Dissertations / Theses: 'Non-destructive testing (NDT)'

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Gros, X. E. "Fusion of multiprobe NDT data." Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294936.

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Smith, Ian Colin. "Vision based systems for hardness testing and NDT." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317273.

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The work presented in this thesis concerns the development of vision based systems for two hardness (destructive) tests, namely; the Shore and Vickers and a quality assurance non-destructive test. In each case the vision system is based on an IBM PC compatible computer fitted with a commercially available frame store. Bespoke image analysis software was written using the C language for each system. In the Shore test, hardness is judged by the maximum rebound height attained by an indenter incident on a test sample. The purpose of the vision system is to measure the rebound height automatically. Laser light is used to illuminate the indenter and a vidicon vision camera is used to view its motion. Two approaches to the problem are considered; one in which image data is analysed in real time and one in which image·data is merely stored in real time and analysed a posteriori. Non-real time analysis is shown to be superior to real time analysis in terms of accuracy and reliablity and its software implementation is discussed in detail. The Vickers test uses the size of the permanent impression left by an indenter forced into the test material under a known load as a hardness index. In this case the purpose of the vision system is to measure the size of the indentation automatically. The original image analysis algorithms are shown to be capable of analysing good quality samples but are unreliable when applied to poor quality specimens. Further, fault-tolerant, algorithms are described to provide reliable and accurate results over wide variations in sample quality.The quality assurance application involves automated visual inspection of novel ferrite components for defects. Each component is approximately 8 mm in diameter, annular in shape, and coated with aluminium. Laser light is used to illuminate individual components which arc viewed using a charge-coupled device (CCD) video camera. Image analysis algorithms for characterising defects in component geometry and surface finish arc discussed. The system is shown to capable of measuring component edge eccentricity and hole offset as well as providing a quantitative description of surface chips and cracks. The system is further shown to be capable of separately classifying surface defects extending to the edge of a component. Calculation of shape parameters for surface defects also provides a means of distinguishing cracks from surface chips.

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Höglund, Kristofer. "Non-destructive Testing Using Thermographic Image Processing." Thesis, Linköpings universitet, Datorseende, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-89862.

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In certain industries, quality testing is crucial, to make sure that the components being manufactured do not contain any defects. One method to detect these defects is to heat the specimen being inspected and then to study the cooling process using infrared thermography. The explorations of non-destructive testing using thermography is at an early stage and therefore the purpose of this thesis is to analyse some of the existing techniques and to propose improvements. A test specimen containing several different defects was designed specifically for this thesis. A flash lamp was used to heat the specimen and a high-speed infrared camera was used to study both the spatial and temporal features of the cooling process. An algorithm was implemented to detect anomalies and different parameter settings were evaluated. The results show that the proposed method is successful at finding the searched for defects, and also outperforms one of the old methods.

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Bale, Jefri Semuel. "The damage observation of composite using non destructive testing (NDT) method." Thesis, Paris 10, 2014. http://www.theses.fr/2015PA100067/document.

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L'objectif de ce travail de thèse est d'étudier le comportement de l'endommagement des matériaux composites sous chargement statique et fatigue par contrôle non destructif (C.N.D) thermographie et soutenu par émission acoustique et la tomographie (CT scan). Pour cela, ce unidirectionnels composite à fibres de verre (GFRP) et discontinue composite à fibres de carbone (DCFC) ont été utilisés comme les éprouvettes qui ont fourni par PSA peugeot citröen, France. Une série d'essais mécaniques a été réalisée pour déterminer le comportement de l'endommagement sous chargement statique et fatigue. Pendant tout des essais mécanique, la thermographie a été utilisé pour l'observation en temps réel pour suivre l'évolution des températures sur la surface de l'éprouvette et supporté par émission acoustique dans certaines conditions. Cette étude a utilisé une forme rectangulaire et se compose d'éprouvettes trouées et non trouées au centre de l'éprouvette. La vitesse de déplacement constante est appliquée pour observer l'effet sur le comportement de l'endommagement sous chargement de traction statique. Sous les essais de fatigue, le paramètre constant de la fréquence et de l'amplitude de stress a été étudiée pour chaque niveau de charge pour avoir les propriétés de fatigue et l'évolution de l'endommagement de l'éprouvette. La tomographie a été utilisée pour confirmer l'apparition de l'endommagement et l'etat du matériau après l'essai de fatigue. L'analyse des résultats de l'expérimentation et de l'observation NDT montré le bon accord entre les résultats mechnical et NDT thermographie avec prise en charge par l'observation de l'émission acoustique en détecter l'apparition et la propagation de l'endommagement de GFRP PRV et DCFC sous chargement de statique en traction. Les essais en fatigue montrent que la dissipation thermique est liée à l'évolution de l'endommagement et également thermographie et peut être utilisé avec succès pour déterminer la limite d'endurance (HCFS) et la courbe de Wöhler du matériau composite. Les résultats par CT scan ont mesurée avec succès les endommagements et l'état du matériau après essai de fatigue du matériau composite
The aim of this study is to investigate the damage behaviour of composite material in static and fatigue condition with non destructive testing (NDT) thermography method and supported by acoustic emission and also computed tomography (CT) scan. Thermography and acoustic emission are used in real-time monitoring techniques during the test. On the other hand, NDT observation of tomography is used for a post-failure analysis. In order to achive this, continuous glass fiber composite (GFRP) and discontinuous carbon fiber composite (DCFC) have been used as the test specimens which supplied by PSA Company, France. A series of mechanical testing was carried out to determine the damage behaviour under static and fatigue loading. During all the mechanical testing, thermography was used in real-time observation to follow the temperature change on specimen surface and supported by acoustic emission in certain condition. This study used rectangular shape and consist of specimen with and without circular notches (hole) at the center. The constant displacement rate is applied to observe the effect on damage behaviour under tensile static loading. Under fatigue testing, the constant parameter of frequency and amplitude of stress was explored for each load level to have the fatigue properties and damage evolution of specimen. The tomography was used to confirm the appearance of damage and material condition after fatigue testing. The analysis from the experiment results and NDT observation shown the good agreement between mechnical results and NDT thermography with supported by acoustic emission observation in detect the appearance and propagation of damage for GFRP and DCFC under static loading. Fatigue testing shows that thermal dissipation is related to the damage evolution and also thermography and can be successfully used to determine high cycle fatigue strength (HCFS) and S-N curve of fiber composite material. From post failure analysis, CT scan analysis successfully measured and evaluated damage and material condition after fatigue test for fiber composite material. v

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Campbell, M. A. "An evaluation of monolithic phased arrays for Non destructive testing." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381502.

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Begum, Rushna. "Neural network processing of impact echo NDT data." Thesis, City University London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340456.

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Hall, Ian Damon. "Generation of high resolution tomographic images for NDT applications." Thesis, University of Strathclyde, 2001. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24263.

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Techniques for the generation of quantitative ultrasonic images in non-destructive testing have generally involved a substantial cost in terms of data storage and computational time, and have thus found limited application. Preference has therefore been given to the more straightforward imaging methods, such as main beam projection, which detect the presence of defects and provide a limited flaw sizing capability. The relatively small number of flaws requiring detailed examination, coupled with substantial increases in available data storage and computational power, have made it possible to use a number of straightforward tomographic reconstruction methods to produce high resolution images of flaws contained within the material under examination. A set of these images are then fused together using a novel fuzzy logic image fusion technique into a single image from which more accurate measurements of flaw size, shape and orientation can be made. However, if the quality of the raw A-scan data is not sufficiently high then the data will be filtered using Maximum Likelihood Deconvolution (MLD). The aim of this blind deconvolution method is to improve the time resolution and Signal to Noise Ratio of the A-scan data with only knowledge obtained from the data, this is in contrast to the majority of techniques currently used for this purpose. The three tomographic methods which have been implemented in this work are Reflection tomography, Time-of-flight Diffraction tomography and Transmission tomography. In addition a Single Bounce Image Enhancement method has been developed to improve the images. Selection of images used in the fusion process depends on the nature of the flaw, as each of these methods identifies different characteristics of the flaw shape. The components of the imaging system have been validated experimentally by the generation of high resolution images from a variety of flaws contained within cylindrical aluminium test specimens.

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Chen, Xiaoran. "Computational and Experimental Approach for Non-destructive Testing by Laser Shearography." Digital WPI, 2014. https://digitalcommons.wpi.edu/etd-theses/928.

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"Non-destructive testing (NDT) is critical to many precision industries because it can provide important information about the structural health of critical components and systems. In addition, NDT can also identify situations that could potentially lead to critical failures. Specifically, NDT by optical methods have become popular because of their non-contact and non-invasive nature. Shearography is a high-resolution optical NDT method for identification and characterization of structural defects in components and has gained wide acceptance over the last decade. Traditional workflow of NDT by shearography has been determined to be inefficient, due to the requirements of having experienced operators that must determine the most suitable loading methods to identify defects in samples under testing as well as to determine the best system arrangement for obtaining the maximum measuring sensitivity. To reduce the number of experiments that are required and to allow inspectors to perform NDT by laser shearography in a more efficient way, it is necessary to optimize the experimental workflow. The goal of the optimization would be an appropriate selection of all experimental variables including loading methods, boundary conditions, and system¡¯s sensitivities, in order to avoid repeating experiments several times in the processes of components characterization and health monitoring. To achieve this goal, a hybrid approach using shearographic fringe prediction with Finite Element Analysis (FEA) has been developed. In the FEA simulations, different loading conditions are applied to samples with defects, and in turn, the shearographic fringes are predicted. Fringe patterns corresponding to specific loading conditions that are capable of detecting defects are chosen and experimental tests are performed using those loading conditions. As a result, using this approach, inspectors could try different combinations of loading methods, and system¡¯s sensitivities to investigate and select appropriate experimental parameters to improve defect detection capabilities of the system by using low-cost computer simulations instead of lengthy and expensive experiments. In addition, to improve the identification of defects on the sample, camera calibration and image registration algorithms are used to project the detected defects on the sample itself to locate and visualize the position of defects during shearographic investigations. This hybrid approach is illustrated by performing NDT of a plate made of acrylic that has a partial hole at the center. Fringe prediction with finite element analysis are used to characterize the optimized experimental procedures and in turn, corresponding measurements are performed. A multimedia projector is employed to project the defects on the surface of the plate in order to visualize the location of the partial hole (defect). Furthermore, shearographic system is used for other applications including NDT of a composites plate and of a thin latex membrane. The procedures shows the effectiveness of the approach to perform NDT with shearography methods. "

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KoÌˆpke, Uwe Gerhard. "Condition monitoring of buried gas pipes using a vibrating PIG." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259460.

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Li, Xin. "Eddy current techniques for non-destructive testing of carbon fibre reinforced plastic (CFRP)." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/eddy-current-techniques-for-nondestructive-testing-of-carbon-fibre-reinforced-plastic-cfrp(e8aa9a3f-108d-49a4-9f32-2e6118195898).html.

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AbstractThis thesis describes research on the use of eddy current techniques for nondestructivetesting of carbon fibre reinforced plastic (CFRP). The research hasinvolved bulk conductivity testing, fibre direction characterization and 3D FEMmodeling of the CFPR and eddy current probes geometry. In the conductivity testing,how the sample thickness, fibre volume content and fibre conductivity affects thesignal from the eddy current has been evaluated. Eddy current testing shows gooddirectionality as CFRP is an anisotropic material, thus is very suitable to characterizethe fibre orientation. Direction sensitive probes have been developed and tested toreveal information about the fibre direction and layer. Computer FEM software hasbeen used to analyze the magnetic field inside the sample and probes. Specific probegeometries have been designed depending on the electrical properties of thecomposites and testing requirement. The experiment, simulation and analysis resultsshow very good agreement. However, when the measuring frequency increases, noisesand parasitic capacitance inevitably become significant and have a negative influenceon the results. Improvements and further research are proposed which are believed tomake eddy-current techniques a more feasible and efficient measurement method, willcontribute to the development and maintenance of light weight CFRP composites.

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Kogia, Maria. "High temperature electromagnetic acoustic transducer for guided wave testing." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/14491.

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This research focuses on the theoretical analysis, development and experimental evaluation of a water cooled Electromagnetic Acoustic Transducer (EMAT) specifically designed for high-temperature Guided Wave Testing (GWT). Its novel design and detailed calculation of its optimum operating conditions resulted in its effectiveness at high temperatures for both short (500oC) and long-term inspection (250oC). All the steps followed for the theoretical and experimental investigation of the limitations of the existing technology and the development of a probe that can overcome these boundaries are presented. Finite Element Analysis (FEA) was performed for the optimization of the EMAT design and estimation of its ultrasonic and thermal properties at room and high temperatures over time. The wave mode purity profile of the Periodic Permanent Magnet (PPM) EMAT was theoretically studied as well as the effect of temperature rise on its ultrasonic performance. Thermal and Computational Fluid Dynamics (CFD) analysis was accomplished for the EMAT design optimization and calculation of its optimum operating conditions. The experimental validation of the theoretical study was also accomplished. The novel water cooled EMAT was developed and experimentally evaluated regarding its ultrasonic and thermal response at room and high temperatures. An empirical method for the enhancement of EMAT performance and its SNR was established. The wave mode purity characteristics of PPM EMAT were experimentally investigated via Laser vibrometry tests, which agreed with FEA results. The impedance analysis and ultrasonic evaluation of the EMAT at both room and high temperatures against various operating conditions were linked and compared to the results obtained from the ultrasonic, thermal and fluid FEA. In all cases, the experimental study is in good agreement with the theoretical results.

