The research presented in this thesis is all based on the impedance method for structural health monitoring. The impedance method is an electro-mechanical technique which utilizes a single piezoelectric transducer as both a sensor and actuator. Due to the high frequencies of excitation used for the method, the sensing area for damage detection can be very localized. Previous work has shown that wave propagation can be added to systems already equipped with hardware for impedance-based structural health monitoring. The work in this thesis shows what happens under varying temperature conditions for a structure being monitored with wave propagation. A technique to compensate for temperature fluctuations is also presented. The work presented here is an initial study to directly correlate the actual amount of damage in a composite specimen with a damage metric indicated by impedance-based structural health monitoring. Two different damage mechanisms are examined: transverse matrix cracking and edge delamination. With both composite defects, a sample is interrogated with the impedance method before and after damage is introduced. The exact amount of damage in each specimen is found using radiography and compared with the health monitoring results. Traditional impedance techniques require the use of a bulky and expensive impedance analyzer. With the trend of structural health monitoring moving towards unobtrusive sensors which can be permanently placed on a structure, an impedance analyzer does not lend itself to these small, low power consuming requirements. In this thesis, an initial attempt to miniaturize the hardware is described. A prototype impedance-based structural health monitoring system, incorporating wireless based communications, is fabricated and validated with experimental testing on a number of different structures. The first steps towards a complete self-contained, robust structural health monitoring sensor are presented. / Master of Science

Structural Health Monitoring (SHM) is the science and technology of monitoring and can assess the condition of aerospace, civil, and mechanical infrastructures using a sensing system integrated into the structure. SHM is capable of detecting, locating, and quantifying various types of damage such as cracks, holes, corrosion, delamination, and loose joints, and can be applied to various kinds of infrastructures such as buildings, railroads, windmills, bridges, and aircraft. A major technical challenge for existing SHM systems is high power consumption, which severely limits the range of its applications. In this thesis, we investigated adoption of acoustic emission detection to reduce power dissipation of SHM systems employing the impedance and the Lamb wave methods. An acoustic emission sensor of the proposed system continuously monitors acoustic events, while the SHM system is in sleep mode. The SHM system is evoked to perform the SHM operation only when there is an acoustic event detected by the acoustic emission sensor. The proposed system avoids unnecessary operation of SHM operations, which saves power, and the system is effective for certain applications such as spacecraft and wind turbine blades. We developed prototype systems using a Texas Instruments TMS320F2812 DSP evaluation board for the Lamb wave method and an MSP430 evaluation board for the impedance method. / Master of Science

The use of metal strain gauges and ultrasonic transducers have long been studied in the field of Nondestructive Evaluation (NDE) as a part of structural health monitoring (SHM). Strain gauges use electrical resistance to monitor strains during the loading of a component. Ultrasonic transducers are piezo devices that use a crystal-like sensing element with very low excitation energy that can monitor small strains such as acoustic emissions (AEs). These types of devices have been used to locate the sources of AEs from artificial sources, such as Hsu-Nielsen pencil lead break (PLB) tests, or natural sources such as quasi-static fracture or crack propagation. This type of evaluation has significant advantages over other types of damage inspections such as liquid die penetrant, Blue Light, Eddy Current, or X-ray inspections where visual inspections, large defects, and high levels of user experience are required. The ultrathin silicon membrane (USM) sensor developed by NanoSonic Inc. is a piezoresistive sensor, incorporating the best aspects of a conventional strain gauge and ultrasonic transducer. The sensor can measure both the strain of a component, as well as any acoustic emission that is emitted on the component. To the author's knowledge this is the only sensor capable of simultaneous measurement of these two data types. This paper presents the sensor's ability to be used for quasi-static fracture monitoring. The sensor is first compared to commercial ultrasonic transducers in an unloaded pencil lead break (PLB) test