Tesi sul tema "Defects propagation"
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Soboyejo, Winston Oluwole. "The propagation of defects under fatigue loading". Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257906.
Hussein, Salah A.-R. Ahmed. "Characterisation of planar defects in solids using ultrasonic pulse echo techniques". Thesis, City University London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389705.
Murat, B. I. S. "Propagation and scattering of guided waves in composite plates with defects". Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1469777/.
Foteinopoulou, Stavroula. "Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals". Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/822058-9BqHHS/native/.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2048" Stavroula Foteinopoulou. 12/12/2003. Report is also available in paper and microfiche from NTIS.
Oliveira, Vanessa Amaral de. "Influence of processing parameters on the generation and propagation of electrically active crystalline defects in monolike silicon". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI021.
The new generation of directionally solidified “monolike” Si ingots presents an attractive alternative to high-cost monocrystals for the manufacture of high performance solar cells with advanced architecture. However, local zones with high densities of dislocations still affect the overall solar cell efficiency.In the present work, the mechanisms of formation of dislocations structures during monolike growth and their influence on the electrical properties of the material were analyzed, and practical conclusions were drawn for the improvement of the process.Pilot scale crystal growth experiments were performed with varying parameters related to seed pavement and seed recycling, crystallographic orientation of the growth, and doping with a strengthening element (Ge). Complementary annealing and 4-point bending tests at high temperature were used to analyze the influence of stress level and time under stress.Advanced structural characterization of dislocations structures was performed by synchrotron X-ray imaging. Behind the growth front, dislocations organize in cellular patterns which correspond to a quasi-stationary creep stage, reached in the solid after long time under stress at high temperature. Dislocations that emerge at the growth front develop, from local sources, cone-shaped misoriented domains, which present increasing tilt around the growth axis and expand laterally as growth proceeds. Characterization by LBIC and Photoluminescence showed that these defects have the highest recombination activities. The sources of these defects located at the seed ingot interface can be suppressed by proper choice of seeds orientations and arrangement. However, another source is bunching of dislocations at the growth front under the higher stresses upper in the ingot.In <110> and <112> grown ingots, dislocation bunching was not observed inside the monocrystalline parts, which shows an advantage of these orientations over <100>. On another hand, twins and sub-grain boundaries propagated from higher angle grain boundaries with these growth directions, and further studies are needed to prevent the generation of such defects. Finally, Ge doping was effective to reduce dislocations multiplication in bending under low stresses. However, its application to crystal growth will require a planar growth interface, and forced melt mixing to avoid Ge radial segregation. New researches inspired by the addition of strengthening elements are now in development
Cini, Andrea. "Scribe marks at fuselage joints : initiation and propagation of fatigue cracks from mechanical defects in aluminium alloys". Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7895.
Ehrlacher, Virginie. "Quelques modèles mathématiques en chimie quantique et propagation d'incertitudes". Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1073/document.
The contributions of this thesis work are two fold. The first part deals with the study of local defects in crystalline materials. Chapter 1 gives a brief overview of the main models used in quantum chemistry for electronic structure calculations. In Chapter 2, an exact variational model for the description of local defects in a periodic crystal in the framework of the Thomas-Fermi-von Weisz"acker theory is presented. It is justified by means of thermodynamic limit arguments. In particular, it is proved that the defects modeled within this theory are necessarily neutrally charged. Chapters 3 and 4 are concerned with the so-called spectral pollution phenomenon. Indeed, when an operator is discretized, spurious eigenvalues which do not belong to the spectrum of the initial operator may appear. In Chapter 3, we prove that standard Galerkin methods with finite elements discretization for the approximation of perturbed periodic Schrödinger operators are prone to spectral pollution. Besides, the eigenvectors associated with spurious eigenvalues can be characterized as surface states. It is possible to circumvent this problem by using augmented finite element spaces, constructed with the Wannier functions of the periodic unperturbed Schr"odinger operator. We also prove that the supercell method, which consists in imposing periodic boundary conditions on a large simulation domain containing the defect, does not produce spectral pollution. In Chapter 4, we give a priori error estimates for the supercell method. It is proved in particular that the rate of convergence of the method scales exponentiall with respect to the size of the supercell. The second part of this thesis is devoted to the study of greedy algorithms for the resolution of high-dimensional uncertainty quantification problems. Chapter 5 presents the most classical numerical methods used in the field of uncertainty quantification and an introduction to greedy algorithms. In Chapter 6, we prove that these algorithms can be applied to the minimization of strongly convex nonlinear energy functionals and that their convergence rate is exponential in the finite-dimensional case. We illustrate these results on obstacle problems with uncertainty via penalized formulations
Aïssani, Amina. "Optimisation fiabiliste des performances énergétiques des bâtiments". Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22677/document.