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Britt, Olivia Grace. "Assessing the Suitability of Typical Timber Testing Methods for Australian Heritage Timber Structures." Thesis, Sydney School of Architecture, Design and Planning, 2023. https://hdl.handle.net/2123/30017.

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This research aims to examine the applicability of conventional inspection methods for timber structures where structures have recognised heritage value. The research seeks to understand the appropriateness of inspection methodologies typically prescribed for timber in heritage applications. A literature review of current inspection methods utilised by engineers, architects and others within the heritage structures field has been undertaken, and the appropriateness of timber structural inspection methods used in practice (destructive testing, semi-destructive testing, and non-destructive testing methods) reviewed in light of heritage aims for Australian structures, and interviews conducted with practicing industry professionals to discuss uptake of these methods in practice. A review of current literature indicates that non-destructive technologies present significant potential for further analysis of timbers in-situ without damage to the fabric itself, and represent a particular opportunity for heritage sites, as analysis can be conducted with minimal invasiveness. Interviews with practicing professionals within this industry indicates that currently, such methods have been incorporated only minimally into standard professional practice methodologies. While a lack of familiarity with many available methods is evident, the reasons behind the limited uptake are complex, including but not limited to a lack of pre-defined Australian guidelines prescribing their use, a perception of high associated costs, and an unwillingness on the part of clients to request the use of these methods. It is found that significant opportunity exists for an improvement in the uptake of non-destructive methods as preferential over semi-destructive test methods. Indicative processes of example best-practice methods incorporating non-destructive testing into a typical assessment regime are presented.

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Fletcher, Adam. "Non-destructive testing of the graphite core within an advanced gas-cooled reactor." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/nondestructive-testing-of-the-graphite-core-within-an-advanced-gascooled-reactor(3ca5c904-6860-46b8-8538-4136cb2aedcd).html.

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The aim of this work has been to apply the techniques of non-destructive testing and evaluation to the graphite fuel channel bricks which form the core of an Advanced Gas-Cooled reactor. Two modes of graphite degradation have been studied: subsurface cracks originating from the keyway corners of the bricks and the reduction in material density caused by radiolytic oxidation. This work has focused on electromagnetic inspection techniques. Brick cracking has been studied using a multi-frequency eddy current technique with the aim of determining quantitative information. In order to accurately control the crack dimensions this work has used radially machined slots as an analogue. Two sensor geometries were studied and it was determined that slots of at least 10 mm through-wall extent could be located. A novel, empirical method of determining the slot size is presented using a brick machined with a series of reference slots. Machined slots originating from a keyway could be sized to within 2 mm using this method. A parametric 3D finite element study was also carried out on this problem. These simulations could distinguish the location of the slots and had some sensitivity to their size, however, the model was found to be overly sensitive to the specific mesh used. Two new contributions to the inverse problem are presented. The first is a minor extension to the usual adjoint problem in which one system now contains a gradiometer. The second is a proposed solution to the ambiguous nature of the inner product required by the sensitivity formulation. This solution has been validated with finite element modelling. Density reduction has been studied via its relationship with electrical conductivity using a technique based on impedance spectroscopy. An inverse eddy current problem has been solved using the regularised Gauss-Newton method to determine the conductivity of the brick over its cross section. The associated forward problem has been solved using the finite element method on a simplified geometry. Tikhonov regularisation has been employed to overcome the ill-posed nature of the inverse problem. This method has been applied to a range of sample and sensor geometries and found to produce excellent results from laboratory data provided the finite element model is well calibrated. Bore or surface conductivity values can be reproduced to better than 1% with the accuracy reducing with distance from the sensor. The sensitivity of the algorithm to the regularisation parameter has been studied using the L-curve method and the effect of two regularisation operators has also been examined. A new method of choosing the regularisation parameter a priori is proposed and tested. Data taken during reactor outages produces physically realistic profiles although the results appear off-set from electrical resistivity values measured using the four-point method. The focus of future work should be to remove this effect which will likely require improvements to the forward model.

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Siu, Frederick Y. K. "Studies of microwaves applications for adhesive, weld joint and NDT technique." Swinburne Research Bank, 2007. http://hdl.handle.net/1959.3/36854.

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Thesis (MEng) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2007.
A thesis submitted for fulfillment of the requirement for the degree of Master of Engineering, Industrial Research Institute, Swinburne University of Technology - 2007. Typescript. Includes bibliographical references (p. 168-193).

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Bertović, Marija [Verfasser], Dietrich [Gutachter] Manzey, and Gerd-Rüdiger [Gutachter] Jaenisch. "Human Factors in Non-Destructive Testing (NDT): Risks and Challenges of Mechanised NDT / Marija Bertović ; Gutachter: Dietrich Manzey, Gerd-Rüdiger Jaenisch." Berlin : Bundesanstalt für Materialforschung und -prüfung (BAM), 2016. http://d-nb.info/1122991371/34.

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Kit, Julian Chua Ying. "The human-machine interface (HMI) and re-bar detection aspects of a non-destructive testing (NDT) robot." Thesis, City University London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245862.

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Bertovic, Marija [Verfasser], Dietrich [Akademischer Betreuer] Manzey, and Gerd-Rüdiger [Akademischer Betreuer] Jaenisch. "Human factors in non-destructive testing (NDT): risks and challenges of mechanised NDT / Marija Bertovic. Gutachter: Dietrich Manzey ; Gerd-Rüdiger Jaenisch. Betreuer: Dietrich Manzey." Berlin : Technische Universität Berlin, 2015. http://d-nb.info/107658814X/34.

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Brashear, Kyle Thomas. "The Assessment of Sonic Waves and Tracer Gases as Non-Destructive Testing (NDT) Methods for In-Situ Underground Mine Seals." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50519.

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

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Gustafsson, Joakim. "AUTOMATIC BRAKING DISC ANALYSIS SYSTEM." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-28217.

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Volvo Group Truck Technology has the ambition to automate parts of their routine service. Therefore a project was launched to investigate which parts of the routine that could be automated. The idea of this project is to lower the time spent on the service and also improve the working environment for the personnel. The purpose of this thesis is to develop and build a conceptional prototype for a low-cost crack detecting sensor. This thesis is a part of a larger proof of concept project which Volvo GTT runs in cooperation with Robotdalen and Robot Application Center (RAC). The work done in this thesis has been based on literature studies, interviews and company visits. The gathered knowledge and observations was translated into what would be required to fit the needs. This thesis covers different techniques that could be used to detect flaws in braking discs. However, this thesis is mostly focused on one non-destructive method technique based on induced eddy currents. Several non-destructive techniques and conceptual designs has been tested and evaluated with varying results during this project. The result of this thesis was a design that reacts to discontinuities in conductive materials, such as the grey cast iron material used in the Volvo trucks braking discs. The results are represented as a voltage drop change and can be visualized by an oscilloscope. This study shows that the method of choice has the potential to be used as a crack detecting system and that the system can be built reliable with rather cheap components. Further development should aim towards making the design even cheaper and the components should be assembled on a PCB instead of a breadboard in order to make the system less sensitive to noise and easier to assemble alongside the trucks braking discs.

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Li, Li. "Vibration analysis in non-destructive detection of milk powder blockage in the cyclone of a spray dryer." AUT University, 2008. http://hdl.handle.net/10292/997.

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This research investigates possible monitoring methods to non-invasively detect blockages in the cyclone of milk powder spray driers to avoid costly production shutdowns. Two possible solutions have been identified. These are guided wave and vibration analysis. This research focuses on vibration analysis method, based on variation in the natural frequencies and/or damping ratios caused by blockages. Experimental simulation studies the performance to assess the viability of the vibration analysis method in identifying blockage in the cyclone. To test this method, a 1.87m long vertical cylindrical steel tube with both ends simply supported was setup as a prototype and flour was used as the powder conveyed by the tube. Analytical, numerical and experimental methods were implemented on the prototype using vibration analysis techniques. Experimental resonant frequencies of the empty shell from the impact hammer excitation were compared with analytical and numerical solutions to analyse the modal shapes. The first bending mode was determined as 79 Hz, which decreased with the amount of added mass and location closer to the middle point. This was validated by the simulated mass experiment, which also matched with the beam-mass theory. Flour induced experiment further validated the variation of the first bending mode. Experimental 270Hz, 380Hz and 398Hz resonant frequencies increased with the amount of added mass, which was validated by the simulated mass and flour induced experiment. Besides the variation of the natural frequencies, the damping ratio was also studied and quantified using the Hilbert transform envelope curve method. Onsite monitoring of the vibration of the cyclone in a spray dryer was done at Fonterra Te Rapa and clear resonant frequencies were obtained. The research results from the prototype demonstrate that vibration analysis as a non-destructive method to detect the milk powder deposition or blockage in the cyclone is possible and promising. However, more work is required before industry application.

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Evans, Robert D. "Optimising ground penetrating radar (GPR) to assess pavements." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/20465.

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Ground penetrating radar (GPR) technology has existed for many decades, but it has only been in the last 20 to 30 years that it has undergone great development for use in near surface ground investigations. The early 1980's saw the first major developments in the application of GPR for pavements (i.e. engineered structures designed to carry traffic loads), and it is now an established investigation technique, with generic information included in several national standard guidance documents. Analysis of GPR data can provide information on layer depths, material condition, moisture, voiding, reinforcement and location of other features. Assessing the condition of pavements, in order to plan subsequent maintenance, is essential to allow the efficient long-term functioning of the structure and GPR has enhanced and improved the range and certainty of information that can be obtained from pavement investigations. Despite the recent establishment of the technique in pavement investigation, the current situation is one in which GPR is used routinely for pavement projects in only a minority of countries, and the specialist nature of the technique and the sometimes variable results that are obtained can mean that there is both a lack of appreciation and a lack of awareness of the potential information that GPR can provide. The fact that GPR is still a developing technique, and that many aspects of its use are specialised in their nature, means that there are also several technical aspects of GPR pavement investigations which have not been fully researched, and knowledge of the response of GPR to some material conditions has not been fully established. The overall aim of this EngD research project was to provide improved pavement investigation capabilities by enhancing the methodologies and procedures used to obtain information from GPR. Several discrete research topics were addressed through various research methods including a literature review, fieldwork investigations, experimental laboratory investigations and a review of previously collected data. The findings of the research allowed conclusions and recommendations to be made regarding improved fieldwork methodologies, enhancing information and determining material condition from previously collected GPR data, assessing the effect of pavement temperature and moisture condition on GPR data and also on managing errors and uncertainty in GPR data. During the EngD project, a number of documents and presentations have been made to publicise the findings both within the EngD sponsoring company (Jacobs) and externally, and an in-house GPR capability has been established within Jacobs as a direct result of the EngD project.

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Richter, Vladislav. "Lokalizace a identifikace typu poškození pneumatických pohonů." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-377884.

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Pneumatic drives are an integral part of many machinery, with high demands on their reliability. Unfortunately, they sometimes fail, either due to improper production or assembly at the factory or by gradual degradation of moving parts and sealing elements during operation. Current diagnostic methods do not allow localization or identification of the type of damage and do not allow the operator to make a qualified decision. This work deals with the use of acoustic emission for these purposes. On PB type cylinders manufactured by Poličské strojírny a.s., a methodology is introduced which leads to the direct identification or at least localization of selected defects. By implementing this methodology in the final inspection of the production plant, the percentage of exposed pieces of waste will be increased, thus preventing accidents of these faulty pieces during operation.

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Kozáček, Vojtěch. "Experimentální stanovení závislosti parametrů NDT a pevnosti v tlaku betonu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2020. http://www.nusl.cz/ntk/nusl-409957.

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The diploma thesis deals with non-destructive testing of concrete as well as with the relationship between determined parameters and the compressive strength of concrete. The thesis is mainly focused on the ultrasonic pulse velocity method and the rebound hammer test. The experimental part of the thesis describes non-destructive tests performed on concrete blocks. The compressive strength was tested on the drill cores taken from the concrete blocks. The aim of this thesis is to find regression models of the relationship between the compressive strength and non-destructive parameters, and the subsequent analysis of the results.

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Selim, Hossam. "Hybrid non-destructive technique for volumetric defect analysis and reconstruction by remote laser induced ultrasound." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669481.

