This project aims to characterise the fatigue behaviour of a crack propagating in a residual stress field changing from tension to compression in the welded zone of a ferritic pressure vessel steel. The fatigue tests were carried out keeping the applied stress intensity factor range constant to determine the role of residual stresses on fatigue crack growth. The residual stresses prior to crack growth were evaluated by X-ray diffraction. The weight function method was used to infer the expected influence of the residual stress on the crack tip in terms of the residual stress intensity factor. Two metrics were used to quantify the crack driving force local to the fatigue crack. Firstly the stress intensity amplitude expressed in terms of the change in the J-integral between maximum and minimum load and secondly the change in the crack opening displacement COD to estimate closure stress intensity factor. The displacement fields local to a fatigue crack were obtained by Digital Image Correlation (DIC) and then analysed by JMAN, an in-house developed algorithm to extract the J-integral based on finite element method and implemented using MATLAB. The difference between the applied stress intensity factor range and the effective crack driving force at the crack tip was determined in order to understand the interaction between the prior residual stresses and crack closure phenomena. Three different R-ratios were evaluated during the experiment (R=0.1, R=0.3 and R=0.5) in order to quantify the effect of residual stress on crack tip stress intensity and crack opening displacement. R-ratio plays a very important role on the fatigue crack growth rate (FCGR): as R increases, FCGR also increases. The COD was assessed by means of the displacements obtained by DIC local to the crack faces. The COD method turned out to be more insightful than the JMAN method for characterising the crack propagation, this is due to the presence of plasticity in the ligament which breaks the non-linear elastic conditions, causing the path-dependence on the J-integral. The FCGR is influenced to a greater degree by the R-ratio and to a lesser degree by the residual stress effect. There is a direct relationship between R and FCGR: as R increases, FCGR also increases, irrespective of the presence of tensile or compressive residual stresses, with the crack closure showing more tendency to occur at low R (i.e. R=0.1) than at high R (i.e. R=0.5). The relationship between R and the residual stress effects on FCGR is inversely proportional: as R increases, the effect of RS decreases.

Une technique de corrélation d’images numériques (DIC) a été adaptée à l’étuded’échantillons de glace polycristalline colonnaire, afin de caractériser le développementdes hétérogénéités de déformation à une échelle intragranulaire au cours du fluage transitoireen compression. Ces hétérogénéités sont dues à la grande anisotropie viscoplastiquedu cristal de glace (avec un seul plan de glissement facile pour les dislocations), qui estresponsable d’interactions fortes entre les grains voisins lorsque l’échantillon se déforme,et de la mise en place de fortes contraintes internes. L’orientation particulière des plans deglissement et la structure colonnaire des échantillons, sans gradient de microstructure dansl’épaisseur, permet de considérer la déformation plastique essentiellement dans le plan.Les champs de déformation mesurés en surface peuvent donc être considérés en premièreapproximation comme représentatifs de tout le volume de l’échantillon. Les orientationscristallographiques, et désorientations locales à l’échelle intragranulaire, ont également étémesurées avec un analyseur optique de texture, avant et après déformation.De très fortes localisations de la déformation sont mises en évidence par la DIC;les déformations équivalentes locales peuvent atteindre plus de dix fois la valeur macroscopique.La structure des motifs de localisation évolue peu durant le régime de fluagetransitoire et elle est caractérisée par des bandes de localisation qui traversent l’échantillonobliquement, sur des distances allant jusqu’à dix fois la taille des grains. La corrélationentre le facteur de Schmid du plan de glissement d’un grain et sa déformation locale esttrès faible : l’agencement local des grains et les interactions intergranulaires jouent doncun rôle primordial dans la distribution spatiale des déformations. A l’échelle du grain, lesfortes désorientations de réseau ont été associées aux composantes locales du déplacement.On a montré en particulier que les distorsions sous forme de ”bandes en genou” (ou kinkbands) étaient corrélées à un déplacement le long de l’axe c du grain, mesuré par DIC.Les microstructures expérimentales ont été implémentées dans un modèle plein champFFT qui simule le comportement élasto-viscoplastique des polycristaux (code CraFT).Les champs de déformation simulés présentent globalement les mêmes caractéristiquesque les champs expérimentaux. En particulier, la majorité des zones de localisation dela déformation sont bien reproduites, spatialement et en intensité. Cependant, il n’a pasété possible de reproduire le comportement macroscopique des échantillons à la décharge.La déformation retardée effective est d’un ordre de grandeur inférieure à celle mesuréeexpérimentalement. Il est probable que cette limitation soit liée à l’e↵et du champ descontraintes internes, généré par la structure des champs de dislocations, et qui n’a pas étépris en compte dans la loi de comportement. / A Digital Image Correlation (DIC) technique has been adapted to polycrystalline icespecimens in order to characterize the development of strain heterogeneities at an intra-granular scale during transient creep deformation. These heterogeneities are due to thestrong viscoplastic anisotropy of the ice single crystal (with only one easy glide planefor dislocations), inducing strong mechanical interactions between adjacent grains duringdeformation, and the establishment of strong internal stresses. Specimens exhibit a co-lumnar microstructure so that plastic deformation is essentially 2-D with few in-depthgradients, and therefore surface DIC analyses are representative for the whole specimenvolume. Local misorientations at the intragranular scale