Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-05-01T14:25:43Z No. of bitstreams: 1 ADALBERTO GOMES TEIXEIRA JÚNIOR - DISSERTAÇÃO PPGCC 2015..pdf: 2611686 bytes, checksum: 6b9c4a2efc3946611ad0263328434bd1 (MD5) / Made available in DSpace on 2018-05-01T14:25:43Z (GMT). No. of bitstreams: 1 ADALBERTO GOMES TEIXEIRA JÚNIOR - DISSERTAÇÃO PPGCC 2015..pdf: 2611686 bytes, checksum: 6b9c4a2efc3946611ad0263328434bd1 (MD5) Previous issue date: 2015-07 / Capes / O som gerado por motores em funcionamento contém informações sobre seu estado e condições, tornando-se uma fonte importante para a avaliação de seu funcionamento sem a necessidade de intervenção no equipamento. A análise do estado do equipamento muitas vezes é realizada por diagnóstico humano, a partir da experiência vivenciada no ambiente ruidoso de operação. Como o funcionamento dos motores é regido por um processo periódico, o sinal de áudio gerado segue um padrão bem definido, possibilitando, assim, a avaliação de seu estado de funcionamento por meio desse sinal. Dentro deste contexto, a pesquisa ora descrita trata da modelagem do sinal acústico gerado por motores em usinas termoelétricas, aplicando técnicas de processamento digital de sinais e inteligência artificial, com o intuito de auxiliar o diagnóstico de falhas, minimizando a presença humana no ambiente de uma sala de motores. A técnica utilizada baseia-se no estudo do funcionamento dos equipamentos e dos sinais acústicos por eles gerados por esses, para a extração de características representativas do sinal, em diferentes domínios, combinadas a métodos de aprendizagem de máquinas para a construção de um multiclassificador, responsável pela avaliação do estado de funcionamento desses motores. Para a avaliação da eficácia do método proposto, foram utilizados sinais extraídos de motores da Usina Termoelétrica Borborema Energética S.A., no âmbito do projeto REPARAI (REPair over AiR using Artificial Intelligence, código ANEEL PD6471-0002/2012). Ao final do estudo, o método proposto demonstrou acurácia próxima a 100%. A abordagem proposta caracterizou-se, portanto, como eficiente para o diagnóstico de falhas, principalmente por não ser um método invasivo, não exigindo, portanto, o contato direto do avaliador humano com o motor em funcionamento. / The sound generated by an engine during operation contains information about its conditions, becoming an important source of information to evaluate its status without requiring intervention in equipment. The fault diagnosis of the engine usually is performed by a human, based on his experience in a noisy environment. As the operation of the engine is a periodic procedure, the generated signal follows a well-defined pattern, allowing the evaluation of its operating conditions. On this context, this research deals with modeling the acoustic signal generated by engines in power plants, using techniques from digital signal processing and artificial intelligence, with the purpose of assisting the fault diagnosis, minimizing the human presence at the engine room. The technique applied is based on the study of engines operation and the acoustic signal generated by them, extracting signal representative characteristics in different domains, combined with machine learning methods, to build a multiclassifier to evaluate the engines status. Signals extracted from engines of Borborema Energética S.A. power plant, during the REPARAI Project (REPair over AiR using Artificial Intelligence), ANEEL PD-6471-0002/2012, were used in the experiments. In this research, the method proposed has demonstrated an accuracy rate of nearly 100%. The approach has proved itself to be efficient to fault diagnosis, mainly by not being an invasive method and not requiring human direct contact with the engine.