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This PhD thesis is devoted to the design, development and implementation of a non-contact hybrid non-destructive testing (NDT) method applied to the analysis of metallic objects that contain embedded defects or fractures. We propose a hybrid opto-acoustic technique that combines laser generated ultrasound as exciter and ultrasound transducers as receivers. This work envisages a detailed study of the detection and one, two or three-dimensional reconstruction of defects, using the proposed hybrid technique and its application as a remotely controlled non-contact NDT. Our device combines several advantages of both photonic and ultrasonic techniques, while reduces some of the drawbacks of both individual methods. Our method relay on the combination of experimental results with high-resolution signal processing procedures based on different mathematical algorithms. Our basic experimental setup uses a nanosecond pulsed laser at 532nm wavelength that impacts onto the surface of the object under study. The laser pulse is rapidly absorbed into a shallow volume of material and creates a localized thermo-elastic expansion inducing a broadband ultrasound pulse that propagate inside the material. The laser beam scans a selected area of the object surface, being remotely controlled by means of a programmable XY scanner. For each excitation point, the ultrasound waves propagate through the object are reflected or scattered by material 3D defects. They are detected by ultrasound transducers and recorded with a PC data-acquisition system for a further process and analysis. As a first step, the time of flight analysis provides enough data for the location and size of the defect in 1D view. The detection capabilities of internal defects in a metallic sample are studied by means of wavelet transform, chosen due to its multi-resolution time-frequency characteristics. A novel algorithm using a density-based spatial clustering is applied to the resulting time frequency maps to estimate the defect’s position. For the 2D visualization and reconstruction of the defects we extended the signal analysis using the synthetic aperture focusing technique (SAFT). We implement a novel 2D apodization window filtering applied along with the SAFT, and we show it removes undesired effects of the side lobes and wide-angle reflections of ultrasound waves, enhancing the reconstructed image of the defect. We move then towards the 3D analysis and reconstruction of defects and in this case we achieve and implement a fully non-contact and automatized experimental configuration allowing the scan areas on different object’s faces. The defect details are recorded from different angles/perspectives and a complete 3D reconstruction is achieved. Finally, we show our results on a complementary topic related to a particular case of the ultrasound propagation in solids. We were concerned on the physical understanding of the propagation and diffraction of ultrasound waves in solid materials from the first moment. The control of the diffraction pattern in solids, using an ultrasonic lens, would help focus/collimate the ultrasound reducing echoes and boundary reflections, resulting in a further improve NDT process. Phononic crystals have been used to regulate the diffraction and frequency response of ultrasonic waves traveling in fluids. However, they were much less studied in solid materials due to the difficulty of building the crystal and to high coupling losses. We perform detailed numerical simulations of the ultrasound propagation in a solid phononic crystal and we show focusing and the self-collimation effects. We further extend our analysis and couple our phononic crystal lens to a solid under study, showing that the diffraction control is preserved inside the target solid object trough the coupling material.
Esta tesis doctoral versa sobre el diseño, estudio e implementación de un método híbrido, sin contacto, de ensayos no destructivos (NDT, non-destructive testing) para el análisis de objetos metálicos que contienen defectos o fracturas internas. Proponemos una técnica híbrida opto-acústica que combina ultrasonidos generados por impacto láser como excitador y transductores de ultrasonidos como receptores. El trabajo plantea un estudio detallado de la detección y reconstrucción en 1D, 2D y 3D de defectos presentes en un objeto metálico, usando la técnica híbrida de NDT sin contacto y controlado remotamente. Nuestro dispositivo presenta varias ventajas de las técnicas fotónicas y de ultrasonidos, reduciendo al mismo tiempo algunos inconvenientes de dichos métodos tomados por separado. Nuestro método combina resultados experimentales con simulaciones numéricas basadas en el procesado de señal de alta resolución. El montaje experimental consiste en un láser pulsado de ns a una longitud de onda de 532 nm, que impacta sobre la superficie del objeto. El pulso láser se absorbe, creando una expansión termoelástica localizada que induce un pulso de ultrasonidos de banda ancha que se propaga en el material. El láser, controlado remotamente, realiza un barrido sobre un área seleccionada de la superficie del objeto. Por cada punto de excitación, el ultrasonido se propaga a través del objeto y se refleja o dispersa en los defectos del material. Dichas ondas se detectan mediante transductores y se registran en un sistema de adquisición de datos para su ulterior procesado. En un primer paso, mediante el análisis del tiempo de vuelo, podemos localizar y determinar el tamaño del defecto en una vista 1D. Las capacidades de detección de defectos internos en una muestra metálica se estudian también mediante transformación wavelet debido a sus características de multi-resolución en tiempo y frecuencia. Se aplica un algoritmo novedoso de agrupamiento (clustering) espacial y se usan los mapas resultantes de tiempo y frecuencia para estimar la posición del defecto. Para la visualización 2D de los defectos ampliamos el análisis de la señal utilizando la técnica de focalización por apertura sintética (SAFT, synthetic aperture focusing technique). Implementamos un novedoso filtro de apodización 2D, juntamente con la técnica SAFT, y demostramos que elimina efectos no deseados, mejorando la resolución de la imagen reconstruida del defecto. El siguiente paso es un análisis y reconstrucción 3D. En este caso conseguimos una configuración experimental totalmente automatizada y sin contacto, permitiendo áreas de barrido sobre diferentes caras de un objeto. Los detalles de los defectos se registran desde diferentes ángulos, consiguiéndose una completa reconstrucción 3D. Finalmente, mostramos nuestros resultados en un tema complementario, relacionado con un caso particular de propagación de ultrasonidos en sólidos. Desde un primer momento, quisimos tener una comprensión física de la propagación y difracción de ondas de ultrasonidos en materiales sólidos. El control de los patrones de difracción en sólidos, mediante el uso de lentes ultrasónicas, ayudaría a la focalización/colimación del ultrasonido, reduciendo ecos y reflexiones en la superficie de contorno, mejorando del proceso de análisis NDT. Los cristales fonónicos se usan para regular la difracción y la respuesta en frecuencia de ondas de ultrasonido que se propagan en fluidos. No obstante, dichas estructuras se han estudiado mucho menos en materiales sólidos. Hemos realizado detalladas simulaciones numéricas de la propagación de ultrasonidos en un cristal fonónico sólido y hemos demostrado efectos de focalización y autocolimación. Finalmente hemos acoplado nuestra lente de cristal fonónico al sólido objeto de estudio, demostrando que el control de la difracción se conserva en el interior de dicho objeto a través del material de acoplamiento. Finalmente, proporcionamos una conclusión general sobre el trabajo declarado en esta tesis y un plan de trabajo futuro donde esta investigación puede extenderse y expandirse aún más a aplicaciones industriales en colaboración con el mercado de producción

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Ghodhbani, Nacef. "Contrôle et suivi des propriétés visco-élastiques d'un composite en cours de fabrication." Thesis, Le Havre, 2016. http://www.theses.fr/2016LEHA0008/document.

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Les transducteurs ultrasonores font l'objet de nombreux développements en contrôle non-destructif (CND) industriel. Utilisé ponctuellement et périodiquement, le CND ultrasonore permet d'établir des diagnostics sur la santé des matériaux. La caractérisation ultrasonore en temps réel constitue un outil de surveillance de l'évolution des propriétés physiques lors de la fabrication des matériaux composites. Dans ce contexte, des études sont menées au LOMC pour optimiser le procédé de fabrication des matériaux composites par RTM (Resin Transfer Molding) afin d’améliorer la qualité du produit. Ce travail de thèse consiste à développer des méthodes ultrasonores pour le suivi des propriétés viscoélastiques d’un composite pendant la phase de production. Les propriétés viscoélastiques sont étudiées à l’aide de modèles théoriques, de simulations numériques et de résultats expérimentaux. Des études de calibration ont été menées afin d’étudier les facteurs d’influence sur le suivi de propriétés ultrasonores lors de la mise en oeuvre d’un procédé RTM. Le suivi des paramètres viscoélastiques de résines époxy est effectué dans un premier temps à basse température au cours d'une polymérisation isotherme et d’une post-cuisson. Ensuite, une approche basée sur la méthode de caractérisation en émission/transmission a été développée afin d’étudier le comportement à haute température. La modélisation de la réponse électroacoustique par série de Debye (DSM) a été effectuée en se basant sur des approches analytiques. L’utilisation des transducteurs multiéléments permet la localisation et le dimensionnement de défauts lors du déplacement de fibres de carbone dans une résine liquide, entre des moules
The developments based on ultrasonic transducers are nowadays numerous in the industrial non-destructive testing (NDT). Used punctually and periodically, the ultrasonic NDT is used for health diagnostics of materials. Ultrasonic characterization in real time allows a physical properties monitoring during the manufacturing of composite materials. In this context, studies are conducted in LOMC in view to optimize the manufacturing process of composite materials using RTM (Resin Transfer Molding) in order to improve the product quality. This work consists to develop ultrasonic methods for the monitoring of viscoelastic properties during the production phase of composites. The viscoelastic properties are studied using theoretical models, numerical simulations and experimental measurements. Calibration studies were carried out to study the influencing factors on the monitoring of ultrasonic properties during the RTM process. The monitoring of viscoelastic parameters of epoxy resins is performed in a first time at low temperature during an isothermal polymerization and a post-curing. Then, an approach based on the transmission mode characterization was developed to study high-temperature behavior. Based on analytical approaches, the electroacoustic response was simulated by Debye series method (DSM). The use of phased array transducers was investigated for the location and sizing of defects during the movement of the carbon fiber in a liquid resin between the molds

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Poggi, Francesco. "Bending properties of commercial wood-based panels by NDT methods." Thesis, Linnéuniversitetet, Institutionen för skog och träteknik (SOT), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-66162.

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This thesis work focuses mainly on the application of non-destructive testing (NDT) methods on wood-based panels (WBP) in order to estimate the bending properties. To prove the accuracy and applicability of these methods on WBP, their results are correlated with results from a standardized static bending test. The behavior in different climate conditions and the application on panels of larger sizes is also questioned to provide an indication about strong points and boundaries of NDT methods applied on WBP.The bending properties are of major importance, especially for materials suited to bear loads. Bending stiffness, represented by the modulus of elasticity (MOE), is an expression of the deflection rate of a material under load. The bending strength, represented by the modulus of rupture (MOR), is an expression of the maximum load withstood by a material before rupture.Before testing, the material is acclimatized in three climate conditions: dry (20°C, 35% RH), standard (20°C, 65% RH) and wet (20°C, 85% RH), to understand the bending properties variation and how the NDT methods are affected by the variation in moisture content.The materials used are seven types of WBP, in particular four types of particleboards (PB), one type of high-density fiberboard (HDF), one type of dual density PB (with high and low density areas along the production direction) and one type of light-weight panel (Board-on-stiles, a composite panel of HDF, PB and paper honeycomb).To test the bending properties the following NDT methods are considered: transversal resonance vibration and longitudinal resonance vibration with the use of the BING system and the time-of-flight with the use of Fakopp Ultrasonic Timer and Silvatest Trio. The resonance vibration methods, transversal and longitudinal, are based on the relation between resonance vibration properties and bending properties of a material. The relation with bending properties also exists for the stress wave velocity (SWV) through a material, calculated with the time-of-flight method. The dynamic MOE resulting from these tests is then correlated with the static MOE and MOR from the static bending test.The NDT methods resulted to be reliable on WBP, with generally high levels of correlation between dynamic MOE and static MOE and MoR. The highest correlation value for MoE is with the transversal resonance vibration while the highest for MOR is with the longitudinal resonance vibration. The results of the dynamic MOE for all the NDT methods are higher than the static MOE, as confirmed also in the literature; the average ratio between the dynamic and the static MOE is, for example, up to 1,6 for WBP in standard climate condition, tested with Fakopp U.T.. These results are extremely higher than values suggested by previous studies. Moreover, the ratio increases with increasing relative humidity of the climate condition. The results from the tests on larger sizes suggest a possible application in this field. The time-of-flight method is suitable for in-plane uniform materials, like the PB and HDF, while the transversal resonance methods give also a good representation of the properties of the dual density PB and the light-weight panel.

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Gómez, García Soledad. "Descriptores Geométricos y de Forma: Aplicación a la caracterización ultrasónica de materiales." Doctoral thesis, Universitat Politècnica de València, 2010. http://hdl.handle.net/10251/8722.