were also extracted from mi-crostructure analyses carried out with an automatic texture analyzer before and afterdeformation. Highly localized strain patterns are evidenced by the DIC technique. Localequivalent strain can reach values as high as one order of magnitude larger than the ma-croscopic average. The structure of the strain pattern does not evolve signicantly withstrain during the transient creep regime. Almost no correlation was measured betweenthe local strain and the Schmid factor of the slip plane of the underlying grain ; thishighlights the importance of the mechanical interactions between neighboring grains. Atthe grain scale, the strong lattice misorientations have been associated to the local com-ponents of the displacement. In particular, kink band distortions could be correlated to adisplacement along the c-axis measured by DIC. The experimental microstructures wereintroduced into a full-eld FFT model that simulates the behaviour of elasto-viscoplasticpolycrystals (CraFT code). The simulated deformation elds present globally the samecharacteristics as the experimental ones. Most of the localization bands are well repro-duced, spatially and quantitatively. However, we could not reproduce the macroscopicbehaviour of the specimens upon unloading. The predicted recovery eective strain is oneorder of magnitude lower than the measured one. This limitation might be linked withthe internal stress eld induced by the dislocation structure, which is not explicitly takeninto account in the local constitutive relation.

Submitted by Flavio Hiochio Sato null (sato@dec.feis.unesp.br) on 2018-02-05T12:49:07Z No. of bitstreams: 1 FLAVIO SATO TESE ELETRICA_Final.pdf: 4905931 bytes, checksum: 7de4992b81a9e515eaf26a3c238221b5 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-02-05T18:40:28Z (GMT) No. of bitstreams: 1 sato_fh_dr_ilha.pdf: 4905931 bytes, checksum: 7de4992b81a9e515eaf26a3c238221b5 (MD5) / Made available in DSpace on 2018-02-05T18:40:28Z (GMT). No. of bitstreams: 1 sato_fh_dr_ilha.pdf: 4905931 bytes, checksum: 7de4992b81a9e515eaf26a3c238221b5 (MD5) Previous issue date: 2017-12-08 / O desenvolvimento de sistemas capazes de monitorar e controlar informações estão sendo cada vez mais utilizados, permitindo maior refinamento e confiança nos resultados. Na área instrumental de laboratório, existem situações que exigem maior controle sobre o ensaio. Com o atual avanço na área de microprocessadores, microcontroladores, sensores inteligentes, entre outros, têm impulsionado a utilização dos mesmos na melhoria e confiabilidade de processos mecânicos, químicos, físicos, biológicos, de inteligência artificial, de melhoria de qualidade de vida de pessoas com deficiência. Os processos podem ser melhorados utilizando equipamentos que possuem sistemas embarcados capazes de processar informações e fazer o controle a partir de sistemas operacionais que antes só eram possíveis nos computadores. Na área das grandes estruturas de concreto não é diferente, deve-se monitorar algumas variáveis que resultam em uma manifestação patológica conhecida como reação álcali-agregado, que é um fenômeno de expansão que afeta a durabilidade e a resistência mecânica do concreto, este fenômeno está ligado à algumas variáveis, a umidade relativa interna é umas delas. Existem várias pesquisas no sentido de inibir as reações álcali-agregados, e é sabido que um importante passo antes do acontecimento da reação álcali-agregado em obras hidráulicas, como as usinas hidroelétricas é o monitoramento da umidade e da temperatura no interior do concreto e, acompanhamento das fissuras inerentes do processo de expansão. O presente trabalho implementou um sistema de monitoramento de baixo custo, de temperatura e umidade para estruturas de concreto de barragens hidroelétricas, demonstrando a desnecessidade de monitoramento da umidade relativa por esta já estar a 100% no interior do concreto, paralelamente, desenvolveu-se um sistema de automação em usinas hidroelétricas para o controle dos deslocamentos desta reação, foi feito o levantamento das técnicas de correlação de imagens digitais (CID) e contatou-se que é promissor desde que o processamento dos programas de refinamento das imagens acompanhe a tecnologia de câmeras com alta resolução. / The development of systems able to monitor and control information is increasingly being used, allowing greater refinement and confidence in results. In the instrumental area of the laboratory, there are situations that require greater control over the test. With the current progress in the area of microprocessors, microcontrollers, intelligent sensors, among others, have encouraged the use of these in the improvement and reliability of mechanical, chemical, physical, biological, artificial intelligence, improving the quality of life of people with deficiency. Processes can be improved by using equipment that has embedded systems that can process information and control from operating systems that were previously only possible on computers. In the area of large concrete structures is not different, it is necessary to monitor some variables that result in a pathological manifestation known as alkali-aggregate reaction, which is an expansion phenomenon that affects the durability and the mechanical resistance of the concrete, this phenomenon is connected to some variables, the relative humidity is one of them. There are several researches to inhibit alkali-aggregate reactions and is known that an important step before the occurrence of the alkali-aggregate reaction in hydraulic works such as hydroelectric plants is the monitoring of humidity and temperature inside the concrete and, the inherent fissures of the expansion process. The present work implemented a low cost, temperature and humidity monitoring system for concrete structures of hydroelectric dams, demonstrating the lack of relative humidity monitoring because it is already 100% inside the concrete, in parallel, a system of automation in hydroelectric power plants to control the displacements of this reaction, a survey of digital image correlation techniques (DIC) was made and it has been contacted since the processing of image refinement programs accompanies the technology of cameras with high resolution.

