This research develops two novel experimental techniques based on nonlinear acoustics/ultrasound to provide an ultra-accelerated characterization of alkali-reactivity of aggregates. Alkali-silica reaction (ASR) is a deleterious reaction occurring between reactive siliceous minerals present in some aggregates and alkalis mainly contributed by the cement, but also present in some deicing chemicals. With increasing reports of ASR-induced damage in transportation structures, there is a critical need for fast and reliable test methods for the screening of aggregates and aggregate/paste combinations. Currently, the accelerated mortar bar test (AMBT), which measures expansion, is the most commonly used test method. Also used is the concrete prism test (CPT), another expansion-based method, which requires at least one year testing time, limiting the practical utility of this method. In addition, petrographic analysis can be performed to identify potentially reactive minerals in aggregates but requires training and may not be appropriate for assessment of aggregate/paste combinations. Finally, linear acoustic methods such as wave speed and attenuation measurements can be used for the assessment of ASR, but the sensitivity of linear acoustic methods to ASR-induced damage is considered to be relatively low. Therefore, critical limitations exist in the existing test methods. In light of recent advances in nonlinear acoustics (which are more sensitive to small-scale damage than linear acoustics), the purpose of this research is the development and assessment of an accelerated method for evaluating the potential for alkali reactivity in aggregate and aggregate/paste combinations by combining advanced ultrasonic methods with standard test procedures. In fact, two nonlinear acoustic methods are developed under this research - nonlinear wave modulation spectroscopy (NWMS) and nonlinear impact resonance acoustic spectroscopy (NIRAS) - and are used to characterize the changes in material nonlinearity as a result of the progressive ASR damage during the standard mortar bar and concrete prism testing. Following the AMBT and CPT, nonlinear acoustic techniques are applied to both mortar bars and concrete prism samples. Nonlinearity parameters are defined as the indicator of growing ASR damage, and measurement results clearly show that these nonlinearity parameters are more sensitive to the ASR damage than the linear parameters used in the linear acoustic measurements, particularly at early ages. Different aggregates with varying alkali-reactivity are effectively distinguished with the proposed experimental techniques in a timely manner, particularly for those aggregates with similar levels of reactivity, as determined by AMBT. The effect of a Class C fly ash addition on nonlinear properties was also investigated using the NIRAS measurements through a comparison of test results between mortar samples blended with fly ash and without fly ash. As complementary supports of the experimental results, petrographic analyses and theoretical modeling are also performed, and these results are well correlated with results from the NWMS and NIRAS techniques. Through a comparison with results from accompanying expansion measurements and linear acoustic methods, the proposed nonlinear acoustic techniques show their advantages to accelerate the assessment of alkali-reactivity of aggregates. Under AMBT, reactive aggregates were identifiable as early as a few days of testing. With CPT, reactive aggregates were differentiated as early as a few weeks. Overall, the coupling of the developed nonlinear test methods with standard expansion tests suggests that test durations could be potentially reduced by half, especially for AMBT tests.

Cracks often exist in structural members that are exposed to repeated loading, which will certainly lower the structural integrity. A crack on a structural member introduces a local flexibility which is a function of the crack depth and location. This may cause nonlinear dynamic response of the structure. In this thesis, a new method is suggested to detect and locate a crack in a structural component. The method is based on the fact that nonlinear response of a structure with a crack will be a function of the crack location and crack magnitude. The method suggested is the extension of a recently developed technique for identification of non-linearity in vibrating multi degree of freedom system. In this method, experimentally measured receptances at different forcing levels are used as input, and the existence and location of a nonlinearity are sought. In order to validate the method, simulated experimental data is used. Characteristics of a cracked beam are simulated by using experimentally obtained analytical expressions, given in the literature. The structure itself is modelled by using finite element method. Several case studies are performed to test and demonstrate the applicability, efficiency and sensitivity of the method suggested. The effect of crack depth on nonlinear system response is also studied in numerical examples.