In the context of growing world energy demand and environmental degradation, many actions are undertaken each year to improve the energy performance of buildings. During the design stage, the use of building energy simulations remains a valuable tool as it evaluates the possible options in terms of energy performance and comfort. However, as precision requirements increase, it becomes essential to assess the uncertainties associated with input data in simulation. This thesis focuses on the insulation design process under uncertainty, in order to limit gaps between real and predicted performance for better control of energy consumptions. This work firstly presents the current alarming energy context. We consider the main uncertainties that affect the insulation, mainly the variability of the thermophysical properties, the uncertainty on climate and the uncertainties due to workmanship defects. Experimental studies were carried out to evaluate the uncertainty associated to the intrinsic performance of healthy insulation materials on one hand, and those associated to defects in insulations on the other hand. A coupling between thermography techniques and finite element models was used to provide analytical models that assess the effective thermal performance of a defective insulation, according to the type and size of the defect. As the performance of insulation also depends on climate, it is necessary to integrate future weather data to evaluate the energy consumption. These weather data are generally estimated based on the historical climatic data of the region. However, it is still difficult to predict climate change as it depends on many uncontrollable factors. In this work, we consider the different climate scenarios proposed by climate expert groups, and the uncertainty associated to each scenario to evaluate the reliability of the insulation and to improve the decision making process. Finally, we propose a probabilistic approach to integrate uncertainties in simulation and an optimization methodology based on reliability. A new cost formulation is also proposed to improve the decision-making, through indirect losses related to comfort, pollution and living space losses
Masmoudi, Mohamed. "Modélisation de la propagation d'ondes guidées, générées et détectées par transducteurs ultrasonores à couplage air : Application au CND de structures aéronautiques composites". Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14483/document.
Non-destructive testing (NDT) using guided waves generated and detected by air-coupled ultrasonic transducers have two main advantages. First, this non-contact technique without coupled medium allows obvious convenience of use. Moreover, the ability of guided waves to carry information about medium quality over long distance. In this context, a numerical model has been developed, which takes into account many parameters of the control system. In order to reduce the number of degrees of freedom, a hybrid model has been developed which consists of a combination between an analytical model, based on the Kirchhoff integral for the propagation of ultrasound in air and a finite element model for the propagation of guided waves in the material. The measured characteristics (efficiency and sensitivity) of two air-coupled transducers allow the prediction of the accurate values of the pressure of bulk waves generated in air and the measurement of the pressure of the radiated field in air by guided waves propagating in a structure. This process enables the comparison between predicted and measured guided waves modes. Based on the hybrid model, an optimization of the parameters of the control system (angle, frequency, diameter, direction of propagation, near and far field) was performed to improve the purity of guided modes along the material plate. To validate some numerical predictions, an aircoupled ultrasonic transducer is used and oriented at a specific angle chosen for generating one specific Lambmode guided along a composite plate sample, and a laser probe measures the normal velocity at different locations on the surface of the plate. Then, the interaction of ultrasonic guided waves with delamination in acomposite plate was studied. In particular, the sensitivity of the two fundamental modes A0 and S0 was analyzed in order to predict the detectability of the defect. In parallel, the inverse problem is solved and the defect size is quantified by calculating the spectrum of the reflection coefficient. Finally, the potential of air-coupled transducers to examine an aircraft structure, has been demonstrated
Touhami, Salah. "Apparition, détection et propagation des défauts à l'anode des piles à combustible à membrane échangeuse de protons". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0151.
Defects known to shorten the lifetime of polymer electrolyte membrane fuel cells (PEMFC) can appear on different membrane electrode assembly (MEA) components and under different forms due to manufacturing processes or operational aging of the fuel cell. This work concerns the occurrence, detection, and propagation of defects in PEMFC MEA, and more specifically at the anode. To this end, an accelerated stress test (AST) combining potential and humidity cycles -induced by load variations-, and open-circuit hold is applied to standard MEA, and to MEA with initial defects. Those customized MEA were intentionally prepared with a lack of active layer at the anode, the defect being located either near the hydrogen inlet or near the hydrogen outlet. Periodic electrochemical characterizations were carried out using a segmented instrumented linear cell, allowing to monitor the cell performance through the currents, electrode potentials, and local impedance, as well as the evolution of the electrochemical active surface (ECSA) at the anode and cathode during the ageing test, with a spatial resolution along the channels. An electrochemical impedance spectroscopy study was conducted jointly, using equivalent electrical circuits, and focusing on the detection of the anodic contribution to the global impedance of the cell. Results showed an accelerated degradation of the MEA and the first evidence of defect propagation, in terms of loss of ECSA at the anode. This propagation occurred in the direction of the hydrogen flow. The ECSA at the cathode also appeared to be impacted, although apparently homogeneously. Significant membrane thinning was also observed in the defective segments, with probable propagation to adjacent segments, but over a longer time period
Šedý, Michal. "Syntéza struktur s elektromagnetickým zádržným pásmem". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-218036.