In rock constructions and mining it is important to know the current stress situation in the rock due to safety and construction reasons. Two of the widely used stress measurement methods are overcoring and hydraulic fracturing. Both methods are expensive, need new boreholes, and are complex and time consuming. The methods are also limited by the number of successfully achieved measurements series. An alternative method is therefore investigated by locally relieving stresses around the borehole wall using sawn slots. To determine the stresses in the rock, strain measurements will be done using optics and image processing of images taken before and after cutting of the slots. The images will be processed by a technique called Digital Image Correlation (DIC), a method where the pixels are fitted between the images by the greyscale. The thesis is roughly divided into three parts. The first part explains the basics of rock stresses and current stress measurement methods. The second part is a literature study of the theory behind optics and DIC. There is also a study about if it is possible to use optics from a smartphone and how it differs from a reference commonly used camera in DIC application. Last part consists of numerical calculations in 2D to investigate if there is a possibility to relieve the stress around the borehole walls by cutting slots. With the optics from a smartphone the borehole wall can be in focus on just a few millimeters distance. DIC is a well-developed method which has a good precision when being conducted right and with a good image quality. The combination of using a smartphone and DIC is, however, not fully investigated yet. Only one comparable study was found. It used a Sony tablet and measured the deformations instead of strains. However, that study showed that the measurement error was around 1% compared to the reference camera. When translating deformations into strains, it is most likely that the error will increase, because the error will also be affected from the difference in deformation before and after cutting the slots. The numerical part showed that it’s possible to relieve the stress at parts of the borehole walls for the investigated conditions. To fully relieve the stresses around the borehole wall, it is necessary to have two slots with a short c-c distance and relatively deep slots. In this case a c-c distance of 15 mm and slot depth of at least 25 mm are recommended. / Vid projekt inom berganläggningar och gruvor är det viktigt att känna till de rådande spänningar i berget i ett säkerhets- och konstruktionsperspektiv. I Sverige används framförallt två undersökningsmetoder - överborrning eller hydraulisk spräckning. Två metoder som dock är dyra och relativt få mätserier kan genomföras. En alternativ metod har därför undersökts där borrhålsväggen lokalt avlastas genom sågade slitsar. Töjningsmätning sker genom att fotografera borrhålsväggen innan och efter sågning av slitsarna. Därefter sker bildbehandling via Digital Image Correlation (DIC). En metod som jämför en pixels placerings förändring genom att matcha pixeln via gråskalan. Examensarbetet kan man säga är grovt indelat i tre delar. Den första delen innefattar teorin som handlar om bergspänningar samt nuvarande mätmetoder för att mäta bergsspänningar. Andra delen är en litteraturstudie som behandlar den bakomliggande teorin för optik och bildbehandling med DIC samt en kort undersökning om det är möjligt att använda den optiska tekniken som finns i en smartphone. Sista delen utgörs av numeriska modelleringar i 2D för att verifiera om det går att fullständigt avlasta ett borrhål genom sågade slitsar. Med optik som finns i en smartphone kan bergväggen vara i fokus på bara ett par millimeters avstånd. DIC i sig är en teknik som är så pass utvecklad att precisionen i mätningarna är väldigt god. Förutsatt att bildbehandling görs korrekt och bildkvalitén är god. Kombinationen med optik liknande den från smartphone och bildbehandling med DIC är dock inte fullständigt undersökt. Enbart en jämförbar studie har hittats där deformationsmätningar har gjort med hjälp av en Surfplatta från Sony. Denna undersökning visade att mätfelet mot en referenskamera är cirka 1%. Dock förstärks mätfelet vid töjningsmätningar. Förstärkningen beror dock även av deformationsskillnaden mellan innan och efter avlastning. Den numeriska delen har visat att det går att lokalt avlasta bergväggen fullständigt för det undersökta spänningsförhållandet. Dock krävs det att två slitsar sitter på ett litet c-c avstånd samt är relativt djupa. Två undersökta slitsuppsättningar har visat på fullständigt avlastning, samt ytterligare ett fall som skulle kunna vara användbart.

