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1
Mirzaei, Majid. "On fatigue crack closure analysis and measurement." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70339.
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This thesis describes a novel approach to the analysis of fatigue crack closure phenomena. Based on the proposed model, the combined effect of residual plastic stretch, asperity mismatch, and corrosion debris on the closure behavior of a fatigue crack can be simulated by a hypothetical rigid insert located in an ideal crack wake. Accordingly, the crack closing period can be modeled by a gradual contact between the ideal crack faces and the rigid insert.The formulation of the model results in a set of equations which can predict the closure load as well as the load-CMOD characteristics using the residual CMOD at zero load as a unique experimental input. Based on the initial model, the final form of the derived equations are either logarithmic or quadratic. While the latter can be solved directly for the closure load, the former requires a numerical solution.
The model qualitatively predicts the effect of gradual crack wake removal on the crack closure load level and the load-CMOD behavior. It also accounts for the response of a cracked component to an anomalous crack wake formed by single or block overloads.
The model is verified, both qualitatively and quantitatively, using specifically designed experimental techniques, a variety of specimen sizes, and two different alloys.
2
Arne, Kevin C. "Crack depth measurement in reinforced concrete using ultrasonic techniques." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51914.
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Concrete is the most widely used construction material in the world, so the assessment of damage in concrete is critical from the point of view of both safety and cost. Of particular interest are macro cracks that extend through the concrete cover of the reinforcement, which can potentially expose the reinforcement to corrosive elements. The high density of scatterers such as aggregate and voids in concrete makes quantitative imaging with coherent ultrasound difficult. As an alternative, this research focuses on diffuse energy based ultrasonic methods rather than coherent ultrasonic methods for crack depth assessment. Two types of ultrasonic measurements were made on real cracks formed under four point bending: one that focuses on time of flight measurements from an impactor; while the other uses the arrival time of maximum energy in a diffuse field excited by an impulsive load from a transducer. Each of these ultrasonic techniques is used to interrogate a macro crack in a concrete beam, and the results are compared to determine their accuracy and robustness. The actual crack depth is determined using direct surface measurements and a destructive dye-injected approach with drilled cores. The results suggest that the diffusion method, using a maximum energy approach, more accurately estimates the crack than visual inspection and impact echo methods, which overestimate the depth.
3
Wallhead, Ian. "Crack closure measurement by the optical method of caustics." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241083.
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Kianzad, Siamak. "Measurement of Thermal Insulation properties of TBC inside the Combustion chamber." Thesis, Luleå tekniska universitet, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-61917.
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This master thesis project was performed in collaboration with Scania CV AB, Engine Materials group. The purpose with the project was to investigate different ceramic TBC (Thermal Barrier Coating) thermal insulation properties inside the combustion chamber. Experimental testing was performed with a Single-Cylinder engine with TBC deposited on selected components. A dummy-valve was developed and manufactured specifically for this test in order to enable a water cooling system and to ease the testing procedure. The dummy-valve consists of a headlock, socket, valve poppet and valve shaft. Additionally, a copper ring is mounted between the cylinder head and the valve poppet to seal the system from combustion gases. Thermocouples attached to the modified valve poppet and valve shaft measured the temperature during engine test to calculate the heat flux. The TBCs consisted of three different materials: 7-8% yttrium-stabilized zirconia (8YSZ), gadolinium zirconia and lanthanum zirconia. The 8YSZ TBC was tested as standard, but also with microstructural modifications. Modifications such as pre-induced segmented cracks, nanostructured zones and sealed porosity were used. The results indicated that the heat flux of 8YSZ-standard, 8YSZ-nano and 8YSZ-segmented cracks was in level with the steel reference. In the case of 8YSZ-sealed porosity the heat flux was measured higher than the steel reference. Since 8YSZ-standard and 8YSZ-sealed porosity are deposited with the same powder it is believed that the high heat flux is caused by radiative heat transfer. The remaining samples have had some microstructural changes during engine testing. 8YSZ-nano had undergone sintering and its nanostructured zones became fewer and almost gone after engine testing leading to less heat barrier in the top coat of the TBC. However, for 8YSZ-segmented cracks and gadolinium zirconia lower heat flux was measured due to the appearance of horizontal cracks. These cracks are believed to act as internal barriers as they are orientated perpendicular to the heat flow. During long-time (5 hour) engine tests the 8YSZ-standard exhibited the same phenomena: a decrease in heat flux due to propagation of horizontal cracks. One-dimensional heat flux was not achieved and the main reason for that was caused by heating and cooling of the shafts outer surface. However, the dummy-valve system has proven to be a quick, easy and stable to perform tests with a Single-Cylinder engine. Both water-cooling and long-time engine tests were conducted with minor issues. The dummy-valve has been further developed for future tests. Changes to the valve shaft are the most remarkable: smaller diameter to reduce heat transfer and smaller pockets to ensure better thermocouple positioning. Another issue was gas leakage from the combustion chamber through the copper ring and valve poppet joint. The copper ring will be designed with a 1 mm thick track to improve sealing, hence better attachment to the valve poppet.
5
Huntley, J. M. "Laser speckle and its application to strength measurement and crack propagation." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233260.
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The technique of laser speckle photography has been developed with the aim of measuring the strain field around the tip of a fast crack. An image processing system to allow automatic point-by-point analysis of a speckle photograph is described. The Young's fringes diffraction pattern, produced by directing a narrow laser beam through the photograph, is digitised and processed by computer. Two algorithms have been developed based on Fourier and Walsh spectral analysis. The system can measure speckle displacements with an accuracy of better than 0.1 μm. A new technique for measuring time-varying displacement fields by multiple exposure of a single photograph is presented. Results are shown from a five-exposure speckle photograph of a cantilever deformed under quasi-static conditions. Extension of the technique to dynamic problems requires a stroboscopic laser light source; one chapter deals with the development of a Q-switched ruby laser for this purpose. Modulation of the cavity losses with a Pockels cell at up to 1 MHz results in a train of short (~50 ns) light pulses at the modulation frequency. Results are presented from the analysis of speckle photographs of cracks in polymethylmethacrylate (PMMA) under quasi-static loading. Three different data analysis methods for estimating the stress intensity factor from the displacement field are proposed and evaluated. Preliminary results from dynamic crack propagation studies are described. The dynamic stress intensity factor is estimated from double exposure speckle photographs of fast cracks in PMMA, recorded with the ruby laser in double pulse mode. The application of the techniques of moire and high speed photography to the study of dynamic fracture is also discussed; results are presented from a sequence of moire photographs recorded at 5 x 105 frames s-1 . Further topics covered in the dissertation include a theoretical analysis of viscoelastic losses as a function of crack velocity, and strain-to-failure measurements on plastic bonded explosives in the Brazilian test using laser speckle photography.
6
Kamil, Ridha. "Processing improvement of moiré interferometry for accurate crack-tip deformation measurement." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=1962.
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Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains v, 81 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 80-81).
7
Sahney, Reena Carleton University Dissertation Engineering Mechanical and Aerospace. "Development of a crack measurement system for CANDU pressure tube burst testing." Ottawa, 1994.
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8
La, Porta Filomena A. "High magnification moireÌ interferometric measurement of crack tip deformation fields in stainless steels." Thesis, Loughborough University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420985.
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Zhang, Cheng. "Influence of surface roughness on thermography measurement." Thesis, Högskolan Väst, Avd för automationssystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-6842.
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This university Bachelor's Thesis was performed to explore the influence of surface roughness on the thermography measurement. Thermography is a non-destructive testing method which can be used to detect cracks. However, it is hard to define how the surface roughness influences the emissivity and the result of a thermography measurement, as well as how the angle of the excitation source influences the result. Therefore, this work aims to define how the heating angle and surface roughness influence the thermography measurement, define the relationship between surface roughness and emissivity for the same crack, and define the influence of the angles which composed of the heating source, the direction of crack and the direction of surface roughness on thermography measurement. In this report, the theories of radiation and Signal-to-noise ratio (SNR) were explained, clearly. Also, two kinds of experiments were set up. One is focus on how the heating angle influence the thermography measurement, the other is focus on how the angle of the heating source, in relation to the crack direction and the direction of surface roughness, influence the SNR value. The conclusions of these experiments are that the heating of a crack increases as the angle decreases (from wide side to narrow side) and the angle ofincreases (from horizontal to vertical). Moreover, the SNR value decreases as the surface roughness increases. For the same surface roughness, the SNR value increases with increased crack angle (0°, 45° or 90°) and with decreased sample position angle (horizontal, 45°or vertical). What is more, the higher surface roughness, the larger the influence of the crack angle and the sample position angle. Finally, when the surface is polish, the crack angle and the sample position angle does not have any influence.
10
Mostafavi, Reza. "Non-uniform AC field measurement in NDE of metals : analysis and an array system." Thesis, University of Essex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285852.
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11
Roberge, Douglas M. "Experimental crack length measurement under variable temperature using a thin film AC potential difference technique." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23477.pdf.
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12
Melin, L. Gunnar. "Moiré techniques for measurement of the deformation field at crack tips in fiber composite materials." Licentiate thesis, Luleå tekniska universitet, 1995. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26502.
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13
Chenelle, Brendan F. "Friction Stir Welding in Wrought and Cast Aluminum Alloys: Microstructure, Residual Stress, Fatigue Crack Growth Mechanisms, and Novel Applications." Digital WPI, 2011. https://digitalcommons.wpi.edu/etd-theses/1215.