田中, 啓介, Keisuke TANAKA, 義明 秋庭, Yoshiaki AKINIWA, 博央 來海, Hirohisa KIMACHI, 和之 伊藤 e Kazuyuki ITOH. "防振ゴム材料における疲労き裂進展挙動へのJ 積分の適用". 日本機械学会, 2003. http://hdl.handle.net/2237/9154.
May, Daniel. "Transiente Methoden der Infrarot-Thermografie zur zerstörungsfreien Fehleranalytik in der mikroelektronischen Aufbau- und Verbindungstechnik". Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-163082.
In this work a new failure analytical method for the industrial application of new technologies in electronic packaging has been developed. The developed method is based on the interaction of the thermal waves and defects. The special fature is non-destructive, speed, resolution and high temperature sensitivity due to latest IR-detectors. It fundamental studies regarding resolution and parasitic effects in the application were carried out cinsidering industrial conditions. Here, a systematic approach regarding the complexity has been selected. This now enables a prediction of the expected test period for detecting buried defects, limits for excitation pulse width (for a given defect depth) and the quantitative determination of the influence of parasitic paints. Methodically always simulations and comparative experiments were used. Simple samples for the isolation and purification of parasitic effects has been used. Finally, the measurement system has been successfully demonstrated on an industrial applications. The developed measurement system is characterized by high flexibility. Different problem-adapted excitation sources (internal and external excitation by numerous physical effects) are used. The measurement system currently consists of four main modules, the difference image method, the pulse thermography, and two variants of LockIn-thermography. Together, the system is capable of detecting voids, delaminations and cracks in various fields of electronic packageing. It will reach temperature resolutions up to 5 mK and lateral resolutions down to 17 µm. This work stes a foundation for the application of thermal failure analysis for industry by showing and charcterization the limits of IR imaging
Tournemenne, Florian. "Impact des défauts d'aspect sur la propagation d'un laser de puissance". Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0189/document.
Each beam of a high power laser facility, such as the Laser MégaJoule, is shaped and amplified thanks to hundreds optical components such as amplifier slabs at Brewster’s angle, lenses, mirrors, phase plates, diffraction gratings... Of course, all these components cannot be perfect; there are some defects on their surface. These imperfections appear at each stage of the life of the component, during polishing, coating, or mitigation process or when the component is used on the facility. They have a huge impact on the energy losses delivered on the target and they decrease the resistance of downstream components to intense light. The ISO 10110-7 standard is currently used to specify the visual defects. However, this standard is poorly justified and do not fit a high power laser needs. In this thesis, we are focused on the fratricide effect. Light propagates through a defect, then, some intensity modulations appear along the propagation. The damage law states that high energy density leads to an increase of the damage probability. Firstly, we investigate the characteristic parameters of the defect morphology linked to the formation of downstream << hot spots >>. Then, the link between these typical parameters and the high intensifications are confirmed by experiments on real defects. Secondly, a power criterion is demonstrated to guarantee the linear propagation hypothesis. This criterion is compared to numerical simulations and it is shown how the nonlinear propagation, induced by Kerr effect, can be different between the << hot spot >> formed by a defect and a Gaussian beam. Finally, the results are used to improve the visual defect specification thanks to a better understanding of the fratricide effect
Piault, Pierre. "Modélisation numérique et caractérisation des défauts dans les miroirs multicouches en vue de leur application en imagerie X cohérente". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLO008/document.
Multilayer mirrors find numerous X-ray applications in synchrotron and X-rays free electron lasers. These multilayers optical devices must take up new challenges raised with the upgrade these radiation sources. To study the origin of intensity contrast in reflected beam, experimental measurements and numerical modeling were performed.Several techniques for multilayer structure charactérization have been implemented at the ESRF beamline BM05. Measurements methods based on 'Rocking Curve Imaging' and 'theta/2theta' Imaging were performed and applied for the first time to multilayer mirrors. Measurements of the wavefront reflected by multilayers were performed using holography and near field speckle techniques. The results obtained allowed a better understanding of the phase effects induced by multilayer reflection of their origin and to reconstruct the topography of the height defects within a multilayer mirror using the numerical model developped in the course of this PhD thesis.A numerical model based on Takagi-Taupin equations was modified to account for defects present in the multilayer mirror structure. Simulations for simple defects were performed to evaluate performance and limits of the numerical model. The propagation and the coherence of the reflected beam were simulated. The measurement and simulation results show the main influence of defect heights on the generation of the intensity contrast observed. The simulations also lead to conclude the equivalency phase effect resulting of the same height defects in multilayers mirror structure and reflecting surface.These modelization and simulations results can be usefull to specify defect feature which minimise reflected intensity contrast. The new developped experimental technics will allows X-rays caracterization for next multilayer mirrors
Taleb, Ali Mahfoudh. "Effet des défauts d'adhésion sur la résistance mécanique des assemblages collés". Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0061/document.
