Letteratura scientifica selezionata sul tema "Defects propagation"
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Articoli di riviste sul tema "Defects propagation":
1
Salim, M. N., M. N. M. Khairy e T. Hayashi. "Effect of Oval Defect on Propagation of Fundamental Lamb Wave". Applied Mechanics and Materials 833 (aprile 2016): 49–58. http://dx.doi.org/10.4028/www.scientific.net/amm.833.49.
Abstract (sommario):
Complicated Lamb wave propagation in structures can cause a misinterpretation in defect location and sizing during nondestructive inspections. A visualization of Lamb wave interactions with oval defects was carried out in our study to investigate the phenomenon of fundamental Lamb wave interaction around defect by using a reduced model of plate in ABAQUS. The visualized wave propagations with oval shape of through defects in plates demonstrated different patterns of wave interactions for the symmetric and anti-symmetric modes. The results also visualized the mode conversions around defects which converted from the incident waves. The visualized changes on the wave structures due to wave interaction with defects is important to increase our understanding on the guided wave propagation and reduce misinterpretation in nondestructive inspection when using the wave modes during inspection on large structures.
2
Wang, Shang, Wei Qiang Wang, Ming Da Song e Hao Zhang. "The Fatigue and Fracture Analysis of Steam Turbine Rotor Shafts Containing Defects". Key Engineering Materials 795 (marzo 2019): 254–61. http://dx.doi.org/10.4028/www.scientific.net/kem.795.254.
Abstract (sommario):
In this study, the assessment and calculation methods for the crack propagation life of steam turbine rotor shafts containing defects are presented. The analytic methods for estimating the average stress and the alternating stress amplitude of the steam turbine rotor shafts are introduced. The defects on/in the rotor shafts were regularized by the method of fracture mechanics, and the high cycle fatigue crack propagation life and low cycle fatigue crack propagation life of the rotor shafts are estimated from Paris formula. Taking the 60MW turbine rotor shafts containing an initial surface defect and an initial internal defect as the examples respectively, the crack propagation life of them were calculated. The results indicated that the assessment method for the crack propagation life can preliminarily be both used to estimate the safety-operating life and to analyze the fracture reason of a steam turbine rotor shaft containing defects. This paper can provide reference for periodic maintenance and safety evaluation of turbine rotor shafts.
3
Huang, Yunqing, e Jichun Li. "Total Reflection and Cloaking by Triangular Defects Embedded in Zero Index Metamaterials". Advances in Applied Mathematics and Mechanics 7, n. 2 (23 marzo 2015): 135–44. http://dx.doi.org/10.4208/aamm.2014.m659.
Abstract (sommario):
AbstractIn this work, we investigate wave propagation through a zero index meta-material (ZIM) waveguide embedded with triangular dielectric defects. We provide a theoretical guidance on how to achieve total reflection and total transmission (i.e., cloaking) by adjusting the defect sizes and/or permittivities of the defects. Our work provides a systematical way in manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical and rectangular geometries.
4
Yu, Shuisheng, Leilei Niu, Jin Chen, Yawei Wang e Honghao Yang. "Study on Bond Defect Detection in Grouted Rock Bolt Systems under Pullout Loads". Advances in Materials Science and Engineering 2022 (31 agosto 2022): 1–9. http://dx.doi.org/10.1155/2022/3282211.
Abstract (sommario):
In grouted rock bolt systems, bond defects often occur, which seriously affects the safety of rock mass structures. Therefore, in this study, based on the existence of bond defects, laboratory tests were conducted to detect the location and length of bond defects and study the guided wave propagation in grouted rock bolt systems under different pullout loads. The guided wave signal was analysed in the time domain and frequency domain. In addition to the laboratory test, a numerical simulation of the effect of different bond defect locations on ultrasonic guided wave propagation in rock bolts was conducted using a damage-based model. The influence mechanism of bond defects on guided wave propagation under different pullout loads was explored. The study confirmed that there existed a stress platform in the rock bolt at the bond defect under a pullout load. The location and length of the bond defect could be detected by the stress platform and guided wave. The debonding length increased exponentially with the amplitude ratio (Q) of low frequency to high frequency, and the Q value could be used as the quantitative index of debonding length. As the pullout load increased, the impedance mismatch between the rock bolt and cement mortar (defect) increased, and the guided wave propagation in grouted rock bolt systems was irregular. The pullout load weakened the guided wave propagation law. The larger the pullout load is, the greater the weakening effect is.
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Basmaci, Ayse. "The Behavior of Electromagnetic Wave Propagation in Photonic Crystals with or without a Defect". Applied Computational Electromagnetics Society 36, n. 6 (6 agosto 2021): 632–41. http://dx.doi.org/10.47037/2020.aces.j.360603.
Abstract (sommario):
In this study, the electromagnetic wave propagation behavior of two-dimensional photonic crystal plates with a defect is investigated. For this purpose, the partial differential equation for the electromagnetic wave propagation in various photonic crystal plates containing a defect or not is obtained by using Maxwell’s equations. The defect is also defined in the electromagnetic wave propagation equation appropriately. In order to solve the electromagnetic wave propagation equation, the finite differences method is used. The material property parameters of the photonic crystal plates are determined with respect to the defects. Accordingly, the effects of material property parameters on electromagnetic wave propagation frequencies, phase velocities, and group velocities are examined. The effects of the size and position of the defects on the electromagnetic wave propagation frequencies are also discussed. The highest electromagnetic wave propagation fundamental frequency value obtained from the analyses performed is 1.198 Hz. This fundamental frequency value is obtained for the electromagnetic wave propagation in the t-shaped photonic crystal plate. Electromagnetic field distribution maps for the fundamental frequencies of the photonic crystal plates whose electromagnetic wave propagation behaviors are examined are obtained with the ANSYS package program based on the finite differences time-domain (FDTD) method.
6
Bultel, Yann, Corine BAS, Florence Dubelley, Fabrice Micoud, Sébastien Rosini e Christine Nayoze-Coynel. "Anode Defects’ Propagation in Polymer Electrolyte Membrane Fuel Cells Stack". ECS Meeting Abstracts MA2023-02, n. 38 (22 dicembre 2023): 1835. http://dx.doi.org/10.1149/ma2023-02381835mtgabs.