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Friction Stir Welding (FSW) is a new solid-state welding process that shows great promise for use in the aerospace and transportation industries. One of the primary benefits of this process is that mechanical properties of the base material are not as severely degraded as they are with conventional fusion welding. However, fatigue crack initiation and growth properties of the resulting weld nugget are not fully understood at this time. The primary goal of this project is to characterize the fatigue crack growth properties of friction stir welds in 6061-T6 aluminum as relates to the microstructural evolution of the weld. This was accomplished by producing friction stir welds and testing fatigue crack growth response in different crack orientations with respect to the weld. In addition, residual stress measurements were conducted for all cases, using both the crack compliance and contour methods. The results from the methods were compared in order to evaluate the accuracy of each method. Being an immature technology, the potential for discovery of new applications for the FSW process exist. With this in mind, novel applications of the FSW process, including the addition of particles during welding were explored. The first step was the investigation of property changes that occur when secondary cast phases are refined using the FSW process. The FSW process successfully refined all secondary phases in A380 and A356, producing an increase in hardness. Next, methods for the creation of particle metal matrix composites using FSW will be investigated. Nano-scale alumina particles were successfully added to the matrix and homogenously distributed. Using multiple weld passes through the composite was found to increase the uniformity of particle distribution. However, the alumina particle composite failed to provide any statistically significant hardness increase over the base material. The FSW process was also evaluated for weldability of traditionally difficult alloy systems. FSW was found to show very good weldability for dissimilar cast and wrought alloys, as well as for high-pressure die castings. Lastly, the feasibility of friction stir welding/processing in repairing crack defects in complex structural members in combination with cold-spray technology was determined. Friction Stir processing was used on a cold spray 6061-T6 block, resulting in significant increases in hardness over the base material, as well as a reduction in porosity. In addition, FSP was shown to eliminate crack-type defects in cold spray materials, a finding that has important applications in part repair. The deliverables of this work include an understanding of the fatigue crack growth response of FSW/FSP 6061-T6, as well as a feasibility study exploring novel uses for the FSW/FSP process. In addition, the deliverables include CNC code, fixtures, procedures, and analytical code for the creation and analysis of FSW/FSP joints. This will be important for the continuation of FSW/FSP work at WPI.
14
Alfredsson, Bo. "A study on contact fatigue mechanisms." Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3028.
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15
Hampel, Uwe. "Photogrammetrische Erfassung der Verformungs- und Rissentwicklung bei baumechanischen Untersuchungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1213691909563-21395.
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Verfahren der digitalen Nahbereichsphotogrammetrie ermöglichen eine dreidimensionale Erfassung von Objekten und stellen damit interessante Lösungsansätze für Messaufgaben im Bautechnischen Mess- und Versuchswesen dar. Ihr Einsatz bietet bei einer Vielzahl baumechanischer Untersuchungen die Voraussetzung für eine kontinuierliche, zeitsynchrone Objektoberflächenerfassung bei kurz- und langzeitigen Belastungsversuchen im Labor und in situ. Die daraus resultierenden Möglichkeiten der kontinuierlichen Erfassung von Verformungs-, Riss- und Schädigungsentwicklungen an Objektoberflächen stellen für viele experimentelle Untersuchungen im Bauingenieurwesen eine signifikante Qualitätssteigerung dar, die mit klassischen Messtechniken – wie z. B. Dehnmessstreifen oder induktiven Wegaufnehmern – nur bedingt bzw. nicht realisiert werden kann. Um das Potential der digitalen Nahbereichsphotogrammetrie zur kontinuierlichen Erfassung der Verformungs-, Riss- und Schädigungsentwicklung an Objektoberflächen bei baumechanischen Untersuchungen erfassen zu können, wurden – aufbauend auf den bekannten Grundlagen und Lösungsansätzen – systematische Untersuchungen durchgeführt. Diese bildeten den Ausgangspunkt für den Einsatz photogrammetrischer Verfahren bei experimentellen Untersuchungen in den verschiedenen Teildisziplinen des Bauingenieurwesens, z. B. im Holz-, Massiv-, Mauerwerks-, Stahl- und Straßenbau. Die photogrammetrisch zu erfassenden Versuchsobjekte – einschließlich ihrer Veränderungen bei den Belastungsversuchen – waren dabei u. a. kleinformatige Prüfkörper und Baukonstruktionen aus den verschiedensten Materialien bzw. Verbundmaterialien. Bei den anwendungsorientierten Untersuchungen musste beachtet werden, dass aufgrund der z. T. sehr heterogenen Anforderungen und der zahlreichen Möglichkeiten, die beim Einsatz photogrammetrischer Verfahren denkbar waren, die Notwendigkeit der Auswahl und ggf. einer Weiter- bzw. Neuentwicklung geeigneter Systeme, effizienter Verfahren und optimaler Auswertealgorithmen der digitalen Nahbereichsphotogrammetrie bestand. In diesem Zusammenhang wurde mit der systematischen Zusammenstellung und Untersuchung relevanter Einflussgrößen begonnen. Diese waren oftmals durch die jeweiligen photogrammetrischen Messprozesse und Messaufgaben beeinflusst. Die Ergebnisse machen deutlich, dass die digitale Nahbereichsphotogrammetrie ein flexibel anwendbares Werkzeug für die Erfassung der Verformungs-, Riss- und Schädigungsentwicklung bei baumechanischen Untersuchungen darstellt. Spezielle Messaufgaben stellen im Bautechnischen Mess- und Versuchswesen oftmals sehr hohe Anforderungen an die Messgenauigkeit, die Robustheit und das Messvolumen. Sie erfordern optimierte Verfahren und führten im Zusammenhang mit der vorliegenden Arbeit zu einer Reihe von Lösungen, wie beispielsweise der 2.5D-Objekterfassung auf Basis der Dynamischen Projektiven Transformation oder der Objekterfassung mittels Spiegelphotogrammetrie. Im Hinblick auf die Objektsignalisierung wurde eine intensitätsbasierte Messmarke entwickelt. Diese ermöglicht besonders bei sehr hochgenauen Deformations- bzw. Dehnungsmessungen ein großes Genauigkeitspotential im Sub-Pixelbereich, das im 1/100 eines Pixels liegt. In Bezug auf die photogrammetrischen Auswerteprozesse wurden optimierte Bildzuordnungsverfahren implementiert, die beispielsweise eine Punkteinmessung von bis zu 60.000 Punkten pro Sekunde ermöglichen und eine Grundlage für die flächenhafte Rissanalyse darstellen. In Bezug auf die qualitative und quantitative Risserfassung wurden verschiedene Verfahren entwickelt. Diese ermöglichen z. B. die lastabhängige Erfassung der Rissposition und -breite in Messprofilen. In einem Messbereich von 100 mm x 100 mm konnten beispielsweise Verformungen mit einer Genauigkeit bis 1 µm und Rissbreiten ab 3 µm erfasst werden. Im Zusammenhang mit den zahlreichen anwendungsbezogenen Untersuchungen entstanden immer wieder Fragen hinsichtlich der Faktoren, die einen Einfluss auf den photogrammetrischen Messprozess im Bautechnischen Mess- und Versuchswesen ausüben. Aufgrund der zahlreichen Einflussgrößen, die als Steuer- bzw. Störgrößen eine mögliche Wirkung auf bauspezifische photogrammetrische Messprozesse ausüben können, wurde im Rahmen der vorliegenden Arbeit mit deren systematischer Zusammenstellung relevanter Einflussgrößen begonnen. Die Relevanz einzelner Einflussgrößen konnte durch Untersuchungen bereits bestätigt werden. Um eine ganzheitliche Bewertung aller relevanten Einflussgrößen aufgabenabhängig vornehmen zu können, wurde ein spezieller Versuchsstand entwickelt. Dieser ermöglicht eine vollautomatisierte systematische Untersuchung bauspezifischer photogrammetrischer Messprozesse unter definierten Versuchsbedingungen und dient dem systematischen Einsatz photogrammetrischer Verfahren im Bautechnischen Mess- und Versuchswesen hinsichtlich der Absicherung bestehender Messaufgaben, kann aber auch zu weiteren neuen und optimierten Messprozessen führenMethods of digital close range photogrammetry are a useful tool for the measurement of three-dimensional objects in civil engineering material testing. They are generally suitable for automatic measurements with chronological synchronism of object-surfaces during short and long time load tests in laboratories and in situ. The methods provide an opportunity for measuring deformations, cracks and damages at the object-surfaces during load tests in civil engineering material testing. These possibilities can present new results for a lot of applications in civil engineering material testing. Displacement and deformation measurements still rely on wire strain gauges or inductive displacement transducers. However, they are not suitable for a large number of measurement points or the detection of cracks during load tests. First of all, a number of systematic investigations was conducted. This was necessary to identify capable methods of the digital photogrammetry for the measuring of deformations, cracks and damages at object-surfaces during load tests in civil engineering material testing. These investigations laid the foundation for practical measurements during short and long time load tests of samples and constructions from different parts of the civil engineering (e.g. timber construction, solid structure, stell and road construction). The application-oriented research in civil engineering material testing demonstrates the wide range of demands on systems and methods of digital close range photogrammetry have to meet. Often the methods and systems of digital close range photogrammetry had to be modified or developed. In this context the systematic analysis of relevant determining factors was started.The results demonstrate that the methods and systems of digital close range photogrammetry are a suitable and flexible tool for the measurement of deformations, cracks and damages at the object-surfaces in civil engineering material testing. In addition, the special experiments in civil engineering material testing demonstrate the high requirements laid upon methods and systems of the digital closed range photogrammetry, for instance regarding with the measurement resolution/range and robustness processes. This was the motivation to optimize and to develop methods and systems for the special measurement tasks in civil engineering material testing, for instance a 2.5D measurement technique based on the Dynamic Projective Transformation (DPT) or the use of mirrors. Also a special measurement target was developed. This type of measurement target modifies intensities and is ideal for high deformation measurements (1/100 pixel). The large number of points in conjunction with area-based measurements require time-optimized methods for the analysis process. The modified and developed methods/programs enable fast analysis-processes, e.g. in conjunction with point-matching process 60.000 points per second.The developed crack-detection-methods allow area- and profile-based to analyze the load-dependent position and width of cracks, e.g. cracks > 3 µm (100 mm x 100 mm). A main target of this work was to compile all relevant determining factors regarding the application of the digital close range photogrammetry during load tests in civil engineering material testing. To a large extent, this target was reached. However, the compilation of all relevant determining factors requires a special experimental set-up. This experimental set-up was developed. In the future, it may enable the automatic research of all significant determining factors. The results can be used to qualify or optimize the established methods and processes. Also it's possible that the results generates new measurement processes
16
Kandili, Kawan. "A research study for inspection and detection on conductive materials." Thesis, Mittuniversitetet, Institutionen för elektronikkonstruktion, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-39619.