Les matériaux de construction par excellence que sont les matériaux à base cimentaire offrent une faible résistance à la traction ainsi qu’une faible capacité de déformation. Ils sont fragiles et particulièrement sensible à la fissuration, notamment la fissuration due au retrait dans le cas d’éléments à grande surface. Des joints de retrait judicieusement espacés permettent de localiser la fissuration et d’éviter le désordre apparent. Malheureusement, ils constituent aussi le point de départ de futurs désordres (pénétration d’agents agressifs, tuilage, etc.). Cette thèse est une contribution au développement d’un nouveau composite cimentaire présentant une capacité de déformation améliorée. Dans cet objectif, des granulats en caoutchouc (G.C.) issus du broyage de pneus usagés ont été utilisés en remplacement partiel du sable. Les résultats obtenus montrent que la présence de ces granulats est préjudiciable vis-à-vis de la rhéologie du matériau à l’état frais mais que l’utilisation d’un superplastifiant et d’un agent de viscosité permet de réaliser les corrections nécessaires. A l’état durci, une chute de la résistance mécanique et du module d’élasticité est observée, en contrepartie la capacité de déformation au stade de la localisation de la macrofissuration est significativement augmentée. Des essais dédiés permettent de démontrer que cette incorporation de G.C. permet de réduire la sensibilité à la fissuration de retrait avec un intérêt évident pour les applications à grande surface comme les chaussées et dallages sur terre-plein. L’influence de la présence de ces G.C. sur la cinétique de la fissuration a été analysée et confirmée par le biais d’une variable d’endommagement et par l’activité (émission) acoustique accompagnant le processus de fissuration.Le potentiel du composite dans les applications à grande surface comme les chaussées en béton a aussi été abordé par le biais de l’indice de qualité élastique qui a confirmé les promesses attendues. Compte tenu du rôle joué par le module d’élasticité du composite sur ces nouvelles propriétés et les applications potentielles, les outils prédictifs de ce module en fonction du dosage en G.C. présentent un intérêt pratique évident. Dans ce sens, cette thèse a permis de tester la pertinence de quelques modèles analytiques. Dans ce cadre, la borne inférieure de Hashin-Shtrikman qui reste perfectible s’est avérée la mieux indiquée.A côté de l’intérêt en termes d’application matériau Génie Civil, l’incorporation de G.C. constitue une voie de valorisation de pneus usagés non réutilisables et une contribution à la protection de l’environnement / Cement-based materials exhibit low tensile strength and poor strain capacity. They are brittle and are very sensitive to cracking particularly to shrinkage cracking in large area applications. Sawn joints allow shrinkage cracking to be localised a way to avoid unsightly cracking. Unfortunately they are also the starting point of future distress (ingress of aggressive agent, curling, etc.).This work is a contribution to the design of a cement-based material exhibiting an enhanced strain capacity. For a such objective rubber aggregates (RAs) obtained from grinding end of life tyres partly replacing natural sand have been used.Results showed that RAs are detrimental to the properties of the fresh materials (workability and segregation). However the use of optimized content of a superplasticiser and of a viscosity agent allows the required behaviour to be achieved.With regard to harden state, RAs reduce the strength and the modulus of elasticity of the composite but the strain capacity corresponding to the macrocracking formation is significantly improved. Specific tests showed that RAs reduced the propensity of the material for shrinkage cracking, offering an interest for large surface area such as pavements.Analysis by a scalar damage variable and by acoustic emission is in a good agreement with expected effect of RAs on the cracking kinetics and on the mechanical behaviour of the composite.The interest of the rubberized concrete in large area application such as concrete pavements has been studied and confirmed through the Elastic Quality Index. Given the major role of the modulus of elasticity of the composite on the new properties and expected applications, tools aimed to predict this modulus of elasticity as a function of RAs content are of practical benefit. With this purpose, the work allowed the relevance of some analytical models to be tested. In this context, the lower Hashin-Shtrikman bound which remains perfectible proved to be the most appropriate.Finally, apart from application of civil engineering material, the use of RAs from grinding end of life tyres is a solution of recovery of an industrial by-product and a contribution to a clean environment

Cette thèse porte sur l’étude du comportement mécanique et vibratoire d’un composite biosourcé incorporant un matériau viscoélastique. Les matériaux étudiés sont des stratifiés en composite lin/greenpoxy et des stratifiés viscoélastiques composés d'un noyau viscoélastique en caoutchouc naturel confiné entre deux composites. La première partie du travail a été consacrée à l’étude de l’influence de l’intégration de la couche viscoélastique sur le comportement mécanique des composites. L’analyse des résultats expérimentaux et l’observation des signaux d’émission acoustique obtenus dans ces composites soumis à différentes sollicitations mécaniques en statique et en fatigue ont permis d’identifier les signatures acoustiques des mécanismes d’endommagement prépondérants dans les deux matériaux. Dans un deuxième temps, les propriétés dynamiques de ces composites ont été déterminées à partir des essais de vibration. Les résultats obtenus ont montré que la couche viscoélastique a joué un rôle majeur dans l'amortissement et la dissipation d'énergie des composites. Suite à cette analyse, nous avons mis en place une procédure, utilisant la méthode des éléments finis, pour calculer l’amortissement de ces matériaux. Dans le but de mettre en évidence l’influence des caractéristiques de la couche viscoélastique, une étude paramétrique a été menée sur le composite viscoélastique, permettant d’optimiser l’amortissement de ce matériau en faisant varier divers paramètres. Enfin, le comportement visqueux des composites a été caractérisé par la méthode de résonance non linéaire en faisant varier l’amplitude d’excitation. / This thesis focuses on the study of the mechanical and vibration behaviour of a flax fibre reinforced composites with and without an interleaved natural viscoelastic layer. The composite materials have been characterized experimentally using different mechanical and vibrational tests. First, both types of composites were studied using uni-axial tensile and three-points bending tests. Acoustic emission (AE) has been often used for the identification and characterization of micro failure mechanisms in composites. The results showed that these composites have very high specific characteristics. It can be used for applications currently using composites reinforced with synthetic fibres such glass, carbon…. Next, experimental and finite element vibration analyses were carried out on the composites with and without an interleaved natural viscoelastic layer. A good agreement between the two methods was obtained. It has been shown that the viscoelastic layer plays a major role in damping because it has a high level of energy dissipation. Therefore, it improves with a significant way the modal properties of the composite. Finally, nonlinear resonance tests were performed on the composites. It has been shown that the viscoelastic layer generates a nonlinear behaviour in the material. The linear and nonlinear, elastic and dissipative parameters have been calculated to deduce finally that nonlinear parameters are more sensitive to heterogeneities than those derived from linear vibration tests.

