined to understand the problem of defective welding in the steel framework. Subsequently, interviews are conducted with professionals within steel and building technology. The result of the report is multiple reinforcement methods for embedded steel beams with a defective weld. Some of the methods are possible to implement with the knowledge available today. Other methods need to be examined and assessed before executed. The reinforcement methods that are possible to perform are: weld the beam from the inside or place a beam underneath the existing beam. The methods that need further analysis are: drill a screw joint through the beam, strain the beam with steel-wires and fill the inside with concrete, place a beam inside the existing beam and fill the inside with concrete and last to reinforce the weld with carbon fibers. The conclusion is that this study can be used when reinforcement methods are needed for embedded steel beams with a defective weld. The objective with these methods is to restore the load-bearing capacity as well as finding a solution that is time efficient, economic and has low climatic influence.