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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.
17
Hampel, Uwe. "Photogrammetrische Erfassung der Verformungs- und Rissentwicklung bei baumechanischen Untersuchungen." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23829.
Full textAbstract:
Verfahren der digitalen Nahbereichsphotogrammetrie ermöglichen eine dreidimensionale Erfassung von Objekten und stellen damit interessante Lösungsansätze für Messaufgaben im Bautechnischen Mess- und Versuchswesen dar. Ihr Einsatz bietet bei einer Vielzahl baumechanischer Untersuchungen die Voraussetzung für eine kontinuierliche, zeitsynchrone Objektoberflächenerfassung bei kurz- und langzeitigen Belastungsversuchen im Labor und in situ. Die daraus resultierenden Möglichkeiten der kontinuierlichen Erfassung von Verformungs-, Riss- und Schädigungsentwicklungen an Objektoberflächen stellen für viele experimentelle Untersuchungen im Bauingenieurwesen eine signifikante Qualitätssteigerung dar, die mit klassischen Messtechniken – wie z. B. Dehnmessstreifen oder induktiven Wegaufnehmern – nur bedingt bzw. nicht realisiert werden kann. Um das Potential der digitalen Nahbereichsphotogrammetrie zur kontinuierlichen Erfassung der Verformungs-, Riss- und Schädigungsentwicklung an Objektoberflächen bei baumechanischen Untersuchungen erfassen zu können, wurden – aufbauend auf den bekannten Grundlagen und Lösungsansätzen – systematische Untersuchungen durchgeführt. Diese bildeten den Ausgangspunkt für den Einsatz photogrammetrischer Verfahren bei experimentellen Untersuchungen in den verschiedenen Teildisziplinen des Bauingenieurwesens, z. B. im Holz-, Massiv-, Mauerwerks-, Stahl- und Straßenbau. Die photogrammetrisch zu erfassenden Versuchsobjekte – einschließlich ihrer Veränderungen bei den Belastungsversuchen – waren dabei u. a. kleinformatige Prüfkörper und Baukonstruktionen aus den verschiedensten Materialien bzw. Verbundmaterialien. Bei den anwendungsorientierten Untersuchungen musste beachtet werden, dass aufgrund der z. T. sehr heterogenen Anforderungen und der zahlreichen Möglichkeiten, die beim Einsatz photogrammetrischer Verfahren denkbar waren, die Notwendigkeit der Auswahl und ggf. einer Weiter- bzw. Neuentwicklung geeigneter Systeme, effizienter Verfahren und optimaler Auswertealgorithmen der digitalen Nahbereichsphotogrammetrie bestand. In diesem Zusammenhang wurde mit der systematischen Zusammenstellung und Untersuchung relevanter Einflussgrößen begonnen. Diese waren oftmals durch die jeweiligen photogrammetrischen Messprozesse und Messaufgaben beeinflusst. Die Ergebnisse machen deutlich, dass die digitale Nahbereichsphotogrammetrie ein flexibel anwendbares Werkzeug für die Erfassung der Verformungs-, Riss- und Schädigungsentwicklung bei baumechanischen Untersuchungen darstellt. Spezielle Messaufgaben stellen im Bautechnischen Mess- und Versuchswesen oftmals sehr hohe Anforderungen an die Messgenauigkeit, die Robustheit und das Messvolumen. Sie erfordern optimierte Verfahren und führten im Zusammenhang mit der vorliegenden Arbeit zu einer Reihe von Lösungen, wie beispielsweise der 2.5D-Objekterfassung auf Basis der Dynamischen Projektiven Transformation oder der Objekterfassung mittels Spiegelphotogrammetrie. Im Hinblick auf die Objektsignalisierung wurde eine intensitätsbasierte Messmarke entwickelt. Diese ermöglicht besonders bei sehr hochgenauen Deformations- bzw. Dehnungsmessungen ein großes Genauigkeitspotential im Sub-Pixelbereich, das im 1/100 eines Pixels liegt. In Bezug auf die photogrammetrischen Auswerteprozesse wurden optimierte Bildzuordnungsverfahren implementiert, die beispielsweise eine Punkteinmessung von bis zu 60.000 Punkten pro Sekunde ermöglichen und eine Grundlage für die flächenhafte Rissanalyse darstellen. In Bezug auf die qualitative und quantitative Risserfassung wurden verschiedene Verfahren entwickelt. Diese ermöglichen z. B. die lastabhängige Erfassung der Rissposition und -breite in Messprofilen. In einem Messbereich von 100 mm x 100 mm konnten beispielsweise Verformungen mit einer Genauigkeit bis 1 µm und Rissbreiten ab 3 µm erfasst werden. Im Zusammenhang mit den zahlreichen anwendungsbezogenen Untersuchungen entstanden immer wieder Fragen hinsichtlich der Faktoren, die einen Einfluss auf den photogrammetrischen Messprozess im Bautechnischen Mess- und Versuchswesen ausüben. Aufgrund der zahlreichen Einflussgrößen, die als Steuer- bzw. Störgrößen eine mögliche Wirkung auf bauspezifische photogrammetrische Messprozesse ausüben können, wurde im Rahmen der vorliegenden Arbeit mit deren systematischer Zusammenstellung relevanter Einflussgrößen begonnen. Die Relevanz einzelner Einflussgrößen konnte durch Untersuchungen bereits bestätigt werden. Um eine ganzheitliche Bewertung aller relevanten Einflussgrößen aufgabenabhängig vornehmen zu können, wurde ein spezieller Versuchsstand entwickelt. Dieser ermöglicht eine vollautomatisierte systematische Untersuchung bauspezifischer photogrammetrischer Messprozesse unter definierten Versuchsbedingungen und dient dem systematischen Einsatz photogrammetrischer Verfahren im Bautechnischen Mess- und Versuchswesen hinsichtlich der Absicherung bestehender Messaufgaben, kann aber auch zu weiteren neuen und optimierten Messprozessen führen.Methods of digital close range photogrammetry are a useful tool for the measurement of three-dimensional objects in civil engineering material testing. They are generally suitable for automatic measurements with chronological synchronism of object-surfaces during short and long time load tests in laboratories and in situ. The methods provide an opportunity for measuring deformations, cracks and damages at the object-surfaces during load tests in civil engineering material testing. These possibilities can present new results for a lot of applications in civil engineering material testing. Displacement and deformation measurements still rely on wire strain gauges or inductive displacement transducers. However, they are not suitable for a large number of measurement points or the detection of cracks during load tests. First of all, a number of systematic investigations was conducted. This was necessary to identify capable methods of the digital photogrammetry for the measuring of deformations, cracks and damages at object-surfaces during load tests in civil engineering material testing. These investigations laid the foundation for practical measurements during short and long time load tests of samples and constructions from different parts of the civil engineering (e.g. timber construction, solid structure, stell and road construction). The application-oriented research in civil engineering material testing demonstrates the wide range of demands on systems and methods of digital close range photogrammetry have to meet. Often the methods and systems of digital close range photogrammetry had to be modified or developed. In this context the systematic analysis of relevant determining factors was started.The results demonstrate that the methods and systems of digital close range photogrammetry are a suitable and flexible tool for the measurement of deformations, cracks and damages at the object-surfaces in civil engineering material testing. In addition, the special experiments in civil engineering material testing demonstrate the high requirements laid upon methods and systems of the digital closed range photogrammetry, for instance regarding with the measurement resolution/range and robustness processes. This was the motivation to optimize and to develop methods and systems for the special measurement tasks in civil engineering material testing, for instance a 2.5D measurement technique based on the Dynamic Projective Transformation (DPT) or the use of mirrors. Also a special measurement target was developed. This type of measurement target modifies intensities and is ideal for high deformation measurements (1/100 pixel). The large number of points in conjunction with area-based measurements require time-optimized methods for the analysis process. The modified and developed methods/programs enable fast analysis-processes, e.g. in conjunction with point-matching process 60.000 points per second.The developed crack-detection-methods allow area- and profile-based to analyze the load-dependent position and width of cracks, e.g. cracks > 3 µm (100 mm x 100 mm). A main target of this work was to compile all relevant determining factors regarding the application of the digital close range photogrammetry during load tests in civil engineering material testing. To a large extent, this target was reached. However, the compilation of all relevant determining factors requires a special experimental set-up. This experimental set-up was developed. In the future, it may enable the automatic research of all significant determining factors. The results can be used to qualify or optimize the established methods and processes. Also it's possible that the results generates new measurement processes.