Em nível microscópico, as rochas apresentam microdefeitos que agem como concentradores locais de tensão, favorecendo a ocorrência de ruptura frágil. O entendimento desse processo requer análises experimentais em rochas submetidas a tensões de tração. O ensaio de compressão diametral é uma alternativa apropriada, pois não apresenta as dificuldades envolvidas no ensaio de tração direta. A propagação de microfissuramento em materiais frágeis produz liberação de energia na forma de ondas elásticas chamadas de emissões acústicas (EA). O monitoramento com EA permite acompanhar a propagação de dano no corpo de prova (CP), sem perturbá-lo. Nesta pesquisa, CPs de mármore e monzogranito são submetidos a ensaios de compressão diametral com deslocamentos monotônicos e cíclicos, com controle de deslocamento. Aplica-se a técnica de EA, em conjunto com análises petrográficas, análises das curvas de força versus deslocamento e exame visual, para caracterizar o seu processo de microfissuramento. A localização tridimensional das fontes de EA foi realizada inicialmente utilizando-se o software AEwin® da PASA. Foi desenvolvido um programa de localização aprimorado que incorpora o cálculo da velocidade de propagação das ondas (vp) média para cada instante em que uma fonte é localizada. O novo programa (Crack Location by Acoustic emission with P Wave Velocity determination, CLAPWaVe) mostra um claro decréscimo da velocidade de propagação com o aumento do dano. O programa desenvolvido (CLAPWaVe) mostrou melhor ajuste e maior coerência com a literatura e com a condição final rompida dos CPs do que o software AEwin. Em mármore e monzogranito o microfissuramento se inicia a 25-30% e 75-85% do carregamento de pico, respectivamente, e localiza-se na vizinhança do centro do CP. Em ambas as rochas se acumulou, também, dano na região dos apoios do CP, associado à transferência de carregamento do berço ao CP. Antes do pico de carregamento, o microfissuramento tornou-se mais denso e localizado no centro e nos apoios do CP, embora a região central ainda concentre a maior parte. Após o pico, o microfissuramento acumulou-se em uma das faces do CP, progredindo até a outra face. O monzogranito apresentou ruptura progressiva do CP, enquanto que no mármore a maior parte da superfície de ruptura já está desenvolvida imediatamente após o pico. Durante o ensaio em ambas as rochas, no núcleo central foram registradas as menores velocidades vp do CP. Na região dos apoios, embora tenha havido microfissuramento, registraram-se as maiores velocidades vp no CP, pois o confinamento produzido pelo contato com o berço aumentou localmente a rigidez do CP. A distribuição não homogênea de vp no CP revelou que a consideração desse parâmetro como constante e igual à condição intacta ao longo do ensaio, como comumente encontrado na literatura, não representa a condição real do CP danificado. O microfissuramento no monzogranito se propaga principalmente através dos cristais de quartzo, seguindo um caminho tortuoso subparalelo à direção de carregamento e liberando altos níveis de energia absoluta. No mármore, a propagação segue os planos de clivagem da calcita, liberando níveis baixos de energia absoluta. Os histogramas da distribuição espacial da resistência em ambas as rochas mostraram bom ajuste a uma distribuição de Weibull, porém o monzogranito mostrou melhor ajuste e menor variabilidade que o mármore. As análises dos sinais no domínio das frequências mostraram que o microfissuramento é caracterizado por emissões de banda larga. / At microscopic level, rocks exhibit microflaws, which act as local stress concentrators, favoring the occurrence of brittle failure. The understanding of this process requires experimental analyses of rock specimens under tensile stresses. The diametral compression test is an adequate alternative for such a studies, because it does not present the difficulties of direct tension tests. Crack propagation in brittle materials releases energy as transient elastic waves known as acoustic emission (AE). Monitoring with AE enables an insight into the cracking process without affecting the integrity of the sample. In this work, marble and monzogranite specimens were subjected to monotonic and cyclic displacementcontrolled diametral compression tests. The AE monitoring technique was applied in conjunction with petrographic analyses, interpretation of the load versus displacement curves and visual examination of the samples for the characterization of their cracking process. The three-dimensional localization of the AE sources was initially carried out by using the software AEwin® from PASA. An improved localization software, which considers the P-wave velocity variation along the damage process (vp) for each AE source was developed. The developed software (Crack Location by Acoustic emission with P Wave Velocity determination, CLAPWaVe) has shown greater consistency with literature and the final cracked samples and better accuracy than AEwin. Microcracking in monzogranite and marble initiated at 25-30% and 75-80% of the peak load, respectively, and is located at the center of the specimen. In addition, both rocks showed concentrated microcracking close to the region of contact between the specimen and the loading platens, related to the loading transference along the loading edge. Before peak load, microcracking becomes denser and localized at the center and the contact region of the specimen, although, the central region still concentrates the main portion of the damage. After the peak load, new microcracks were first concentrated on one of the faces at the center of the specimen and then propagated through its thickness all the way to the other face. The progressive failure in monzogranite extended through to the end of the test, while in marble the main portion of the failure surface of the specimen developed just after peak. During the whole test in both rocks, the lowest velocities (vp) of the specimen were recorded in the central core. Although microcracking was induced at the contact region, the highest velocities vp of the