Structural adhesive bonding has known an increasing use in many fields like aeronautics, aerospace and automotive and other fields like construction and sports. This very advantageous technique allows the assembly of similar or different materials using an adhesive, the significant reduction in weight and a uniform distribution of loads on the assembly. Despite its advantages, the bonding still suffers from some disadvantages related to the existence of defects in the bonded joints. Among them, there are defects that are located at the interface glue / substrate as "kissing bond" or poor surface due to bad surface treatment, which remain undetectable or hardly detectable using non-destructive control techniques. Therefore, in order to take into account the existence of adhesion defects in bonded assemblies during the design phase, it is necessary to provide an analytical model capable of predicting crack propagation and estimate the criticality of a defect. In this thesis, an analytical model that predicts crack propagation and evaluates the effective strength of a bonded assembly containing adhesion defects has been developed. A defect usually has a complex geometry, and a generic study is difficult to achieve, which leads us to consider ideal defect geometries. The model was verified by experiments performed on DCB specimens. Numerical simulations using the cohesive zone method were also performed to more fully describe the decohesion process and to simulate the experimental tests. The last part of this work was devoted to the study of titanium alloy assembly containing patterns. Taking advantage of the collaboration with Safran and Alphanov, the substrates underwent a laser surface treatment leaving untreated areas. The purpose of this part was to check the proposed analytical model with more complex configurations
Romero, García Vicente. "On the control of propagating acoustic waves in sonic crystals: analytical, numerical and optimization techniques". Doctoral thesis, Universitat Politècnica de València, 2010. http://hdl.handle.net/10251/8982.
Romero García, V. (2010). On the control of propagating acoustic waves in sonic crystals: analytical, numerical and optimization techniques [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8982
Palancia
Junet, Arnaud. "Étude tridimensionnelle de la propagation en fatigue de fissures internes dans les matériaux métalliques". Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI006.
Fatigue is the main phenomenon causing the failure of mechanical structures. For very long service lives the initiation of cracks leading to the failure of in service mechanical parts changes from surface to volume. Due to experimental difficulties the propagation of internal cracks has only been studied to a limited extent in situ and in 3D. However, it is crucial from a dimensional point of view to know the behaviour of such cracks. In this work, in situ monitoring of the initiation and propagation of internal cracks was carried out by X-ray tomography (synchrotron source). Firstly, a method for manufacturing specimens was developed to enable systematic, non-destructive, and 3D visualization of the propagation of internal cracks in a titanium alloy (Ti-6Al-4V) at 20 Hz. For this purpose, an artificial defect was drilled on the surface of a rolled sheet of this material. A second sheet, placed on top of the first one, was diffusion bonded by spark plasma sintering, making it possible to make the defect volumetric. In situ fatigue tests showed the crucial role of the environment (vacuum) and, to a lesser extent, that of the crystallographic texture on the internal crack propagation rates. Secondly, an ultrasonic fatigue machine (cycling frequency of 20 kHz) allowing in situ testing at the synchrotron was used to study the 3D propagation of internal cracks in A357-T6 aluminium alloy specimens containing an artificial internal defect. The 3D grain distribution obtained by Diffraction Contrast Tomography (DCT) was used to study the interaction mechanisms between the microstructure and the 3D crack path
Fabregue, Pascal. "Debut de propagation de fissures de fatigue dans un superalliage base nickel de metallurgie des poudres". Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0033.
Moutaouekkil, Mohammed. "Etude de la propagation des ondes élastiques de Lamb dans les matériaux composites micro/nano structurés : Application pour l’ingénierie des propriétés physiques des résonateurs électromécaniques". Thesis, Ecole centrale de Lille, 2018. http://www.theses.fr/2018ECLI0011/document.
The control of elastic wave propagation relies mainly on the design of artificial media based on structured materials to achieve advanced propagation dispersion engineering. During the thesis, the dispersion of the mode (S0) in micro-structured membranes based on AlN was numerically investigated and the resulting applications explored. The strong link between mode dispersion and sensitivity to external disturbances is highlighted by combining the AlN membrane with a layer of SiO2 structured into strips. In particular, it is shown that it is possible to obtain a TCF = 0 for the resonators without any degradation of the K2 coefficient. It is shown that it is possible to open wide band-gaps of 50% by structuring the AlN in the shape of strips or using pillars to form a PhnC. On this basis, designs of cavities and waveguides are proposed and their performances are studied according to the geometrical parameters. It is also proposed a new cavity design based on the introduction of a resonant defect with a disc shape in the PhnC and presenting very small size in comparison to the unit cell. The defect makes it possible to introduce quasi-flat modes in the band diagram and consequently allows the design of a new generation of phononic devices for signal processing and sensor applications. The optimal structures are used to design a magnetic field sensor design, a sensitivity of 5% is obtained for the localized mode in the case of defect based on magneto-elastic thin film
Tricoit, Sandy. "Modélisation et simulation numérique de la propagation de la corrosion par piqûres du fer en milieu chloruré : contribution à l'évaluation de la durabilité des aciers au carbone en conditions de stockage géologique". Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS054/document.