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GOMES, PAULO de T. V. "Contribuicoes para melhoria das metodologias de avaliacao de choque termico pressurizado em vasos de pressao de reatores PWR." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11278.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Barbosa, José Fernando Cárdenas. "Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-27062017-111140/.
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Main extrinsic and intrinsic modifiers factors of crack growth rate in AA7050-T7451 were assessed in order to provide tools for aeronautical structures designers. These tools cover most necessary information to project aircraft\'s structures using the studied alloy, under damage tolerance philosophy. The experimental methodology consisted of use CT specimens, on TL and LT rolling direction to test its behavior under different conditions of stress ratio, force waveform, and the environment. The stress ratio values were 0.1 and 0.5, the force waveform used were sine and trapezoidal or Dwell under normal air laboratory conditions and salt fog 3.5%NaCl weight in order to simulate the marine environment. In Dwell tests, results were checked with the electrical potential drop technique (DCPD) in addition to the crack opening displacement (COD) method. Using the Walker coefficients, calculated on the present research, could be projected accurately the crack propagation behavior on Paris region and do fatigue life predictions using da/dN and S-N diagrams for different stress ratio values. The corrosion environment increases both crack growth rate and ΔKth due to oxides formation on the crack path that generates a crack closure effect. Dwell carrying makes decrease the crack growth rate by decreasing the slope of the Paris line on log (da/dN) versus log (ΔK) curve, instead of shifting down the line as occurs on titanium alloys. Rolling direction change from LT to TL increase the FCG rate in both threshold and Paris region, where the rate change use to be small.Os principais fatores modificadores extrínsecos e intrínsecos da taxa de propagação de trincas na liga AA7050-T7451 foram avaliados para fornecer subsídios para projetistas de estruturas aeronáuticas, com base na filosofía de tolerância ao dano. A metodologia experimental consistiu em ensaiar corpos de prova do tipo compact tension (CT) da liga nas direções de laminação TL e LT, para verificar seu comportamento sob diferentes razões de tensões, forma de onda e condição ambiente. Os valores de razão de tensão estudados foram 0,1 e 0,5, as formas de onda foram senoidal e trapezoidal ou de Dwell, em condições normais de laboratório, ao ar, e névoa salina 3,5% NaCl, em massa, para simular um ambiente marinho. No caso dos ensaios Dwell, os resultados foram conferidos pelo método de queda de potencial eléctrico (QPE), além do método de flexibilidade elástica. Usando os coeficientes de Walker calculados a partir dos resultados obtidos, pôde-se projetar com precisão o comportamento da propagação de trinca na região de Paris e prever a vida em fadiga usando os diagramas da/dN e S-N para diferentes valores da razão de tensões. O ambiente corrosivo aumenta tanto a taxa de propagação de trinca, quanto o valor de ΔKth por causa da formação de óxidos na trajetória da trinca, que geram um efeito de fechamento sobre a mesma. Quanto à forma de onda, verificou-se que o carregamento Dwell diminui a taxa de propagação de trinca, diminuindo a inclinação das curvas log (da/dN) versus log (ΔK) na região de Paris, ao invés de deslocá-la paralelamente como ocorre com ligas de titânio. A mudança da direção de laminação de LT para TL aumenta a taxa de propagação de trinca por fadiga (PTF) tanto na região de threshold, quanto na região de Paris, onde a mudança de taxa é pequena.
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Lama, Salomon Abraham. "Digital State Models for Infrastructure Condition Assessment and Structural Testing." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84502.
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This research introduces and applies the concept of digital state models for civil infrastructure condition assessment and structural testing. Digital state models are defined herein as any transient or permanent 3D model of an object (e.g. textured meshes and point clouds) combined with any electromagnetic radiation (e.g., visible light, infrared, X-ray) or other two-dimensional image-like representation. In this study, digital state models are built using visible light and used to document the transient state of a wide variety of structures (ranging from concrete elements to cold-formed steel columns and hot-rolled steel shear-walls) and civil infrastructures (bridges). The accuracy of digital state models was validated in comparison to traditional sensors (e.g., digital caliper, crack microscope, wire potentiometer). Overall, features measured from the 3D point clouds data presented a maximum error of ±0.10 in. (±2.5 mm); and surface features (i.e., crack widths) measured from the texture information in textured polygon meshes had a maximum error of ±0.010 in. (±0.25 mm). Results showed that digital state models have a similar performance between all specimen surface types and between laboratory and field experiments. Also, it is shown that digital state models have great potential for structural assessment by significantly improving data collection, automation, change detection, visualization, and augmented reality, with significant opportunities for commercial development. Algorithms to analyze and extract information from digital state models such as cracks, displacement, and buckling deformation are developed and tested. Finally, the extensive data sets collected in this effort are shared for research development in computer vision-based infrastructure condition assessment, eliminating the major obstacle for advancing in this field, the absence of publicly available data sets.Ph. D.
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Hartmann, Christoph [Verfasser], Wolfram [Akademischer Betreuer] Volk, den Boogaard Ton [Gutachter] van, and Wolfram [Gutachter] Volk. "Spatio-temporal optical flow methods for process analysis : Robust strain, strain rate, and crack propagation measurement in shear cutting / Christoph Hartmann ; Gutachter: Ton van den Boogaard, Wolfram Volk ; Betreuer: Wolfram Volk." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1240832680/34.
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Lima, Toni Roger Schifelbain de. "Desenvolvimento de metodologia para determinação de curvas de resistência à fratura de materiais elasto-plásticos pela análise do campo deformacional à frente da ponta da trinca." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/36011.
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Os conceitos de mecânica da fratura têm sido cada vez mais utilizados em projetos de engenharia, permitindo a determinação de tamanhos críticos de defeito ou limites de solicitação em função da presença de trincas. No entanto, para aplicar com sucesso esses conceitos em uma avaliação de integridade estrutural é de suma importância a determinação exata do comportamento a fratura do material. Materiais com comportamento elasto-plástico têm ocupado cada vez mais lugar de destaque em estruturas e componentes críticos de engenharia e a maneira mais utilizada para caracterização da tenacidade à fratura desse tipo de material é a curva J-R. Embora existam métodos normatizados para determinação dessas curvas, esses possuem muitas vezes inconvenientes e limitações que tem justificado o desenvolvimento de vários estudos com vista à determinação de métodos alternativos. Nesse trabalho foi investigada a hipótese de que, a partir do estudo do campo deformacional nas proximidades da ponta de uma trinca, é possível desenvolver uma metodologia para determinação da curva de resistência à fratura de um material com comportamento elasto-plástico. Para tanto, um sistema óptico de medição de deformação baseado na técnica de correlação de imagem digital foi empregado para monitorar a deformação na superfície de corpos de prova do tipo SE(B) durante o ensaio de tenacidade à fratura. O objeto de estudo foi uma junta do aço API X65 soldada por processo de soldagem a laser. Os resultados obtidos demonstram o sucesso da técnica utilizada para obtenção da evolução do campo deformacional durante o ensaio. Além disso, a metodologia empregada possibilitou a determinação de expressões matemáticas que permitem associar valores de deformação com valores de integral J e Δa. Essas expressões são válidas para qualquer uma das três distintas regiões da junta soldada e permitem determinar com sucesso a curva J-R a partir da evolução da deformação durante o ensaio de um único corpo de prova.The use of fracture mechanics has become increasingly popular in damage tolerance analysis or during determination of load limits in engineering components and structures. Nevertheless, the success of applying the concepts of fracture mechanics to investigate structural integrity assessment is highly dependent upon the correct determination of fracture mechanics material properties. The accurate prediction of ductile fracture behavior plays an important role in structural integrity assessment of critical engineering structures, including nuclear reactors, petrochemical vessels and tanks, pipelines in oil and gas industries and aircraft structures. J-R curve has become the most popular material parameters in elastic-plastic fracture mechanics and has been applied widely in practical engineering. There are procedures to determine J-R curves and they are widely presented in books and international standards. However, these procedures sometimes present some practical limitations or restrictions which have prompted research effort to develop alternative methods. In this work the hypothesis that is possible to develop a methodology to determinate J-R curve to materials with elastic-plastic behavior from analysis of near crack tip strain field was verified. For this purpose, an optical strain measurement system (OSMS) was used in order to monitor strains on surface of SE(B) specimens during fracture toughness testing. The methodology was applied to a laser welded joint of API X65 steel. The measurements successfully evaluate the strain field during testing. Besides of this, the methodology proposed allowed the determination of mathematical expressions to associate strain values with values of J-integral and crack extension (Δa). These expressions are valid to characterize these fracture toughness parameters to any one of the three distinct regions of the weld joint and made possible to determine J-R curve by monitoring the surface strain field evolution during a testing of a single specimen.
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Aydogan, Mustafa Ozgur. "Damage Detection In Structures Using Vibration Measurements." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1058809/index.pdf.