specimen were registered there, because of the confinement effect produced by the platens, which lead to a local increase in the stiffness of the specimen. The non-homogeneous distribution of vp in the specimen has revealed that the utilization of this parameter as a constant and equal to the value measured in the specimen before testing (as usually adopted in the literature), does not represent the real condition of the damaged specimen. In monzogranite, microcracks propagate mainly through quartz crystals, following a tortuous path subparallel to the loading direction, by releasing high-level of absolute energy, while in marble the propagation of microcracks follows the cleavage planes of calcite, by releasing low-level of absolute energy. The histograms of spatial strength distribution in both rocks have shown good adjustment to a Weibull distribution, but monzogranite exhibited a more accurate adjustment with lower variability than marble. The analysis of signals in the frequency domain showed that the microcracking is characterized by wide band emissions.

Orientador: Stelamaris Rolla Bertoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-05T23:46:28Z (GMT). No. of bitstreams: 1 Santos_Christiandos_M.pdf: 3511506 bytes, checksum: d365f6dc71d5566b93533834923018e0 (MD5) Previous issue date: 2004 / Resumo: A existência de fenômenos acústicos depende de três fatores: a fonte, o meio e o receptor. Para a prevenção de condições ruidosas em certos ambientes, é necessário o conhecimento de uma característica própria da fonte que não sofre interferência do meio na propagação da energia sonora, como é o caso da potência sonora. O IBAMA em conjunto com o INMETRO iniciou um programa que visa informar e minimizar o ruído (nível de potência sonora) produzido por aparelhos elétricos etiquetando-os. Este programa se chama Selo Ruído. Existe uma previsão de inclusão de ferramentas elétricas neste programa de etiquetagem. A furadeira elétrica é uma destas ferramentas que tem inclusão prevista. Com o intuito de investigar os métodos de ensaio para determinação de potência sonora, este trabalho propõe a realização de ensaios de diversos métodos normalizados de determinação de nível de potencia sonora aplicando-os para furadeiras elétricas. Os métodos escolhidos para os ensaios foram os que utilizam salas reverberantes especiais (ISO 3743 ¿ Engineering Methods for Special Reverberations test Rooms e ISO 3741 ¿ Precision Methods for Special Reverberations test Rooms). Estes métodos são referenciados na norma nacional NBR 13910:1997-Parte 1- Diretrizes de ensaios para a determinação de ruído acústico de aparelhos eletrodomésticos e similares. Com os resultados obtidos dos ensaios realizados, foi feita uma análise de qualificação das metodologias empregadas. A partir de cada item destas metodologias foi analisada a aplicabilidade destes itens a ser empregado no método de ensaio proposto. A construção das etapas do método foi obtida a partir dos itens qualificados e aplicáveis ao programa de etiquetagem Selo Ruído / Abstract: In the acoustic phenomena there are three main variables: the source, the medium and the receptor. For the prevention of noise conditions in certain places, it is necessary to know a source characteristic that does not change with medium variations. This characteristic is the sound power radiated by the source. To consider this prevention, IBAMA and INMETRO started a program that labels the household appliances according to the noise level emitted by them. This program is called ¿Selo Ruído¿. There is a prevision to include the electric tools in this label program. The drill is one of these electric tools that will be included. To investigate the methods for determination of the sound power levels, this work proposes some tests of drills in several standarded methods. The methods used for the tests were the ones that use reverberation rooms (ISO 3743 ¿ Engineering Methods for Special Reverberations test Rooms and ISO 3741 ¿ Precision Methods for Special Reverberations test Rooms). These methods are referenced at the Brazilian standard NBR 13910:1997 ¿ Part 1 ¿ ¿Diretrizes de ensaios para a determinação de ruído acústico de aparelhos eletrodomésticos e similares¿. A qualification analysis of the methodologies applied was done, based on the tests results. An application of these items was done from each item of these methodologies in the test method proposed. The construction of the steps in the proposed method was made from the items qualified and applied to the ¿Selo Ruído¿ program / Mestrado / Edificações / Mestre em Engenharia Civil

Ce travail de thèse décrit l’application de méthodes d’analyse innovantes à la caractérisation des propriétésmécaniques et électriques de matériaux composites.Le Chapitre premier dresse un état de l’art des fondamentaux théoriques et pré requis nécessaires à lacompréhension du manuscrit. Un regard critique permet de dégager une stratégie pour l’analyse, basée d’une partsur des méthodes holographiques numériques et d’autre part sur des techniques de mesure diélectrique.Le Chapitre second est dédié au choix de la méthode d’holographie numérique. En particulier, la configurationimage montre quelques particularités qui sont analysées en détail : le rôle du diaphragme d'ouverture du systèmed'imagerie. Nous concluons que la méthode d’holographie de Fresnel présente des avantages d’achromatismepour les applications avec plusieurs longueurs d’onde.Le 3ème Chapitre présente deux applications de l’holographie numérique au contrôle de structures compositesincorporées avec des pastilles piézoélectriques dédiées à l’émission acoustique. Nous avons démontré en premiertemps, la possibilité d’analyser par holographie numérique de Fresnel en temps moyenné le comportementvibratoire des poutres composites excitées harmoniquement. Dans un second temps, on a montré que les pastillesutilisées influencent le comportement mécanique des matériaux en régime statique.Le Chapitre 4 présente l’analyse expérimentale et numérique des structures composites soumises à un essai decisaillement