abstract: The main objective of this study is to investigate the mechanical behaviour of cementitious based composites subjected dynamic tensile loading, with effects of strain rate, temperature, addition of short fibres etc. Fabric pullout model and tension stiffening model based on finite difference model, previously developed at Arizona State University were used to help study the bonding mechanism between fibre and matrix, and the phenomenon of tension stiffening due to the addition of fibres and textiles. Uniaxial tension tests were conducted on strain-hardening cement-based composites (SHCC), textile reinforced concrete (TRC) with and without addition of short fibres, at the strain rates ranging from 25 s-1 to 100 s-1. Historical data on quasi-static tests of same materials were used to demonstrate the effects including increases in average tensile strength, strain capacity, work-to-fracture due to high strain rate. Polyvinyl alcohol (PVA), glass, polypropylene were employed as reinforcements of concrete. A state-of-the-art phantom v7 high speed camera was setup to record the video at frame rate of 10,000 fps. Random speckle pattern of texture style was made on the surface of specimens for image analysis. An optical non-contacting deformation measurement technique referred to as digital image correlation (DIC) method was used to conduct the image analysis by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-filed strain distribution, strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and corrected the stress-strain responses. / Dissertation/Thesis / M.S. Civil Engineering 2013

O presente trabalho tem por objetivo desenvolver um aparato experimental para estudar, em modelo físico de escala reduzida, o comportamento mecânico de um duto enterrado submetido a variações do estado de tensões da massa de solo circundante e a um potencial movimento de massa gravitacional, com avaliação concomitante das deformações desenvolvidas no solo por meio da técnica de correlação de imagens digitais. A alteração do estado de tensão no maciço foi feita por meio da aplicação de incrementos de inclinação ao modelo. Foram realizados ensaios com o duto nas posições transversal e longitudinal no interior da caixa de ensaios, enterrado em areia pura e seca, com razão entre altura de cobertura e diâmetro do duto de 3,55. A compacidade do maciço, controlada por meio da utilização da técnica de chuva de areia, foi avaliada nas situações densa (D = 111,5 %) e fofa (Dr = 58,2%). O comportamento mecânico do duto foi avaliado por meio de instrumentação para medição da deformação específica e deflexão da parede, sendo verificado efeito de flexão lateral no duto disposto na transversal, com maiores deformações observadas na situação de maciço fofo. Para o duto disposto na longitudinal, maiores deformações específicas foram observadas para a seção instrumentada central na situação de maciço denso, contudo verificou-se a necessidade de realização de ensaios adicionais para elucidação dos resultados, em termos da interação solo/tubo ao longo do comprimento do elemento. Para a utilização da técnica de correlação de imagens digitais, as imagens foram adquiridas em um ambiente com iluminação padronizada e resolução de partícula igual a 4. A qualidade da textura da imagem foi garantida por meio da preparação de material com adição de 20% de areia colorida. O refinamento da malha de análise, avaliado por meio da alteração do tamanho dos subsets e espaçamento entre subsets, não exerceu grande influência nos campos de deslocamentos obtidos, porém maiores refinamentos permitiram extrair observações mais detalhadas do campo de deformações. A utilização da técnica permitiu ainda avaliar a evolução dos vetores de deslocamento ao longo das etapas de inclinação e a influência do duto enterrado, na posição transversal, nos deslocamentos das partículas de solo circundante. / The present work aims the development of an experimental apparatus to study the behavior of a buried pipe under different soil stress states and potential landslides in a small-scale physical model. Digital image correlation technique is also used to evaluate soil deformation. A controlled slope increment squeme were responsible for soil stress state changes. The tests were performed with the model pipe buried in pure dry sand with a buried depth ratio of 3.55. A series of four tests involving two pipe configurations inside the test box (transversal and longitudinal) and two relative density (111.5% and 58.2%) was conducted. Soil density was controlled by pluviation method. The model pipe was instrumented in order to evaluate its behavior in terms of linear strain and deflection of the pipe wall. For the transversely disposed pipe, it was observed lateral bending effect and larger strains when buried in loose sand. For the longitudinally diposed pipe, the largest strains occurred in the pipe central cross section and in the tests conducted in dense sand. Nevertheless, additional testing is needed to better clarify the results, in terms of soil/pipe interaction along the pipe length. Daily digital images were acquired under standardized conditions of illumination for the use of digital image correlation technique. The particle/pixel size ratio was set equal to 4. Image texture quality was improved by adding 20% colored sand to the material used in the investigation. The level of refinement of the analysis mesh, evaluated by varying the subset size and the spacing of subsets, did not shown significant effect in the displacement fields. However, finer meshes allowed more detailed observations in the engineering shear strain fields obtained. Additionally, the digital image correlation technique allowed the evaluation of the displacement vectors evolution along the different slope stages considered. Moreover, this technique also captured the effect of the transversely disposed pipe on surrounding soil particles displacements.