Abstract (sommario):
Reliability and durability are key considerations to successfully deploy Proton Exchange Membrane Fuel Cells (PEMFCs). Defects induced by manufacturing processes and fuel cell operating conditions may shorten the lifetime of PEMFC due to membrane electrode assembly (MEA) components degradations. If the degradation mechanisms occurring along ageing are now well-known, the propagation of these defects to other materials or to other locations in the stack was poorly investigated in the literature. Recently, we investigated a defect-propagation in MEA via accelerated stress tests combining load and load-driven humidity cycling, and open-circuit voltage. Results highlighted a defect propagation in term of anode and cathode ECSA losses. Significant membrane thinning is also observed for the defective segments. If, the defect propagation was investigated at the cell scale, it has been barely studied in the literature at the stack level. The objective of this work is to quantify the impact of MEA manufacturing defects on the performance and durability in stack and to analyze how these defects can propagate within healthy areas of the same MEA or to healthies MEAs within a stack. Tests were carried out on two stacks with metallic bipolar plates. The stacks were assembled using 35 defect-free MEAs for the healthy stack and using 30 homogeneous MEAs and 5 MEAs with controlled anode defects over 25% of the active area (absence of anode catalyst layer) for the faulty one. The two stacks were operated on a test bench able to control operating conditions and electrochemical characterizations were regularly made in order to evaluate the impact of the defects on the stack behavior. The initial characterization of the stack contained faulty MEAs showed, as expected, that the defects in the anode active layers have a significant effect on the performance of the cells from the conditioning stage. The analysis of the degradation rate showed that the cells directly in contact with the defected MEAs were the ones whose performance degraded the fastest, which implies that the presence of defects within the stack induces a propagation of the performance decrease. This phenomenon could be linked to a significant increase in hydrogen leakage through the membrane identified both by off-line electrochemical characterization and by thermal camera measurements in post-mortem analysis. The mechanism of degradation is still difficult to understand but the presence of defects within the stack could lead to constriction of the current lines around the defect and to localized heating which could degrade the membrane relatively rapidly. Figure 1
7
Huang, Chen, Zong-Xian Zhang, Adeyemi Aladejare, Xianbo Guan, Bingbing Yu e Liyun Yang. "The Effect of Preloaded Compressive Stress and Curvature of Defect on Blast-Induced Fracture Behavior by Caustic and Numerical Models". Mathematics 11, n. 21 (3 novembre 2023): 4532. http://dx.doi.org/10.3390/math11214532.
Abstract (sommario):
In this study, the effects of preloaded uniaxial compressive stress and defect (prefabricated by laser cutting) curvature on blast-induced cracks and stress wave propagation were investigated in polymethyl methacrylate (PMMA) specimens using caustics theory. Based on the mathematical relationship between stress and optics, the fracture behavior (the propagation path, dynamic stress intensity factors (DSIFs), propagation velocity, initiation angle of the main crack, and damage degree between the defect and the blasthole) was calculated and analyzed quantitatively. The results show that the preloaded stress could mainly restrain the main crack propagation in the horizontal direction and reduce the initiation angle and damage degree at the defects. Meanwhile, the crack initiation position of the positive curvature defect was not at the end of the defect. In addition, the curvature of the defect significantly affected the blast-induced fracture compared to preloaded stresses. Comparing the main crack with other curvature defects, the DSIFs, velocity, crack arrest time, crack length, and horizontal offset distance of the main crack with negative curvature defect were the largest. The variation in the full stress field in the specimen under blasting and preloaded stress was simulated by a numerical model. The results show that the curvature of the defect has a significant effect on tensile waves at the end of defects, and the tensile stress from high to low was C-25, C0, and C25, in that order.
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Cao, Andong, Zhen Zhang e Qian Li. "Frequency shifting of transmitted ultrasound in thick composites containing fiber wrinkles and its application in non-destructive evaluation". Journal of the Acoustical Society of America 154, n. 4_supplement (1 ottobre 2023): A246. http://dx.doi.org/10.1121/10.0023434.
Abstract (sommario):
Thick composite structures are prone to defects such as fiber wrinkles and voids during manufacturing. It is challenging to accurately evaluate the forming quality of the structures using conventional ultrasonic inspection, due to the coupling effects between time-frequency features of ultrasound and mixed-type defects. Propagation behaviors of through-thickness transmitted ultrasound in thick composites with fiber wrinkles, voids and no defects were comparatively investigated by both simulation and experiment in this study. Influence of out-of-plane fiber wrinkles on the ultrasonic frequency shifting was studied by comparing the time-frequency characteristics of simulated ultrasonic signals after propagating different distances in the intact and wavy composites. Changes of transmission coefficients of converted transverse waves caused by fiber wrinkles were concluded be the reason for the appearance of high-frequency components above the excitation frequency in the transmitted ultrasound signal. Thereby ultrasonic defect inspection indices based on the phenomenon of ultrasonic frequency shifting were defined. Effects of interaction angles between ultrasonic propagation direction and fibers on the defined inspection indices was further investigated quantitatively. The thick composites with diverse defects were successfully diagnosed using the ultrasound frequency shifting and energy dissipation behaviors.
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Yilmaz, Ayca, Dilek Helvacioglu-Yigit, Cansu Gur, Handan Ersev, Gullu Kiziltas Sendur, Egemen Avcu, Canan Baydemir e Paul Vincent Abbott. "Evaluation of Dentin Defect Formation during Retreatment with Hand and Rotary Instruments: A Micro-CT Study". Scanning 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/4868603.
Abstract (sommario):
The purpose of this study was to compare the incidence and longitudinal propagation of dentin defects after gutta-percha removal with hand and rotary instruments using microcomputed tomography. Twenty mandibular incisors were prepared using the balanced-force technique and scanned in a 19.9 μm resolution. Following filling with the lateral compaction technique, gutta-percha was removed with ProTaper Universal Retreatment (PTUR) or hand instruments. After rescanning, a total of 24,120 cross-sectional images were analyzed. The numbers, types, and longitudinal length changes of defects were recorded. Defects were observed in 36.90% of the cross sections. A total of 73 defects were comprised of 87.67% craze lines, 2.73% partial cracks, and 9.58% fractures. No significant difference in terms of new defect formation was detected between the retreatment groups. The apical and middle portions of the roots had more dentin defects than the coronal portions. Defects in three roots of the PTUR instrument group increased in length. Under the conditions of this in vitro study, gutta-percha removal seemed to not increase the incidence of dentin defect formation, but the longitudinal defect propagation finding suggests possible cumulative dentinal damage due to additional endodontic procedures. Hand and rotary instrumentation techniques caused similar dentin defect formation during root canal retreatment.
10
Xie, Mingjiang, Yifei Wang, Weinan Xiong, Jianli Zhao e Xianjun Pei. "A Crack Propagation Method for Pipelines with Interacting Corrosion and Crack Defects". Sensors 22, n. 3 (27 gennaio 2022): 986. http://dx.doi.org/10.3390/s22030986.
Abstract (sommario):
Corrosion and crack defects often exist at the same time in pipelines. The interaction impact between these defects could potentially affect the growth of the fatigue crack. In this paper, a crack propagation method is proposed for pipelines with interacting corrosion and crack defects. The finite element models are built to obtain the Stress Intensity Factors (SIFs) for fatigue crack. SIF interaction impact ratio is introduced to describe the interaction effect of corrosion on fatigue crack. Two approaches based on extreme gradient boosting (XGBoost) are proposed in this paper to predict the SIF interaction impact ratio at the deepest point of the crack defect for pipelines with interacting corrosion and crack defects. Crack size, corrosion size and the axial distance between these two defects are the factors that have an impact on the growth of the fatigue crack, and so they are considered as the input of XGBoost models. Based on the synthetic samples from finite element modeling, it has been proved that the proposed approaches can effectively predict the SIF interaction impact ratio with relatively high accuracy. The crack propagation models are built based on the proposed XGBoost models, Paris’ law and corrosion growth model. Sensitivity analyses regarding corrosion initial depth and axial distance between defects are performed. The proposed method can support pipeline integrity management by linking the crack propagation model with corrosion size, crack size and the axial distance. The problem of how the interaction between corrosion and crack defects impacts crack defect growth is investigated.
Tesi sul tema "Defects propagation":
1
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.
2
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.
3
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/.