en flexion trois points rapprochés. Nous présentons les résultats obtenus pour des applications à deséchantillons lin/époxy et lin/carbone/époxy.Le 5ème Chapitre aborde l’analyse des propriétés diélectriques des composites renforcés par fibres de lin. Deuxtechniques expérimentales sont mises en oeuvre : la calorimétrie différentielle à balayage (DSC) et l’impédancemètre de type Novocontrol. Nous concluons que les fibres de lin seules dans le composite sont moinshydrophiles que celles incorporées avec des fibres de carbone, ce qui explique la meilleure adhérencefibres/matrice dans le premier cas. / This PhD thesis describes the application of innovative analytical methods for the characterization of mechanicaland electrical properties of composite materials.The first chapter provides a state of the art of theoretical fundamentals and prerequisites needed to understandthe manuscript. A critical survey leads to a strategy for the analysis, based partly on digital holographic methodsand dielectric techniques.The second chapter is devoted to the choice of method of digital holography. In particular, this configurationshows some features that are analyzed in detail: the role of the aperture stop of the imaging system. We concludethat the Fresnel holography method has the advantage of achromatism for applications with multiplewavelengths.The third chapter presents two applications of digital holography control of composite structures with embeddedpiezoelectric patches dedicated to acoustic emission. We first demonstrate the possibility of analyzing thevibration behavior of composite beams using time averaged digital holography. Then, it was shown that thepellets used influence the mechanical behavior of materials under static conditions.Chapter 4 presents the experimental and numerical analysis of composite structures subjected to a shear test inclose three-point bending. We present the results obtained for samples with linen / flax and epoxy / carbon /epoxy.The last chapter deals with the analysis of the dielectric properties of composites reinforced with flax fibersstudied in the preceding chapter. We conclude that the flax fibers incorporated in the composite are lesshydrophilic than those incorporated with carbon fibers, which explains the improved adhesion fiber / matrix inthe first case.

Concrete, which was hitherto considered as a brittle material, has shown much better softening behavior after the post peak load than anticipated. This behavior of concrete did put the researchers in a quandary, whether to categorize concrete under brittle materials or not. Consequently concrete has been called a quasi-brittle material. Fracture mechanics concepts like Linear elastic fracture mechanics (LEFM) and Plastic limit analysis applicable to both brittle and ductile materials have been applied to concrete to characterize the fracture behavior. Because of quasi-brittle nature of concrete, which lies between ductile and brittle response and due to the presence of process zone ahead of crack/notch tip instead of a plastic zone, it is found that non-linear fracture mechanics (NLFM) principles are more suitable than linear elastic fracture mechanics (LEFM) principles to characterize fracture behavior. Fracture energy, fracture process zone (FPZ) size and the behavior of concrete during fracture process are the fracture characteristics, which are at the forefront of research on concrete fracture. Another important output from the research on concrete fracture has been the size effect. Numerous investigations, through mathematical modeling and experiments, have been carried out and reported in literature on the effect of size on the strength of concrete and fracture energy. Identification of the sources of size effect is of prime importance to arrive at a clear analytical model, which gives a comprehensive insight into the size effect. With the support of an unambiguous theory, it is possible to incorporate the size effects into codes of practices of concrete design. However, the theories put forth to describe the size effect do not seem to follow acceptable regression. After introduction in Chapter-1 and literature survey in Chapter-2, Chapter-3 details the study on size effect through three point bend (TPB) tests on 3D geometrically similar specimens. Fracture behavior of beams with smaller process zone size in relation to ligament dimension approaches LEFM. The fracture energy obtained from such beams is said to be size independent. In the current work Size effect law (Bazant et al. 1987) is used on beams geometrically similar in three dimensions with the depth of the largest beam being equal to 750mm, and size independent fracture energy G Bf is obtained. In literature very few results are available on the results obtained from testing geometrically similar beams in three dimensions and with such large depth. In the current thesis the results from size effect tests yielded average fracture energy of 232 N/m. Generally the fracture energies obtained from 2D-geometrically similar specimens are in the range of 60-70 N/m as could be seen in literature. From 3D-geometrically similar specimens, the fracture energies are higher. The reason is increased peak load, could be due to increased width. The RILEM fracture energy Gf , determined from TPB tests, is said to be size dependent. The assumption made in the work of fracture is that the total strain energy is utilized for the fracture of the specimen. The fracture energy is proportional to the size of the FPZ, it also implies that FPZ size increases with increase in (W−a) of beam. This also means that FPZ is proportional to the depth W for a given notch to depth ratio, because for a given notch/depth, (W−a) which is also W(1 − a ) is proportional to W`because (1 − a ) is a constant. WWThis corroborates the fact that fracture energy increases with size. Interestingly, the same conclusion has been drawn by Abdalla & Karihaloo (2006). They have plotted a curve relating fracture process zone length and overall depth the beam. In the present study a new method namely