This study deals with the understanding of the mechanisms of pitting corrosion susceptible to occur on carbon steel selected for high level nuclear waste containers. Transport/reaction models have been developed in order to simulate, by finite element method, the propagation of a pit on iron in chlorinated medium. For conservative models, pit is activated by imposing a potential on metal. Thanks to different parametric studies (geometry, environment…) simulations have permitted to classify, by severity order, the factors responsible of the increase or the inhibition of the localized corrosion rate. Otherwise, experiments on occluded (called « lead-in-pencil ») electrodes confirm that confinement favors the formation of a salt film at the bottom of the pit. Finally, the simulation of galvanic coupling between the pit and the surrounding cathodic surface has permitted to describe the realistic evolution of the localized corrosion rate in aerated medium and for free corroding conditions. The analysis of the results from these three ways of investigation has demonstrated that the ohmic drop inside the pit is the most important factor controlling his growing. In most study cases, any increase of this ohmic drop (due to precipitation, confinement or augmentation of the cathodic /anodic surfaces ratio), leads to a faster corrosion rate of the surrounding surface. This phenomenon is called “opening” of the pit. The progression at the pit bottom for a pH-dependant oxidation rate is still to confirm. In order to simulate the long term behavior of iron during pitting, in storage application, new models require a more accurate determination of the environment conditions, dissolution and precipitation laws
Luppé, Francine. "Contribution a l'etude de l'onde de scholte-stoneley a differentes interfaces fluide parfait/solide elastique". Paris 7, 1987. http://www.theses.fr/1987PA077222.
Sanchis, Kilders Pablo. "Coupling techniques between dielectric waveguides and planar photonic crystals". Doctoral thesis, Universitat Politècnica de València, 2008. http://hdl.handle.net/10251/1854.
Sanchis Kilders, P. (2005). Coupling techniques between dielectric waveguides and planar photonic crystals [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1854
Palancia
Sy, Kombossé. "Étude et développement de méthodes de caractérisation de défauts basées sur les reconstructions ultrasonores TFM". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS040/document.
In non-destructive testing, with a view to improving defect images but also to simplify their interpretation by non-specialized operators,new ultrasonic imaging methods such as TFM imaging (Total Focusing Method ) have appeared for some years as an alternative to conventional imaging methods. They offer realistic images of defects and allow from the same acquisition to have a large number of images each that can carry different and complementary information on the characteristics of the same defect. When properly selected, these images are easier to analyze, they present less risk of misinterpretation and allow to consider faster fault characterizations by less specialized operators.However, for an industrial operation, it remains necessary to strengthen the robustness and ease of implementation of these imaging techniques. All the work carried out during the thesis allowed to develop new tools to improve the characterization of defects by TFM imaging techniques in terms of position,orientation and sizing
Chehami, Lynda. "Surveillance passive des milieux réverbérants par corrélation de bruit ambiant : application à la localisation de défauts". Thesis, Valenciennes, 2015. http://www.theses.fr/2015VALE0035/document.
Green’s functions retrieval from ambient noise correlation has recently drawn a new interest in structural health monitoring. In this manuscript, we propose an original method based on this approach to detect and locate defects (cracks, holes, grooves) in a reverberant thin plate with a limited number of sensors. Flexural waves that propagate on the plate are generated by either a set of sources distributed randomly on the surface or an ambient noise. Covariance matrices are estimated from the sparse array after damage and compared to baseline-correlation matrix recorded from the healthy plate. An evaluation criterion has developed in the form of relative noise level to predict the quality of the GF reconstruction. The differential correlation matrix w/o defect is used to localize the defect. We have shown numerically and experimentally that this technique is exploitable for defect detection and localization, despite a non-perfect estimation of the GF. We have also proposed a passive technique to identify the regions of noise. A filtering technique based on the singular value decomposition is shown to improve the detection. A secondary acoustic sources have been developped to harvesting the LF ambient noise to HF field, used to localize defects in platelike structures. Finally, it was shown that such method could also be used to characterize a defect in a reverberant structure, in particular, it has been drawn that the obtained images intensity is related to the defect cross-section
Chen, Yu-Hong, e 陳語鋐. "Propagation Behaviors of ASF modes Propagating Along Wedge Tips with Defects". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/ng7xy4.
國立臺北科技大學
機電整合研究所
98
Wedge wave is a kind of elastic wave propagat along the tip of wedges. Its energy is concentrated on the range of about one wavelength of tip. A combined experimental / numerical investigation employing a laser ultrasound technique and finite element analysis is used to characterize the propagation behaviors of ASF modes propagating along wedge tips with defects. More specifically, reflection coefficient and transmission coefficients are modeled and measured for several of defect depths on the wedge tip. Good agreement is obtained between the modeled and measured reflection and transmission coefficients. And this study discovers wedge wave has mode conversion phenomenon similar to Lamb wave.