A utilização de técnicas de emissão acústica para detectar e mapear o dano em estruturas tem sofrido grandes avanços nos últimos anos, em parte devido a possibilidade de poder contar com instrumentos de maior exatidão e precisão. Metodologias são utilizadas para, através dos resultados adquiridos, obter informação de como e onde a estrutura investigada está rompendo. Desenvolvimentos teóricos importantes na área de análise sísmica tem trazido um ferramental teórico que pode ser aplicado em estudos de estruturas e corpos de prova. Dentro deste contexto, neste trabalho é apresentado o estudo da localização e caracterização de defeitos utilizando técnicas conhecidas de emissão acústica. Ensaios em materiais de baixo módulo de elasticidade (poliestireno expandido) possibilitou o trabalho com os microfones de baixa frequência disponíveis para realização dos experimentos. Juntamente com os ensaios experimentais, simulações utilizando o método numérico dos elementos discretos (DEM) foram realizados. Os resultados obtidos nos ensaios e nas simulações foram processados e conclusões sobre a forma de ruptura esperada foram feitas. Informações relativas à evolução das cargas durante os ensaios e simulações, e comparativos da evolução com o número de eventos são apresentados. Ensaios de três tamanhos diferentes de corpos de prova permitiram medir o efeito de escala esperado. Técnicas de localização dos eventos em corpos de prova de maiores dimensões também são aplicadas para efetuar a localização de defeitos utilizando emissão acústica, bem como a interpretação e análise dos dados obtidos. Utilizando o cálculo da velocidade de propagação da onda sonora no material, uma técnica de localização foi apresentada e utilizada para calcular posições de zona de fratura, a fim de identificar regiões que possuem defeitos. / The usage of acoustic emission techniques in order to detect damage in structures has undergone great advances in the last years, partly because of the possibility to rely on instruments of highest accuracy and precision. Methodologies are used to obtain information about how and where the structure cracks. Important theoretical developments in the seismic analysis field have provided tools that can be applied in studies on structures and specimens. This work aims to study the localization and characterization of defects using acoustic emission techniques. Experimental tests on specimens with low elasticity modulus gave the possibility to work with the piezoeletric sensors available. Computational analyses using the discrete elements method (DEM) were performed. Conclusions about the expected rupture characteristics are shown. Information about the evolution loading during the tests, and a comparative of events evolution are shown. Tests on three different sizes of specimens allowed the scale effect analysis. Event location techniques on higher length specimens, using acoustic emission, are used to perform defects localization in order to obtain information about the defects position.

A utilização de técnicas de emissão acústica para detectar e mapear o dano em estruturas tem sofrido grandes avanços nos últimos anos, em parte devido a possibilidade de poder contar com instrumentos de maior exatidão e precisão. Metodologias são utilizadas para, através dos resultados adquiridos, obter informação de como e onde a estrutura investigada está rompendo. Desenvolvimentos teóricos importantes na área de análise sísmica tem trazido um ferramental teórico que pode ser aplicado em estudos de estruturas e corpos de prova. Dentro deste contexto, neste trabalho é apresentado o estudo da localização e caracterização de defeitos utilizando técnicas conhecidas de emissão acústica. Ensaios em materiais de baixo módulo de elasticidade (poliestireno expandido) possibilitou o trabalho com os microfones de baixa frequência disponíveis para realização dos experimentos. Juntamente com os ensaios experimentais, simulações utilizando o método numérico dos elementos discretos (DEM) foram realizados. Os resultados obtidos nos ensaios e nas simulações foram processados e conclusões sobre a forma de ruptura esperada foram feitas. Informações relativas à evolução das cargas durante os ensaios e simulações, e comparativos da evolução com o número de eventos são apresentados. Ensaios de três tamanhos diferentes de corpos de prova permitiram medir o efeito de escala esperado. Técnicas de localização dos eventos em corpos de prova de maiores dimensões também são aplicadas para efetuar a localização de defeitos utilizando emissão acústica, bem como a interpretação e análise dos dados obtidos. Utilizando o cálculo da velocidade de propagação da onda sonora no material, uma técnica de localização foi apresentada e utilizada para calcular posições de zona de fratura, a fim de identificar regiões que possuem defeitos. / The usage of acoustic emission techniques in order to detect damage in structures has undergone great advances in the last years, partly because of the possibility to rely on instruments of highest accuracy and precision. Methodologies are used to obtain information about how and where the structure cracks. Important theoretical developments in the seismic analysis field have provided tools that can be applied in studies on structures and specimens. This work aims to study the localization and characterization of defects using acoustic emission techniques. Experimental tests on specimens with low elasticity modulus gave the possibility to work with the piezoeletric sensors available. Computational analyses using the discrete elements method (DEM) were performed. Conclusions about the expected rupture characteristics are shown. Information about the evolution loading during the tests, and a comparative of events evolution are shown. Tests on three different sizes of specimens allowed the scale effect analysis. Event location techniques on higher length specimens, using acoustic emission, are used to perform defects localization in order to obtain information about the defects position.