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Entre otras aplicaciones, el Grupo de Tratamiento de Señal (GTS) de la Universidad Politécnica de Valencia ha trabajado tradicionalmente en el campo de los ensayos no destructivos por ultrasonidos. el GTS ha desarrollado sofisticados algoritmos de procesado de señal para la detección y caracterización en materiales dispersivos. El procedimiento de inspección ultrasónica de materiales implica la obtención de un registro o señal mediante un equipo emisor-receptor de ultrasonidos. Este registro será posteriormente procesado para obterner información del material. La extracción de características puede realizarse calculando parámetros temporales y/o frecuenciales de los registros en cuestión. Estos parámetros contienen información que está relacionada con propiedades físicas de los materiales y que podrán ser empleados en definitiva para clasificar y caracterizar el material. El objetivo de la tesis es el de ampliar el conjunto de parémetros que se han venido usando de manera tradicional en el grupo. Los nuevos parámetros proponen un cambio de perspectiva mediante el uso de técnicas basadas en el tratamiento digital de imagen. Se presenta una colección de descriptores geométricos y de forma que serán aplicados a las imágenes obtenidas a partir de los diagramas tiempo-frecuencia. Los citados parámetros se aplicarán junto con los parámetros que componen el modelo tradicional, o versiones modificadas de éstos, a la caracterización ultrasónica de materiales dispersivos blandos. En la tesis se presenta un modelo matemático afín a los tipos de materiales que han sido evaluados en este trabajo. Se define así un esquema que modela en el dominio de la frecuencia el registro de señal procedente de la inspección ultrasónica del material. Se proponen y estudian además diferentes métodos con el objetivo de llevar a cabo el análisis espectral de la señal ultrasónica y se discuten diferentes alternativas para la obtención y mejora de los diagramas tiempo-frecuencia.
Gómez García, S. (2010). Descriptores Geométricos y de Forma: Aplicación a la caracterización ultrasónica de materiales [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8722
Palancia

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Rodat, Damien. "Simulation opérationnelle en contrôle non destructif." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS535.

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La simulation opérationnelle a déjà été développée pour diverses activités dont l'exercice en conditions réelles peut s'avérer coûteux voire dangereux : le pilotage d'avion, les interventions chirurgicales, etc. L'idée consiste à remplacer la réalité par une simulation suffisamment réaliste pour donner l'impression aux utilisateurs qu'ils réalisent réellement l'activité.Le Contrôle Non-Destructif (CND) regroupe l'ensemble des méthodes mises en œuvre pour tester l'intégrité des pièces mécaniques sans les altérer. Dans ce domaine, la simulation opérationnelle n'a été introduite que très récemment par un brevet déposé par Airbus. Cette approche permet de simuler numériquement la présence de défauts sans avoir à les ajouter réellement dans les pièces. Les pièces aéronautiques étant coûteuses, la simulation opérationnelle permet de réduire les coûts liés à la formation des opérateurs, à l'évaluation des performances des méthodes ou aux tests en conditions réelles de nouvelles procédures.La présente thèse vise à développer les outils scientifiques et technologiques nécessaires à donner vie au concept de simulation opérationnelle en CND. Pour remplacer la réalité par la simulation, les défis à relever sont de trois ordres : le réalisme de la simulation, la rapidité des calculs et l'instrumentation. Nous avons choisi d'illustrer ces trois aspects dans le cadre de l'inspection par ultrasons de pièces en matériaux composites. Les modèles de simulation couramment employés --- basés sur la résolution des équations de la physique --- n'offrent pas des temps de calculs suffisamment courts pour satisfaire les pré-requis de la simulation opérationnelle. Par ailleurs, le réalisme des simulations souffre parfois de la difficulté à paramétrer correctement les modèles. Nous explorons donc une autre approche : les modèles sont construits à partir de données expérimentales. Cette stratégie est exploitée pour traiter différents types de phénomènes tels que l'endommagement par impact, le trou à fond plat ou encore les perturbations de la micro-structure des matériaux. Par ailleurs, une solution matérielle et logicielle sont proposées et un premier prototype de simulateur opérationnel est mis au point. Ce système permet d'exploiter les modèles développés et de montrer que les signaux synthétiques peuvent sembler aussi réalistes que la réalité. Cette thèse court ainsi du concept jusqu'au prototype
Several fields have already adopted the concept of operational simulation to limit risks and costs. For instance, part of the training phase of airline transport pilots or surgerons can now rely on simulations instead of real-life situations.Non-Destructive Testing (NDT) assesses the integrity of structural and mechanical components without damaging them. Operational simulation has drawn attention of the NDT community only recently through an Airbus patent. In this field, the operational simulation can be used to simulate the presence of a defect in a component without actually inserting the defect. For expensive parts such as aeronautical structures, this approach can reduce the costs of training operators, evaluating NDT method performances or testing new procedures in real-conditions.This thesis work aims to apply the concept of operational simulation to NDT. Three main scientific and technological challenges are to be tackled: the simulation realism, the computation speed and the instrumentation. We chose to focus this study on the ultrasound NDT technique applied to composite materials. Classical simulation approaches based on physical equations are not fast enough for a real-time synthesis of ultrasound signals. Moreover, the realism is often limited by the fidelity of the inspection set-up description. For instance, the material properties are not always well-known and bring to a drop of realism. Thus, we investigate an alternative way: the models are built directly from experimental data. This strategy is applied to model the effect of several phenomena such as impact damages, flat bottom holes or material micro-structure. Hardware and software solutions are also studied to propose a first prototype. We have shown that the replacement of real signals by on-the-fly simulated ones is achievable: the simulation is realistic enough to be considered as reality by operators. thus, this thesis work brings the concept to a first prototype dedicated to ultrasound NDT

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Gränne, Fredrik. "Air and Water Tightness in Building Envelopes - Evaluation of Methods for Quality Assurance." Doctoral thesis, KTH, Building Sciences and Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3264.

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The purpose of this work is to contribute to a process formaking buildings with good function and to avoid prematurefaults.

The design, construction and installation of low-slopedroofs are important parts of creating a durable building. Mostof the leakages in low-sloped roofs occur where materials withdifferent thermomechanical properties are joined together. Withbetter knowledge about these joints, the expected service lifecould better be estimated. Common roofing materials onlow-sloped roofs are roof membranes.

To avoid damages and to minimise energy consumption thedetection of air and water leaks is essential. It can bedifficult to localise a leak in e.g. a roof since water canflow far within the construction. Leakage detection can beapplied both as a quality assurance method after installationof low-sloped roofs and as field inspection methods. Theleakage detection can also be extended to terrace slabs and thewhole building envelope.

To investigate the strength of jointsbetween sheet metaland roofing membranes, several small-scale tests and somelarge-scale tests were performed. The test methods weredeveloped to match the loads that can be expected on this kindof joints.

A number of water leak-detection methods were evaluatedthrough application on test roofs. Some of the methods todetect leaks on low-sloped roofs can also be used to detect airleakage in other parts of the building envelope. To develop andevaluate air leak-detection procedures, selected methods wereused in two case studies.

The circumstances regarding welding of the material jointswere found to have great impact on the strength. The roofshould be designed so no long-term strain will appear since acomparatively low stress may damage the joint over time.

The performance of the leak-detection methods depends on theroofing material. All methods tested were an improvementcompared to visual inspections. Different recommendedapproaches for leakage detection and quality control is given.The case studies show that air leakage detection could beperformed with good accuracy. The potential difference methodcould without doubt be a tool for leakage localisation inwaterproofing layers both on roofs and in terrace slabs.

Keywords:Roofing, roof membrane, durability,waterproofing, leakage, wind-load, non-destructive testing,NDT, BSL4, BSL3, air leakage, building envelope

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Nguyen, Ngoc tan. "Évaluation non destructive des structures en béton armé : étude de la variabilité spatiale et de la combinaison des techniques." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0115/document.

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Les budgets alloués aux réparations des ouvrages et du patrimoine bâti ont atteint un niveau important. Une démarche scientifique est donc réfléchie pour réduire ces budgets par la mise en place d’outils visant à optimiser et fiabiliser le diagnostic structural des ouvrages. Les méthodes de contrôle non destructif (CND) constituent l’une des voies adaptées. Ces techniques reposent sur des principes physiques bien connus et les sociétés de service en proposent aujourd’hui un emploi courant, mais de nombreux verrous subsistent. Les deux besoins majeurs des gestionnaires d’ouvrages sont celui de l’optimisation de la stratégie de reconnaissance (où mesurer ? en combien de points ? avec quelle(s) techniques(s) et quelle précision ?) et celui de la quantification des propriétés mécaniques des matériaux ou des indicateurs de durabilité telles que la résistance à la compression, l’épaisseur carbonatée, le taux d’humidité. La question est comment déduire ces propriétés et ces indicateurs des mesures faites ? Et quelles sont la précision et la fiabilité de l’évaluation ?Cette thèse s’inscrit dans le cadre de deux projets nationaux de recherche : le projet ACDC-C2D2 et le projet ANR EvaDéOS. L’objectif principal est d’analyser la variabilité issue du CND pour ensuite remonter à la variabilité spatiale des bétons en conditions réelles. Les techniques de CND considérées sont choisies parmi les plus complémentaires : radar, résistivité électrique, ultrasons et rebond (scléromètre). Les résultats sont obtenus à partir d’une large campagne expérimentale effectuée sur des dalles d’un site test et sur deux ouvrages. L’analyse de la variabilité des CND a permis d’évaluer le nombre minimal de mesures nécessaire pour un niveau de confiance souhaité. D’autre part, la corrélation spatiale des données a été modélisée par l’analyse variographique. Les résultats montrent que, dans certain cas, les mesures de CND ne sont pas spatialement indépendantes. Les longueurs de corrélation identifiées dépendent de la propriété mesurée ainsi que du béton de l’ouvrage ausculté. La connaissance de ces longueurs de corrélation est un résultat nouveau qui permettra d’une part de mieux estimer la variabilité spatiale des bétons et d’autre part d’alimenter de manière plus réaliste les calculs fiabilistes des ouvrages. Elle permet également d’identifier un pas d’échantillonnage optimal sur ouvrage dans le cadre du suivi temporel ou pour effectuer des analyses complémentaires (ex. carottage, CND complémentaire ou plus fiable) et de représenter au mieux la cartographie spatiale des propriétés du béton.Dans le cadre du projet de recherche ANR EvaDéOS, les effets de la carbonatation et des gradients de teneur en eau (gradient d’humidité) sur les techniques CND ont été étudiés. Ce travail a pour objectifs d’étudier la sensibilité des techniques de CND à évaluer ces deux indicateurs de durabilité ainsi que leur impact sur la variabilité des mesures de CND. En laboratoire, des campagnes expérimentales ont été réalisées sur corps d’épreuve ayant différentes profondeurs de carbonatation ou des gradients d’humidité. L’effet de la carbonatation a été quantifié pour certains observables : résistivité électrique, vitesse ultrasonore et rebond. En ce qui concerne la variabilité des mesures de CND, l’effet de la carbonatation est seulement notable dans le cas du béton saturé, en particulier pour la variabilité locale de la résistivité électrique et du rebond. Cet effet reste faible par rapport à l’effet du degré de saturation. Les premiers résultats montrent également que les mesures de la résistivité électrique permettraient de suivre des gradients d’humidité dans le béton
The budgets assigned to the repair of structures and built heritage have reached an alarming level. A scientific approach is needed to reduce these budgets by implementing tools for a more reliable and optimal assessment of existing structures. Non-destructive testing (NDT) techniques constitute one of approaches adapted to real conditions. These techniques are based on well-known physical principles. Many companies offer their services in NDT domain today but many challenges remain. The two particular needs of structure managers are the optimization of the assessment strategy (where to measure? how many testing points? what technique(s) and what precision?) and the quantification of mechanical properties of materials or durability indicators such as the compressive strength, the carbonation depth, the moisture content. The questions are how to estimate these properties from measurements performed, and what are the accuracy and reliability of the evaluation?This thesis is part of two French research projects: ACDC-C2D2 and ANR EVaDéOS. The main objective is to analyze the variability of non-destructive testing (NDT) measurements for assessing the spatial variability of concrete in real conditions. NDT techniques considered are chosen as being complementary: radar, electrical resistivity, ultrasonic, rebound hammer. The results are obtained from a wide campaign of measurements, which was performed on concrete slabs of a testing site and on two existing structures. The analysis of the NDT variability makes it possible to assess the necessary minimum number of measurements for a desired level of confidence. Furthermore, the spatial correlation of the data was modeled using the variogram analysis. In some cases, the results show that NDT measurements are not spatially independent. The correlation lengths identified depend on the measured property and the concrete of the structure inspected. They are a new result, which will provide on one hand a better evaluation of spatial variability of concrete and on the other hand a more realistic input of reliability calculations of structures. The correlation length allows also the identification of an optimal sampling distance on existing structure within the monitoring time or the implementation of additional analyses (eg. core, complementary or more reliable NDT) and a better representation of the spatial mapping of concrete properties.Within the framework of the ANR EvaDéOS research project, the effects of carbonation and of moisture gradients on NDT measurements were studied. This work aims to study the sensitivity of NDT techniques for assessing these two durability indicators and their impact on the variability of NDT measurements. In laboratory, the experimental surveys were carried out on testing specimens having different depths of carbonation or moisture gradients. The effect of carbonation was quantified for several parameters: electrical resistivity, ultrasonic pulse velocity and rebound hammer. With respect to the variability of NDT measurements, the effect of carbonation is only significant in the case of saturated concrete, in particular for the local variability of electrical resistivity and rebound hammer. This effect is weak in comparison with the effect of saturation degree. The first results show also that the measurements of electrical resistivity would follow moisture gradients in concrete

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Ozturk, Emre. "Estimation Of The Height Of Surface Breaking Cracks Using Ultrasonic Timing Methods." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607176/index.pdf.