Lucas, Nuno Filipe Mota. "Lamb wave propagation for evaluating defects in structural adhesive joints". Master's thesis, 2020. https://hdl.handle.net/10216/129859.
Lucas, Nuno Filipe Mota. "Lamb wave propagation for evaluating defects in structural adhesive joints". Dissertação, 2020. https://hdl.handle.net/10216/129859.
Fang, Chi-Chong, e 枋啓中. "Influence of Periodic Defects on the Propagation of Wedge Waves". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/adg2ty.
國立臺北科技大學
製造科技研究所
106
Wedge Wave (WW) is a kind of elastic wave propagate along the tip of a wedge that energy is concentrated near wedge tip to in 1 wavelength. According to the study, when the wedge tip has no truncation, there is no dispersion relationship that changes its corresponding velocity with frequency. In the literatures have been many related studies on wedge-shaped guided waves, However, the study of combining wedges with phononic crystals has not yet been studied. Therefore, this article will explore it. Phononic Crystal, a study extended by Photonic Crystal, is characterized in that when sound waves pass through a periodic arrangement structure, the acoustic wave will cause interference of the penetrating wave and the reflected wave due to the structure. We call this Band Gap, which blocks the passage of acoustic wave with certain frequency oscillations. This study is divided into two parts, experimental measurement and finite element analysis method are used to investigate the wave propagation behavior of regular periodic defects at wedge tip, and to explore the influence of different periodic defect parameter changes on the guided wave of the wedge body. In this study, a brass wedge with a apex angle of 60° was used as the substrate test piece, the periodic defects were designed at the wedge tips, the ratio of the defects width and spacing width was 1:1,.Explore its influence after obtaining the frequency-domain by laser ultrasonic technique and finite element analysis. Laser ultrasonic technique and finite element analysis were used to investigate the influence of periodic defects on wedges, although the results couldn’t be observed band gap. However, in the experimental results, it is found that the frequency domain signals would be effected by periodic defects on wedge tips, basic frequency would be downgraded by increase in defect width or increase in number of defects.
CHEUNG, Jin-Hwan, Yoshito ITOH e In-Tae KIM. "DURABILITY PREDICTION OF STEEL BRIDGE PAINTINGS WITH INITIAL DEFECTS". 2006. http://hdl.handle.net/2237/18856.
"Fast Forward and Inverse Wave Propagation for Tomographic Imaging of Defects in Solids". Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.53454.
Dissertation/Thesis
Doctoral Dissertation Mechanical Engineering 2019
Chuang, Feng-Ko, e 莊豐閣. "Application of Back-Propagation Neural Network for Inspection and Measurement of BGA Shape Defects". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/77308125722189831379.
龍華科技大學
機械系碩士班
94
This study is mainly utilizing Back-Propagation Neural Network technology to identify the shape of defective tin ball and to promote the accuracy of the inspection. By developing two dimensional BGA optical inspecting system, incorporate with Halcon which developed by Visual Basic as developing tool of function database for image process. Inspecting system is capable of detecting the shape of tin ball and its location precisely and classifying its quality under the condition of BGA board offsetting and rotating at any angle. Inspecting items include, ball offset, ball presence, over size, under size, ball deformation, ball bridging and ball absence. For the study and processing procedure developments of the automatic inspecting system, image is processed by preprocess and sub-pixel basing on its grey value to identify the edge accuracy in order to acquire the coordinate of the tin ball precisely, the nearly ellipse axis scale, compactness, radius of tin ball, BGA board bias angle relevant information. Based on the predefined criteria, defines the dimension and location defects of the tin ball and utilizes Back-Propagation Neural Network technology identifying and classifying the shape defects of the tin ball. Experiments within this study prove that Back-Propagation Neural Network technology can correctly identify and classify the shape defects of the tin ball which also can achieve and contribute the requirements for the automatic inspection and high efficiency of identification capabilities.
Szelengowicz, Ivan Michel Nicolas. "Analysis and Optimization of Stress Wave Propagation in Two-Dimensional Granular Crystals with Defects". Thesis, 2013. https://thesis.library.caltech.edu/7685/1/Szelengowicz_Ivan_Thesis_v6.pdf.
Munian, Rajendra Kumar. "Time Domain Spectral Finite Element Simulation of Ultrasonic Wave Propagation in Composite with Defects". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5502.
Lo, Pei-Yuan, e 羅培元. "Behaviors of Wedge Waves Propagating Along Blade Tips with Defects". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/2at8ru.