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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.
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Jones, Kim Ingrid Carleton University Dissertation Engineering Mechanical and Aerospace. "Direct current potential difference crack measurements system for Zr-2Nb specimens." Ottawa, 1996.
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Seher, Matthias Eugen. "Finite element simulation of crack depth measurements in concrete using diffuse ultrasound." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42751.
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Surface-breaking cracks pose a serious threat to the service life of concrete structures and health monitoring is presently conducted by a visual inspection method, yielding a potential risk to safety. Diffuse ultrasonic techniques have shown their potential as an ultrasonic technique for measuring crack depth in concrete and are currently under development. In this research, the finite element method (FEM) is employed to model the ultrasound diffusion in a concrete specimen. The objectives are to use the commercial finite element (FE) tool Ansys to develop the finite element model of a concrete specimen and verify the applicability of the model by comparing with an analytic solution and experiment data. Further, various crack types are analyzed with the FE model in order to gain physical insight into the interpretation of experimental measurements.
The results of this research suggest that a preliminary knowledge of the cracking process is required to correctly interpret the measured impulse responses for an unknown crack geometry, as the impulse response expresses the response of the shortest path through a system of cracks between source and receiver. Moreover, the impulse response can carry some ambiguity, as certain crack types are not uniquely determined.
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Husseini, Hassan Al. "Adaptation de la méthode de corrélation d'images numériques pour la gestion des discontinuités du milieu et de la transformation." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2270/document.
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Le travail présenté dans ce mémoire consiste à adapter la méthode de corrélation d'images numériques (CIN) pour la gestion des discontinuités du milieu et de la transformation. Le cadre d'utilisation des méthodes optiques de mesure i.e. celui de la mécanique des milieux continus, impose une continuité matérielle : i) du domaine et ii) de la transformation. Pour traiter les discontinuités en question, on peut reconsidérer la continuité (milieu et transformation) par morceaux. Dans le cadre de la CIN, cela se traduit par la possibilité d'adapter localement la forme et la taille des fenêtres de corrélation à la zone d'intérêt et à sa cinématique. Pour ce faire, il est possible d'utiliser des masques : un masque-objet pour traiter les discontinuités du milieu et un masque-discontinuité pour traiter les discontinuités de la transformation. Cependant, avant l'implémentation des masques dans la procédure de corrélation, plusieurs essais expérimentaux de déplacement sur des modèles comportant les deux types de discontinuité, ont été conduits. Ces essais ont permis de prouver l'influence des discontinuités sur la dégradation de la précision de mesure par CIN. Ensuite, des essais de traction ont été menés sur une éprouvette en polycarbonate conduisant à un mode I d'ouverture ou de fermeture de fissure. Après l'implémentation des masques dans le logiciel de corrélation Correla, le calcul des champs de déplacement et de déformation a été opéré avec succès à la surface de cette éprouvette, démontrant ainsi l'efficacité de la CIN adaptéeThe development of the digital image correlation method (DIC) for the management of discontinuities of the material and the transformation is discussed in this thesis. As we know, the framework for the use of the optical measurement methods i.e. of continuum mechanics requires a continuity of: i) domain and ii) transformation. To treat those discontinuities, we can consider a piecewise continuity (material and transformation). In the case of DIC method, this can be done by adapting locally the shape and size of the correlation subsets to the zone of interest and its kinematics. A novel way to do it, is by using masks: an object mask to process material discontinuities and a discontinuity mask to process transformation discontinuities. However before the implementation of masks in the correlation process, several experimental displacement tests on models reproducing the two types of discontinuity at small scale were performed. Those tests proved the influence of discontinuities on the degradation of the measurement accuracy by DIC. Then, tensile tests were conducted on a polycarbonate made specimen knowing a mode I opening or closing crack. After implementing masks in the correlation software Correla, the calculation of displacement and deformation fields was successfully performed on the surface of this specimen for all its edges, demonstrating the effectiveness of the adapted DIC
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Cook, Daniel Adam. "Monitoring small fatigue cracks using ultrasonic surface waves." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17381.
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De, Vittorio Giancarlo. "Crack measurements in structural concrete with D.I.C. system and validation of a tensile constitutive law." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2048/.
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Compared with other mature engineering disciplines, fracture mechanics of concrete is still a developing field and very important for structures like bridges subject to dynamic loading. An historical point of view of what done in the field is provided and then the project is presented. The project presents an application of the Digital Image Correlation (DIC) technique for the detection of cracks at the surface of concrete prisms (500mmx100mmx100mm) subject to flexural loading conditions (Four Point Bending test). The technique provide displacement measurements of the region of interest and from this displacement field information about crack mouth opening (CMOD) are obtained and related to the applied load. The evolution of the fracture process is shown through graphs and graphical maps of the displacement at some step of the loading process. The study shows that it is possible with the DIC system to detect the appearance and evolution of cracks, even before the cracks become visually detectable.
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Harnekar, Abraar. "Development of image based crack measurements, to investigate delamination in different weave Fibre Reinforced Polymers." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31367.
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This project investigates the delamination dependence of fibre reinforced polymers, of different weave patterns, using an image-based crack measurement method. Glass fibre reinforce polymer (FRP) with three different weave pattern namely Unidirectional, Plain weave and Twill weave patterns were manufactured using the infusion process. Waterjet cutting was used to cut the panels to produce the test specimens. The Double Cantilever Beam (DCB) test was used to measure the Mode I fracture toughness, following the standardised test method ASTM D5528. DCB tests requires two hinge blocks to be bonded to the specimens and is conducted using the Zwick machine which actively measures force and opening displacement. In order to calculate the fracture toughness from a DCB test, the crack length must be measured. An image-based crack measurement method was developed, using still images that were extracted from a digital video of the DCB experiment. The image-base method involved scripting a MATLAB file to detect the specimen surface as edges. The specimen was painted white and the test had a black background. This caused a sharp change in intensity which made the specimen edge easier to detect. The detection algorithm only catered for accuracy and not speed. A series of tests were conducted to verify the detection algorithm, of which included designing an Ultrasound Wedge device. The Wedge device was used to emulate a DCB tests in a static position whereby an Ultrasound Thickness Tester was used to obtain and verify the position of the crack tip obtained by the algorithm. DCB tests showed that the Twill weave specimens had the greatest resistance to delamination, while the Unidirectional weave offered the least resistance to delamination. The Plain weave pattern was inconclusive due to the large variation between the Plain weave specimens.
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Aghili, Ali, and Haris Ribac. "Prediction of early age and time dependent deformations in a massive concrete structure." Thesis, KTH, Betongbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231551.
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The heat development that occurs due to the hydration of cement is important to consider during casting of massive concrete structures. By using computer programs that are based on finite element methods (FEM), simulations can be performed on the heat- and strength development. In this project, a FE program called ConTeSt has been used in order to predict the temperature- and strain development in a massive concrete wall. If the potential risks in a concrete structure are evaluated before casting, economical savings, including a better casting plan could be obtained. The structure under investigation was a concrete wall behind one of the spillways in the hydro power dam of Storfinnforsen. Due to a re-construction of the wall, an opportunity occurred to develop a measurement plan of the casting and perform simulations on the wall. A sensitivity analysis was performed in order to investigate the effects on the temperature- and strain development, by varying the cement content, ambient temperature, wind speed and degree of restraint in translation. The results showed, that a higher cement content increased the rate of hydration and hence the temperature in the concrete. Higher wind speeds contributed to more cooling of the concrete which, in some cases, resulted in cracking due to contraction of the material. Cracking due to contraction also occurred when the ambient temperature was decreased. The ambient temperature did not have a significant impact on the rate of hydration, but instead the impact was larger from the initial temperature of the fresh concrete. A higher initial temperature of the fresh concrete increased the rate of hydration, which increased the temperature in the material. The degree of restraint could only be varied in translation in ConTeSt and hence the effect on the strain development was not that significant. A crack risk analysis was performed where the developed tensile stresses were compared with the tensile strength of the concrete. The same factors were varied as in the sensitivity analysis. The results showed that the tensile strength was exceeded for most of the cases and thus that the crack risk was high. The required equipment, in order to perform the measurements on site, consisted of 7 strain gauges of the module KM-100B from TML Tokyo Sokki Kenkyujo, 2 data loggers of the module Spider-8 from HBM, at least a 25 m ø9 mm 5-core shielded cable and a computer with the software Catman Easy.Värmeutvecklingen som uppstår på grund av hydratationen av cement är viktig att beakta vid gjutning av massiva betongkonstruktioner. Detta brukar göras genom simuleringar av värmeutvecklingen och hållfasthetstillväxten med hjälp av olika finita element (FE) program. I detta projekt har programmet ConTeSt använts för att på förhand kunna förutse temperatur - och töjningsutvecklingen i en massiv betongvägg. I och med detta kan bl.a. gjutningen planeras bättre samtidigt som ekonomiska besparingar kan åstadkommas om eventuella risker kan kartläggas innan gjutningen påbörjas. En ledmur bakom ett av utskoven i Storfinnforsens kraftverk undersöktes närmare i samband med en ombyggnad. Möjligheten uppstod att planera en mätning av gjutningen av ledmuren samt att utföra simuleringar av väggen i ConTeSt. En känslighetsanalys utfördes för att undersöka effekterna på temperatur- och töjningsutvecklingen genom att variera cementhalten, omgivningstemperaturen, vindhastigheten och graden av tvång i förskjutningen i längdriktningen av väggen. Resultaten visade att högre cementhalter ökade graden av hydratation vilket ökade temperaturen i betongen. Högre vindhastigheter bidrog till snabbare kylning av betongen vilket i vissa fall lett till sprickor på grund av kontraktion av materialet. Sprickor till följd av kontraktion uppstod även då omgivningstemperaturen sänktes. Omgivningstemperaturen hade ingen större påverkan på hydratationen, utan istället var det temperaturen av den färska betongmassan som visade större påverkan. Högre temperatur av den färska betongmassan ökade graden av hydratation vilket ökade temperaturen i betongen. Graden av tvång kunde i ConTeSt endast varieras i förskjutningen i längdriktningen av väggen vilket inte hade någon större effekt på töjningsutvecklingen. En sprickrisk analys utfördes där den utvecklade dragspänningen jämfördes med draghållfastheten. Analysen utfördes genom att variera samma faktorer som varierades i känslighetsanalysen. Resultaten visade att draghållfastheten överskreds i de flesta fall och att därmed sprickrisken var hög. För att genomföra mätningen blev slutsatsen att det behövs 7 st töjningsgivare av modell KM-100B från TML Tokyo Sokki Kenkyujo, 2 st data logger av typ Spider8 från HBM samt minst en 25 m ø9 mm skärmad 5-kärnkabel, inklusive en dator med programvaran Catman Easy.