Cette thèse a pour objet la mesure de déformations sans contact lors d'un essai de traction à l'aide de la méthode de corrélation d'images numériques DIC (Digital Image Correlation). Cette technologie utilise le repérage d'un motif aléatoire de tachetures pour mesurer avec précision les déplacements sur une surface donnée d'un objet subissant une déformation. Plus précisément, un algorithme DIC plus efficace a été formulé, appliqué et validé. La présente thèse comporte cinq parties consacrées au développement et à la validation du nouvel algorithme DIC: (a) la formulation mathématique et la programmation, (b) la vérification numérique, (c) la validation expérimentale, par essai de traction, en comparant les mesures DIC à celles obtenues par des jauges de déformation, (d) l'étude d'un procédé d'atomisation novateur pour générer de façon reproductible le motif de tachetures pour un repérage plus exact, et (e) l'analyse des sources d'erreur dans les mesures DIC. Plus précisément, l'algorithme DIC a servi à analyser, à titre d'exemple d'application, les propriétés mécaniques du polyméthyl métacrylate utilisé pour la reconstruction du squelette. Avec l'algorithme DIC, les images d'un objet sont acquises pendant la déformation de celui-ci. On applique ensuite des techniques d'optimisation non linéaire pour suivre le motif de tachetures à la surface des objets subissant une déformation en traction avant et après le déplacement. Ce procédé d'optimisation demande un choix de valeurs de déplacement initiales. Plus l'estimation de ces valeurs de déplacement initiales est juste, plus il y a de chances que la convergence du processus d'optimisation soit efficace. Ainsi, cette thèse présente une technique de traitement novatrice reposant sur une logique floue incluant aussi l'approximation des valeurs initiales du déplacement pour démarrer un processus itératif d'optimisation, ayant pour résultat une reproduction plus exacte et efficace des déplacements et des déformations. La formulation mathématique du nouvel algorithme a été développée et ensuite mise en œuvre avec succès dans le langage de programmation MATLAB. La vérification de l'algorithme a été faite à l'aide d'images de synthèse simu­lant des déplacements de corps rigides et des déformations de traction uniformes. Plus particulièrement, les images de déplacement simulaient (1) des déplacements de 0, 1 - 1 pixel en translation, (2) des angles de rotation de 0, 5 - 5°, et (3) de grandes déformations en traction de l'ordre de 5000 à 300000µE déformation, respectivement. Les processus de vérification ont démontré que le taux d'exactitude du nouvel algorithme DIC est supérieur à 99% en ce qui concerne les mesures des différents types et niveaux de déplacements simulés. Une validation expérimentale a été menée afin d'examiner l'efficacité de la nouvelle tech­nique dans des conditions réalistes. Des échantillons de PMMA normalisés, respectant la norme ASTM F3087, ont été produits, inspectés et soumis à une charge de traction jus­qu'à la rupture. La déformation de la surface des échantillons a été mesurée au moyen (a) du nouvel algorithme DIC, et (b) des techniques utilisant des jauges de déformation de type rosette. La force maximale moyenne et la limite de résistance mécanique des quatre échantillons étaient de 880 ± 110 N et 49 ± 7 MPa, respectivement. La limite moyenne de déformation mesurée par la jauge de déformation et provenant de l'algorithme DIC étaient de 15750±2570 et 19890±3790 µs déformation, respectivement. Des déformations d'un tel ordre sont courantes pour les matériaux polymériques, et jusqu'à maintenant, la technique DIC n'n’était pas développée pour faire des mesures de déformations aussi importantes. On a constaté que l'erreur relative de la mesure DIC, par rapport à la technique de la jauge de déformation, s'élevait à 26 ± 8%. Par ailleurs, le module de Young moyen et le coefficient de Poisson moyen mesurés en utilisant des jauges de déformations étaient de 3, 78 ± 0, 07 G Pa et 0, 37 ± 0, 02, alors qu'ils étaient de 3, 16 ± 0, 61 GPa et 0, 37 ± 0, 08, respectivement lorsque mesurés avec l'algorithme DIC. L'écart croissant entre les mesures de déformation DIC et celles obtenues au moyen de jauges de déformation est probablement lié à la dis­torsion graduelle du motif de tachetures à la surface des échantillons de traction. Par la suite, on a introduit un facteur de correction de 1, 27 afin de corriger l'erreur systématique dans les mesures de déformation provenant de l'algorithme DIC. La limite de déformation des mesures DIC a été rajustée à 15712±357 µs déformation avec un taux d'erreur moyen relatif de -0, 5 ± 7, 1 %, comparé aux déformations mesurées par la jauge de déformation. Le module de Young moyen et le coefficient moyen de Poisson de l'algorithme DIC et des mesures obtenues par la jauge de déformation ont par ailleurs été rajustés à 3, 8 ± 0, 4 GPa et 0, 368 ± 0, 025, respectivement. Au moyen d'un procédé d'atomisation, des taches de peinture ont été générées de façon reproductible sur la surface d'un objet. Une approche expérimentale de planification facto­rielle a été utilisée pour étudier le motif de tachetures (répartition et gradient de l'échelle des tons de gris) pour mesurer l'exactitude de l'algorithme DIC. Plus particulièrement, neuf motifs de tachetures différents ont été générés au moyen du procédé d'atomisation et testés pour la translation et la rotation de corps rigides. Les résultats ont révélé que l'erreur moyenne relative parmi les neuf motifs de tachetures