Abstract (sommario):
Failure in composite structures due to low-velocity impact damage raises a significant maintenance concern because it can lead to a barely visible and difficult-to-detect damage. Depending on the severity of the impact, fiber and matrix breakage or delaminations can occur, reducing the load carrying capacity of the structure. Efficient structural health monitoring (SHM) of composite structures can be achieved by using low- frequency guided ultrasonic waves as they have advantages of propagating over large structure and being sensitive to defects located at any thickness position. This work focuses on the use of first antisymmetric guided wave mode (A0) for health monitoring in laminated composite plates. The first part of this work is to investigate the propagation of A0 mode in undamaged composite plates experimentally and compare the results to Finite Element simulations and semi-analytical analysis. This study is essential in order to improve understanding of the guided waves behavior in composite plates and would benefit the interpretation of received signals particularly for defect characterization. To gain a good understanding of the A0 mode interaction with defects in composites, a full three- dimensional (3D) Finite Element (FE) analysis is used. A systematic study of the influence of defect geometry and range of situations on guided wave scattering is demonstrated. Combined delamination with material degradation to simulate mixed- modes defect is shown. Two dimensional FE simulations used for analysis of large delamination are also presented. The final part of this thesis presents the scattering of guided waves at the impact damage using a non-contact laser interferometer. In this study, the results were quantified and compared to baseline measurements on undamaged composite panels. Significant scattering activities were observed, allowing for the detection of impact damage in composite plates. The impact damage was further characterized using standard ultrasonic C-scans. Good agreement between experiments and predictions was found.
4
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/.
Abstract (sommario):
Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.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.
5
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.
Abstract (sommario):
Le nouveau procédé d’élaboration par solidification dirigée de lingots de Si quasi-monocristallin (« monolike ») offre une alternative séduisante à l’utilisation plus coûteuse de monocristaux pour la fabrication de cellules photovoltaïques à architecture avancée et haut rendement. Toutefois, la présence locale de zones de fortes densités de dislocations entraîne une dispersion des rendements obtenus.Cette Thèse présente une analyse détaillée des mécanismes de formation des structures de dislocations lors de la cristallisation monolike et de leur influence sur les propriétés électriques du matériau. Des conclusions pratiques en sont tirées pour l’amélioration du procédé.Des expériences de cristallisation en four pilote ont été réalisées en faisant varier les paramètres tenant à la mise en œuvre du pavage de germes et à la réutilisation de ceux-ci, à l’orientation cristallographique de croissance, et au dopage en élément durcissant (Ge). Des tests complémentaires de recuit et de flexion 4 points à haute température ont été utilisés pour analyser l’influence du niveau de contrainte et du temps.Une caractérisation avancée des structures de dislocations a été réalisée par imagerie X synchrotron. En arrière du front de croissance, les dislocations s’organisent en structures cellulaires qui correspondent à l’état final de fluage stationnaire. Les dislocations qui émergent au front peuvent, par accumulation locale, générer des domaines désorientés de forme conique, qui présentent des angles de rotation croissants autour de la direction de solidification, et s’étendent latéralement lors de la progression du front. Les fortes activités recombinantes de ces défauts ont été caractérisées par LBIC et Photoluminescence. Un choix approprié des orientations et des conditions de mise en œuvre des germes permet de s’affranchir des défauts initiés à l’interface germes/lingot. Toutefois, de tels défauts peuvent aussi être générés par accumulation locale de dislocations en partie supérieure des lingots sous l’effet de contraintes élevées.Ces derniers défauts n’ont pas été observés dans les lingots cristallisés dans les directions <110> et <112>, ce qui constitue un avantage par rapport aux lingots <100>. Par contre, des macles et sous-joints se sont propagés à partir des joints de grains de rotation créés volontairement, de sorte que l’effet de l’angle de rotation reste à analyser. Enfin, l’addition de germanium s’est révélée très efficace pour ralentir la multiplication des dislocations lors de tests de flexion sous faibles contraintes. Toutefois, son application à la cristallisation nécessitera une meilleure planéité du front de cristallisation et un brassage forcé du bain pour éviter une ségrégation radiale de Ge. L’utilisation d’autres éléments durcissants est également envisagéeThe 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
6
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.
Abstract (sommario):
Mechanical damages, like scratches, are commonly detected on the surfaces of aircraft components and structures. They can be accidentally introduced during machining or maintenance operations or be the result of wear and impacts during aircraft service. Under the action of service loads, such mechanical damage can generate fatigue cracks reducing the component fatigue life and compromising the aircraft structural integrity. The evaluation of the effect of scratches and other small mechanical defects on the structure and component fatigue lives is therefore necessary to define an inspections programme and ensure the structural safety. Conventional fatigue life prediction methods generally consider scratches tents of microns deep too shallow to appreciably affect the fatigue performances of structural components. However the discovery of the scribe marks on fuselage joints disproved that prediction. In fact several commercial airlines discovered during inspections that aircraft which have been repainted showed multiple scratches on the fuselage skin along longitudinal and circumferential joints. Those scratches, referred to scribe marks, appear to have been caused by use of sharp tools during sealant removal process prior repainting. Scratches less than 200 μm deep were capable of severely reducing the fatigue life performance under service load rendering some aircraft beyond economical repair. This thesis investigates the fatigue performances of 2024-T531 aluminium alloy sheets weakened by mechanically machined scratches. 2 mm thick clad and unclad samples were scribed at their gauge section using a diamond tipped tool. The scribing process produced very regular rounded V-shaped notches with an included angle of 60° across the sample width. Scratches from 25 μm to 185 μm deep, with 5 μm, 25 μm and 50 μm root radii were cut on the sample surfaces. Scribed sample were subsequently fatigue tested under constant amplitude tensile and bending load with a stress ratio of R=0.1 at a maximum stress of 200 MPa. Scribes were found to reduce the fatigue life of tension and bending samples up to 97% compared to that of smooth unscribed specimens. Both scribe shape and size affected the fatigue life of tensile and bending aluminium samples. The sharper and the larger the notch, the shorter the fatigue life. Post failure fractography investigations were performed on sample fracture surfaces by means of optical and scanning electron microscope. Crack nucleation sites, fracture morphology and peculiar features left during crack propagation were analysed. Finally crack propagation data under different loading conditions were obtained by striation counting performed on fracture surfaces. Multiple crack initiation occurred at scribe roots usually from inclusions, defects or weak points along the root. The number and density of crack nucleation sites appeared to be determined by the scribe; increasing for notches with larger stress concentrations. Scribe geometry did not affect the fatigue growth rate but the propagation life for cracks deeper than 50-100 μm was influenced. Cracks nucleated from scribe marks showed a typical short crack behaviour growing faster than long cracks with the same linear elastic stress intensity factor. Finite element calculations were performed on scribed samples evaluating how the presence of scribes altered the local stress and strain fields. Monotonic elastic and elastic-plastic and cyclic elastic-plastic analyses were carried out under tensile and bending loads. Local elastic-plastic stress and strain fields in the neighbourhood of different scribes were determined by the notch shape and size. According to the occurrence of mechanical similitude conditions, scribes with the same shape but different size showed similar plastic zone and stress and strain distributions. A stabilised cyclic plastic zone was developed just at the root of scribes with a ratio between the root radius and depth ρ/d≤0.2. No correlations were observed between the occurrence of a stabilised cyclic plastic zone and the sample nucleation lives defined as the number of cycles to obtain an initial crack 50 μm deep from the notch root. Traditional fatigue life prediction methods, based on the notch sensitivity factor, were not able to correctly characterise the effect of scratches few tens of microns deep on the fatigue life of 2024-T351 aluminium alloy components. An approach based on the critical distance theory was developed to characterise the total fatigue life reduction produced by the introduction of scribes relating the fatigue live to a critical stress range Δσlm. The critical stress range was capable of describing the effect of the elastic stress distribution produced by dissimilar notches on the nucleation and propagation of fatigue crack considering also the effect of the variation of the fatigue load nominal applied stress.