Fracture energy release rate method is suggested. In the new method the plot of Gf / (W−a) versus (W−a) is obtained from a set of experimental results. The plot is found to follow power law and showed almost constant value of Gf / (W−a) at larger ligament lengths. This means that fracture energy reaches a constant value at large ligament lengths reaffirming that the fracture energy from very large specimen is size independent. The new method is verified for the data from literature and is found to give consistent results. In a quasi-brittle material such as concrete, a fracture process zone forms ahead of a pre-existing crack (notch) tip before the crack propagates from the tip. The process zone contains a scatter of micro-cracks, which coalesce into one or more macro-cracks, which eventually lead to fracture. These micro-cracks and macro-cracks release stresses in the form of acoustic waves having different amplitudes. Each micro or macro crack formation is called an acoustic emission (AE) event. Through AE technique it is possible to locate the positions of AE events. The zone containing these AE events is termed the fracture process zone (FPZ). In Chapter-4, a study on the evolution of fracture process zone is made using AE technique. In the AE study, the fracture process zone is seen as a region with a lot of acoustic emission event locations. Instead of the amplitudes of the events, the absolute AE energy is used to quantify the size of the process zone at various loading stages. It has been shown that the continuous activities during the evolution of fracture process zone correspond to the formation of FPZ, the size of which is quantified based on the density of AE events and AE energy. The total AE energy released in the zone is found to be about 78% of the total AE energy released and this is viewed as possible FPZ. The result reasonably supports the conclusion, from Otsuka and Date (2000) who tested compact tension specimens, that zone over which AE energy is released is about 95% can be regarded as the fracture process zone. As pointed out earlier, among the fracture characteristics, the determination of fracture energy, which is size independent, is the main concern of research fraternity. Kai Duan et al. (2003) have assumed a bi-linear variation of local fracture energy in the boundary effect model (BEM) to showcase the size effect due to proximity of FPZ to the specimen back boundary. In fact the local fracture energy is shown to be constant away from boundary and reducing while approaching the specimen back boundary. The constant local fracture energy is quantified as size independent fracture energy. A relationship between Gf , size independent fracture energy GF , un-cracked ligament length and transition ligament length was developed in the form of equations. In the proposed method the transition ligament length al is taken from the plot of histograms of energy of AE events plotted over the un-cracked ligament. The value of GF is calculated by solving these over-determined equations using the RILEM fracture energies obtained from TPB tests. In chapter-5 a new method involving BEM and AE techniques is presented. The histogram of energy of AE events along the un-cracked ligament, which incidentally matches in pattern with the local fracture energy distribution, assumed by Kai Duan et al. (2003), along the un-cracked ligament, is used to obtain the value of GF , of course using the same equations from BEM developed by Kai Duan et al. (2003). A critical observation of the histogram of energy of AE events, described in the previous chapter, showed a declining trend of AE event pattern towards the notch tip also in addition to the one towards the specimen back boundary. The pattern of AE energy distribution suggests a tri-linear rather than bi-linear local fracture energy distribution over un-cracked ligament as given in BEM. Accordingly in Chapter-6, GF is obtained from a tri-linear model, which is an improved bi-linear hybrid model, after developing expressions relating Gf , GF , (W−a) with two transition ligament lengths al and blon both sides. The values of Gf , and GF from both bi-linear hybrid method and tri-linear method are tabulated and compared. In addition to GF , the length of FPZ is estimated from the tri-linear model and compared with the values obtained from softening beam model (SBM) by Ananthan et al. (1990). There seems to be a good agreement between the results. A comparative study of size independent fracture energies obtained from the methods described in the previous chapters is made. The fracture process in concrete is another interesting topic for research. Due to heterogeneity, the fracture process is a blend of complex activities. AE technique serves as an effective tool to qualitatively describe the fracture process through a damage parameter called b-value. In the Gutenberg-Richter empirical relationship log 10N=a−bM, the constant ‘b’ is called the b-value and is the log linear slope of frequency-magnitude distribution. Fault rupture inside earth’s crust and failure process in concrete are analogous. The b-value, is calculated conventionally till now, based on amplitude of AE data from concrete specimens, and is used to describe the damage process. Further, sampling size of event group is found to influence the calculated b-value from the conventional method, as pointed out by Colombo et al. (2003). Hence standardization of event group size, used in the statistical analysis while calculating b-value, should be based on some logical assumption, to bring consistency into analytical study on b-value. In Chapter-7, a methodology has been suggested to determine the b-value from AE energy and its utilization to quantify fracture process zone length. The event group is chosen based on clusters of energy or quanta as named in the thesis. Quanta conform to the damage stages and justify well their use in the determination of the b-value, apparently a damage parameter and also FPZ length. The results obtained on the basis of quanta agree well with the earlier results.