variait de 1, 1 ± 0, 3% à -6, 5 ± 3, 6%. Le motif de tachetures préféré, lequel se démarquait par une large gamme de taches claires et de valeurs de tons de gris, a produit une erreur relative de 1, 1 ± 0, 3%. Une analyse des erreurs et des sources d'erreurs relatives de la mesure de l'algorithme DIC a été menée. Ti-ois catégories de sources d'erreurs, incluant l'algorithme lui-même, les paramètres du processus (taille des sous-ensembles, nombre de pixels calculés) et l'en­vironnement physique (uniformité des échantillons, motifs de tachetures, effet thermique de la caméra CCD et distorsion de la lentille, erreur de non-linéarité dans le circuit de la jauge de déformation) ont fait l'objet d'une étude et de discussions. Enfin, des solutions ont été amenées afin d'aider à réduire les erreurs systématiques et aléatoires en lien avec les trois catégories de sources d'erreurs susmentionnées. Pour terminer, un nouvel algorithme DIC permettant une approximation plus juste de l'estimation initiale, entraînant par conséquent une convergence efficace et précise de l'op­timisation a été développé, programmé, mis en oeuvre et vérifié avec succès pour ce qui est des déformations importantes. La validation expérimentale a fait ressortir une erreur systé­matique inattendue des mesures DIC lorsque comparées aux mesures obtenues au moyen de la technique des jauges de déformation. Plus l'échantillon se déformait, plus l'erreur augmentait proportionnellement. Par conséquent, la distorsion graduelle des tachetures sur la surface de l'objet était probablement la cause de l'erreur. L'erreur étant systéma­tique, elle a été corrigée. Le procédé d'atomisation a permis de générer des tachetures de façon reproductible sur la surface d'un objet. Grâce aux mesures DIC, le comportement mécanique des polymères soumis à des déformations importantes, comme le polyméthyl métacrylate servant à la reconstruction du squelette, peut être étudié et une fois maîtrisé, servir à l'élaboration de matériaux plus efficaces. / Abstract : The present thesis is focused on the non-contact and efficient strain measurement using the Digital Image Correlation (DIC) method, which employs the tracking of random speckle pattern for accurate measurement of displacements on a surface of an object undergoing deformation. Specifically, a more efficient DIC algorithm was successfully developed, implemented, and validated. This thesis consists of five parts related to the novel DIC algorithm: (a) the development and implementation, (b) the numerical verification, (c) the experimental validation, for tensile loading, by comparing to the deformation measurements using the strain gauge technique, (d) the investigation of a novel atomization process to reproducibly generate the speckle pattern for accurate tracking, and (e) the analysis of the error sources in the DIC measurements. Specifically, the DIC algorithm was used to exemplarily examine the mechanical properties of polymethyl methacrylate (PMMA) used in skeletal reconstruction. In the DIC algorithm, images of an object are captured as it deforms. Nonlinear optimization techniques are then used to correlate the speckle on the surface of the objects before and after the displacement. This optimization process includes a choice of suitable initial displacement values. The more accurate the estimation of these initial displacement values are, the more likely and the more efficient the convergence of the optimization process is. The thesis introduced a novel, fuzzy logics based processing technique, approximation of the initial values of the displacement for initializing iterative optimization, which more accurately and efficiently renders the displacements and deformations as results. The mathematical formulation of the novel algorithm was developed and then successfully implemented into MATLAB programming language. The algorithmic verification was performed using computer-generated images simulating rigid body displacements and uniform tensile deformations. Specifically, the rigid motion images simulated (1) displacements of 0.1-1 pixel for the rigid body translation, (2) rotation angles of 0.5-5 ̊ for rigid body rotation and (3) large tensile deformations of 5000-300000µɛ, respectively. The verification processes showed that the accuracy of the novel DIC algorithm, for the simulated displacement types and levels above 99%. The experimental validation was conducted to examine the effectiveness of the novel technique under realistic testing conditions. Normalized PMMA specimens, in accordance to ASTM F3087, were produced, inspected and subjected to tensile loading until failure. The deformation of the specimen surface was measured using (a) the novel DIC, and (b) strain gauge rosette techniques. The mean maximum force and ultimate strength of four specimens were 882.2±108.3 N and 49.3±6.2 MPa, respectively. The mean ultimate deformation from the gauge and DIC groups were 15746±2567µɛ and 19887±3790µɛ, respectively. These large deformations are common in polymeric materials, and the DIC technique has thus far not been investigated for large deformation. The relative mean error of the DIC measurement, in reference to those of the strain gauge technique, was found to be up to 26.0±7.1%. Accordingly, the mean Young's modulus and Poisson's ratio of strain gauge measurement were 3.78±0.07 GPa and 0.374±0.02, and of the DIC measurements were 3.16±0.61 GPa and 0.373±0.08, respectively. The increasing difference of the DIC strain measurements relative to those of