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Ehrlacher, Virginie. "Quelques modèles mathématiques en chimie quantique et propagation d'incertitudes". Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1073/document.
Abstract (sommario):
Ce travail comporte deux volets. Le premier concerne l'étude de défauts locaux dans des matériaux cristallins. Le chapitre 1 donne un bref panorama des principaux modèles utilisés en chimie quantique pour le calcul de structures électroniques. Dans le chapitre 2, nous présentons un modèle variationnel exact qui permet de décrire les défauts locaux d'un cristal périodique dans le cadre de la théorie de Thomas-Fermi-von Weiszäcker. Celui-ci est justifié à l'aide d'arguments de limite thermodynamique. On montre en particulier que les défauts modélisés par cette théorie ne peuvent pas être chargés électriquement. Les chapitres 3 et 4 de cette thèse traitent du phénomène de pollution spectrale. En effet, lorsqu'un opérateur est discrétisé, il peut apparaître des valeurs propres parasites, qui n'appartiennent pas au spectre de l'opérateur initial. Dans le chapitre 3, nous montrons que des méthodes d'approximation de Galerkin via une discrétisation en éléments finis pour approcher le spectre d'opérateurs de Schrödinger périodiques perturbés sont sujettes au phénomène de pollution spectrale. Par ailleurs, les vecteurs propres associés aux valeurs propres parasites peuvent être interprétés comme des états de surface. Nous prouvons qu'il est possible d'éviter ce problème en utilisant des espaces d'éléments finis augmentés, construits à partir des fonctions de Wannier associées à l'opérateur de Schrödinger périodique non perturbé. On montre également que la méthode dite de supercellule, qui consiste à imposer des conditions limites périodiques sur un domaine de simulation contenant le défaut, ne produit pas de pollution spectrale. Dans le chapitre 4, nous établissons des estimations d'erreur a priori pour la méthode de supercellule. En particulier, nous montrons que l'erreur effectuée décroît exponentiellement vite en fonction de la taille de la supercellule considérée. Un deuxième volet concerne l'étude d'algorithmes gloutons pour résoudre des problèmes de propagation d'incertitudes en grande dimension. Le chapitre 5 de cette thèse présente une introduction aux méthodes numériques classiques utilisées dans le domaine de la propagation d'incertitudes, ainsi qu'aux algorithmes gloutons. Dans le chapitre 6, nous prouvons que ces algorithmes peuvent être appliqués à la minimisation de fonctionnelles d'énergie fortement convexes non linéaires et que leur vitesse de convergence est exponentielle en dimension finie. Nous illustrons ces résultats par la résolution de problèmes de l'obstacle avec incertitudes via une formulation pénaliséeThe 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
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Aïssani, Amina. "Optimisation fiabiliste des performances énergétiques des bâtiments". Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22677/document.
Abstract (sommario):
Dans un contexte de forte compétitivité économique et de respect de l’environnement, de nombreuses actions sont entreprises chaque année dans le but d’améliorer la performance énergétique des bâtiments. En phase de conception, le recours à la simulation permet d’évaluer les différentes alternatives au regard de la performance énergétique et du confort des occupants et constitue ainsi un outil d’aide à la décision incontournable. Toutefois, il est courant d’observer des écarts entre les performances énergétiques réelles et celles prévues lors de la conception. Cette thèse porte sur l’amélioration du processus de conception de l’isolation dans le but de limiter les déviations des consommations réelles par rapport à celles prévues lors des simulations. Dans un premier temps, nous situons le contexte énergétique actuel puis nous présentons les différentes sources d’incertitudes qui affectent les résultats des simulations. Dans ce travail, nous nous intéressons particulièrement à la variabilité des propriétés thermophysiques des isolants, au caractère variable de la mise en œuvre et à l’impact du changement climatique. Des études expérimentales ont permis de quantifier l’incertitude associée à la performance des matériaux sains d’une part, et celle associée à des isolants défectueux d’autre part. Un couplage entre des techniques de thermographie infrarouge et des modèles éléments finis ont permis de proposer des modèles paramétriques permettant d’évaluer la performance effective d’un isolant défectueux, en fonction du type et de la taille du défaut dans l’isolant. Pour une bonne estimation à long terme de la performance de l’isolation, il est nécessaire d’intégrer les prévisions météorologiques. Ces dernières sont généralement estimées sur la base des données historiques de la région. Toutefois, il est encore difficile de prévoir avec exactitude l’évolution climatique car elle dépend de nombreux facteurs socio-économiques, démographiques et environnementaux. Dans ce travail, nous proposons de considérer les différents scénarios climatiques proposés par les climatologues et de prendre en compte leur variabilité de manière à vérifier la fiabilité de l’isolation. Enfin, nous proposons d’utiliser des approches probabilistes pour intégrer ces différents types d’incertitudes dans le processus de simulation. Pour optimiser le dimensionnement de l’isolation, nous proposons une méthodologie de conception basée sur la fiabilité. Un nouveau modèle de coût est également proposé dans le but d’améliorer l’aide à la décision, en considérant les pertes indirectes, jusqu’à présent négligées dans la conceptionIn 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
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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.
Abstract (sommario):
Le contrôle non destructif par ondes guidées générées et détectées par des transducteurs ultrasonores à couplage par air, présente deux avantages majeurs. Le premier réside dans la capacité des ondes guidées à transporter l’information sur la qualité du milieu sur une grande distance. De plus, l’absence d’un milieu de couplage liquide entre les capteurs et le milieu à tester, rend le contrôle plus commode. Ce travail consiste d’abord à développer un procédé de simulation numérique qui prend en considération de nombreux paramètres du système de contrôle. Dans une optique de réduire le nombre de degrés de liberté, un modèle hybride a été développé qui consiste en une combinaison entre un modèle analytique basé sur l’intégrale de Kirchhoff pour la propagation des ultrasons dans l’air et un modèle éléments finis de la propagation des ondes guidées dans le matériau. La mesure des caractéristiques du transducteur à couplage par air (efficacité de l’émetteur et sensibilité du récepteur) permet, d’une part, de calculer la valeur exacte de la pression dans l’air et les valeurs exactes des champs de contraintes et de déplacements dans la structure, pour une tension et une fréquence d’excitation, et d’autre part, de remonter à la tension électrique aux bornes de ce récepteur pour une pression rayonnée par le matériau. Par suite, cette caractérisation rend possible la comparaison entre les prédictions numériques de la réponse (en niveau de tension) du système et les mesures expérimentales correspondantes. A la lumière du modèle numérique développé, une optimisation des paramètres du système de contrôle (angle, fréquence,diamètre, direction de propagation, champ proche et champ lointain) a été effectuée pour améliorer la pureté des modes guidés par le matériau. Une manipulation expérimentale, basée sur un transducteur à couplage par air pour l’émission et une sonde laser pour la réception, a été alors mise en place pour valider quelques prédictions numériques. Ensuite, on a étudié l’interaction des ondes guidées ultrasonores avec des défauts de type délaminage enfouis dans une plaque composite à symétrie quadratique. Pour cela, on a analysé la sensibilité des deux modes fondamentaux A0 et S0 au délaminage en terme de détectabilité. En parallèle, on a traité un problème inverse qui consiste à dimensionner un délaminage par le calcul du spectre fréquentiel du coefficient de réflexion. Enfin, on a mis en évidence le potentiel des transducteurs à couplage par air à ausculter des pièces aéronautiques impactéesNon-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
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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.