國立臺北科技大學
製造科技研究所
101
Wedge waves are guided acoustic waves along the wedge tip. Wedge wave is not only highly concentrated, but also difficult to decay characteristics. These reasons let it used in non-destructive evaluation. Laser beam excites ultrasound has advantages those are long-range detection and high-resolution. With the time-domain signal integral can calculate energy of wave. This study developed a method to analyze the defect depth and shape affect the transmission and reflection coefficient. This study use Laser ultrasonic technique (LUT) and finite element method (FEM) to characterize the anti-symmetrical flexural (ASF) modes propagation along wedge tips with a natural crack. The mode conversion (MC) will emerge when ASF wave encounter a defect on the wedge tip. Reflection coefficient (RC) and transmission coefficient (TC) are obtained from energy ratio that calculated from simulation and measurement results with different defect depths and different crack’s shape on the wedge tip. The results showed that when the defect depth increases, reflected wave energy will rise and transmitted wave energy decreased appears the phenomenon of high and low level mode conversion. Finite element analysis can show the behavior of wedge propagation, and thus to estimate the transmission coefficient and reflection coefficient.
Chang, Po Nien, e 張柏年. "The Automated Wafer Defect Detection based on Back-Propagation Network". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/38406688334990623594.
國立清華大學
工業工程與工程管理學系
91
For semiconductor industry, the complicated chips manufacturing process, expensive raw materials and demanding production environment make the cost relatively high. Every fabrication company eagerly searches through different manufacturing control and analysis methods to reach the goals of production cost reduction and yield improvement. In a fabrication line, the most direct and efficient way to identify an abnormal process during manufacture is by analyzing the defect maps of semiconductor wafers. Hence it is really crucial to construct a defect inspection system for semiconductor chips, which can provide better judgment and response to the detection of faults. The outcome would be an improved yield rate, the timely identification and elimination of malfunctions and eventual cost reduction. Our current research proposed a defect detection system for semiconductor wafers based on Back-Propagation Network .The major purpose of the current study is to evaluate the characteristics of defects on observed defect maps or bin maps and, thus, obtain the most related defect characteristics through the network training process. Our research will show the effect of different data conversion on the defect detection rate and provide a better output model among the various combinations of parameters. Moreover, our detection system can differentiate between the distinguishable and indistinguishable situations. Based on the verification of real-time manufacturing data provided by online engineers, it is proven that our system can correctly diagnose and analyze the defects such that it fulfills the requirements of semiconductor industry. This system could help engineers find out the problems on the fabrication line in a more timely and efficient manner so that engineers can modify the process to prevent similar problems from recurring, which would consequently stabilize the production process and even improve the yield rate.
Wang, Bo-Wei, e 王柏崴. "Application Of Back-Propagation Neural Network To LED Die Defect Inspection". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/37603930264899335770.
遠東科技大學
機械工程研究所
100
This thesis uses the back-propagation neural network to recognize two types defects of LED die automatically. First of all, a LED die recognition process will be developed. The Otsu's method and template-matching techniques are employed in this recognition process to find a single LED die from the LED wafer image. Through the multi-sample algorithm and the simple logic operators, the characteristics of LED die defects will be obtained quickly. These characteristics of LED die defects will be the training samples of the neural network. After the training process, the LED die defects detection system will be examined by a lot of the single LED die images. The defects detection system will identify whether the defect of the sample images. The results show that the proposed feature extraction method can increase the detection accuracy effectively. The detection accuracy of these two types of LED die are 99.23% and 84.81%. The time of detection for every single die is about 70 milliseconds on average.
Chiang, Cheng-An, e 江承恩. "A Cloud System for Back-Propagation Neural Network based Surface Defect Classification". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/96315557340383604906.
中原大學
機械工程研究所
103
In order to meet the industry needs for high-speed high-precision automated detection and remote monitoring, a defective part that has undergone line inspection is subjected to a fast classification scheme consisting of an algorithm which can feed the results directly to a cloud storage server. The purpose of this study is to develop a combination of cloud storage and defect classification system where the detection results are stored to the cloud server and then accessed via web presentation to a remote user. The classification of defect profile is implemented by means of comparing a defect’s luminance characteristics to a target pixel value using the Hu set of invariant moments. The characteristic values normalization and the Back-Propagation Neural Network (BPN) model are implemented to train the algorithm to recognize defect information their characteristics. The classification results are saved to an established Mysql database and use PHP to communicate with the database side of the page. The user can view and access the test results via a website. Defect maps from the optical inspection of touch panel glass samples were used to evaluate experimentally the classification algorithm. Each map records a 350 * 350 pixel region of the glass sample, with each pixel equal to 3.5 m. Different iterations of the BPN were implemented to seek optimized classification by comparing the mean square error (MSE) between target output and defect profile of the test sample. Defect classification of microscopic scratches, bubbles, and dusts on 20 different defect maps yielded accuracy rates above 90%. Classification of each image was completed in 0.1 ms.
Lai, Chin-Chih, e 賴俊志. "Back-Propagation Neural Network Used in Defect Classification of TFT-LCD Photolithography Process". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/44875630608065934428.