the strain gauge technique is likely related to the gradual distortion of the speckle pattern on the surface of the tensile specimen. Subsequently, a Correction Factor (CF) of 1.27 was introduced to correct for the systematic error in the deformation measurements of the DIC group. The corrected ultimate deformation of the DIC measurements became 15712±357µɛ with the relative mean error of -0.5±7.1%, if compared to those measurements of the strain gauge techniques. Correspondingly, the mean Young's Modulus and Poisson's ratio of the DIC and of the strain gauge measurements became 3.8±0.4 GPa and 0.368±0.025, respectively. Using an atomization process, paint speckles were reproducibly generated on the surface of an object. A factorial design of experiments was used to investigate the speckle pattern (grey value distribution and gradient) for the DIC measurement accuracy. Specifically, nine different speckle patterns were generated using the atomization process and tested for rigid body translation and rotation. The results showed the relative mean errors among the nine speckle patterns varied from 1.1±0.3% to -6.5±3.6%. The preferred speckle pattern, which was characterized by a wide range of sharp speckle and of grey values, produced a mean error of 1.1±0.3%. The analysis of errors and relating sources in the DIC measurement was conducted. Three categories of sources including algorithmic sources, processing parameters sources (subset size, number of pixels computed) and physical environment sources (specimen uniformity, speckle pattern, self-heating effect of the CCD camera and lens distortion of the camera, non-linearity error in strain gauge circuit) were investigated and discussed. Finally, the solutions were provided in order to help reduce the systematic and random errors relating to the aforementioned three categories of sources for errors. In conclusion, a novel DIC algorithm for a more accurate approximation of the initial guess and accordingly for an efficient and accurate convergence of the optimization was successfully formulated, developed, implemented and verified for relatively large deformations. The experimental validation surprisingly showed a systematic error of the DIC measurements, if compared to the measurements of the strain gauge technique. The larger the deformation applied to the specimen, the larger the error gradually became. Therefore, the gradual distortion of the speckles on the surface of the object was likely the underlying cause of the error. The error was systematic and therefore corrected. The atomization process allowed generating reproducible speckles on the surface of an object. Using the DIC measurements, the mechanical behavior of polymers, undergoing large deformations, such as polymethyl methacrylate used in skeletal reconstruction can be investigated and, once understood, the knowledge gained can help develop more effective materials.

Cette étude porte sur l’analyse de l’influence de l’eau sur des composites chanvre/époxy. Deux résines ont été utilisées, l’une 100 % pétrochimique (Epolam) et l’autre partiellement bio-sourcée (Greenpoxy). L’absorption d’eau d’éprouvettes de composites tissés a d’abord été suivie par des mesures gravimétriques. Les résultats ont mis en évidence une cinétique d’absorption de type Langmuir dépendant de plusieurs paramètres (types de résine, de fibres et de tissu, fraction volumique de fibres et épaisseur). Des essais de DMA et DSC sur les résines ont montré un effet plastifiant de l’eau ainsi qu’une modification irréversible de leurs propriétés après le vieillissement hydrique. Des observations microscopiques réalisées sur le composite et à l’échelle du fil ont permis de détecter que des fissures entre les fibres de chanvre et la matrice époxy apparaissent et se développent dès le début de la désorption. De surcroît, des observations en photoélasticimétrie ont montré une réorganisation des contraintes internes irréversible due à ces endommagements. Des essais de traction quasi-statiques ont ensuite été réalisés sur des composites tissés et sur les résines seules. Le vieillissement hydrique modifie les grandeurs mécaniques ainsi que l’évolution des endommagements, suivie par émission acoustique et tomographie X.Pour mieux appréhender le comportement de l’interface fil/matrice, différents tests ont été développés sur des éprouvettes monofilamentaires spécifiques dans lesquelles le fil est orienté à 45° ou 90° par rapport à l’axe de sollicitation. Tout d’abord, des tests de nanoindentation ont été effectués de manière à mesurer in situ les propriétés de chaque constituant des composites avant et après vieillissement hydrique. Un second type de test basé sur le principe du choc laser a été utilisé pour déterminer la qualité de l’adhérence entre le fil et la résine. Enfin, des essais de traction sur micromachine sous microscope optique ont été mis au point dans le but de mesurer les champs de déformations par corrélation d’images. Les résultats ont démontré que les déformations locales sont plus importantes après un vieillissement hydrique et que ce phénomène est plus accentué dans le chanvre/Greenpoxy que dans le chanvre/Epolam. Le développement d’un modèle numérique simplifié a permis d’approcher la loi de comportement locale des différents constituants du composite et d’étudier l’évolution des modules après vieillissement. / This study deals with the analysis of the influence of water on hemp/epoxy composites. Two resins have been used, one being 100 % petrochemical (Epolam) and