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In this thesis, two ultrasonic timing methods are used in order to investigate the accuracy and reliability of measurements for surface breaking cracks having different orientations and heights. Also the best applicable measurement technique is searched by comparing the received test results. These methods are the Time of Flight Diffraction (TOFD) Method using diffraction of longitudinal waves and another method using the reflection of shear waves from the crack tips. In order to simulate and measure the height of surface breaking cracks three sets of test blocks from steel, and two sets of wedges from plexiglas material are manufactured. Also several probes having frequencies of 2Mhz, 4Mhz, 5Mhz and angles of 45o and 70o are used. Some test procedures are created to make realistic comparisons between the test results and the ones found by previous studies in literature. The results are compared according to the standard deviations of errors in crack height measurements and it is found that the depth, orientation of defects and the frequency of probes have considerable affect on the results. With wider probe angles and higher frequencies of probes to some extent the errors are observed to be running low and the height of cracks could be measured closer to the original size. The amount of the errors is increased in measurements with the increasing angle of cracks. The results of both methods are found to be very satisfactory. A range of ±
0.5 mm for means of error from the original vertical crack heights is determined. The results agree with the previous studies.

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ACCORNERO, FEDERICO. "Structural Health Monitoring for Preservation and Safeguard of Architectural Cultural Heritage." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2566947.

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The preservation of architectural cultural heritage is a complex problem that requires the use of innovative Structural Health Monitoring (SHM) and non-destructive investigation methodologies to assess the integrity of decorated artworks without altering their state of conservation. A complete diagnosis of crack pattern regarding not only the external decorated surface but also the internal support is of great importance due to the criticality of internal defects and damage phenomena, which may suddenly degenerate into irreversible failures Objective of the research is to use the Acoustic Emission monitoring to assess the support of the decorated mural surfaces of the Sacred Mountain of Varallo Renaissance Complex (Italy), developing the application aspects of this technique, which has been widely studied from a theoretical and experimental point of view by some Authors in the safeguard of civil and historical buildings. Moreover, a correlation exists between the regional seismic activity and the AE signals collected during structural monitoring. Therefore, the AET can be also used for the preservation of decorated artworks from the seismic risk. Then, the assessment of damage by electrical resistance measurements on laboratory mortar specimens and terracotta statues belonging to Chapel XVII of the Sacred Mountain of Varallo experiencing different stress conditions is presented. The evolution of damage based on changing electrical resistance shows agreement with theoretical predictions of continuum damage mechanics. The continuum damage models provide also theoretical support to estimate statues’ residual lifetime by correlating in situ electrical resistance measurements with measurements on the laboratory specimens. Finally, the collapse mechanisms of sculpture and building decoration materials is investigated by means of the Overlapping Crack Model and AE technique. These methods permit to explain the size and slenderness effects on the structural ductility and to show that the energy release during the cracks evolution is a surface-dominated phenomenon.

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Nilsson, Erik, and Daniel Johansson. "Testing and evaluation of component made using electron beam melting and Alloy 718 powder." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-35566.

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The aerospace industry is constantly striving to becoming more economical and environmentally friendly. One of many efforts to achieve this is the Lightcam project which in this case is evaluating the use of additive manufacturing in the form of electron beam melting in conjunction with the nickel-based superalloy, Alloy 718. This combination is not fully explored and examined. For this purpose, a demonstrator vane was produced and it was subsequently evaluated in this thesis. The evaluation was performed in as-built condition and was divided in non-destructive testing, evaluation of these methods and metallographic review to confirm the results, and potentially revealing more properties. The non-destructive testing was performed using conventional radiography and computed tomography. Both methods struggled to deliver complete and reliable results, for varying reasons. Radiography could deliver results of the whole vane, but these were impossible to evaluate due to the rough surface created by the electron beam melting process. The computed tomography on the other hand was not affected by the rough surface and produced usable, though not complete, results of the vane. The reason for the computed tomography’s inability to deliver complete results was the material, varying thickness and complex geometry of the vane. As a complement and to verify the results from the non-destructive testing, a metallographic examination was conducted. These tests were conducted with the aim of answering the following three questions: What non-destructive testing methods are suitable to evaluate Alloy 718 components manufactured with electron beam melting? - Neither radiography nor computed tomography are suitable as a sole evaluation method, for various reasons. All surface dependent methods were deemed unsuitable without testing due to the rough surface. What types of defects and in what quantity can they be found in the produced vane? - Defects found are: Porosity and lack of fusion, both found as internal and partially external and in varying sizes. Where are the defects located? - Pores are mainly found in the center of sections modeled to a 3mm thickness. Lack of fusion was found between build layers in all thicknesses. Apart from these results, hardness was found to vary depending on build height, increasing from the bottom towards the top. Microstructure was also found to vary with the build height, but always consisting of either equiaxed or columnar grains.
Lightcam

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Gäbler, Simone. "Untersuchung des Anwendungspotenzials der Hochfrequenzwirbelstrommesstechnik zur Charakterisierung dielektrischer Eigenschaften von Epoxidharzen und Faserverbundmaterialien." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-230419.

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Die dielektrischen Eigenschaften, also die Interaktion mit elektrischen Feldern, sind ein wichtiger Qualitätsparameter der Matrix in Faserverbundmaterialien und allgemein in Harzen. Sie werden bisher mit Hilfe von kapazitiven Verfahren oder Hochfrequenzverfahren wie z. B. der Mikrowellentechnik gemessen. Allerdings können beide Verfahren nicht an elektrisch leitfähigen Materialien wie Kohlenstofffaserverstärkten Kunststoffen (CFK) eingesetzt werden und auch bei der Anwendung der Methoden an Kunststoffen oder elektrisch isolierenden Faserverbundmaterialien gibt es Nachteile. So benötigt die kapazitive Messtechnik meist eine spezielle Probenpräparation für quantitative Messungen und erreicht eine vergleichsweise schlechte Ortsauflösung beim Permittivitätsmapping. Die vorliegende Arbeit widmet sich daher der Untersuchung einer alternativen, in diesem Kontext neuen Methode zur Charakterisierung dielektrischer Eigenschaften: Die Hochfrequenzwirbelstrommesstechnik, welche bisher zur Messung der elektrischen Leitfähigkeit und magnetischen Permeabilität genutzt wird, wird theoretisch und praktisch hinsichtlich ihres Anwendungspotentials zur Permittivitätsmessung an Epoxidharzen und Faserverbundwerkstoffen diskutiert. Dabei werden zuerst Grundlagen wie Anwendungsfelder für die Nutzung dielektrischer Eigenschaften von Harzen und Verbundwerkstoffen zur Qualitätssicherung bzw. gängige Messverfahren erläutert. Anschließend wird theoretisch gezeigt, warum dielektrische Eigenschaften auf das Hochfrequenzwirbelstrom (HFWS)-Signal wirken. Dabei werden sowohl die Maxwell-Gleichungen genutzt, als auch Finite Elemente (FE)-Simulationen. Der Schwerpunkt der Forschungsarbeit liegt dann auf der experimentellen Untersuchung der Permittivitätsmessung mittels HFWS. Es werden verschiedene Anwendungsfälle betrachtet: von zeitlich kontinuierlichen Permittitivitätsänderungen (am Beispiel der Aushärtung von Epoxidharzen), über lokale Permittivitätsabweichungen (in Folge von Defekten, Textureigenschaften oder thermischen Überlasten) bis hin zu quantitativen Permittivitätsmessungen (zur Materialcharakterisierung bzw. Alterungsuntersuchung). Dabei kann gezeigt werden, dass es möglich ist, die Permittivität von Faserverbundwerkstoffen und Epoxidharzen mittels HFWS zu charakterisieren, selbst wenn das zu prüfende Material elektrisch nicht leitfähig ist.

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Herbig, Michael. "3D short fatigue crack investigation in beta titanium alloys using phase and diffraction contrast tomography." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00690521.

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X-Ray Diffraction Contrast Tomography (DCT) is a recently developed, non-destructive synchrotron imaging technique which characterizes microstructure and grain orientation in polycrystalline materials in three dimensions (3D). By combining it with propagation based phase contrast tomography (PCT) it is for the first lime possible to observe in situ the 3D propagation behavior of short fatigue cracks (SFCs) within a set of fully characterized grains (orientation and shape). The combined approach, termed 3D X-ray Tomography of short cracks and Microstructure (3DXTSM), has been developed on the metastable beta titanium alloy "Beta21S". A large part of this work deals with the development of the 3DXTSM methodology. In the combined dataset, each point on the 3D fracture surface can be associated with a multidimensional data structure containing variables describing the grain orientation, the local fracture surface normal and the propagation history. The method uses a surface mesh composed of triangles that describes the crack (in other words: the fracture surface) in the last propagation state measured. Grain orientations, crack fronts, local growth rates and grain boundaries can be visualized by assigning colors to this mesh. The data structure can be interrogated in a number of different ways. Tools for extracting pole figures and pole density distribution functions have been implemented. An algorithm was developed that is capable of measuring the 3D local growth rate of a crack containing branches. The accuracy of the grain boundaries as reconstructed with OCT was evaluated and the elastic constants of Beta21S were determined.

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Yan, Guqi. "Zero-group-velocity Lamb modes in laser ultrasonics : fatigue monitoring and material characterization." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1026/document.

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

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Mohamed, elarif Abderemane. "Évaluation et contrôle non destructifs des barreaux et plaques par génération acoustique induite par absorption de micro-ondes." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14235/document.

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De nombreuses études ont été menées jusqu’ici afin d’analyser l’apport de la technique de génération acoustique par micro-ondes dans le domaine de l’évaluation et du contrôle non destructifs des structures mécaniques. Le caractère entièrement sans contact de cette nouvelle technique en ferait un moyen pouvant être adopté pour générer aisément des ondes acoustiques dans les matériaux diélectriques absorbants. Ce travail porte d’abord sur l’étude des vibrations latérales engendrées dans les barreaux viscoélastiques placés dans un guide d’ondes électromagnétiques contenant une ouverture sur l’une des faces latérales et soumis à de brèves excitations de micro-ondes. Un modèle paramétrique prédit la forme de l’élévation de la température à l’intérieur de l’échantillon. Ses résultats soulignent que l’utilisation des guides partiellement ouverts provoque une distribution asymétrique de la température générant ainsi des modes de flexion. Par ailleurs, un modèle numérique tridimensionnel par éléments finis a permis de mettre en évidence l’existence d’autres modes liés aux déformations des sections-droites lorsqu’elles sont soumises à une brusque dilatation thermique. Ensuite, l’élaboration de méthodes directes pour compléter l’évaluation des propriétés viscoélastiques des mêmes barreaux placés dans les guides conventionnels est considérée. Différents modèles analytiques sont construits pour analyser l’effet du coefficient de Poisson sur le rapport des vibrations induites dans les directions latérale et longitudinale d’une part, et sur la dispersion des ondes acoustiques de type traction compression d’autre part. Un algorithme d’optimisation permettant d’estimer le coefficient de Poisson et la partie réelle de la lenteur à valeurs complexes par une méthode inverse est élaboré puis appliqué dans le cas concret de deux barreaux polymériques. Enfin, une étude analytique et numérique par éléments finis est menée afin d’analyser les vibrations générées sur un défaut circulaire (trou) contenu dans une plaque et chauffé localement par des micro-ondes. Deux approches acoustiques sont construites pour prédire la forme de la zone chauffée par une température uniforme ou gaussienne. Une relation directe entre la taille du défaut et les fréquences de certains pics qui apparaissent sur les spectres des vibrations de la plaque ont été mises en évidence. Celle-ci conviendrait à l’élaboration d’une méthode inverse permettant de dimensionner ces types de défauts
Many studies in the field of both nondestructive evaluation and testing of mechanical structures have been conducted so far by analyzing the contribution of the microwaves induce acoustic technique. This new non-contact technique can be easily adopted to generate acoustic waves in non-conducting materials. This work begins with studying the lateral vibrations generated within viscoelastic bars hold inside grooved electromagnetic waveguides and subjected to short microwave irradiations. A parametrical model is established in order to predict the shape of the temperature rise within the sample. Results emphasize the fact that these types of waveguides generate a sudden asymmetric temperature rise, which produces some flexural modes. Besides, the development of a 3D numerical model allow the prediction of new vibration modes which are related to the deformations of the bar cross-sections during the sudden thermal heating. Then, direct methods are developed to complete the assessment of the viscoelastic properties of bars placed inside conventional electromagnetic waveguides. Different analytical models are proposed to study the effects of the Poisson ratio either on the ratio between lateral and longitudinal vibrations or on the dispersion of longitudinal waves. An optimization algorithm that allows the Poisson ratio and the real part of the complex slowness evaluation by means of dispersion curves is elaborate before being applied in the specific case of two polymeric bars. Finally, analytical and numerical finite element methods are conducted to analyze the acoustic waves generated by a circular defect (hole) contained in a plate and heated locally by microwaves. Two acoustic approaches are performed to predict the temperature rise form. Furthermore, a nondestructive testing method is highlighted by a direct relationship between the size of the defect and the frequencies of some peaks that appear on the velocity spectra of the plate. This method could be applied to set up an inverse procedure that can be used to size these kinds of defects

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Aschy, Ameni. "Imagerie ultrasonore de strucutres composites hétérogènes." Thesis, Le Mans, 2018. http://www.theses.fr/2018LEMA1008.