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Paris, Isabelle. "In-situ measurements of delamination crack tip behaviour in composite laminates inside a scanning electron microscope." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/nq27222.pdf.
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Feng, Tao. "Measurements on stress corrosion crack initiation for A533B steel in BWR water using tapered tensile specimens." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388128.
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Dirks, Babette. "Simulation and Measurement of Wheel on Rail Fatigue and Wear." Doctoral thesis, KTH, Spårfordon, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-168023.
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The life of railway wheels and rails has been decreasing in recent years. This is mainly caused by more traffic and running at higher vehicle speed. A higher speed usually generates higher forces, unless compensated by improved track and vehicle designs, in the wheel-rail contact, resulting in more wear and rolling contact fatigue (RCF) damage to the wheels and rails. As recently as 15 years ago, RCF was not recognised as a serious problem. Nowadays it is a serious problem in many countries and ''artificial wear'' is being used to control the growth of cracks by preventive re-profiling and grinding of, respectively, the wheels and rails. This can be used because a competition exists between wear and surface initiated RCF: At a high wear rate, RCF does not have the opportunity to develop further. Initiated cracks are in this case worn off and will not be able to propagate deep beneath the surface of the rail or wheel. When wheel-rail damage in terms of wear and RCF can be predicted, measures can be taken to decrease it. For example, the combination of wheel and rail profiles, or the combination of vehicle and track, can be optimised to control the damage. Not only can this lead to lower maintenance costs, but also to a safer system since high potential risks can be detected in advance. This thesis describes the development of a wheel-rail life prediction tool with regard to both wear and surface-initiated RCF. The main goal of this PhD work was to develop such a tool where vehicle-track dynamics simulations are implemented. This way, many different wheel-rail contact conditions which a wheel or a rail will encounter in reality can be taken into account. The wear prediction part of the tool had already been successfully developed by others to be used in combination with multibody simulations. The crack prediction part, however, was more difficult to be used in combination with multibody simulations since crack propagation models are time-consuming. Therefore, more concessions had to be made in the crack propagation part of the tool, since time-consuming detailed modelling of the crack, for example in Finite Elements models, was not an option. The use of simple and fast, but less accurate, crack propagation models is the first step in the development of a wheel-rail life prediction model. Another goal of this work was to verify the wheel-rail prediction tool against measurements of profile and crack development. For this purpose, the wheel profiles of trains running on the Stockholm commuter network have been measured together with the crack development on these wheels. Three train units were selected and their wheels have been measured over a period of more than a year. The maximum running distance for these wheels was 230,000 km. A chosen fatigue model was calibrated against crack and wear measurements of rails to determine two unknown parameters. The verification of the prediction tool against the wheel measurements, however, showed that one of the calibrated parameters was not valid to predict RCF on wheels. It could be concluded that wheels experience relatively less RCF damage than rails. Once the two parameters were calibrated against the wheel measurements, the prediction tool showed promising results for predicting both wear and RCF and their trade-off. The predicted position of the damage on the tread of the wheel also agreed well with the position found in the measurements.QC 20150526
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Jendoubi, Khemaïs. "Mesures locales et globales des paramètres mécaniques gouvernant la fissuration par fatigue." Poitiers, 1987. http://www.theses.fr/1987POIT2312.
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Etude sur l'alliage d'aluminium a haute resistance 2024t351 et sur l'acier inoxydable aisi316. Determination, par mesures locales a l'aide de microjauge, du champ de deformation existant au voisinage de la pointe de fissure pour differentes conditions de chargement. Mesures globales a l'aide d'un capteur de deplacement a lames monte sur l'axe de chargement, de l'energie q dissippee par cycle et le facteur d'intensite de contraintes effectif. Mesure de l'ouverture de fissure par microscopie electronique a balayage. Proposition de la modelisation experimentale du champ de deformation pour des facteurs d'intensite de contrainte correspondant aux valeurs de la loi de paris
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Bhana, Vishal Bhooshan. "Online damage detection on shafts using torsional and undersampling measurement techniques." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/25437.
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The presence of cracks in rotors is one of the most dangerous defects of rotating machinery. This can lead to catastrophic failure of the shaft and long out-of-service periods. The occurrence of a crack in a rotating shaft introduces changes in flexibilities which alters the dynamics during operation. This research deals with detecting damage in rotors by means of constantly monitoring the variation in the rotor’s dynamics during normal operating conditions. This project entails a computer finite element section as well as an experimental investigation. The flexibility in the region of the crack is different from an uncracked section. A finite element model of a shaft is built and investigated. The damaged model is the same except that the nodes in the location of the crack are not equivalenced in order to represent the crack. A simple constant cross-sectional shaft with semi-circular transverse surface cracks varying in size have been modelled on the Patran finite element software and a normal modes analysis was done using the Nastran solver. The results revealed a change in the natural frequencies due to the variation in the size of the crack. The experimental investigation involved creating sample shafts with damage positioned in them that would closely resemble what one may find in actual real-life situations and the dynamics during rotation with various torsional loadings are investigated and monitored using three methods. A fibre-optical sensor, Digital image correlation system and telemetry strain gauges were used. Undersampling techniques were used for the DIC system. Results showed that the fibre-optic sensor is by far the most favourable as it is able to detect damage under constant operation. The finite element model was updated by re-modelling the geometry, damage and material properties. The solution of the analysis matched the experimental results closely and model verification was achieved.Dissertation (MEng)--University of Pretoria, 2013.
Mechanical and Aeronautical Engineering
unrestricted
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Shen, Jialong. "Responses of alternating current field measurement (ACFM) to rolling contact fatigue (RCF) cracks in railway rails." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/93593/.
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Rolling contact fatigue (RCF) cracks are a widespread problem that impairs the service life of railway rails and wheels, with an associated high cost of labour and capital expenditure for remediation. Severe RCF cracks cause serious safety issues as they can turn down at a larger propagation angle into the rail potentially leading to a rail break. Rail grinding can effectively eliminate RCF cracks if they are detected when they are small enough to be removed. Alternating current field measurement (ACFM) is one of the electromagnetic (EM) techniques that can be used for defect detection and sizing in the rail industry. ACFM has been reported to be more accurate in providing length and depth information than conventional UT for small RCF cracks and is less sensitive to lift-off than eddy current methods. The aim of the present research is to analyse the response of ACFM signals to single and multiple RCF cracks in railway rails using experimental measurements and FE based modelling tools, focusing on the influences of crack vertical angle and multiple cracks (number, spacing, size, uniformity) on the ACFM signal to improve the accuracy of dimension predictions. A novel method (using the Bz signal) is proposed to determine the vertical angle of the RCF cracks, which then allows the crack vertical depth to be determined from the pocket length (standard output from ACFM measurements) and therefore the appropriate amount of rail grinding to remove the RCF cracks. It was found that the vertical angle influences the pocket length determined from the measured ΔBxmax/Bx value when the cracks are shallow (vertical angles < 30°), therefore greater accuracy can be obtained when compensating the ΔBxmax/Bx value using the determined vertical angle. It is shown that the variations of crack surface length, crack inner spacing and crack number for multiple cracks also influence the ΔBxmax/Bx values determined for multiple cracks. The influences of asymmetrical crack shapes on crack sizing are discussed, in general it has been found that for accurate sizing of RCF cracks using a single ACFM scan the cracks should be regular, where the assumption of semi ellipse shapes is appropriate. The methods developed in the project were assessed using calibration samples (machined cracks with different sizes and vertical angles) and rails removed from service containing single and multiple RCF cracks. It was found that the new approach proposed in this work allowed the vertical angle to be predicted well for single and multiple RCF cracks (difference to measurements < 14.3 %). In addition the error in pocket length prediction is greatly decreased when using the sizing method including compensation determined from the crack vertical angle.
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Furfari, Domenico. "Short track growth from artificial defects in Ti-10V-2Fe-3Al : a study using optical techniques for crack measurements and detection." Thesis, Cranfield University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427204.