Abstract (sommario):
Les défauts connus pour réduire la durée de vie des piles à combustible à membrane électrolyte polymère (PEMFC) peuvent apparaître sur différents composants de l'assemblage membrane-électrode (AME) et sous différentes formes en raison des procédés de fabrication ou du vieillissement -en fonctionnement- de la pile à combustible. Ce travail concerne l’étude de l’apparition, la détection et la propagation de défauts dans les AME de PEMFC, et plus spécifiquement à l’anode. À cet effet, un protocole de vieillissement accéléré (AST) combinant des cycles de potentiel et d'humidité -induits par les variations de courant-, et de maintien en circuit ouvert est appliqué à des AME standard ou avec défauts initiaux. Les AME avec défauts ont été fabriqués avec un manque de couche active à l’anode, ce défaut pouvant être localisé près de l'entrée ou bien près de la sortie d’hydrogène. Des caractérisations électrochimiques sont réalisées périodiquement à l'aide d'une cellule linéaire instrumentée et segmentée, permettant de suivre les performances de la cellule à travers les courants, les potentiels d’électrode, les impédances locales, ainsi que l’évolution de la surface active électrochimique (ECSA) à l’anode et à la cathode pendant le test de vieillissement, avec une résolution spatiale le long des canaux. Une étude par spectroscopie d’impédance a été menée conjointement, basée sur une interprétation par circuits électriques équivalents et se focalisant sur la détection de la contribution anodique à l’impédance globale de la cellule. Les résultats mettent en évidence une dégradation accélérée de l’AME ainsi que les premières preuves de propagation de défauts, en termes de perte de l’ECSA à l’anode. Cette propagation se produit dans le sens du flux d'hydrogène. L’ECSA de la cathode semble également impactée, bien qu'apparemment de manière homogène. Un amincissement important de la membrane a également été observé dans les segments défectueux, avec propagation probable aux segments adjacents, mais à plus long termeDefects 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
Libri sul tema "Defects propagation":
1
D, Noebe R., e United States. National Aeronautics and Space Administration., a cura di. Low cycle fatigue behavior of polycrystalline NiAl at 300 and 1000K. [Washington, DC]: National Aeronautics and Space Administration, 1993.
2
D, Noebe Ronald, e United States. National Aeronautics and Space Administration., a cura di. Low cycle fatigue behavior of polycrystalline NiAl at 300 and 1000K. [Washington, DC]: National Aeronautics and Space Administration, 1993.
3
United States. National Aeronautics and Space Administration., a cura di. Prediction and verification of ductile crack growth from simulated defects in strength overmatched butt welds: A thesis ... [Washington, D.C: National Aeronautics and Space Administration, 1997.
4
O, Harris David, Thomas Jerrell M, George C. Marshall Space Flight Center. e United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch., a cura di. A review of fracture mechanics life technology. [Washington, D.C.]: National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1986.
5
Nazer, Hisham. Power of a Third Kind. Praeger, 1999. http://dx.doi.org/10.5040/9798400699740.
Abstract (sommario):
This thought-provoking book points out that the most significant change in international relations in the 20th century was not the defeat of communism, nor the end of the Cold War, but the huge advances in communications technologies. Hisham Nazer, a leading Saudi Arabian intellectual and petroleum industry leader, argues that the West has used its control over these capabilities to superimpose its cultural and political values on the rest of the world. CNN, films and television, and the Internet have become the means of promoting Western products—including soft drinks, detergents, and even the ideals of democracy and human rights—in relatively powerless non-Western nations. This process of creating a global culture through the propagation of Western political and philosophical constructs as world brands poses grave dangers for the entire international community. As countries become aware of their exploitation, the possibilities for frustration and violence become increasingly real. Power of a Third Kindis directed toward Western and non-Western leaders alike. For the former, it provides a new perspective from outside the mirror of our Western culture, pointing out that current practices are actually endangering the security of our hemisphere. The author calls on Western leaders to work on a dialogue with other societies as an alternative to exporting to them a monologue designed for passive absorption. And for the latter, this book will inspire them to steer out of their current course in time to protect their histories and the integrity of their cultures. Through meaningful dialogue, well-meaning nations will find a way for the most beneficial aspects of Western culture—self-rule and basic human rights—to evolve within the context of local cultures, resulting in a world both more stable and more humane.
Capitoli di libri sul tema "Defects propagation":
1
Harris, John G. "Modeling Scanned Acoustic Imaging of Defects at Solid Interfaces". In Inverse Problems in Wave Propagation, 237–57. New York, NY: Springer New York, 1997. http://dx.doi.org/10.1007/978-1-4612-1878-4_11.
2
Chang, Zensheu, e Ajit Mal. "Wave Propagation in a Plate with Defects". In Review of Progress in Quantitative Nondestructive Evaluation, 121–28. Boston, MA: Springer US, 1998. http://dx.doi.org/10.1007/978-1-4615-5339-7_15.
3
Abdollahi, Amir, e Irene Arias. "Numerical simulation of intergranular and transgranular crack propagation in ferroelectric polycrystals". In Micromechanics of Defects in Solids, 3–15. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-4626-8_2.
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Klapper, Helmut. "Generation and Propagation of Defects During Crystal Growth". In Springer Handbook of Crystal Growth, 93–132. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-540-74761-1_4.
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Weidner, Anja, Alexander Schmiedel, Mikhail Seleznev e Horst Biermann. "Influence of Internal Defects on the Fatigue Life of Steel and Aluminum Alloys in the VHCF Range". In Multifunctional Ceramic Filter Systems for Metal Melt Filtration, 605–43. Cham: Springer International Publishing, 2024. http://dx.doi.org/10.1007/978-3-031-40930-1_24.
Abstract (sommario):
AbstractThis chapter concerns the influence of internal defects (i.e. nonmetallic inclusions, secondary phases and cast defects) on the fatigue lifetime of steel and aluminum alloys in the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regime. The detrimental effect of internal defects depends on multiple factors such as size, morphology, chemical composition, test temperature or position in the material. Specimens were tested after active and/or reactive melt filtration processes of the materials which served to influence the amount and size distribution of internal defects. Fatigue experiments up to 109 cycles were carried out using ultrasonic fatigue testing equipment. In addition, in situ methods, as e.g. full surface view thermography and acoustic emission (AE), were applied to study the processes of crack initiation and propagation, which finally lead to fatigue failure. Furthermore, the cyclically strained samples were subjected to fractographic analysis and the S–N-curves were discussed according to the characteristics of the crack-initiating defects. Based on these investigations, an enhanced knowledge about the correlation of internal defects on the materials’ fatigue strength enables a specific melt filtration strategy adjusted to the materials’ service conditions.
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Xu, Liu-Jun, e Ji-Ping Huang. "Theory for Thermal Edge States: Graphene-Like Convective Lattice". In Transformation Thermotics and Extended Theories, 305–15. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-5908-0_22.