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Ce travail de thèse a pour objectif de développer une méthodologie visant à imager les défauts dans les structures composites moyennant les ultrasons multiéléments. Plus précisément, la motivation essentielle réside dans la difficulté d’application des méthodes ultrasonores conventionnelles pour le contrôle de structures composites épaisses et hétérogènes. En effet, l’application de ces méthodes est d’autant plus difficile en présence d’anisotropie structurelle où les paramètres vitesse et atténuation changent de façon importante en fonction du trajet ultrasonore considéré. Cela pourrait même se compliquer en présence de dispersion fréquentielle des propriétés viscoélastiques du matériau composite. Les méthodes d’imagerie étudiées sont appliquées dans le cas de structures composites hétérogènes de forte épaisseur. Dans un premier temps, les paramètres vitesse et atténuation des ondes élastiques de volume se propageant dans le composite sous différentes incidences ont été déterminées.Ce travail a également permis de remonter aux caractéristiques viscoélastiques par méthode inverse.Les différents paramètres trouvés par méthodes directe et inverse sont ensuite intégrés au modèle direct de calcul de trajets ultrasonores pour corriger les effets d’anisotropie dans l’imagerie Total Focusing Method (TFM) et Plane Wave Imaging (PWI) et étudier ainsi les possibilités d’amélioration de la détection et de la caractérisation des défauts pouvant exister au sein des structures composites étudiées. Enfin, il est important de souligner que ce même travail discute de la nécessité de connaître le tenseur d’élasticité pour une prise en compte optimale de l’anisotropie. À cet effet, une comparaison avec un modèle simplifié mettant en jeu les vitesses de groupe est proposée
This work aims to develop a methodology to image defects in composite structures by using Phased Array ultrasonic techniques. More specifically, the essential motivation lies in the difficulty of applying conventional ultrasonic methods for the control of thick and heterogeneous composite structures. Indeed, the application of these methods is more difficult in the presence of structural anisotropy where the velocity and the attenuation parameters change significantly depending on the ultrasound considered path. This could be more complicated in the presence of the viscoelastic properties frequency dispersion of the composite material. The studied imaging methods are applied in the case of heterogeneous and thick composite structures. First, the velocity and attenuation parameters of the elastic volume waves propagating in the composite under different incidences is determined. This work also allowed to go back to the viscoelastic characteristics by inverse method. The various parameters found by direct and inverse methods are then integrated into the direct ultrasound path calculation model to correct the anisotropy effects in the Total Focusing Method (TFM) and Plane Wave Imaging (PWI) imagery and thus to study the possibilities of improvement of the detection and characterization of defects that may exist within the studied composite structures. Finally, it is important to emphasize that this same work discusses the need of the tensor of elasticity for an optimal characterization of the anisotropy. For this purpose, a comparison with a simplified model involving group velocity is proposed

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Lin, Xin-Yu. "Lossless image compression for aerospace non-destructive testing applications." Thesis, University of Central Lancashire, 2004. http://clok.uclan.ac.uk/18830/.

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This thesis studies areas of image compression and relevant image processmg techniques with the application to Non-destructive Testing (NDT) images of aircraft components. The research project includes investigation of current data compression techniques and design of efficient compression methods for NDT images. Literature review was done initially to investigate the fundamental principles of data compression and existing methods of lossless and lossy image compression techniques. Such investigation provides not only the theoretical background, but also the comparative benchmarks for the research project. Chapter 2 provides general knowledge of image compression. The basic predictive coding strategy is introduced at the beginning of chapter 3. Fundamental theories of the Integer Wavelet Transform (IWT) can be found in chapter 4. The research projects proposed mainly three innovative methods for lossless compression of NDT images. Namely, the region-based method that employs regionoriented adaptation; the texture-based method that employs a mixed model for the prediction of image regions with strong texture patterns; and a hybrid method that utilizes advantages from both predictive coding and IWT coding. The main philosophy of lossless image compression is to de-correlate the original image data as much as possible by mapping from spatial domain to spatial domain in the predictive coding strategy or from spatial domain to transform domain in the IWT coding strategy. The proposed region-based method aims to achieve the best mapping by adapting the de-correlation to the statistical properties of decomposed regions using the component's CAD model. With the aid of component CAD models to divide the NDT images of aircraft components into different regions based on the material structures, the design of the predictors and the choice of the IWT are optimised according to the specific image features contained in each region having the same material structure. The texture-based method achieves the best de-correlation by using a mixed data model in the region possessing strong texture patterns. A hybrid scheme for lossless compression of the NDT images of aircraft components is presented. The method combines the predictive coding and the IWT. After region-based predictive coding, the IWT is applied to the error images produced for each decomposed region to achieve further image de-correlation by preserving the information contained in the error images with fewer transform coefficients. The main advantages of using the IWT are its multi-resolution nature and lossless property with integer grey level values in images mapped to integer wavelet coefficients. The proposed methods are shown to offer a significantly higher compression ratio than other compression methods. The high compression efficiency is seen to be achieved by not only a combination of the predictive coding and the IWT, but also optimisation in the design of the predictor and the choice of the transform according to the specific image features contained in each region having similar material structures.

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Sogbossi, Hognon Eric Arnaud. "Etude de l'évolution de la perméabilité du béton en fonction de son endommagement : transposition des résultats de laboratoire à la prédiction des débits de fuite sur site." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30210/document.

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Les enceintes de confinement des centrales nucléaires sont conçues pour assurer des propriétés de confinement et d'étanchéité précises en situations d'usage normal et en cas d'accident nucléaire, afin d'éviter la dissémination de radioéléments dans l'environnement. Ces enceintes étant construites en béton, la maîtrise de l'évaluation de la perméabilité du béton et de ses évolutions sous contraintes permettrait d'évaluer les débits de fuite susceptibles d'intervenir dans le temps sous certaines sollicitations. Jusqu'aujourd'hui, il existe plusieurs techniques de mesure de la perméabilité et ces techniques aboutissent à des résultats différents pour une même éprouvette de béton. La première étude que nous avons réalisée a été donc de proposer une normalisation de la mesure de la perméabilité : cette normalisation a abouti à la détermination d'une perméabilité caractéristique du béton et indépendante de la technique de mesure. Parallèlement à cette démarche, nous avons aussi proposé d'évaluer la perméabilité du béton à l'aide d'observables du Contrôle Non Destructif comme la permittivité et la résistivité électrique. Les résultats obtenus montrent la possibilité d'estimer la perméabilité dans les conditions du béton sur site. La deuxième étude réalisée est relative à la maîtrise de la perméabilité sous contraintes. Au laboratoire, nous avons étudié la perméabilité d'éprouvettes en béton de différentes tailles dans diverses conditions de séchage, de sollicitation thermique, d'endommagements mécanique et couplés. Nous avons ainsi pu établir des modèles perméabilité-endommagements en fonction de chaque source d'endommagement. La troisième étude réalisé porte sur la transposition des résultats de laboratoire au site, à travers l'utilisation de maquette d'enceinte nucléaire de dimensions plus importantes et représentatives de l'ouvrage réel (VeRCoRs à l'échelle 1/3). L'ensemble des résultats des deux premières études ont été mise à contribution et ont permis d'aboutir à des calculs des débits de fuite et des Temps d'Etablissement du Régime Permanent d'Ecoulement cohérents avec les hypothèses de calculs
The building reactor of the nuclear power plants are designed to provide precise containment and sealing properties in normal use situations and in the event of a nuclear accident, to prevent the spread of radioelements in the environment. Since these enclosures are made of concrete, controlling the evaluation of the permeability of concrete and its evolutions under stress would make it possible to evaluate the leakage rates that may occur over time under certain conditions. Until today, there are several techniques for measuring permeability and these techniques lead to different results for the same concrete specimen. The first study we carried out was therefore to propose a standardization of the permeability measurement: this standardization resulted in the determination of a characteristic permeability of concrete and independent of the measurement technique. In parallel with this approach, we also proposed to evaluate the permeability of concrete using observables from Non-Destructive Testing such as permittivity and electrical resistivity. The results obtained show the possibility of estimating the permeability under concrete conditions on site. The second study carried out relates to the control of the permeability under constraints. In the laboratory, we investigated the permeability of concrete specimens of different sizes under various conditions of drying, thermal stress, mechanical and coupled damage. We could establish permeability-damage models according to each source of damage. The third study carried out relates to the transposition from laboratory results to the site, using nuclear power plants mock-up of larger dimensions and representative of the actual structure (VeRCoRs at scale 1/3). All the results of the first two studies have been used and have led to calculations of leak rates and Time to Reach Steady State (TRSS) consistent with the calculation assumptions

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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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Tejedor, Herrán Blanca. "Contributions to the determination of thermal behaviour of façades using quantitative internal IRT (Infrared Thermography)." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/665319.

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Within the European framework, most of residential buildings do not satisfy the minimum thermal specifications. In fact, the renovation rate across the EU is estimated at 1% per year. To fulfil with the goals stated by European Directives 2010/31/EU and 2012/27/EU, it is necessary to ensure a minimum energy performance gap. From a thorough literature review, it was detected that the thermal behavior of a building is often underestimated or neglected during its construction and operation stages. For this reason, an accurate non-destructive testing (NDT) should be required, improving the shortcomings given by the current modelling tools and diagnostic techniques. The purpose of this thesis was to develop a method for determining in-situ the thermal behavior of façades under steady-state conditions using quantitative internal infrared thermography (IRT). After drawing up a numerical model to estimate the thermal transmittance (U-value) as a key parameter of the built quality, the dissertation continued with a validation process that was executed in two typical Spanish walls from different construction periods. This allowed: (i) refining the proposed method; (ii) exploring the boundaries conditions; (iii) assessing the influence of tabulated values set by international standards for wall emissivity and convective heat transfer coefficients among other aspects. The results revealed lower deviations related to the theoretical U-values (1.24 to 3.97%) for test durations of 2-3 hours. Furthermore, the results demonstrated that the use of tabulated values might entail high deviations (40%) in heavy multi-leaf walls with low U-values. Broadly, construction project documents for existing buildings, especially the oldest ones, are not available. Hence, this method may provide information about the building envelope for future refurbishment. In the case of new buildings, the method might allow the thermal behaviour of building façades to be checked according to the design parameters. Despite this, a subsequent literature review highlighted that a gap in the standardization of this method for in-situ building diagnostics is still to fill. Considering this aspect, three studies were developed in order to enhance the applicability of the quantitative internal IRT within the construction industry field. Firstly, the most influential operating conditions were analyzed through an experimental room with a heavy single-leaf wall tested under a wide temperature difference range (3.8 < DT < 21ºC). Secondly, this dissertation performed tests in a public housing stock comprised of four unoccupied buildings (without electric and heating systems in operation), to assess the influence of non-transient thermophysical properties of the wall (i.e. heat capacity per unit of area) on the accuracy of the method. Thirdly, a data-processing method based on U-value time series analysis was proposed and validated through six building façades with heavy multi-leaf walls. The aim was to find a common criterion for stopping the test when it is not necessary more data to obtain a reliable result. Having investigated the aspects mentioned above, it can be extrapolated that: (i) the optimum temperature difference range is found to be between 7 and 16ºC; (ii) the variance in the thermal transmittance could mainly be predicted by changes in the outer air temperature; (iii) the quantitative internal IRT is more accurate in heavy multi-leaf walls with high heat capacities per unit of area, reaching maximum deviations of 0.20%; (iv) the test might be executed in only 30 minutes; (v) the method could allow the assessment of aspects related to the determination of U-value of unoccupied buildings for DT under 10ºC, especially in Spain or European countries with a Mediterranean climate where these test conditions might represent a limitation. Hence, the decision-making could be streamlined in real built environments, increasing the European renovation rate in the mid-term.
Dins el Marc Europeu, la majoria dels edificis residencials no satisfan les especificacions tèrmiques mínimes. De fet, la taxa de renovació a Europa és estimada en 1% anual. Per complir amb els objectius de les Directives Europees 2010/31/UE i 2012/27/UE, és necessari assegurar una bretxa energètica mínima. A partir d'un estat de l'art exhaustiu, es va detectar que el comportament tèrmic d'un edifici sovint és subestimat o negligit durant les etapes de construcció i operació. Per aquest motiu, una prova no destructiva i precisa hauria de ser requerida, per tal de millorar les deficiències donades per les actuals eines de modelització i diagnosi d'edificis. El propòsit de la tesi era desenvolupar un mètode per determinar in-situ el comportament tèrmic de les façanes sota condicions estacionàries mitjançant la termografia quantitativa interna (IRT). Després d'elaborar un model numèric per estimar la transmitància tèrmica (U-value) com a paràmetre clau de la qualitat construïda, la dissertació va continuar amb un procés de validació executat en dues parets típiques espanyoles de diferents períodes de construcció. Això va permetre: (i) refinar el mètode proposat; (ii) explorar les condicions de contorn; (iii) avaluar la influència dels valors tabulats establerts per les normatives internacionals per l'emissivitat de la paret i els coeficients de transferència de calor per convecció. Els resultats van revelar baixes desviacions respecte als valors teòrics de transmitància tèrmica (1.24 a 3.97%) per duracions de test entre 2 i 3 hores. A més a més, els resultats van demostrar que l’ús de valors tabulats podria implicar altes desviacions (40%) en parets compostes. En general, els projectes de construcció d'edificis existents antics no estan disponibles. Per tant, aquest mètode podria proporcionar informació sobre la façana per futures rehabilitacions. En el cas d’edificis nous, el mètode podria permetre verificar el comportament tèrmic de les parets d’acord amb els paràmetres de disseny. Malgrat això, una revisió bibliogràfica posterior va posar de manifest que encara hi ha una bretxa en la estandardització d’aquest mètode per la diagnosi in-situ. Considerant aquest aspecte, es van desenvolupar tres estudis per tal de millorar l’aplicabilitat de la termografia quantitativa interna dins el camp de la indústria de la construcció. En primer lloc, es va analitzar la influència de les condicions operatives en la determinació de la transmitància tèrmica mesurada a través duna cambra experimental amb una façana simple sota un ampli rang de diferència de temperatura (3.8 < DT < 21ºC). En segon lloc, es van dur a terme tests en un parc d’habitatges públics constituïts per quatre pisos desocupats (sense sistemes elèctrics ni de calefacció en funcionament), amb la finalitat d’analitzar la influència de les propietats termofísiques no transitòries (ex. la capacitat de calor per unitat d’àrea) en la precisió del mètode. En tercer lloc, es va proposar i validar un mètode de processat de dades basat en l’anàlisi de sèries de temps de la U-value mitjançant sis parets compostes. L’objectiu era trobar un criteri comú per aturar la prova quan no són necessàries més dades per obtenir un resultat fiable. Havent investigat els aspectes mencionats anteriorment, es pot extrapolar que: (i) el gradient de temperatura òptim es troba entre 7 i 16ºC; (ii) la variància en la transmitància tèrmica podria ser principalment atribuïda a canvis en la temperatura ambient de l’aire exterior; (iii) la IRT quantitativa interna és més acurada en parets compostes amb altes capacitats de calor per unitat d’àrea, aconseguint unes desviacions màximes del 0.20%; (iv) el test podria ser executat en només 30 minuts; (v) el mètode podria permetre l’avaluació d’aspectes relacionats amb la determinació de la U-value en edificis desocupats per T sota 10ºC, especialment a Espanya o països europeus amb un clima mediterrani on aquestes condicions de test podrien representar una limitació. Per tant, la presa de decisions es podria simplificar en entorns construïts reals. De fet, aquesta recerca podria conduir a una millor execució del procés de rehabilitació en edificis que s’espera que tinguin deficiències l’any 2050, augmentant així la taxa de renovació europea a mig termini. La dissertació conclou resumint les principals aportacions d’aquesta investigació. Els temes que s’han plantejat durant la recerca realitzada, i que no es van poder abordar, es comenten i es proposen com a línies de treball futures.