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Berge-Gras, Rébécca. "Analyse expérimentale de la propagation de fissures dans des tôles minces en al-li par méthodes de champs." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2011. http://tel.archives-ouvertes.fr/tel-00716429.
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Ce travail porte sur des essais de traction réalisés sur des éprouvettes d'aluminium lithium entaillées, avec des observations in-situ du champ de déformations.La réduction de consommation de carburant est actuellement une priorité pour l'aviation. Les alliages d' Al-Li sont d'excellents candidats pour réduire le poids des avions puisqu'ils combinent de très bonnes propriétés mécaniques avec une densité inférieure à celle des alliages conventionnels. Cependant, les propriétés mécaniques de ces matériaux sont fortement anisotropes, et il est essentiel de contrôler ce phénomène afin d'utiliser le matériel à bon escient. À cette fin, il est nécessaire d'avoir le maximum d'informations sur le matériau tant sur ses propriétés microstructurales (taille et forme des grains...) que mécaniques (élasticité, module de Young, résistance à la fissuration ...). Mais la connaissance de ces propriétés mécaniques globales n'est pas suffisante pour maximiser la résistance à la fissuration (critique dans l'application aéronautique). Dans ce contexte, ce travail vise à quantifier l'influence de la microstructure locale (orientation et la taille des grains) sur la fissuration.La propagation des fissures dans des tôles d'épaisseur 2 mm a été analysée. Les essais de traction ont été effectués sur des échantillons entaillés avec observation in-situ du champ de déplacement.Ainsi, la méthode de la grille a été adaptée pour déterminer de grandes déformations dans les grains. Le champ de déplacement a été caractérisée par la déformation d'une grille croisée collée (pas 30 um), et les paramètres affectant la qualité des résultats (résolution et résolution spatiale) ont été optimisés. Afin de compenser le mouvement du corps rigide, un nouveau système automatique d'acquisition d'image conduisant à de petites déformations entre chaque image a été développé. Une nouvelle méthode d'extraction de phase a été instauré, permettant un déroulage temporel de la phase.
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Ignatiev, Konstantin I. "Development of x-ray phase contrast and microtomography methods for the 3D study of fatigue cracks." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-08202004-114942/unrestricted/ignatiev%5Fkonstantin%5Fi%5F200407%5Fphd.pdf.
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Thesis (Ph. D.)--Materials science and engineering, Georgia Institute of Technology, 2005.Stock, Stuart, Committee Chair ; Sanders, Thomas, Committee Member ; Snyder, Robert, Committee Member ; Johnson, Steven, Committee Member ; Wilkinson, Angus, Committee Member. Vita. Includes bibliographical references.
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Juna, Anwar Pervez. "On the characterisation and detection of rolling contact fatigue (RCF) type cracks in railway vehicle wheels using an alternating current field measurement (ACFM) technique." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7945/.
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The development of the alternating current field measurement (ACFM) technique for high-speed inspection of railway wheels/track is important to ensure the integrity of railway assets. The stress and conditions at the wheel/rail contact patch, severity of rolling contact fatigue (RCF) damage and changes in microstructure and hardness with tread depth for railway wheels are investigated. This study employs experimental measurement of RCF defects in railway wheels to understand ACFM sensor signal - RCF defect relationships. The influence of sensor frequency and speed, sensor angle relative to crack angle, lift-off distance, crack propagation angle and inter-crack spacing distance are investigated. Low rather than high frequency sensors are better suited at sizing cracks in railway wheels and track. The optimum signal is obtained when the sensor is oriented parallel to the crack angle. The signal is reduced at higher speeds. The maximum change in the normalised Bx signal component of the sensor’s magnetic field is greater for closely spaced cracks (< 5 mm) and thus overestimates the defect. Inter-crack spacing distances of 15-20 mm yield estimates for crack pocket depths that are oversized by 20-36%. The inner cracks in a cluster with four defects yields higher Bₓ values than expected and thus significantly over sizes the defects at 15-20 mm inter-crack spacing distances, whereas, the sensor provides reasonable depth estimates for the outer cracks. Crack propagation angle affects the signal. Scans conducted with the probe oriented at 90° to the cluster of cracks consisting of a deep central crack surrounded by shallow cracks results in a distinct central sensor Bₓ signal that consists of a peak due to a flux leakage effect, thus, identifying the critical defect.
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Goubet, Étienne. "Contrôle non destructif par analyse supervisée d'images 3D ultrasonores." Cachan, Ecole normale supérieure, 1999. http://www.theses.fr/1999DENS0011.
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L'objet de cette thèse consiste en l'élaboration d'une chaine de traitements permettant d'extraire l'information utile de données 3d ultrasonores et de caractériser les défauts éventuellement présents dans la pièce inspectée. Cette caractérisation a été abordée pour des fissures contrôlées par un même émetteur/récepteur. Dans une première partie nous rappelons les principes du contrôle non destructif par ultrasons ainsi que les représentations classiques des données ultrasonores. La deuxième partie est consacrée à l'étude d'un modèle d'extraction de l'information d'échos présents sur les données au moyen d'une base d'ondelettes adaptée. L'utilisation d'une ondelette unique translatée dans le temps est rendue possible par un travail sur une représentation complexe des données réelles originales. Une première étape permet de détecter et de positionner les échos d'amplitude significative. Dans un deuxième temps, on effectue une régularisation spatialement cohérente des instants de détection à l'aide d'un modèle markovien. On élimine ainsi les échos dont les instants de détection ne font pas partie de surfaces d'instants régulières. Les parties suivantes traitent de la localisation et du dimensionnement des fissures. On utilise des caractéristiques extraites du faisceau ultrasonore afin de déterminer le trajet de l'onde ultrasonore du capteur à l'objet diffractant lorsque la réponse de l'écho est maximale. On met en correspondance l'instant de détection obtenu pour cet écho et le temps de parcours selon le trajet défini afin de positionner un point d'arête dans la pièce. On obtient ainsi un ensemble de points de discrétisation pour chaque arête. Dans le cadre de données 3d obtenues sur un matériau isotrope, on élimine les points d'arête extrêmes en utilisant un critère de comparaison sur les courbes échodynamiques associées aux points de détection sur les données réelles et sur des données simulées équivalentes. La localisation est abordée pour des fissures situées dans un matériau isotrope ou acier revêtu d'anisotrope.
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Selén, Niklas, and Tom Söderström. "Fukttillstånd i betongplatta på mark : Ett experimentellt försök att jämföra teori med praktik." Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-24058.
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When casting the slab in a slab-on-ground structure most of the drying will occur through the surface of the slab, which is in contact with the air. This will create a non-uniform internal moisture distribution. With the top of the slab drying faster it will also have a faster shrinkage due to drying, which in turn leads to stress in the surface layers of the slab as these wants to contract. With the slab wanting to assume a curled geometry, but being restricted by external loads and self-weight, cracks will usually appear in the surface (Lange, Lee & Liu, 2011). A concrete slab-on-ground does not dehydrate the same way as, for example, floor bellows or wall elements which has the same climate on both sides. The ground beneath a heated building standing on a slab-on-ground structure is warm and moist with a relative moisture close to 100%. After carefully examining moisture damaged slab-on-ground structures it was concluded that the temperature and moisture behavior in this type of structure is more complicated than earlier presumed. In an attempt to broaden the basis of knowledge about humidity conditions under a concrete slab-on-ground structure, measurements were performed on an existing slab. The Council for Construction Competence (Rådet för ByggKompetens, RBK) sets the industry standard regarding moisture measurement in Sweden. In 2017 the method recommended by RBK for moisture measurement in concrete includes drilling a hole in the slab, sealing it with a plastic pipe and mounting the sensor inside. This is the method that was used for measurements in this paper. Three different measurement locations in the slab along with two sensors mounted at every location was used to gather data. The results from the measurements show that the relative humidity near the bottom of the slab is close to 100%. The results from the sensors range from 90% to 100% RH with the majority of the results very close to 100% RH. The results discovered in this paper supports the assumption that the ground beneath a slab-on-ground structure is close to 100% RH.Vid gjutning av en betongplatta på mark sker uttorkning främst genom ovansidan av plattan. De övre skikten av betongen får en snabbare uttorkning än de undre skikten, detta tillsammans med den krympning som sker under uttorkningen skapar spänningar i betongplattan. Fenomenet gör att plattan vill böja upp sig i kanterna men på grund av egentyngd samt laster ovanifrån uttrycker sig spänningarna istället som sprickor på ovansidan (Lange, Lee & Liu, 2011). Uttorkning av en betongplatta på mark skiljer sig från uttorkning av t.ex. väggelement och mellanbjälklag som har samma klimat på bägge sidor. Marken under en uppvärmd byggnad med grundkonstruktionen platta på mark antas vara varm och fuktig med en relativ fukthalt nära 100 %. Efter noggrann undersökning av fuktskadade platta på mark konstruktioner har det visat sig att temperatur- och fuktbeteende i dessa konstruktioner är mer komplicerade än tidigare förmodat. För att bredda underlaget för de fuktförhållanden som råder i underkant av en betongplatta på mark utfördes mätningar i en befintlig betongplatta. Rådet för ByggKompetens, RBK är de som bestämmer branschstandarden inom fuktmätning i Sverige. Från 2017 är den enda metoden för fuktmätning i betong som RBK rekommenderar en metod där ett hål borras i betongplattan, tätas med ett foderrör och en RF-givare monteras inuti. Denna metod användes vid mätningarna i detta arbete. Tre olika mätpunkter med två RF-givare vid varje mätpunkt har använts vid mätningarna. Resultaten från mätningarna visar på att den relativa fuktigheten i betongplattans underkant är nära 100 %. Resultaten från givarna varierade mellan 90 % till 100 % RF där majoriteten av resultaten ligger väldigt nära 100 % RF. I och med dessa resultat styrker denna rapport antagandet om att marken under en platta på mark har en RF på 100 % eller väldigt nära.