for determining the ability in measuring lamb waves for source location estimation. The NanoSonic USM sensor is further compared to commercial strain gauges and ultrasonic transducers during a PLB test under a tensile load where it is demonstrated the USM sensor yields similar measurements to both commercial sensors. The final test was a quasi-static fracture test, where the NanoSonic USM sensor was able to detect substantially lower energy AEs than the previous test and record the strain history during fracture. This duality of the USM sensor demonstrates an inherent usefulness to NDE and SHM fields. The sensor offers sensing capabilities comparable to commercially available sensors in a smaller package, with less power consumption, at a lower cost. / Master of Science / Nondestructive evaluation (NDE) is a field within structural health monitoring (SHM) that refers to determining any defects within a component that would hinder its performance without modifying its existing condition. This has historically been done by visual inspection by which experienced personnel examine the part for defects. This is inherently flawed as cracking below the surface of a component is common and would not be detected and extensive experience is required to successfully complete this task. Components in hard-to-reach places, with coatings, or that are small also prove challenges to visual inspection. Engineers have developed several new testing methods to combat these flaws. The use of acoustic emission (AE) testing allows sensors, called ultrasonic transducers, to receive and emit sounds at high frequencies to conduct the inspection. This can be done by emitting a sound which is then propagated as a wave along the surface of the component, if the wave hits a defect, it is scattered. A receiving sensor would then receive an unexpected signal, indicating that there is a problem. Furthermore, an array of these sensors can be employed to 'listen' for these surfaces waves that may be emitted during the standard operation of the components. Things like high loads, cracking, and impacts will all be able to be detected. The use of an array of sensors will allow the location of these events. This paper will discuss a new type of sensor, an ultrathin silicon membrane (USM) sensor developed by NanoSonic Inc. This type of sensor can detect high frequencies similar to an ultrasonic transducer, as well as measure large loads that would deform the part, resulting in an event known as strain. The novelty of the NanoSonic USM sensor is its ability to monitor both pieces of information simultaneously, which is believed to be the first to do so in the field. The ability to obtain information on strain and locations of acoustic events within a component during standard operation would be a valuable prospect for the aerospace, civil, and automotive industries.

Yes / Ultra-high performance concrete (UHPC) is an innovative cementitious composite, that has been widely applied in numerous structural projects because of its superior mechanical properties and durability. However, ensuring the safety of UHPC structures necessitates an urgent need for technology to continuously monitor and evaluate their condition during their extended periods of service. Self-sensing ultra-high performance concrete (SSUHPC) extends the functionality of UHPC system by integrating conductive fillers into the UHPC matrix, allowing it to address above demands with great potential and superiority. By measuring and analyzing the relationship between fraction change in resistivity (FCR) and external stimulates (force, stress, strain), SSUHPC can effectively monitor the crack initiation and propagation as well as damage events in UHPC structures, thus offering a promising pathway for structural health monitoring (SHM). Research on SSUHPC has attracted substantial interests from both academic and engineering practitioners in recent years, this paper aims to provide a comprehensive review on the state of the art of SSUHPC. It offers a detailed overview of material composition, mechanical properties and self-sensing capabilities, and the underlying mechanisms involved of SSUHPC with various functional fillers. Furthermore, based on the recent advancements in SSUHPC technology, the paper concludes that SSUHPC has superior self-sensing performance under tensile load but poor self-sensing performance under compressive load. The mechanical and self-sensing properties of UHPC are substantially dependent on the type and dosage of functional fillers. In addition, the practical engineering SHM application of SSUHPC, particularly in the context of large-scale structure, is met with certain challenges, such as environment effects on the response of SSUHPC. Therefore, it still requires further extensive investigation and empirical validation to bridge the gap between laboratory research and real engineering application of SSUHPC.