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Le, Gall Thomas. "Simulation de l'émission acoustique : Aide à l'identification de la signature acoustique des mécanismes d'endommagement." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI005/document.

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L’Emission Acoustique (EA) est une technique de contrôle non-destructif consistant en la mesure et l’interprétation de la signature acoustique de mécanismes d’endommagement. Dans l’approche conventionnelle (approche phénoménologique), l’interprétation des données issues des mesures par EA s’appuie sur des corrélations empiriques entre des caractéristiques de la source (le mécanisme d’endommagement) et le signal mesuré. Les modifications dues à la chaine d’acquisition de l’EA sont donc ignorées. Or, la propagation dans le matériau, la mesure par le capteur et le traitement par le système d’acquisition modifient la forme du signal et l’information qu’il transporte. Cela rend difficile l’identification de la source, et la comparaison des résultats issus d’essais effectués dans des conditions différentes. Une partie de la réponse à ces problèmes réside dans la prise en compte des étapes de transformation du signal d’EA. C’est l’objectif de l’approche quantitative de l’EA. Cette approche repose sur l’utilisation de techniques de modélisation pour évaluer l’impact de chaque étape de transformation sur le signal. Le premier volet de cette étude porte sur la validation des techniques utilisées pour simuler les étapes de transformation du signal d’EA. La méthode des éléments finis (MEF) est utilisée pour simuler la propagation du signal au sein du matériau. L’effet du capteur est quant à lui simulé par sa fonction de sensibilité, mesurée par la méthode de réciprocité, et utilisée comme fonction de transfert. Le second volet porte sur l’utilisation de ces techniques pour évaluer l’impact, sur le signal d’EA, des paramètres (position, temps de montée, amplitude) d’une source simple modélisée par des dipôles de force. Trois géométries d’éprouvette sont étudiées : une première éprouvette assimilable à une plaque, une seconde assimilable à une poutre de section rectangulaire et une dernière dont les dimensions sont intermédiaires entre une plaque et une poutre. Les résultats obtenus montrent que les signaux se propagent au sein des éprouvettes suivant des modes bien définis. Ces modes de propagation sont dépendants de la géométrie de l’éprouvette. Chaque source sollicite les modes différemment. Ainsi leur étude permet de réunir des informations sur la source afin de l’identifier. Par ailleurs, cette étude a permis de mettre en évidence des descripteurs pertinents pour l’identification des sources d’EA. Les descripteurs, corrélés entre eux, permettent une nette séparation des signaux en classes en fonction de la source. Ces résultats, obtenus en surface matériau, ne prennent pas en compte l’effet du capteur. Lorsque celui-ci est pris en compte, la signature modale des sources est modifiée ainsi que la valeur des descripteurs calculés. Cela conduit à un recouvrement des classes de signaux rendant plus difficile l’identification des sources
Acoustic emission (AE) is a non-destructive testing technique consisting in measuring and interpreting the acoustic signature of damage mechanisms. In a conventional treatment approach (phenomenological approach), the interpretation of data measured by AE is based on empirical correlations between the source (the damage mechanism) parameters and the measured signal. Therefore, the modifications due to the acquisition chain of acoustic emission are ignored. Yet, propagation of the waves in the material, measures made by the sensor and signal treatments made by the acquisition system modify the signal and the information it carries. As a consequence, identification of the source and comparison with results from other tests made in different conditions are difficult. To find a solution to these problems, one can take into account the different steps of the acquisition chain. This is the goal of Quantitative Acoustic Emission (QAE). This approach is based on modelling techniques to evaluate the impact of each step of the acquisition chain on the AE signal. The first part of this study concerns the experimental validation of the modelling techniques that were used in simulating the steps of the acquisition chain. The Finite Element Method (FEM) is used in simulating the signal propagation inside the material. The sensor effect on the signal is simulated by its sensitivity function, measured by the reciprocity method and used as a transfer function. The second part deals with using these techniques to evaluate the impact of simple AE sources on the AE signal. These simple sources are considered as a point source and modelled by dipole forces. Three tensile specimen geometries are studied: a first specimen that can be compared to a plate, a second specimen that can be compared to a beam and a third specimen of intermediate dimensions. The obtained results show the mechanical waves propagate inside the specimens as modes. These modes depend on the specimen geometry. Each source excites the wave propagation modes in a different manner. Consequently, studying the excited modes, one can gather useful information on the AE source to identify it. In addition, this study highlighted relevant signal parameters to identify AE sources. The correlation of these parameters allows segregating the signals as a function of the source. These results obtained at the material surface don’t take into account the sensor modifications on the signal. The sensor modifies the modal signature of the sources as well as the value of the calculated parameters. This leads to more difficulties in identifying the AE sources

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Ezziani, Youness. "Caractérisatiοn ultrasοnοre haute résοlutiοn d’un film adhésif dans un assemblage aérοnautique." Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMLH14.

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Cette thèse s'intéresse à la caractérisation des propriétés d'un film adhésif dans un assemblage aéronautique tricouche de type Titane-Adhésif-Composite, représentatif de l’aube de fan du moteur LEAP. L'objectif principal est de déterminer avec précision l'épaisseur du film adhésif, ses propriétés mécaniques, ainsi que la qualité d’adhésion qu’il assure entre le titane et le composite, en utilisant des méthodes ultrasonores non destructives à haute fréquence, et donc à haute résolution. Cependant, cette détermination fine de l'épaisseur du joint adhésif et de ses propriétés mécaniques, des indicateurs clés de la qualité de l'adhésion, reste un verrou technologique non encore résolu dans l'industrie aéronautique en raison du contraste d'impédance très marqué dans ce type de structure : fort entre le titane et l’adhésif, et faible entre l’adhésif et le composite. L’enjeu de cette thèse est donc de relever le défi de la détection de l’écho de fond à l’interface Adhésif-Composite à haute fréquence. Ce défi est d'autant plus difficile que les hautes fréquences s'accompagnent d'une atténuation importante. Il est donc essentiel de trouver un compromis optimal entre une fréquence suffisamment élevée pour adapter la longueur d'onde à l'épaisseur de l'adhésif, mais pas trop élevée pour détecter les échos de fond, notamment l’écho de fond à l’interface Adhésif-Composite, avec une amplitude suffisamment exploitable. Dans un premier temps, une étude qualitative a été menée sur six échantillons tricouches (TA6V-Epoxy-Composite, fournis par Safran) à l’aide du microscope acoustique à balayage (SAM) PVA TEPLA 301, permettant la mesure précise de l’épaisseur du film adhésif époxy et l’évaluation de la qualité d’adhésion, en analysant l’écho de fond du film d’époxy, et en examinant la quantité d’énergie transmise à la couche composite en exploitant l’imagerie X-scan. Différents niveaux d'adhésion ont été identifiés : fort, moyen et faible. Par la suite, une étude quantitative a été réalisée à l’aide d’un modèle aux interphases, résolu par la méthode des séries de Debye, qui a permis de quantifier les niveaux d’adhésion de ces échantillons : un fort niveau d’adhésion pour l’échantillon 2 avec des coefficients d’adhésion (α = 1 et β = 1), un faible niveau d’adhésion pour l’échantillon 1 avec (α = 1 et β = 10⁻³), et un niveau d’adhésion moyen pour les échantillons 3, 4, 5 et 6 avec α = 1 et des valeurs de β intermédiaires
This thesis focuses on the characterization of the properties of an adhesive film in a three-layer aeronautical assembly of the Titanium-Adhesive-Composite type, representative of the fan blade in the LEAP engine. The main objective is to accurately determine the thickness of the adhesive film, its mechanical properties, and the quality of adhesion it provides between the titanium and the composite, using high-frequency, and therefore high-resolution, non-destructive ultrasonic methods. However, this precise determination of the thickness of the bonded joint and its mechanical properties, which are key indicators of the quality of the bond, remains an unresolved technological challenge in the aeronautical industry due to the significant impedance contrast in this type of structure : high between the titanium and the adhesive, and low between the adhesive and the composite. Therefore, the challenge of this thesis is to address the detection of the background echo at the Adhesive-Composite interface at high frequency. This challenge is further complicated by the significant attenuation associated with high frequencies. It is essential to find an optimal compromise between a frequency high enough to match the wavelength to the thickness of the adhesive, but not too high, in order to detect the background echoes, particularly the background echo at the Adhesive-Composite interface, with a sufficiently exploitable amplitude. Initially, a qualitative study was conducted on six three-layer samples (TA6V-Epoxy-Composite, provided by Safran) using the PVA TEPLA 301 scanning acoustic microscope (SAM), which allows the precise measurement of the epoxy adhesive film's thickness and the assessment of the quality of the adhesion by analyzing the background echo of the epoxy film and examining the amount of energy transmitted to the composite layer using X-scan imaging. Different levels of adhesion were identified : strong, medium, and weak. A quantitative study was then carried out using an interphase model solved by the Debye series method, which allowed for the quantification of the adhesion levels in these samples: a strong adhesion level for sample 2 with adhesion coefficients (α = 1 and β = 1), a weak adhesion level for sample 1 with (α = 1 and β = 10⁻³), and a medium adhesion level for samples 3, 4, 5 and 6 with α = 1 and intermediate β values

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45

Gex, Dominique. "Ultrasonic NDE testing of a gradient enhanced piezoelectric actuator (GEPAC) undergoing low frequency bending excitation." Thesis, Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04062004-171807/unrestricted/gex%5Fdominique%5Fc%5F200405%5Fmast.pdf.

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Thesis (M.S.)--Mechanical Engineering, Georgia Institute of Technology, 2004.
Berthelot, Committee Chair; Lynch, Committee Member; Jacobs, Committee Member. Includes bibliographical references (leaves 111-113).

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46

Kerouedan, Julien. "Conception et réalisation de sondes hyperfréquences pour la détection de micro-fissures de fatigue à la surface des métaux." Brest, 2009. http://www.theses.fr/2009BRES2058.