A utilização de técnicas de emissão acústica para detectar e mapear o dano em estruturas tem sofrido grandes avanços nos últimos anos, em parte devido a possibilidade de poder contar com instrumentos de maior exatidão e precisão. Metodologias são utilizadas para, através dos resultados adquiridos, obter informação de como e onde a estrutura investigada está rompendo. Desenvolvimentos teóricos importantes na área de análise sísmica tem trazido um ferramental teórico que pode ser aplicado em estudos de estruturas e corpos de prova. Dentro deste contexto, neste trabalho é apresentado o estudo da localização e caracterização de defeitos utilizando técnicas conhecidas de emissão acústica. Ensaios em materiais de baixo módulo de elasticidade (poliestireno expandido) possibilitou o trabalho com os microfones de baixa frequência disponíveis para realização dos experimentos. Juntamente com os ensaios experimentais, simulações utilizando o método numérico dos elementos discretos (DEM) foram realizados. Os resultados obtidos nos ensaios e nas simulações foram processados e conclusões sobre a forma de ruptura esperada foram feitas. Informações relativas à evolução das cargas durante os ensaios e simulações, e comparativos da evolução com o número de eventos são apresentados. Ensaios de três tamanhos diferentes de corpos de prova permitiram medir o efeito de escala esperado. Técnicas de localização dos eventos em corpos de prova de maiores dimensões também são aplicadas para efetuar a localização de defeitos utilizando emissão acústica, bem como a interpretação e análise dos dados obtidos. Utilizando o cálculo da velocidade de propagação da onda sonora no material, uma técnica de localização foi apresentada e utilizada para calcular posições de zona de fratura, a fim de identificar regiões que possuem defeitos. / The usage of acoustic emission techniques in order to detect damage in structures has undergone great advances in the last years, partly because of the possibility to rely on instruments of highest accuracy and precision. Methodologies are used to obtain information about how and where the structure cracks. Important theoretical developments in the seismic analysis field have provided tools that can be applied in studies on structures and specimens. This work aims to study the localization and characterization of defects using acoustic emission techniques. Experimental tests on specimens with low elasticity modulus gave the possibility to work with the piezoeletric sensors available. Computational analyses using the discrete elements method (DEM) were performed. Conclusions about the expected rupture characteristics are shown. Information about the evolution loading during the tests, and a comparative of events evolution are shown. Tests on three different sizes of specimens allowed the scale effect analysis. Event location techniques on higher length specimens, using acoustic emission, are used to perform defects localization in order to obtain information about the defects position.