Dimensionality reduction techniques (DR) enhance data interpretability and reduce space complexity, though at the cost of information loss. Such methods have been prevalent in the Structural Health Monitoring (SHM) anomaly detection literature. While DR is favorable in supervised anomaly detection, where possible novelties are known a priori, the efficacy is less clear in unsupervised detection. In this work, we perform a detailed assessment of the DR performance trade-offs to determine whether the information loss imposed by DR can impact SHM performance for previously unseen novelties. As a basis for our analysis, we rely on an SHM anomaly detection method operating on input signals' fast Fourier transform (FFT). FFT is regarded as a raw, frequency-domain feature that allows studying various DR techniques. We design extensive experiments comparing various DR techniques, including neural autoencoder models, to capture the impact on two SHM benchmark datasets exclusively. Results imply the loss of information to be more detrimental, reducing the novelty detection accuracy by up to 60\% with autoencoder-based DR. Regularization can alleviate some of the challenges though unpredictable. Dimensions of substantial vibrational information mostly survive DR; thus, the regularization impact suggests that these dimensions are not reliable damage-sensitive features regarding unseen faults. Consequently, we argue that designing new SHM anomaly detection methods that can work with high-dimensional raw features is a necessary research direction and present open challenges and future directions. / M.S. / Structural health monitoring (SHM) aids the timely maintenance of infrastructures, saving human lives and natural resources. Infrastructure will undergo unseen damages in the future. Thus, data-driven SHM techniques for handling unlabeled data (i.e., unsupervised learning) are suitable for real-world usage. Lacking labels and defined data classes, data instances are categorized through similarities, i.e., distances. Still, distance metrics in high-dimensional spaces can become meaningless. As a result, applying methods to reduce data dimensions is currently practiced, yet, at the cost of information loss. Naturally, a trade-off exists between the loss of information and the increased interpretability of low-dimensional spaces induced by dimensionality reduction procedures. This study proposes an unsupervised SHM technique that works with low and high-dimensional data to assess that trade-off. Results show the negative impacts of dimensionality reduction to be more severe than its benefits. Developing unsupervised SHM methods with raw data is thus encouraged for real-world applications.

Das 12. Symposium „Experimentelle Untersuchungen von Baukonstruktionen“ (SEUB) fand am 1. Juni 2023 an der TU Dresden statt. Das Tagungsprogramm war mit insgesamt 14 Vorträgen zu den vier Schwerpunkten • Methoden und Bewertung von Zustand, Tragsicherheit und Restlebensdauer von Bauwerken, • Zustandsprognose, Monitoring und prädiktives SHM, • Neue Messverfahren und • Aktuelle Bauwerksuntersuchungen sehr gut gefüllt. In seiner Keynote Lecture gab Prof. Marc Gutermann (Hochschule Bremen) einen Überblick über experimentelle Belastungsversuche an mehr als 180 verschiedensten Deckenplatten, die er und sein Team in den vergangenen 15 Jahren durchgeführt haben. Insgesamt nahm die Thematik der Weiterentwicklung und Anwendung von zerstörungsfreien oder -armen Mess- und Analysemethoden und deren vorteilhafte Kombination einen hohen Stellenwert ein. Die Anwendung reicht hierbei von der Stunde null mit dem Erstellen eines sogenannten Geburtszertifikats über die messtechnische Überwachung von Strukturen im laufenden Betrieb bis zur Datengewinnung beim Rückbau. Eindrücklich wird gezeigt, wie mit Methoden der experimentellen Bauwerksuntersuchung zum Erhalt des Baubestandes beigetragen werden kann. Das 13. SEUB ist für 2025 geplant.:Grußwort Marc Gutermann, Werner Malgut: Experimentell gestützter Tragsicherheitsnachweis von Massivdecken – Erfahrungen, Potenzial und Grenzen Markus Fischer, Gunter Hahn, Martin Löhr, Horst Peseke: Systematische Bauwerksanalyse mittels ZfP-Verfahren mit anschließenden Belastungsversuchen im Alten Polizeipräsidium in Frankfurt a. M. Maria Schartner, David Sanio: Monitoring der Theodor-Heuss-Brücke zur messdatenbasierten Lebensdauerprognose Alois Vorwagner, Christian Gasser, Vazul Boros, Alfred Lechner, Lukas Hausner: Betonieren unter Verkehr: Untersuchung der Auswirkungen von Erschütterungen auf jungen Beton Sven Kromminga, Katarzyna Zdanowicz, Max Käding, Tomasz Howiacki: Zustandsüberwachung einer integralen, mehrfeldrigen Eisenbahn-Stahlverbundbrücke mit verteilten faseroptischen Sensoren Iris Hindersmann, Matthias Müller, Felix Kaplan: Strategischer Einsatz von Monitoring bei Ingenieurbauwerken mit Anwendungsbeispielen Balthasar Novák, Franziska Stein, Jochen Reinhard, Andrian Dudonu, Tanja Zeller: Neues Potential im Structural Health Monitoring: Verteilte faseroptische Sensoren für Bestandsbauwerke Fritz Binder, Stefan L. Burtscher: Verbesserte Bestimmung des Chloridgehalts in Beton durch neues Messverfahren Sebastian Schulze: Radiographie im Bauwesen – Ein neues altes Verfahren für die zerstörungsfreie Bauwerksuntersuchung Volker Wetzk, Christian Quos: Das Potenzial der Spektralanalyse für die Werkstoffcharakterisierung von Stahlguss im Bestand Max Herbers, Bertram Richter, Benjamin Schwarz, Steffen Marx: Messtechnische Überwachung von Spannbetonbauteilen mit faseroptischen Sensoren Ronghua Xu, Konstantin Hicke, Sebastian Chruscicki, Steffen Marx: Akustisches SpRK-Monitoring mit SEA und verteilten faseroptischen Sensoren Alexander Dreiling, Marco Rieche, Peter Kretzschmar: Ersatz von Auflagerkonsolen für schwere Kranbahnträger im Bauwerksbestand Christina Fritsch, Gregor Schacht, Johannes Diers, Torsten Harke, Peter Betz: Erfassung und Bewertung des Bauwerkszustandes als Grundlage für die Rückbauplanung

Dans le but de reconnaitre et répondre de manière efficace à une très grande variétés d’agents pathogènes, les cellules B ont développé au cours des mécanismes de diversifications des immunoglobulines contrôlés par des processus génétiques complexes comme la recombinaison V(D)J, l’hypermutation somatiques (SHM), et le changement de classe par recombinaison (CSR). L’ensemble de ces processus est contrôlé par différentes voies de réparations de l’ADN. L’anémie de Fanconi est une maladie génétique rare caractérisée par une défaillance progressive de la moelle osseuse, des anomalies de développement et un risque accru de développer des leucémies et des cancers oesopharyngés. La voie FANC est impliquée dans la réparation des pontages de l’ADN et dans le maintien de la fourche de réplication en cas de stress génotoxique. Il est également bien décrit que la voie FANC joue un rôle important dans la coordination des voies de réponses aux dommages à l’ADN. Dans ce travail de thèse, nous nous sommes intéressés au rôle de la voie FANC dans les processus de diversifications des immunoglobulines.En utilisant des souris déficientes pour le gène Fanca, nous montrons que la voie FANC (ou FANCA) participe à la recombinaison V(D)J en contrôlant, dans la moelle osseuse, la transition des cellules B, du stade pre-B au stade de cellules B immatures. Ceci se ferait probablement par le contrôle de la transcription des gènes codant les chaines légères κ des immunoglobulines. Nous montrons également que Fanca pourrait avoir un rôle dans l’addition de nucleotides aux extrémités codantes, en régulant d’une manière indéterminée l’activité et/ou l’activation de l’enzyme TdT ou de la polymérase Polµ. Par ailleurs, nous avons montré que Fanca est nécessaire pour l’induction des mutations de type transitions A/T pendant le processus de SHM en régulant l’expression ou la stabilisation de Polη. Enfin, Fanca (ou la voie FANC) participe à l’inhibition de la recombinaison non homologue (NHEJ) et est requis durant le CSR pour stabiliser les duplexes entre 2 régions de microhomologies qui facilitent le recrutement d’endonucléases et réguler l’accès des DNA polymérases aux cassures de l’ADN. / To recognize and respond dynamically to an enormous variety of different pathogens, B lymphocytes of the immune system have evolved controlled genetic processes at their immunoglobulin (Ig) loci that are known as Ig diversification including V(D)J recombination, somatic hypermutation (SHM), and class switch recombination (CSR). These complex and vulnerable processes are orchestrated by multiple DNA repair pathways. Fanconi anemia (FA) is a rare genetic disorder that can lead to bone marrow failure, congenital abnormalities, and an increased risk of leukemia and cancer. FANC pathway has been implicated in DNA interstrands crosslinks (ICL) repair and in the rescue of stalled replication forks. The FANC pathway also plays a fundamental role in coordinating the DNA repair pathways. Several lines of evidence suggest a possible involvement of the FANC pathway in Ig diversification processes, thus we are particularly interested in revealing function of FANC pathway during these processes. By using Fanca-/- mice, our results first show that during V(D)J recombination, Fanca (or FANC pathway) participates to the control of the transition from pre-B to immature B cells in bone marrow (BM), probably through transcriptional activation of post-rearranged κ light chain. In addition, Fanca might play a role in nucleotide addition at coding end, possibly by regulating either TdT or Polµ activity/activation. Secondly, we found that Fanca is required for the induction of transition mutations at A/T during SHM via regulation of Polη expression/stabilization. Finally, Fanca (or FANC pathway) inhibits short-range recombination and is required during CSR to stabilize duplexes between 2 short microhomology regions that facilitate the recruitment of endonucleases to trim overhangs and avoid unscheduled access of polymerases to DNA ends.