the other one partially bio-based (Greenpoxy). The water absorption of the woven composites have been measured with gravimetric analyses. The results showed a Langmuir-type absorption, and depends on several parameters (type of resin, fibres and fabric, fibre ratio and thickness). DMA and DSC tests realised on resins showed the plasticizing effect of water and an irreversible modification of their properties after the water ageing. Microscopic observations of the composite at the yarn scale helped to detect that cracks between hemp fibres and epoxy matrix appear and develop right from the start of the desorption. Moreover, observations by photoelasticimetry showed an irreversible reorganisation of internal stresses due to this damage. Next, quasi-static tensile tests have been performed on woven composites and resins. The water ageing has modified the mechanical properties of the materials as well as the evolution of damage, which has been studied by acoustic emission and X-ray tomography.For a better understanding of the yarn/matrix interface behaviour, different tests have been developed with specific single yarn composites, in which the yarn is oriented at 45° or 90° in regard to the main axis of the specimen. First, nanoindentation tests have been performed, to measure the properties in situ of each component of the composites before and after water ageing. A second type of tests, based on the laser shock wave method, has been used to determine the quality of adhesion between the yarn and the resin. Finally, tensile tests on a micromachine under an optical microscope have been developed with the aim of measuring strain fields by digital image correlation. The results demonstrated that local strains are higher after a water ageing and that this phenomenon is more pronounced in the hemp/Greenpoxy than in the hemp/Epolam. The development of a finite element model led to estimate the local constitutive law of the different components of the composites and to study the evolution of the modulus after the ageing.

Les composites à matrice organiques (CMO) et fibre de carbone sont de plus en plus employés dans la réalisation de structures « tièdes » (aubes de fan, nacelles …) ; ces pièces peuvent être soumises, en service, à la fatigue mécanique, au cyclage thermique et à la fatigue thermo-mécanique. Bien qu’il existe une littérature consistante sur le comportement en fatigue des composites tissés, l'interaction entre fatigue et la dégradation liée à l'environnement à haute température n’a pas été encore bien exploitée. Le couplage entre les effets de la thermo-oxydation, le comportement mécanique (viscoélastique, viscoplastique) de la matrice organique à températures élevées et la dégradation par fatigue peut être néfaste pour le composite.Le but de ce travail est de caractériser et de modéliser - pour les composites tissés C/matrice organique - le comportement thermomécanique, l'apparition et le développement de l’endommagement liés aux mécanismes mécaniques cycliques (fatigue) sous environnement contrôlé (température et gaz).Une étude préliminaire sur un composite stratifiée [02/902]s a été menée pour pouvoir analyser les effets de l’environnement sur une architecture simple. La corrélation d’image numérique (CIN) et des scans μ-tomographiques (μCT) ont été employés pour le suivi et la caractérisation de l’endommagement de fatigue de composites tissés 2D à architecture complexe pour applications aéronautiques. Les effets de l’environnement sur la dégradation par fatigue ont été également explorés.L'objectif à long terme de cette étude est de fournir des outils expérimentaux et numériques pour renforcer la compréhension et la modélisation du couplage mécanique/endommagement/environnement pour la prédiction de la durée de vie et pour la proposition de protocoles d’essais accélérés réalistes de pièces « tièdes » en CMO. / In the next future, the employment of organic matrix/carbon fibre composites (OMC) is foreseen for the realization of “hot” structures: these parts may be subjected, in service, to mechanical fatigue (e.g. fan blades turbo-engines), thermal cycling and thermo-mechanical fatigue (e.g. aircraft structural parts). Though there is a consistent literature concerning the fatigue behaviour of woven composites, the interaction between fatigue and environmental degradation at high temperature has been poorly explored. Coupling between thermo-oxidation effects, mechanical (viscoelastic, viscoplastic) behaviour of the polymer matrix at high temperatures and degradation due to fatigue may be highly detrimental for the material. This work aims at characterizing and modelling - for carbon fibre/organic matrix (polyimide) textile composites – the thermomechanical behaviour, the onset and the development of damage related to cyclic mechanical mechanisms (fatigue) under controlled (temperature and gas) environment.A preliminary study on a cross-ply laminate [02/902]s has been carried out in order to analyse the environmental effect on a model sample. Digital Image Correlation (DIC) and μ-Computed Tomography (μCT) have been used to monitor and characterize the fatigue damage of 2D woven composites for aeronautical applications. The environmental effect on fatigue degradation have been also explored.The long-term aim of the study is to provide experimental and numerical tools to strengthen the understanding and the modelling of mechanics/damage/environment coupling for durability prediction.

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