Aerospace structures comprising of metals and composites are exposed to extreme loading and environmental conditions which necessitates regular inspection and maintenance to verify and monitor overall structural integrity. The timely and accurate detection, characterization and monitoring of structural cracking, corrosion, delaminating, material degradation and other types of damage are of major concern in the operational environment. Along with these, stringent requirements of safety and operational reliability have lead to evolutionary methods for evaluation of structural integrity. As a result, conventional nondestructive evaluation methods have moved towards a new concept, Structural Health Monitoring (SHM). SHM provides in-situ information a bout the occurrence of damage if any, location and severity of damage and residual life of the structure and also helps in improving the safety, reliability and confidence levels of critical engineering structures. While the concepts underlying SHM are well understood, development of methods is still in a nascent stage which requires extensive research that is challenging and has been the main motivating factor for undertaking the work reported in the thesis. Under the scope of the investigations carried out in this thesis, an integrated approach using Ultrasonic (active) and Acoustic Emission (passive) methods has been explored for SHM of metallic and composite plate structures using a distributed array of surface bonded circular piezoelectric wafer active sensors(PWAS). In ultrasonic method, PWAS is used for actuation and reception of Lamb waves in plate structures. The damage detection is based on the interaction of waves with defects resulting in reflection, mode conversion and scattering. In acoustic emission (AE) technique, the same sensor is used to pick up the stress waves generated by initiation or growth of defects or damage. Thus, both the active and passive damage detection methods are used in this work for detection, location and characterization of defects and damage in metallic and composite plates with complex geometries and structural discontinuities. And, thus the strategy adopted is to use time-frequency analysis and time reversal technique to extract the information from Lamb wave signals for damage detection and a geodesic based Lamb wave approach for location of the damage in the structure. To start with experiments were conducted on aluminum plates to study the interaction of Lamb waves with cracks oriented at different angles and on a titanium turbine blade of complex geometry with a fine surface crack. Further, the interaction of Lamb wave modes with multiple layer delaminations in glass fiber epoxy composite laminates was studied. The data acquired from these experiments yielded complex sets of signals which were not easily discern able for obtaining the information required regarding the defects and damage. So, to obtain a basic understanding of the wave patterns, Spectral finite element method has been employed for simulation of wave propagation in composite beams with damages like delamination and material degradation. Following this, time-frequency analysis of a number of simulated and experimental signals due to elastic wave scattering from defects and damage were performed using wavelet transform (WT) and Hilbert-Huang transform(HHT).And, a comparison of their performances in the context of quantifying the damages has given detailed insight into the problem of identifying localized damages, dispersion of multi-frequency non-stationary signals after their interaction with different types of defects and damage, finally leading to quantification. Conventional Lamb wave based damage detection methods look for the presence of defects and damage in a structure by comparing the signal obtained with the baseline signal acquired under healthy conditions. The environmental conditions like change in temperature can alter the Lamb wave signals and when compared with baseline signals may lead to false damage prediction. So, in order to make Lamb wave based damage detection baseline free, in the present work, the time reversal technique has been utilized. And, experiments were conducted on metallic and composite plates to study the time reversal behavior ofA0 andS0Lamb wave modes. Damage in the form of a notch was introduced in an aluminum plate to study the changes in the characteristics of the time reversed Lamb wave modes experimentally. This experimental study showed that there is no change in the shape of the time reversed Lamb wave in the presence of defect implying no breakage of time reversibility. Time reversal experiments were further carried out on a carbon/epoxy composite T-pull specimen representing a typical structure. And, the specimen was subjected to a tensile loading in a Universal testing machine. PWAS sensor measurements were carried out at no load as also during different stages of delamination due to tensile loading. Application of time reversed A 0 and S0 modes for both healthy and delaminated specimens and studying the change in shape of the time reversed Lamb wave signals has resulted in successful detection of the presence of delamination. The aim of this study has been to show the effectiveness of Lamb wave time reversal technique for damage detection in health monitoring applications. The next step in SHM is to identify the damage location after the confirmation of presence of damage in the structure. Wave based acoustic damage detection methods (UT and AE) employing triangulation technique are not suitable for locating damage in a structure which has complicated geometry and contains structural discontinuities. And, the problem further gets