Photogrammetrische Methoden gewinnen zunehmend an Bedeutung im bau­tech­nischen Versuchswesen. Die Auswertung von Bildsequenzen ermöglicht eine kontakt­lose, flächenhafte, hochaufgelöste und hochgenaue Veränderungs­detek­tion von Ober­flächen in der Materialprüfung und Bauwerksüberwachung. Diese Arbeit behan­delt einige Aspekte der Deformationsanalyse auf Basis von Bild­sequenzen mit Hilfe triangulierter Verschiebungsfelder. Zunächst wird auf Unter­suchungen zu Defor­ma­tionen ebener Objektoberflächen, die mit mono­kularen Bild­sequenzen beo­bachtet wurden, eingegangen. Im weiteren Verlauf wird auf Stereobildsequenzen über­ge­gangen, die Deformations­mes­sungen für beliebige Ober­flächen erlauben. Im ersten Teil der Arbeit wird gezeigt, wie Verschiebungsfelder in monokularen Bild­sequenzen bestimmt werden können. Die Bildpunkte, an welche die Verschie­bungen geknüpft sind, werden zu einem Dreiecksnetz trianguliert. Jedes einzelne Dreieck wird auf Änderungen zu der Referenzepoche, die als die erste Epoche ohne jegliche Defor­mation definiert ist, untersucht. Ein gängiges Verfahren zur Analyse solcher Verän­derungen ist die Berechnung von Haupt­dehnungen für jedes Dreieck. Schwell­werte können zur Erkennung deformierter Bereiche und die farbkodierte Darstellung der Hauptdehnungen für eine visuelle Betrachtung genutzt werden. In den räumlich verteilten Hauptdehnungen sowie im zeitlichen Ablauf treten Rausch­effekte auf. Deshalb werden verschiedene Filtermethoden zur Rausch­unter­drückung untersucht. Dabei kommt ein Filter zum Einsatz, der gleichzeitig in der räumlichen sowie der zeitlichen Dimension filtert. Es werden aber auch Filter unter­sucht, die in beiden Dimensionen getrennt filtern. Aus den Hauptdehnungen können nicht direkt Rissbreiten abgeleitet werden. Diese spielen für die Materialprüfung im Bauwesen allerdings eine wichtige Rolle, wes­wegen sich diese Arbeit auch mit der Berechnung von Riss­breiten in Dreiecks­netzen befasst. Als deformierte Dreiecke werden diejenigen detektiert, deren Hauptdehnung einen Schwellwert überschreiten. Für diese Kandidaten werden im Folgenden Rissbreiten bestimmt. Drei verschiedene Verfahren für die Ermittlung von Rissbreiten werden vorgestellt und verglichen. Die Dehnbarkeit faserbewehrter Komposite, die unter anderem zur Verstärkung von Mauern und anderen Bauwerken verwendet werden, wird bei Belastung durch die Bildung multipler Rissstrukturen gewährleistet. Auf Grund dessen widmet sich ein weiterer Teil der Dissertation der Auswertung multipler Riss­strukturen. Hierzu werden dichte Verschiebungsfelder berechnet. Dann wird zunächst eine Auswahl der verfolgten Punkte genutzt, um ein grobes Dreiecks­netz zu generieren. Deformierte Dreiecke der ausgedünnten triangu­lierten Punktmenge werden mit dem Betrag des relativen Trans­lations­vektors, der als Deformations­maß eingeführt wird, detektiert. Eine iterative Verdichtung des Dreiecknetzes in defor­mierten Bereichen ermöglicht die Auswertung enger Riss­muster. Zudem erlaubt eine Ausgleichung, dass nicht-triangulierte Punkte des dichten Verschie­bungs­feldes in die Rissbreiten­berechnung einbe­zogen werden können. Ein weiterer Bestandteil der Arbeit ist die Betrachtung unebener Oberflächen, die mit Stereokamerasystemen beobachtet werden. Dazu werden die Algorithmen für die zweidimensionale Auswertung entsprechend übertragen und erweitert. Auf Basis von Verschiebungsfeldern dreidimensionaler Punkte wird auch hier ein Dreiecksnetz zur Änderungsdetektion genutzt. So wird am Beispiel von dynamischen Dehnungstests an zylindrischen Probe­körpern ein Algorithmus zur Rissbreitenmessung auf nicht ebenen Ober­flächen vorge­stellt. Dabei wird angenommen, dass die Defor­mationen ausschließlich tangential zur Oberfläche auftreten. Dies erlaubt die Transformation (Kongruenz­abbildung) der Dreiecke in einen zwei­dimen­sionalen Raum und auch eine zwei­dimensionale Auswertung. Außerdem wird eine Methode zur Berechnung des dreidimensionalen Riss­öffnungs­vektors präsentiert. Dieses Verfahren ist eine Erweiterung zum vorher­gehenden Algorithmus und erlaubt zudem die Vermessung vertikaler Defor­ma­tionen. Defor­mierte Dreiecke im trian­gulierten dreidimensionalen Verschie­bungs­feld werden mit Hilfe des zwei­dimen­sionalen Relativ­translations­vektor­betrags der in den zwei­dimen­sionalen Raum transformierten Dreiecke detek­tiert. Anschließend folgt für alle defor­mierten Dreiecke durch Hinzunahme min­des­tens eines undeformierten Nachbar­dreiecks die Berechnung eines drei­dimen­sionalen relativen Trans­lations­vektors, mit Hilfe dessen die Komponenten des Riss­öffnungsvektors ermittelt werden.:Kurzfassung iii Abstract v 1. Einführung 1 1.1. Struktur der Arbeit 1 1.2. Motivation 