Abstract (sommario):
AbstractIn this chapter, we reveal that edge states are not necessarily limited to wave systems but can also exist in convection-diffusion systems that are essentially different from wave systems. For this purpose, we study heat transfer in a graphene-like (or honeycomb) lattice to demonstrate thermal edge states with robustness against defects and disorders. Convection is compared to electron cyclotron, which breaks space-reversal symmetry and determines the direction of thermal edge propagation. Diffusion leads to interference-like behavior between opposite convections, preventing bulk temperature propagation. We also display thermal unidirectional interface states between two lattices with opposite convection. These results extend the physics of edge states beyond wave systems.
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Nasedkina, A. A., A. Alexiev e J. Malachowski. "Numerical Simulation of Ultrasonic Torsional Guided Wave Propagation for Pipes with Defects". In Springer Proceedings in Physics, 475–88. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-26324-3_33.
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Yang, W., e T. Kundu. "Lamb Wave Propagation in Multilayered Anisotropic Solids and its Application Towards Imaging Material Defects". In Acoustical Imaging, 23–30. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1943-0_3.
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Zotov, Vladimir V., Vitaly V. Popuzin e Alexander E. Tarasov. "An Experimental Model of the Ultrasonic Wave Propagation Through a Doubly-Periodic Array of Defects". In Advanced Structured Materials, 189–204. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-3797-9_11.
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Mieloszyk, Eligiusz, Anita Milewska e Sławomir Grulkowski. "Assessment of Image Processing Methods for the Determination of Propagation of Squat-Type Defects in Rails". In Lecture Notes in Electrical Engineering, 211–19. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11187-8_17.
Atti di convegni sul tema "Defects propagation":
1
ZIELIŃSKI, P. "PROPAGATION OF WAVES THROUGH ANHARMONIC DEFECTS". In Proceedings of the 7th International School on Theoretical Physics. WORLD SCIENTIFIC, 2003. http://dx.doi.org/10.1142/9789812704474_0040.
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Sargent, R. B., Dar-Yuan Song e H. Angus Macleod. "Computer simulation of defect propagation in thin films". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.tur2.
Abstract (sommario):
Two-dimensional film growth models were introduced by Henderson et al.1 and Dirks and Leamy.2 These early models displayed several effects commonly observed in conventionally deposited thin films: columnar microstructure and the tangent rule relating the angle of columnar growth to the angle of vapor incidence. A model of this general type has been under development at the Optical Sciences Center for several years. The model incorporates mobility parameters for the condensing molecules, oblique angles of vapor incidence, substrate rotation effects, evaporant molecules of varying sizes, and various substrate defects. Recently the scale of the simulation has been expanded to realistic dimensions, of the order of an optical wavelength, which permits the inclusion of substrate variation effects up to this scale. The film growth model propagates substrate defects through a multilayer coating. Assuming a perfectly flat substrate surface, the dominant feature is an intrinsic film roughness. If a departure from perfection of the substrate surface is assumed, in a range of conditions diminution of the defect amplitude is observed as the defect propagates through the multilayer.
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"3D WAVE PROPAGATION IN MATERIALS WITH FRICTIONAL DEFECTS". In Fizicheskaya mezomekhanika. Materialy s mnogourovnevoy ierarkhicheski organizovannoy strukturoy i intellektual'nye proizvodstvennye tekhnologii. Tomsk State University, 2020. http://dx.doi.org/10.17223/9785946219242/134.
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Kim, Kukbin, Byung-Joo Kim, Jinsoo Park, Young-Cheol Yoon e Deukjin Park. "Fatigue Strength Evaluation of Defects Embedded in Large-Sized Stud Bolt of Marine Engine". In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-82663.
Abstract (sommario):
Millimeter-sized defects are often found during inspection near the centerline of the shank of large-sized stud bolts. Determination of allowable defect size is practically required in view of safety. An experimental investigation on the fatigue strength of the stud bolt has been carried out in order to evaluate the effect of defects embedded in the stud bolt on the fatigue strength. Fatigue testing was conducted for stress ratios of 0.0, 0.4 and 0.7 using plain specimens and defected specimens having a defect embedded inside to examine the fatigue limit according to the stress ratio. Macroscopic and microscopic analyses were also conducted in order to determine initial defect size, crack initiation site and propagation rate from beach marks on the fracture surface. Existing small defect evaluation methods currently available were used for the strength evaluation. Allowable internal defect size was determined based on the high mean and high cycle stress states of the bolt by linear elastic fracture mechanics.
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Feroz, K. T., e S. O. Oyadiji. "Damage Detection in Rods Using Wave Propagation and Regression Analysis". In ASME 1999 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/detc99/vib-8372.
Abstract (sommario):
Abstract The phenomena of wave propagation in rods was studied both numerically and experimentally. The finite element (FE) code ABAQUS was used for the numerical study while PZT (lead zirconium titanate) sensors and a 50 MHz transient recorder were used experimentally to monitor and to capture the propagation of stress pulses. For the study of damage detection in the rods the analyses and the experiments were repeated by introducing slots in a fixed axial location of the rod. A longitudinal wave was induced in the rod via collinear impact which was modelled in the FE analyses using the force-time history computed from the classical Hertz contact theory. In the experimental measurements this was achieved by a spherical ball impact at one plane end of the rods. It is shown that the predicted and measured strain-time histories for the defect-free rod and for the rods with defect correlate quite well. These results also show that defects can be located using the wave propagation phenomena. A regression analysis technique of the predicted and measured strain histories of the defect free rod and of the rod with defect was also performed. The results show that this technique is more efficient for smaller defects. In particular, it is shown that the area enclosed by the regression curve increases as the defect size increases.
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Kakoyiannis, Constantine G., Evangelos S. Angelopoulos e Philip Constantinou. "Radiation properties of wireless-sensor-targeted compact arrays loaded by ground defects". In Propagation Conference (LAPC). IEEE, 2009. http://dx.doi.org/10.1109/lapc.2009.5352374.
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Das, Poulomi, Alain Moussa, Christophe Beral, Mihir Gupta, Mohamed Saib, Sandip Halder, Anne-Laure Charley e Philippe Leray. "Printability and propagation of stochastic defects through a study of defects programmed on EUV mask". In International Conference on Extreme Ultraviolet Lithography 2021, a cura di Kurt G. Ronse, Paolo A. Gargini, Eric Hendrickx, Patrick P. Naulleau e Toshiro Itani. SPIE, 2021. http://dx.doi.org/10.1117/12.2602034.
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Favalli, M., e C. Metra. "Pulse propagation for the detection of small delay defects". In Design, Automation & Test in Europe Conference. IEEE, 2007. http://dx.doi.org/10.1109/date.2007.364476.
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Wang, Donghui, Qingna Zeng, Fenggang Zang e Yixiong Zhang. "Vibration Propagation Analysis of Periodic Pipeline With Crack Defects". In ASME 2021 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/pvp2021-60988.