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La fatigue mécanique et thermique des structures métalliques est l’une des altérations majeures dans les centrales de production d’énergie. Une détection précoce des défauts de surface par des procédés de contrôle non destructif (CND) permet une maintenance préventive pertinente des installations en évitant d’avoir à démonter ou remplacer des composants sains. Actuellement, la majorité des solutions automatisées de CND est basée sur des techniques utilisant les ultrasons ou les courants de Foucault. Cependant, malgré leurs sensibilité et résolution spatiale élevées, ces méthodes ne sont pas nécessairement adaptées à la détection de tous les défauts de surface rencontrés en pratique. Les limites des méthodes de contrôle conventionnelles par courants de Foucault et ultrasons pour détecter des micro-fissures de surface dans les métaux justifient l’intérêt d’évaluer le potentiel de nouvelles techniques. Les travaux de thèse présentés dans ce mémoire se focalisent sur l’apport des méthodes microondes, Dans ce document, nous démontrons la faisabilité de la détection de micro-fissures de surface dans les métaux à l’aide de sondes micro-ondes résonantes en champ proche. En particulier, à partir de simulations et de mesures réalisées sur des maquettes de test contenant des entailles électroérodées rectangulaires, nous mettons en évidence la sensibilité et la résolution spatiale élevées des sondes originales de type filtre Dual-Behavior Resonator (DBR)
The fatigue and ageing of metal materials under operation conditions are major concerns in energy production plants. An early and non-destructive diagnostic of surface defects would allow one to carry out relevant preventive maintenance operations without dismantling or prematurely changing healthy components. Nowadays, most of the automated non-destructive testing (NDT) solutions available to detect the surface-breaking defects are based on ultrasound or eddy current techniques. Despite their high sensitivity and spatial resolution, they are unable to meet all the requirements of every real situation. Consequently, in order to supplement the available acoustic and electromagnetic NDT toolkits, it sounds relevant to evaluate the potential of new techniques to detect micro-cracks on metal surfaces. The aim of this work is the development of microwave methods allowing the detection of surface-breaking defects on metals. In this report, we demonstrate how micro-cracks at the surface of metals can be detected and imaged by using near-field microwave resonators. In particular, we present simulation data and measurement results carried out on mock-ups with EDM rectangular surface notches highlighting the high sensitivity and spatial resolution of the original dual-behavior resonator (DBR) filter probes

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47

Shum, Pak W. "A critical analysis of the acoustic emmission technique for NDE of pressure vessels." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040341/.

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48

Kergosien, Nina. "Etude de l'intégration de transducteurs piézoélectriques à coeur de matériaux composite de type aéronautique pour le contrôle santé intégré par ondes de Lamb." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0008.

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Des systèmes CSI sont actuellement à l'étude pour vérifier l'intégrité des matériaux composites des aéronefs. Ils permettent d’optimiser la maintenance, en donnant la possibilité de suivre l’état des structures en temps réel ou de contrôler ponctuellement des pièces difficiles d’accès par les méthodes de CND courantes. Les matériaux composites offrent la possibilité d’intégrer un système CSI directement à cœur du matériau. De cette façon, l’instrumentation est protégée de l’environnement et les problématiques de collage en surface sont résolues. L'objectif de cette thèse est de déterminer les effets de l'intégration de transducteurs ultrasonores piézoélectriques à cœur d'un composite PRFC stratifié de type aéronautique sur leur comportement en émission et en réception afin de montrer les avantages et inconvénients d'une telle intégration à cœur pour le monitoring de ces structures par ondes de Lamb. Les transducteurs PZT minces se sont révélés être les transducteurs les plus adaptés à l'intégration, car ils supportent les conditions d'élaboration d'un composite de structures aéronautiques élaboré en autoclave (7 bar et 180°C) et sont capables d'émettre et de recevoir des ondes guidées se propageant dans les plaques. La méthode d'intégration a été adaptée pour préserver l'intégrité des PZT et optimiser leur capacité d'émission d'ondes dans un composite. A cette occasion, la capacité des mesures d'impédance électromécanique à vérifier rapidement l'efficacité de la mise en œuvre de l'intégration a été validée. La caractérisation du champ d'onde qA0 a été réalisée expérimentalement, grâce aux déplacements hors plan mesurées avec un vibromètre laser suite à l'excitation de disques PZT intégrés à des fréquences comprises entre 30 et 200 kHzLa capacité du PZT intégré à détecter un défaut simulé de type aimant est aussi étudiée en essai d'émission-réception et est comparé avec le comportement de PZT couplés en surface de composite. Une étude par modélisation fréquentielle multiphysique a ensuite été réalisée afin de mettre en évidence les phénomènes physiques mis en jeu par l'intégration d'un PZT à cœur de composite. Ainsi, la direction des plis en contact du PZT intégré, la profondeur d'intégration et le couplage du PZT au composite influent sur le mécanisme de transduction ultrasonore. De plus, les contraintes induites par l'actionneur PZT ne permettent pas d'être simplifiées sous forme d'un modèle de type pin-force habituellement utilisé comme chargement d'un PZT en surface de matériau isotrope. En effet, les contraintes induites localement par l'excitation du PZT intégré ne sont pas radiales et dépendent de l'électrode du PZT considérée ainsi que des fréquences de génération d'ondes
SHM systems are currently being developed to check the integrity of aircraft composite materials. These systems will help optimize maintenance by enabling real-time monitoring of structural condition, or spot-checking of parts that are difficult to access using conventional NDT methods. Composite materials offer the possibility of integrating a SHM system directly into the material. In this way, the instrumentation is protected from the environment and surface bonding issues are resolved. The aim of this thesis is to determine the effects of integrating piezoelectric transducers into the core of an aeronautical laminated CFRP composite on their Lamb-wave emission and reception abilities, in order to demonstrate the advantages and disadvantages for the design of a defect detection SHM system. Thin PZT transducers proved to be the most suitable ones for integration, as they can withstand the processing conditions of an autoclave-processed composite (7 bar and 180°C). They are also capable of transmitting and receiving guided waves, which are propagating in the plates. Moreover, the integration method was adapted to preserve the integrity of the PZTs and to optimize their ability to transmit waves in a composite. In order to assess the effectiveness of the integration, electromechanical impedance measurements were made a fast checking process. Characterization of qA0 mode wavefield transmitted by embedded PZT was carried out experimentally. Surface-bonded and embedded PZT were excited at frequencies between 30 and 200 kHz, while out-of-plane displacements were measured with a laser vibrometer. The ability of the embedded PZT to detect a simulated magnet-type defect are also studied in pitch-catch tests, and compared with the behavior of surface-bonded PZT to the composite surface. A dynamic finite element modelling study was then conducted to highlight the physical phenomena induced by the integration of a PZT in the composite core. The direction of the plies in contact with the embedded PZT, the depth of integration and the coupling of the PZT with the composite are influencing the ultrasonic transduction mechanism. Furthermore, it appears that the stresses induced by the PZT actuator cannot be simplified by the pin-force model usually used to load a PZT on an isotropic material surface in flaw detection models. These stresses are not radially oriented and depend on the PZT electrode considered, as well as on the wave generation frequencies

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Ayvazyan, Vigen. "Etude de champs de température séparables avec une double décomposition en valeurs singulières : quelques applications à la caractérisation des propriétés thermophysiques des matérieux et au contrôle non destructif." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14671/document.

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La thermographie infrarouge est une méthode largement employée pour la caractérisation des propriétés thermophysiques des matériaux. L’avènement des diodes laser pratiques, peu onéreuses et aux multiples caractéristiques, étendent les possibilités métrologiques des caméras infrarouges et mettent à disposition un ensemble de nouveaux outils puissants pour la caractérisation thermique et le contrôle non desturctif. Cependant, un lot de nouvelles difficultés doit être surmonté, comme le traitement d’une grande quantité de données bruitées et la faible sensibilité de ces données aux paramètres recherchés. Cela oblige de revisiter les méthodes de traitement du signal existantes, d’adopter de nouveaux outils mathématiques sophistiqués pour la compression de données et le traitement d’informations pertinentes. Les nouvelles stratégies consistent à utiliser des transformations orthogonales du signal comme outils de compression préalable de données, de réduction et maîtrise du bruit de mesure. L’analyse de sensibilité, basée sur l’étude locale des corrélations entre les dérivées partielles du signal expérimental, complète ces nouvelles approches. L'analogie avec la théorie dans l'espace de Fourier a permis d'apporter de nouveaux éléments de réponse pour mieux cerner la «physique» des approches modales.La réponse au point source impulsionnel a été revisitée de manière numérique et expérimentale. En utilisant la séparabilité des champs de température nous avons proposé une nouvelle méthode d'inversion basée sur une double décomposition en valeurs singulières du signal expérimental. Cette méthode par rapport aux précédentes, permet de tenir compte de la diffusion bi ou tridimensionnelle et offre ainsi une meilleure exploitation du contenu spatial des images infrarouges. Des exemples numériques et expérimentaux nous ont permis de valider dans une première approche cette nouvelle méthode d'estimation pour la caractérisation de diffusivités thermiques longitudinales. Des applications dans le domaine du contrôle non destructif des matériaux sont également proposées. Une ancienne problématique qui consiste à retrouver les champs de température initiaux à partir de données bruitées a été abordée sous un nouveau jour. La nécessité de connaitre les diffusivités thermiques du matériau orthotrope et la prise en compte des transferts souvent tridimensionnels sont complexes à gérer. L'application de la double décomposition en valeurs singulières a permis d'obtenir des résultats intéressants compte tenu de la simplicité de la méthode. En effet, les méthodes modales sont basées sur des approches statistiques de traitement d'une grande quantité de données, censément plus robustes quant au bruit de mesure, comme cela a pu être observé
Infrared thermography is a widely used method for characterization of thermophysical properties of materials. The advent of the laser diodes, which are handy, inexpensive, with a broad spectrum of characteristics, extend metrological possibilities of infrared cameras and provide a combination of new powerful tools for thermal characterization and non destructive evaluation. However, this new dynamic has also brought numerous difficulties that must be overcome, such as high volume noisy data processing and low sensitivity to estimated parameters of such data. This requires revisiting the existing methods of signal processing, adopting new sophisticated mathematical tools for data compression and processing of relevant information.New strategies consist in using orthogonal transforms of the signal as a prior data compression tools, which allow noise reduction and control over it. Correlation analysis, based on the local cerrelation study between partial derivatives of the experimental signal, completes these new strategies. A theoretical analogy in Fourier space has been performed in order to better understand the «physical» meaning of modal approaches.The response to the instantaneous point source of heat, has been revisited both numerically and experimentally. By using separable temperature fields, a new inversion technique based on a double singular value decomposition of experimental signal has been introduced. In comparison with previous methods, it takes into account two or three-dimensional heat diffusion and therefore offers a better exploitation of the spatial content of infrared images. Numerical and experimental examples have allowed us to validate in the first approach our new estimation method of longitudinal thermal diffusivities. Non destructive testing applications based on the new technique have also been introduced.An old issue, which consists in determining the initial temperature field from noisy data, has been approached in a new light. The necessity to know the thermal diffusivities of an orthotropic medium and the need to take into account often three-dimensional heat transfer, are complicated issues. The implementation of the double singular value decomposition allowed us to achieve interesting results according to its ease of use. Indeed, modal approaches are statistical methods based on high volume data processing, supposedly robust as to the measurement noise

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Machado, Miguel Araújo. "Development of Non-Destructive Testing by Eddy Currents for Highly Demanding Engineering Applications." Doctoral thesis, 2018. http://hdl.handle.net/10362/58443.

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Defect detection with Non-Destructive Testing (NDT) is essential in accidents prevention, requiring R&TD to generate new scientific and procedural knowledge for new products with high safety requirements. A current challenge lies in the detection of surface and sub-surface micro defects with NDT by Eddy Currents (EC). The main objective of this work was the development of applied research, technological innovation and experimental validation of EC customized systems for three highly demanding inspection scenarios: micro defects in tubular geometries; brazed joints for the automotive industry; and high-speed moving composite materials. This objective implied starting from the scientific fundamentals of NDT by EC to design and simulate EC probes and the prototypes developed were tested in industrial environment, reaching a TRL ≈ 5. Another objective, of a more scientific and disruptive nature, was to test a new technique for the creation of EC in the materials to be inspect, named Magnetic Permeability Pattern Substrate (MPPS). This technique consists on the development of substrates/films with patterns of different magnetic permeabilities rather than the use of excitation bobbin coils or filaments of complex geometry. The experimental results demonstrated that the prototypes developed for the three industrial applications studied outperformed the state of the art, allowing the detection of target defects with a very good signal-to-noise ratio: in tubular geometries defects with depth of 0.5 mm and thickness of 0.2 mm in any scanning position; in the laser brazed weld beads pores with 0.13 mm diameter and internal artificial defects 1 mm from the weld surface; in composite materials defects under 1 mm at speeds up to 4 m/s and 3 mm lift-off. The numerical simulations assisted the probe design, allowing to describe and characterize electrical and magnetic phenomena. The new MPPS concept for the introduction of EC was validated numerically and experimentally.

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