2 1.3. Verwandte Arbeiten 4 1.4. Ziele der Arbeit 7 2. Photogrammetrische Deformationsmessung in monokularen Bildsequenzen 8 2.1. Filtermethoden in Dreiecksnetzen 9 2.2. Rissbreitenberechnung mit Hilfe von Dreiecksnetzen 19 2.3. Strategie zur Rissbreitenmessung für multiple Rissstrukturen 29 3. Photogrammetrische Deformationsmessung in Stereobildsequenzen 50 3.1. Rissbreitenberechnung für tangentiale Deformationen auf nicht ebenen Oberflächen mit gegebenem 3D-Verschiebungsfeld 51 3.2. Berechnung des dreidimensionalen Rissöffnungsvektors bei gegebenem 3D-Verschiebungsfeld 59 4. Diskussion 70 5. Ausblick 77 5.1. Bestimmung der Anzahl der Risse 77 5.2. Rissspitzenbestimmung und -verfolgung 78 5.3. Anwendung der entwickelten Algorithmen auf Voxeldaten 78 5.4. Modellerweiterung durch Relativrotation 82 5.5. Genauigkeitssteigerungen für die Rissposition 82 5.6 Verbesserung der Rissnormalenschätzung 82 Literaturverzeichnis 83 Abkürzungsverzeichnis 89 Tabellenverzeichnis 90 Abbildungsverzeichnis 90 / Photogrammetric methods are gaining importance in civil engineering material testing and structural health monitoring. The analysis of image sequences ensures an extensive change detection of surfaces with a high spatial resolution and a high accuracy. This thesis deals with some aspects of deformation analysis based on image sequences and triangulated displacement fields. At the beginning, the examination of planar surfaces of specimens observed with monocular image sequences is considered. Later, a transition to stereo image sequences is given because they allow a deformation measurement of arbitrary surfaces. The first part of the thesis shows how to derive displacement fields from monocular image sequences. The matching points corresponding to the displace­ments are triangulated into a mesh. Each triangle is compared to the reference epoch which is defined as the first time epoch under zero load without any deformation. As a current method, principal strains are used to detect deformations. Thresholds can be used to find deformed areas. In addition, color-coded maps of the principal strains are helpful for a visual detection. In the field of the principal strains, noise effects appear in the spatial as well as in the temporal domain. Therefore, different filter methods are applied to reduce noise. In addition to filter techniques that are applied independently in the time and the spatial domain, a combined spatio-temporal filter is tested. Crack widths cannot be derived directly from principal strains but crack widths are an important issue in civil engineering material testing. For this reason, this thesis also gives attention to the computation of crack widths in triangle meshes. The principal strains of the triangles are tested for exceeding a threshold to detect deformed triangles. For the deformed triangles, crack widths are computed. Three different methods for the crack width determination are presented and compared. Multiple cracking ensures the ductility of loaded fiber-reinforced composites used to strengthen walls among other things. Therefore, another part of the dissertation deals with the photogrammetric analysis of multiple crack patterns. Herein, dense displacement fields are computed. Then, a thinned-out set of points is triangulated into a mesh. For each triangle, the norm of the relative translations vector defined as a new quantity to detect deformations is deter­mined and used to find cracked triangles. The mesh is densified iteratively in deformed areas to ensure an analysis of narrow crack structures. In addition, a least squares algorithm is presented which allows that points of the displace­ment field, that are not part of the mesh, can be included in the crack width computation. A further part of the dissertation deals with non-planar surfaces observed with stereo camera systems. The algorithms of the two dimensional analysis are adapted and extended to use them for these applications. These methods are based on three dimensional displacement fields and also use triangle meshes to detect deformed areas. One algorithm concentrates on the crack width measurement of non-planar surfaces with deformations that are only tangential to the surface. The method is applied on a cylindrical specimen in a dynamic tension test. The assumption that deformations are tangential to the surface allows the transformation of the triangles in the two dimensional space and also a two dimensional analysis. In addition, an algorithm for the computation of the three dimensional crack opening vectors is presented. This method is an extension to the foregoing algorithm and is capable of measuring vertical deformations. To find deformed triangles in the