compounded if the material of the structure is anisotropic warranting complex analytical velocity models. In this work, a novel geodesic approach using Lamb waves is proposed to locate the AE source/damage in plate like structures. The approach is based on the fact that the wave takes minimum energy path to travel from the source to any other point in the connected domain. The geodesics are computed numerically on the meshed surface of the structure using Dijkstra’s algorithm. By propagating the waves in reverse virtually from these sensors along the geodesic path and by locating the first inter section point of these waves, one can get the AE source/damage location. Experiments have been conducted on metallic and composite plate specimens of simple and complex geometry to validate this approach. And, the results obtained using this approach has demonstrated the advantages for a practicable source location solution with arbitrary surfaces containing finite discontinuities. The drawback of Dijkstra’s algorithm is that the geodesics are allowed to travel along the edges of the triangular mesh and not inside them. To overcome this limitation, the simpler Dijkstra’s algorithm has been replaced by a Fast Marching Method (FMM) which allows geodesic path to travel inside the triangular domain. The results obtained using FMM showed that one can accurately compute the geodesic path taken by the elastic waves in composite plates from the AE source/damage to the sensor array, thus obtaining a more accurate damage location. Finally, a new triangulation technique based on geodesic concept is proposed to locate damage in metallic and composite plates. The performances of triangulaton technique are then compared with the geodesic approach in terms of damage location results and their suitability to health monitoring applications is studied.

Une option à l'étude pour le recyclage des actinides mineurs consiste à en incorporer environ 10% à une matrice d'UO2. La présence de pores ouverts interconnectés au sein de ce combustible devrait permettre d'évacuer l'hélium et les gaz de fission pour prévenir le gonflement de la pastille et in fine son interaction avec la gaine qui l'entoure. La mise en oeuvre des actinides mineurs oblige à travailler en cellule blindée, à minimiser leur rétention et à proscrire les ajouts de produits organiques. L'emploi de particules fragmentables de quelques centaines de micromètres paraît une solution intéressante pour contrôler la microstructure des comprimés crus et ainsi maîtriser la porosité ouverte après frittage. L'étude consiste à suivre par émission acoustique la compaction de particules fragiles d'UO2 et à relier leurs caractéristiques à la porosité ouverte obtenue après frittage des compacts. Le signal acquis lors d'essais de cisaillement sur des granulés individuels et sur des compacts montre que l'émission acoustique autorise la détection de la fragmentation et permet l'identification d'une forme d'onde caractéristique. Les influences de la contrainte de compaction, de la distribution granulométrique initiale et de la cohésion interne des granulés, sur la tenue mécanique des compacts et sur la microstructure des frittés, en particulier sur la porosité ouverte sont analysées. Moyennant quelques précautions, l'émission acoustique, par sa capacité à déterminer le domaine de fragmentation des granulés pendant la mise en forme, paraît une technique prometteuse pour suivre la compaction de particules fragiles en vue de la fabrication de combustibles à porosité maîtrisée. / One of the options considered for recycling minor actinides is to incorporate about 10% to UO2 matrix. The presence of open pores interconnected within this fuel should allow the evacuation of helium and fission gases to prevent swelling of the pellet and ultimately its interaction with the fuel clad surrounding it.Implementation of minor actinides requires working in shielded cell, reducing their retention and outlawing additions of organic products. The use of fragmentable particles of several hundred micrometers seems a good solution to control the microstructure of the green compacts and thus control the open porosity after sintering.The goal of this study is to monitor the compaction of brittle UO2 particles by acoustic emission and to link the particle characteristics to the open porosity obtained after the compact sintering.The signals acquired during tensile strength tests on individual granules and compacts show that the acoustic emission allows the detection of the mechanism of fragmentation and enables identification of a characteristic waveform of this fragmentation.The influences of compaction stress, of the initial particle size distribution and of the internal cohesion of the granules, on the mechanical strength of the compact and on the microstructure and open porosity of the sintered pellets, are analyzed.By its ability to identify the range of fragmentation of the granules during compaction, acoustic emission appears as a promising technique for monitoring the compaction of brittle particles in the manufacture of a controlled porosity fuel.

This paper discusses the possible use of Hilbert-Huang transform to analyze the data obtained from physical experiments. Specifically for the analysis of acoustic emission in the form of acoustic shock. The introductory section explains the concept of acoustic emission and its detection process. Subsequently are discussed methods for signal analysis in time-frequency domain. Specifically, short-term Fourier transform, Wavelet transform, Hilbert transform and Hilbert-Huang transform. The final part contains the proposed method for measuring the performance and accuracy of different approaches.