Abstract (sommario):
Abstract In this paper, the vibration propagation characteristic is investigated for periodic composite pipeline with crack damage. A novel modified transfer matrix method (TMM) is developed to investigate transverse Band Gap structures (BGs) considering fluid structure interaction, and validated by frequency response function (FRF) for finite period. Field transfer matrix is developed for straight pipeline conveying fluid, and point transfer matrix is derived for circumferential cracks damage based on spring hinge model, which could estimate the equivalent rotational stiffness by local flexibility coefficient method. It’s demonstrated that the existence of small crack damage has negligible effect on BGs, while severe crack damage has significant influence on vibration propagation even it only exists in a single cell. Meanwhile, the difference of FRF between cracked and perfect pipeline provides new idea in diagnosing the crack status. The influence of crack damage on BGs is mainly attributed to the equivalent rotational stiffness. Location of crack damage could affect the stiffness ratio of composite pipeline, and result in the change of original BGs. This study enriches the theoretical TMM for pipeline systems vibration with crack damage, and provides some reference for the stability design of periodic pipeline structures.
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Fan, Y., S. Dixon, R. S. Edwards e X. Jian. "Ultrasonic Surface Wave Propagation and Interaction with Surface Defects". In REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION. AIP, 2007. http://dx.doi.org/10.1063/1.2718063.
Rapporti di organizzazioni sul tema "Defects propagation":
1
Leis, B. N. Leis, e R. J. Eiber. PR-003-00108-R01 Fracture Control Technology for Natural Gas Pipelines Circa 2001. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), luglio 2001. http://dx.doi.org/10.55274/r0011879.
Abstract (sommario):
Fracture control procedures are presented for new lines and existing lines, and illustrated with examples. Such procedures and the plans based on them address requirements to assure pipelines can tolerate large defects before leaks or ruptures occur, as well as requirements to control the length of a fracture as a secondary level of control. The report is divided into three sections. This first section defines basic terminology, describes how fracture control fits into an operator's overall assurance plan for pipeline integrity and discusses general philosophies of fracture control. The remaining two sections describe fracture initiation control and fracture propagation control procedures. Background information needed to understand the fracture concepts is presented in each of the sections. Example problems are presented in the appendices along with computer programs to facilitate the use of the fracture control procedures.
2
McKinley, W. G., H. T. Yura e S. G. Hanson. Optical System Defect Propagation in ABCD Systems. Fort Belvoir, VA: Defense Technical Information Center, ottobre 1988. http://dx.doi.org/10.21236/ada200480.
3
Rose, Luo e Minachi. ZZ44154 Circumferential Guided Waves for Defect Detection in Tar Coated Pipe. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), gennaio 2008. http://dx.doi.org/10.55274/r0010958.
Abstract (sommario):
The study reports on circumferential guided wave inspection potential and propagation in a tar coated pipe. A computer code based on a matrix technique was developed to calculate the circumferential guided wave dispersion curves and wave structures in a viscoelastic multi-layered pipe. Experiments utilizing the SwRI Magnetostrictive ILI inspection technique were conducted under different coating conditions. There was a favorable agreement with theory. This study provides an insight into attenuation effect, ways to improve propagation distance, and a baseline for further studies on wave scattering, defect classification and sizing.
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Nestleroth. L52298 Augmenting MFL Tools With Sensors that Assess Coating Condition. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), marzo 2009. http://dx.doi.org/10.55274/r0010396.
Abstract (sommario):
External coatings are routinely used to protect transmission pipelines from corrosion; however, coatings may degrade or disbond over time enabling corrosion to occur. Transmission pipeline operators often use magnetic flux leakage (MFL) in-line inspection tools to detect metal loss corrosion defects. Rather than finding the cause of a problem, failure of the coating within a corrosive environment, MFL corrosion surveys only find the result of the problem, corrosion defects that may permanently alter the pressure carrying capacity of the pipeline. Stress corrosion cracking (SCC) can be detected using in-line inspection (ILI) technology, but the availability of tools is limited and the cost of inspection is high compared to MFL inspection. SCC almost always occurs at coating faults; direct coating assessment could indicate future problems that could degrade the serviceability of the pipeline. In this project, a new sensor was developed to assess external coating that could work with currently available ILI tools for minimal additional cost to perform the inspection. The sensors, electromagnetic acoustic transducers (EMATs), generate ultrasonic waves that are guided by the pipe material around the circumference of the pipe. The coating material and adherence can influence the propagation of the ultrasonic waves; changes in ultrasonic signal features were attributed to coating faults. This development used modeling and experiments to establish a more optimal configuration for coating assessment. A multiple feature approach was used. A commonly used feature, signal amplitude, provided good sensitivity to coating condition but was influenced by inspection variables. One unique feature identified in this development is arrival time of the ultrasonic wave. For the wave type and frequency selected, the wave velocity was different for bare and coated pipe. Therefore, disbonded or missing coating can be detected by monitoring arrival time of the ultrasonic wave, a feature that is amplitude independent. Another feature for assessing coating, absorption of selective frequencies, was also demonstrated. Coating assessment capability was experimentally demonstrated using a prototype EMAT ILI tool. All three detection features were shown to perform well in an ILI environment as demonstrated at Battelle"s Pipeline Simulation Facility and BJ Inspection Services pull rigs. Improvement to the prototype occurred between each test; the most significant improvement was the design and construction of a novel set of thick-trace transmitting and receiving Printed Circuit Board (PCB) EMAT coils. Implementation variables such as moisture and soil loading were shown to have a minimal influence on results.
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Arnold, Joshua. DTPH56-16-T-00004 EMAT Guided Wave Technology for Inline Inspections of Unpiggable Natural Gas Pipelines. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), settembre 2018. http://dx.doi.org/10.55274/r0012048.
Abstract (sommario):
This project developed compact, lightweight, prototype Electro-Magnetic Acoustic Transducers (EMATs) and studied guided waves for defect detection, classification, and characterization in cast iron and steel pipes. Through lab testing, design, and Finite Element Analysis (FEA), guided wave propagation and defect interactions were evaluated, and the results were employed to optimize the prototype EMATs through successive design and testing iterations. The goal of developing EMATs for robotic inspection of unpiggable pipe was successfully achieved and demonstrated not only through prototype fabrication and testing but also through conceptual design modifications to ULC's CIRRIS XITM robot that incorporated EMATs onto the robot.
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Dawalibi. L51925 Detection of Anomalies in Coated Pipelines Using Long Range Ultrasonics. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), ottobre 2002. http://dx.doi.org/10.55274/r0010644.
Abstract (sommario):
Long-range guided wave pipeline inspection is claimed to be able to inspect ranges of well over 30 meters (100 Feet) in either direction (i.e. total inspection greater than 60 Meters or 200 Ft.) from a single position. In terms of inspected meters per measurement and cost per meter this technique can be a fundamental improvement from conventional methods for pipeline inspection. For inspection of hard-to-access locations it offers a good on-stream screening alternative by being able to image the pipe section from an easier-access location. Examples of inaccessible locations are road-, railway-, river-, dike- and other crossings. Excavating the pipeline for inspection at these locations is expensive and the potential cost savings of a technique like long-range pipeline inspection are attractive. The objective of this project was to combine theory, modeling and experimental/operational elements in order to be able to handle the more complex situations as found at buried sections of pipelines, more specifically bitumen coating. Laboratory and field experiments supported by modeling and developing an approach to inspect a coated pipe configuration are parts of this work in order to get both reliable and practical knowledge. Another important part was the evaluation of the different transducer and equipment concepts available and establish their merits. In the project the propagation and reflection of guided waves was modeled and simulated for relevant situations. Two suppliers, SwRI and PiL, were involved in laboratory trials and field trials both to confirm the modeling and obtain a clear view of the practical aspects in operation and the actual capabilities of their systems. Modeling resulted in a formula providing estimates for the reflectivity of defects. Using scaling rules these were compared to data obtained in the laboratory trials.