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Podesta, Laurie. "Etude expérimentale de la fissuration en fluage de l'acier 316H vieilli sous environnement CO2." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTS011/document.
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Des fissures intergranulaires ont été observées sur des composants évoluant dans un environnement CO2 à haute température (550°C). Le matériau, un acier austénitique inoxydable de nuance 316H, est soumis à des sollicitations en fluage. L'objectif de la thèse est de permettre une meilleure compréhension du mécanisme d'endommagement par fluage et des effets de l'environnement sur l'apparition et la propagation de ces fissures. Une synergie entre la simulation par éléments finis et la mesure de champs cinématiques au moyen de la Corrélation d'Images Numériques (CIN) a été créée pour aborder ce problème avec une approche locale, à l'échelle de la microstructure. Une méthode de CIN adaptée au suivi de la fissuration basée sur l'utilisation des expressions de la Mécanique Linéaire Elastique de la Rupture a été développée. Une validation expérimentale sur essai de traction in-situ sur microéprouvettes pré-fissurées de matériau 316H est proposéeAt elevated temperature (550°C) in CO2 environment, intergranular creep cracks have been observed in thermally and environmentally aged 316H austenitic stainless steel. The objective of this work is to enhance the understanding of the creep crack mechanism and the effects of environment on crack initiation and growth. Some microtests on Single Edge Notched Tensile specimen (SENT) have been performed to better describe the interaction between chemistry and mechanics at the microstructural scale. A creep crack monitoring procedure using Digital Image Correlation (DIC) have been developped and assessed using Finite Element Modelling (FEM) of cracked bi-crystal. Based on a projection on Linear Elastic Fracture Mechanics expressions, the crack parameters (crack tip position, orientation) can be determined and the growth can be measured. A validation on in-situ tensile tests on SENT 316H specimen is proposed
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Moustafa, Abdel Rahman. "Mesure thermographique des effets dissipatifs accompagnant le fretting : d'une construction rapide des cartes d'amorçage vers une meillleure compréhension des mécanismes d'endommagement." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC012/document.
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This study is part of an original approach based on quantitative imaging techniques, such as Infrared Thermography, to study the damage under fretting loadings. The main objective was the establishment of new experimental method for a rapid determination of crack initiation conditions under fretting loadings, based on the analysis of the thermal signal. One other objective was the determination of the different heat sources in order to assess a local analysis of the fretting damage. This work underlined the great potential of Infrared Thermography to study this damageCette étude s'inscrit dans une approche originale basée sur des techniques d'imagerie quantitatives comme la thermographie infrarouge pour étudier l'endommagement sous chargement de fretting. Le premier objectif était de développer une méthode de construction rapide de carte de fretting basée sur l'analyse du signale thermique au cours d'essais de fretting. Un deuxième objectif était de déterminer les sources de chaleurs accompagnant le fretting pour une meilleure compréhension des mécanismes d'endommagement. Ce travail a souligné le grand potentiel de la thermographie infrarouge pour l'étude de c'est phénomènes
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Klusáček, Stanislav. "Metody bezdemontážní diagnostiky." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-233581.
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The main objective of the presented thesis is to contribute to the development of diagnostic methods for piezoelectric sensor testing. The thesis describes the methods for piezoelectric sensors microcracks identification and diagnostics. The core of the thesis presents the development of a knock sensor prototype, design of suitable methods for the knock sensors diagnosis and evaluation of developed methods with focus on detection of microcracks in the sensor piezoceramic. The last part of the thesis deals with the influence of cracks and splits on the measured data from the piezoelectric transducer. The presented methods are focusing on impedance measurements and sensors frequency response measurements. Known properties of used piezoelectric material as an information source for measurement and diagnosis are provided. The main result of the work is the evaluation of the methods developed for the piezoelectric sensors self-diagnosis.
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Lin, Sheng-Tung, and 林盛棟. "The Measurement of Crack Depth by Ultrasonics." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/94549373331993053607.
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碩士元智大學
機械工程研究所
88
The capability of detecting defects inside the structures and on the surface such as cracks and voids, make the ultrasonics become the most common use of non-destructive examination technique. It is always difficulty to fabricate a real crack in the laboratory. Present investigation uses a finite width of artificial slot made by electrical discharge machining, to simulate the real crack. Five different methods of measuring the depth of surface crack are presented. The effects of frequency and incident angle on the measurement accuracy for these five methods are evaluated. Comparisons are made among those methods to examine their advantages and disadvantages. The results can provide useful information to determine the best way of detecting defects.
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Zhang, Dao-wu, and 張道武. "Measurement method of crack density in concrete." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/q6uph9.
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碩士國立中央大學
土木工程研究所
97
The factors of measuring cracks in concrete include crack widths, crack depth, crack spacing, crack density etc., yet this thesis will focus on developing an uncomplicated and understandable method to gauge the cracks block on crack spacing and crack density. According to the similarity of polygons of irregular map cracks, the purpose of the method is exploring the relations between the quantity of intersection point and percentage of the crack-crossed cells of the lattice-arranged lines and crack spacing and crack density by counting the numbers of complete cells instead of the current measurement - counting the numbers of intersection point. Under the hypotheses that crack widths could be passed over, cracks spread averagely, the lines are infinite and crack-based is square, inferring the product of crack spacing and crack density is π/2 by the geometry theory, fractal theory and scale effect are not considered in the study.
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Wang, Yin-Ting, and 王尹廷. "The measurement and analysis of crack induced by AAR." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/44244283377355991774.
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碩士國立中央大學
土木工程研究所
92
ABSTRACT Generally, standard test methods for potential alkali activity is to measure the expansion of specimens, mortar bars(ASTM C227) or concrete prisms(ASTM C1293), for instance. It just shows the change in total length of the specimen, but the behavior and development of cracks can not be investigated. In this article, the relationship between expansion and crack of the specimens is established with image measurement. So scanner is used to record the surface image of concrete plates which are made of andesite and aggregate from Heping river. The image is analyzed with software, Simple PCITM, to give the quantitative description of the cracks and expansion. The results indicate that the surface crack is map-like, similar to those observed from in-situ concrete structures and development of cracks almost start from mortar part and then extended to aggregate part in concrete specimens, even cut over the aggregate. From the analysis of image, the crack area contributes the most in the total expansion after the first crack. The expansion threshold for cracking to exist on concrete specimen is 0.15%.
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Shies, Chi-Tai, and 謝其泰. "The Measurement of the Crack Propagation in Rock Slab." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/93117900041947733000.
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碩士國立成功大學
資源工程學系碩博士班
91
A WLCT(Wedge Loading Compact Tension) system was built in this study to investigate the phenomenon of crack propagation in rock slabs. The rock slabs under investigation were selected from natural building stones. Two samples were investigated: Dark Granite and White Marble. A high-speed video system was used to monitor the crack propagation, while a high-resolution crack-strain-gage system was used to measure the crack propagation velocity. In this study, the loading method is displacement-controlled and the loading rates are chosen in the range of 0.5 to 100 mm/min. This study finds: (1)For Dark Granite samples, the average crack velocity near the crack tip is measured in the range of 0.67 to 325 cm/sec; the maximum crack velocity near the crack tip is measured in the range of 12.6 to 2520 cm/sec; the fracture toughness is found to be 1.96 to 3.59. (2)For White Marble samples, the average crack velocity near the crack tip is measured in the range of 7.66 to 277 cm/sec; the maximum crack velocity near the crack tip is measured in the range of 72.5 to 3360 cm/sec; the fracture toughness is found to be 1.03 to 1.35. Experimental results from this study have not indicated that the crack velocity and the fracture toughness have a direct relationship for both samples. It is also found that White Marble show a strong boundary effect and the resulting crack path could deviate. The measured crack velocity in this study is much lower than the theoretical upper bound of crack velocity.
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Liu, Yu-Hsien, and 劉育賢. "The Application Of Ultrasonic Detection On The Measurement Of Fatigue Crack." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/07109916488384663535.
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碩士國立成功大學
系統及船舶機電工程學系碩博士班
92
Abstract This thesis is using ultrasonic detected skill on fatigue crack. The point is on realizing the ability of ultrasonic system for detecting un-simple geometry shape surface crack and the application of ultrasonic detected skill on measurement of open load. Our lab has established an automatic ultrasonic testing system which can examine oblique、camber and turned crack for simulating the situation on work field. After experiments, the result is that ultrasonic testing system can handle the surface shape and way of surface crack. In depth aspect, because of real crack is closure below unloading and crack growth in the interface of material pellet, producing diffraction wave from tip is been influenced. We can almost get real crack dimension accurately by way of repeating measurement and eliminate odd point. To break through the defect of adopting strain gage for measuring open load, by way of the change of ultrasonic reflection energy ,cause of the difference of crack tip angle in different loading, to judge the open load. We can obtain different type of echo curve in diverse condition, but the turning point of slope of ultrasonic reflection energy will occur in the same load and the load is the open load of the crack.