triangulated three dimensional displacement field, the triangles are transformed in the two dimensional space in a first step. In a second step, the norm of the two dimensional relative translation vector is determined and tested if it exceeds a threshold. In the following, for each deformed triangle, the three dimensional relative translation vector is computed using a undeformed neighbor triangle. At the end, the three dimensional relative translation vectors can be transformed to the crack opening vectors.:Kurzfassung iii Abstract v 1. Einführung 1 1.1. Struktur der Arbeit 1 1.2. Motivation 2 1.3. Verwandte Arbeiten 4 1.4. Ziele der Arbeit 7 2. Photogrammetrische Deformationsmessung in monokularen Bildsequenzen 8 2.1. Filtermethoden in Dreiecksnetzen 9 2.2. Rissbreitenberechnung mit Hilfe von Dreiecksnetzen 19 2.3. Strategie zur Rissbreitenmessung für multiple Rissstrukturen 29 3. Photogrammetrische Deformationsmessung in Stereobildsequenzen 50 3.1. Rissbreitenberechnung für tangentiale Deformationen auf nicht ebenen Oberflächen mit gegebenem 3D-Verschiebungsfeld 51 3.2. Berechnung des dreidimensionalen Rissöffnungsvektors bei gegebenem 3D-Verschiebungsfeld 59 4. Diskussion 70 5. Ausblick 77 5.1. Bestimmung der Anzahl der Risse 77 5.2. Rissspitzenbestimmung und -verfolgung 78 5.3. Anwendung der entwickelten Algorithmen auf Voxeldaten 78 5.4. Modellerweiterung durch Relativrotation 82 5.5. Genauigkeitssteigerungen für die Rissposition 82 5.6 Verbesserung der Rissnormalenschätzung 82 Literaturverzeichnis 83 Abkürzungsverzeichnis 89 Tabellenverzeichnis 90 Abbildungsverzeichnis 90

This master thesis is about to investigate what opportunities we have with a impedance varying probe on different material under test. This report begins with a theory part with the focus on; electromagnetic principles, material characterizations and the principle behind the measurement setup. The methods is describing the sensor probes affection on the specimen, the induced currents location and the method for crack detection and lift-off measurements. The result chapter shows the measured impedance created by our setup, as well as the potential and the weak points of the system. In the conclusion and discussion chapter we will go through what modifications can be done to increase the quality of the measurements.

No description available.

Sand casting is used to manufacture large metal workpieces. The processing is executed by pouring molten metal into a sand mold. During the process, the mold is subjected to mechanical and thermal stress. It is of economic interest to inspect the molds for defects that can affect casting results, in the worst case leading to discarded products. This thesis investigates and proposes an automated solution for inspecting surface cracks in sand molds. A hybrid solution using image processing and convolutional neural networks has been developed. The first is to find and implement a crack detection method that can perform equally well or better than a human. The second objective is to investigate the amount of training data needed. Twenty-one machine learning models have been trained to evaluate the impact training data size along with transfer learning, fine-tuning, data augmentation, and image processing have on performance. As a result, it was found that the image processing part of the method is not effective in finding cracks in its current form. However, the convolutional neural network still achieves good performance. The method has been trained and tested on sand mold core images captured with a test workbench along with images of concrete walls and pavement acquired from the SDNET2018 data set. Sand mold images achieve 82% accuracy and 79% recall when training on 90 images while testing on 28 images separate from training. A maximal performance of 97.9% accuracy and 99.7% recall is achieved when training on 5400 SDNET2018 images and then testing on 608 images. When training on 100 SDNET2018 images and tested on the same 608 images, a performance of 86.0% and 96.7% recall is achieved. It is concluded that the proposed solution is feasible. Transfer learning and data augmentation are essential techniques to achieve good performance if a small amount of data is available, while fine-tuning may give a slight performance boost. Further work should be performed considering the impact of curved geometry on performance. Investigating alternative structures of the convolutional neural network and testing alternative hyperparameters may improve generalization performance. The image processing performance may be improved if the manufacturing process is more precisely defined, as parameters can be more optimally tuned.

No description available.