O presente trabalho correlacionou diversas funções de respostas em frequência (FRF) de juntas do tipo simples, coladas e fabricadas em titânio-compósito (resina epóxi reforçada por fibra de carbono). As FRFs produzidas foram investigadas (experimental e numericamente) tanto para juntas intactas como para juntas com falha, estas provenientes, por exemplo, do uso em serviço ou então, com resultado do processamento inadequado de um reparo. Com base nessas análises buscou-se, portanto, subsidiar o desenvolvimento de um sistema de monitoramento estrutural a partir da avaliação de seu comportamento dinâmico, medido pelo uso de pastilhas piezelétricas integradas à estrutura. Para que o respectivo objetivo fosse alcançado. Num primeiro momento, a fim de compreender os fenômenos envolvidos, conduziu-se a atividade de revisão bibliográfica, que baseada na consulta dos trabalhos mais recentes publicados sobre a análise de juntas coladas empregando abordagem numérica, analítica e/ou experimental. Em seguida, foram desenvolvidos modelos computacionais preliminares com solução via Método dos Elementos Finitos (MEF), a fim de se obter as diretrizes mínimas para uma proposta de fabricação das juntas híbridas (metal-compósito). Tal estratégia permitiu reduzir efeitos indesejados, que pudessem comprometer os resultados experimentais. Em posse dos resultados computacionais fabricou-se amostras de juntas metal-compósito com e sem dano. Num primeiro momento, foram realizadas análises numéricas através do desenvolvimento de modelos computacionais (com solução via MEF) das juntas, metal-compósito, monitoradas por transdutores piezelétricos. Em seguida, as juntas híbridas foram submetidas a ensaios experimentais dinâmicos, empregando técnicas de monitoramento com auxílio de transdutores piezelétricos e acelerômetros. Por fim, avaliaram-se potencialidades e limitações dos modelos computacionais desenvolvidos, através de estudos de caso, comparando os resultados experimentais com os resultados numéricos. / The herein proposed research has correlates Frequency Response Functions (FRF) of several hybrid titanium-composite (epoxy resin reinforced with carbon fiber) single lap bonded joints. The FRFs were investigated (numerically and experimentally) for joints with and without failures which may arise as the result of in service events or bad maintenance practices. The result of the dynamic analyses provided by the FRFs has substantiated the proposal of a damage detection method using piezoelectric elements capable which are capable to detect minor alterations on the dynamic behavior of the joint. In order to reach the proposed objective, the first action towards the given objective was study the problem through a bibliographic revision of the research subject, for this purpose the most recent published works related to numerical, analytical and experimental analyses of bonded joints were thoroughly evaluated and segregated. Afterwards, models of the joints were proposed using Finite Element Models (FEM) to obtain a preliminary result of the joints behavior to eventually substantiate the manufacturing processes, reducing the amount of material, time and cost of the experiments. Based upon the results of the FEM the coupons were manufactured with and without damages, using the methods and techniques available on the maintenance field for restoration of composite elements. Before proceed to the comparison between the modeled and experimental results, additional models were proposed using previous work\'s results to get results from the piezoelectric monitored joints. Afterwards, all experimental tests were conducted using accelerometers and piezoelectric elements to provide the means through it the advantages and drawbacks of the proposed monitoring method could be checked, by comparison between the experimental and modeled results.