龍華科技大學
工程技術研究所
99
This research is conducted mainly by using the Auto Optical Inspection (AOI) in the fifth generation TFT-LCD factory. This machine is specifically fit the substrates with the size 1100*1300 mm. It performs image-scanned inspection in the active area and then obtains the photos by the 10X electronic microscope. Then, the classification of defects is made by using the back-propagation neural network. In the development of detect-classification system, we designed the back-propagation neural network which combined with Visual Basic as the interface and MATLAB as an image-processing tool. The system is able to determine and display the detected results. The defect classification mainly designed to detect and classify the following defects: the second layer of the photo resist residue (AS-Residue), the second layer of large-area photo resist residue (AS-BPADJ), and the third layer of photo resist residue (M2-residue) in the Array Photolithography Process. In the processing procedure, we first took four 640*480 pictures with three different types of defects and a normal one by using AOI Microscope camera. Secondly, we utilized the MATLAB for image processing and did Blob analysis and binary operation. After the training in the back-propagation neural network, we input all the defected images and data, such as weights and bias values of input layer, output layer, and hidden layer, into Visual Basic software, and the software will display the result of the judgments, which including the four classifications of defects in this experiment. Finally, the result shows the fact that without complicated processing procedure, the four defects in the TFT-LCD Array Photo Process can be precisely and quickly classified only by imaging processing and back-propagation neural network training. As result, it is feasible to reduce the costs and the risk of human judgments.
Han, Je Heon. "Investigation on Wave Propagation Characteristics in Plates and Pipes for Identification of Structural Defect Locations". Thesis, 2013. http://hdl.handle.net/1969.1/151345.
Chi, Fang-chi, e 紀芳琪. "The research of wave propagating behavior of bulk wave near-surface defect". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/95789811029609395796.
國立雲林科技大學
環境與安全衛生工程系碩士班
99
In the industry, non-destructive testing was commonly used for detecting quality of steel materials or inner defects, defects might be located at the surface or inside the material, surface defects could easily be found to immediately eliminate or replace, But the material contained an internal defect, if not find it in time, when the stress concentrate on these defects, the defects grew up easily, and then damaged, even ruptured, affecting the facilities’ structure safety. Ultrasonic techniques are suitable for examining metals or nonmetallic materials, using the difference of acoustic properties between material and defects, that affecting the propagation of ultrasonic, it had a good ability for detecting inner or near-surface defects. However, on-site detection process, the measured error of low-frequency probe for near-surface defect’s detection was large, because the initial echo too large to hide defect echo. Then we could adopt simulation method to simulate wave propagation, to reduce uncertainty waste, and reduce experimental error because of human factor. In this study, we design and process nine defects which under surface 2 mm ~ 10 mm respectively. Each defect was carried out ultrasonic detection (Frequencies were 2, 4, 5, 10 MHz respectively) and ANSYS finite element analysis, then compared their results. The simulate results errors by four frequency probes were less than experimental errors. Hence, we could confirm that using ANSYS finite element analysis to simulate near-surface defects could improve the accuracy of detection.
Ting, Kuan-Wen, e 丁冠文. "Fuzzy Control with Back-Propagation Neural Network Used in Shape Defect Inspection of BGA Solder Ball". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/31749418769431937918.
Wang, Shih-Hsien, e 王世憲. "Study of Character Recognition and Defect Inspection of IC Laser Marking Using Back-Propagation Neural Networks Method". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/75853008571618266439.
國立臺灣科技大學
自動化及控制研究所
98
This thesis presents a recognition system that contains optical character recognition (OCR) and automatic optical inspection (AOI) proceedings for laser marking of IC system. The recognition system can be divided into three flows: IC location alignment, characters extraction and recognition, and defects inspection. For the OCR system, eighty image features are designed and applied to the Back-Propagation Neural Network (BPNN). The experimental rusts show that the OCR system can achieve 100 of correct recognition rate. For the AOI system, we use four image process methods to detect six kinds of defects for the IC laser marking. From the experimental result, the correct detection rate is 96.3% achieved. In addition, the time required for the OCR and AOI proceeding is averaged about 0.189 seconds.
Li, Kuo-Chang, e 李國彰. "An Investigation on the Mode Conversion Behaviors of Wedge Waves Propagating Along a Defected Wedge Tip". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/2zus2v.
國立臺北科技大學
材料科學與工程研究所
98
This study is focused on the propagation conducts of elastic wedge waves (WW) propagating along the tips. Employing a laser ultrasound technique (LUT) and finite element method (FEM) is used to characterize the more specifically, reflection coefficient and transmission coefficients is obtained between the modeled and measured coefficients are modeled and measured for several of defect depths on the wedge tip. In this study, mode conversion phenomenon commonly known in plates are also observed in ASF modes. When ASF modes are partially reflected and partially transmitted, with the RC and TC highly depending on the defect depth.