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Rose e Luo. L52069 Guided Wave Sizing and Discrimination for SCC Magnetostriction ILI Inspection. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), gennaio 2003. http://dx.doi.org/10.55274/r0011179.
Abstract (sommario):
With the goal to be able to inspect a large area of the pipe from a single sensor position, hence the development of what we call guided wave inspection. From one point on the circumference of the pipe, it is therefore proposed to inspect the entire circumferential area of the pipe. This approach leads to inspection efficiency.� Experimental techniques cannot be developed on a trial and error basis. The purpose of this work is therefore to develop a guided wave propagation model and subsequent numerical solutions to assist in the �theoretically driven� sensor design and data acquisition systems for improved nondestructive testing including defect detection, location, and potential classification and sizing analysis in a pipe.
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Engel, Bernard, Yael Edan, James Simon, Hanoch Pasternak e Shimon Edelman. Neural Networks for Quality Sorting of Agricultural Produce. United States Department of Agriculture, luglio 1996. http://dx.doi.org/10.32747/1996.7613033.bard.
Abstract (sommario):
The objectives of this project were to develop procedures and models, based on neural networks, for quality sorting of agricultural produce. Two research teams, one in Purdue University and the other in Israel, coordinated their research efforts on different aspects of each objective utilizing both melons and tomatoes as case studies. At Purdue: An expert system was developed to measure variances in human grading. Data were acquired from eight sensors: vision, two firmness sensors (destructive and nondestructive), chlorophyll from fluorescence, color sensor, electronic sniffer for odor detection, refractometer and a scale (mass). Data were analyzed and provided input for five classification models. Chlorophyll from fluorescence was found to give the best estimation for ripeness stage while the combination of machine vision and firmness from impact performed best for quality sorting. A new algorithm was developed to estimate and minimize training size for supervised classification. A new criteria was established to choose a training set such that a recurrent auto-associative memory neural network is stabilized. Moreover, this method provides for rapid and accurate updating of the classifier over growing seasons, production environments and cultivars. Different classification approaches (parametric and non-parametric) for grading were examined. Statistical methods were found to be as accurate as neural networks in grading. Classification models by voting did not enhance the classification significantly. A hybrid model that incorporated heuristic rules and either a numerical classifier or neural network was found to be superior in classification accuracy with half the required processing of solely the numerical classifier or neural network. In Israel: A multi-sensing approach utilizing non-destructive sensors was developed. Shape, color, stem identification, surface defects and bruises were measured using a color image processing system. Flavor parameters (sugar, acidity, volatiles) and ripeness were measured using a near-infrared system and an electronic sniffer. Mechanical properties were measured using three sensors: drop impact, resonance frequency and cyclic deformation. Classification algorithms for quality sorting of fruit based on multi-sensory data were developed and implemented. The algorithms included a dynamic artificial neural network, a back propagation neural network and multiple linear regression. Results indicated that classification based on multiple sensors may be applied in real-time sorting and can improve overall classification. Advanced image processing algorithms were developed for shape determination, bruise and stem identification and general color and color homogeneity. An unsupervised method was developed to extract necessary vision features. The primary advantage of the algorithms developed is their ability to learn to determine the visual quality of almost any fruit or vegetable with no need for specific modification and no a-priori knowledge. Moreover, since there is no assumption as to the type of blemish to be characterized, the algorithm is capable of distinguishing between stems and bruises. This enables sorting of fruit without knowing the fruits' orientation. A new algorithm for on-line clustering of data was developed. The algorithm's adaptability is designed to overcome some of the difficulties encountered when incrementally clustering sparse data and preserves information even with memory constraints. Large quantities of data (many images) of high dimensionality (due to multiple sensors) and new information arriving incrementally (a function of the temporal dynamics of any natural process) can now be processed. Furhermore, since the learning is done on-line, it can be implemented in real-time. The methodology developed was tested to determine external quality of tomatoes based on visual information. An improved model for color sorting which is stable and does not require recalibration for each season was developed for color determination. Excellent classification results were obtained for both color and firmness classification. Results indicted that maturity classification can be obtained using a drop-impact and a vision sensor in order to predict the storability and marketing of harvested fruits. In conclusion: We have been able to define quantitatively the critical parameters in the quality sorting and grading of both fresh market cantaloupes and tomatoes. We have been able to accomplish this using nondestructive measurements and in a manner consistent with expert human grading and in accordance with market acceptance. This research constructed and used large databases of both commodities, for comparative evaluation and optimization of expert system, statistical and/or neural network models. The models developed in this research were successfully tested, and should be applicable to a wide range of other fruits and vegetables. These findings are valuable for the development of on-line grading and sorting of agricultural produce through the incorporation of multiple measurement inputs that rapidly define quality in an automated manner, and in a manner consistent with the human graders and inspectors.
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L51742 Serviceability of Corroded Girth Welds. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), maggio 1996. http://dx.doi.org/10.55274/r0010362.
Abstract (sommario):
Prior research conducted for PRCI and others led to the development of criteria for estimating the burst strength of corroded pipe, and corollary criteria for establishing allowable defect sizes. These criteria have become widely used in the pipeline industry. That research revealed that the severity of metal-loss corrosion in the context of pressure integrity is directly affected by the length of the corroded area (as measured parallel to the pipe longitudinal axis) and the depth of the corrosion. Moreover, the length and depth affect burst strength independently, meaning a long shallow defect may be more severe than a shorter but deeper defect representing the same area of metal loss in the cross section. Another significant finding was that if fracture initiation is ductile, the failure stress is insensitive to actual (dynamic) toughness as measured by Charpy impact energy, although the toughness level does influence propagation of the fracture. This research had as its objective the development of guidelines for assessing the serviceability of circumferentially oriented corrosion defects found within the girth weld zone. The results of this program were: (1) a database (314 experiments) on the failure stress of circumferential defects in pipe; (2) analysis of 24 methodologies for calculating the failure stress of circumferential defects, and (3) a recommended procedure for addressing circumferentially oriented metal loss corrosion in the girth weld zone. The recommended procedure relates the linear parameters of the corroded area, material strength properties, the possible presence of other flaws in the girth weld and the operating stresses to a pass/fail criterion.
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THE CRACK DETECTION METHOD OF LONGITUDINAL RIB BUTT WELD OF STEEL BRIDGE BASED ON ULTRASONIC LAMB WAVE. The Hong Kong Institute of Steel Construction, agosto 2022. http://dx.doi.org/10.18057/icass2020.p.265.
Abstract (sommario):
Ultrasonic Lamb wave is an efficient and fast new nondestructive testing technology. Due to its characteristics of wide detection range, high efficiency and strong defect identification ability, ultrasonic Lamb wave has developed rapidly in the field of nondestructive testing in recent years. Meanwhile, the longitudinal rib butt weld is one of the most important failure modes of steel bridge deck, which seriously endangers the safety and durability of long-span steel bridges. In this paper, the fatigue failure mode of longitudinal rib butt weld is considered, the propagation process of ultrasonic guided wave in longitudinal rib butt weld is studied by using finite element real-time simulation, and the influences of different weld and crack parameters on ultrasonic guided wave is analyzed. The results show that the method based on ultrasonic Lamb wave has good applicability to crack detection of longitudinal rib butt weld of steel bridge deck. And this method provides a new idea and method for steel structure damage detection and monitoring.