[pt] O aumento dos custos relacionados aos processos de manutenção em estruturas como aeronaves, aliadas à crescente demanda das mesmas, alimentam a necessidade de investimentos em técnicas inovadoras de monitoramento estrutural. Dessa forma, o trabalho realizado nesta tese, busca o desenvolvimento de uma técnica de monitoramento ativo, visando o acompanhamento de parâmetros da estrutura analisada, a fim de identificar e caracterizar processos de dano não visíveis, tais como corrosão e delaminação. A metodologia empregada, teve como base a análise dos padrões de deformação superficial, obtidos com o uso de grades de sensores à fibra óptica baseadas em redes de Bragg (FBG). Inicialmente, tais padrões foram provocados por carregamentos estáticos (tração), e posteriormente por atuadores PTZ fixados à estrutura. Estes últimos são submetidos a uma voltagem alternada e frequência fixa. Esta técnica apresenta todas as vantagens dos sensores FBG (massa e dimensões reduzidas, imunidade eletromagnética, elevado poder de multiplexação e alta sensibilidade entre outras), alem de permitir a visualização de alterações nos padrões de deformação, provocados por danos, através da variação da frequência de excitação. Com relação à interpretação dos resultados, a estratégia empregada consistiu em separar o problema de detecção e caracterização dos danos. Dessa forma, a detecção é realizada comparando a energia das deformações superficiais dos corpos de prova nos casos com e sem defeito, enquanto a caracterização é obtida através a utilização de redes neurais artificiais (RNA), por meio de rotinas de reconhecimento de padrões. / [en] The higher costs related to maintenance processes in structures such as aircraft, coupled with the growing demand of them, fueling the need for investment in innovative techniques for structural monitoring. Thus, the work done in this thesis seeks to develop a technique of active monitoring, aiming at monitoring of structure parameters analyzed in order to identify and characterize processes of hidden damage such as corrosion and delamination. The maid methodology was based on the analysis of patterns of surface deformation, obtained with the use of nets of optical fiber sensors based on fiber Bragg gratings ( FBG ). Initially, these patterns were caused by static loads (tension ), and later by PTZ actuators fixed to the frame, who are subjected to an AC voltage and fixed frequency. This technique has all the advantages of the FBG s sensors (mass and small dimensions, electromagnetic immunity, high multiplexing s power and high sensitivity among others), in addition to allowing visualization of changes in the patterns of deformation caused by damage, by varying the frequency excitation. With respect to the interpretation of the results, the strategy employed was to separate the problem of detection and characterization of damage. Thus, the detection is performed by comparing the deformation energy of the surface of the specimens in the cases with and without defect, whereas the characterization is obtained through the use of artificial neural networks (ANN) by means of pattern recognition routines.

Ce travail porte sur la réalisation de capteurs interdigités (IDT pour InterDigital Transducer) sur des supports piézoélectriques. L’enjeu est double puisqu’il s’agit premièrement de disposer de capteurs efficaces pour générer des ondes de surface acoustiques (SAW pour Surface Acoustic Wave) afin de caractériser la qualité des revêtements et des surfaces de structures. Le deuxième objectif de cette étude est de rendre ces capteurs IDT flexibles afin qu’ils puissent s’adapter non seulement aux différentes géométries planes ou non mais aussi pour qu’ils soient capables de supporter les déformations des structures au cours de leur utilisation. En général, les matériaux piézoélectriques sont rigides et le caractère souple des matériaux est souvent en opposition avec les performances piézoélectriques de ces derniers ; nous avons donc développé des matériaux qui répondent à ces deux exigences : la performance piézoélectrique et la souplesse. Enfin, nous avons privilégié des technologies relativement bon marché pour développer ces capteurs afin d’envisager par la suite, un contrôle continu des structures en intégrant ces capteurs à demeure sur ces dernières. / This work deals with the realization of interdigital sensors (IDT for InterDigital Transducer) on piezoelectric substrates. There is a dual challenge since firstly, the aim is to have efficient sensors to generate surface acoustic waves (SAW) in order to characterize the quality of the coatings and structure surfaces. The second objective of this study is to make these IDT sensors flexible so as to adapt to different geometries of structures and to be able to put up with the deformations of structures in use. Typically, piezoelectric materials are rigid and the flexible nature of the materials is often in opposition to the piezoelectric performance of the latter. We developed materials that meet these two requirements: piezoelectricity and flexibility. Finally, we gave greater importance to relatively cheap technologies to develop these sensors because this allows then to consider continuous monitoring (structural health monitoring) by incorporating these sensors permanently on the structures to be tested.