This thesis is concerned with the evaluation, in-situ, of the elastic strain energy release rate of cracks. This can define the criteria for crack propagation, and it is usually necessary to obtain this via calculation from the geometry and applied load. A new method is proposed, based on the conjoint use of digital image correlation to measure full-field displacements and finite element to extract the strain energy release rate of surface cracks. It has been extended to 3-D datasets with the use of digital volume correlation and tomographic imaging. A finite element model with imported full-field displacements measured by DIC/DVC acting as boundary conditions is solved and the J-integral is calculated. For linear elastic materials, modal contributions can be separated via the interaction integral. The method has been benchmarked using synthetic datasets to assess its sensitivity to noise and experimental uncertainties. It is very robust to experimental noise and can be used without knowledge of the specimen geometry and applied loads. The application of the method in 2-D is demonstrated in an analysis of experimental data for a mode I fatigue crack, introduced to an aluminium alloy compact tension specimen. Analysis of mixed-mode cracks in 2-D is shown on a PMMA sample with the Arcan geometry. In 3-D, static loading of a fatigue crack in nodular graphite cast iron is studied and the results from the method are compared with those obtained via a field-fitting approach. Diffraction analysis of polycrystalline materials can determine the full tensor of the elastic strains within them. Maps of elastic strains can thus be obtained typically using synchrotron X-rays or neutrons. A method is presented to calculate the elastic strain energy release rate of a crack from 2-D diffraction strain maps. The diffraction data is processed via a finite element approach to obtain the parameters required to calculate the $J$-integral. A validation is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of synchrotron X-ray diffraction strain maps of a propagating fatigue crack in a bainitic steel, before and after an overload. Finally, a complex case study of stable fracture propagation in polygranular isotropic nuclear graphite is presented. Synchrotron X-ray tomography and strain mapping by diffraction were combined with DVC and image analysis to extract the full-field displacements and elastic crystal strains. The displacement fields have been analysed using the developed methods to extract the critical strain energy release rate for crack propagation. Non-linear properties described the effect of microcracking on the elastic modulus in the fracture process zone. The analysis was verified by comparison of the predicted and measured elastic strain fields.

Le stress hydrique menacera plus que 40% de la population mondiale en 2050. Plus de 240 millions de personnes seront dépourvues d’accès à une source d’eau améliorée. En effet, pour assurer une gestion durable de cette ressource, la minimisation des ruptures dans les réseaux d'adduction d'eau potable est primordiale. La rupture des canalisations, phénomène assez fréquent en milieu urbain, s’amorce sur un défaut et sous l’effet des contraintes engendrées par un chargement inhabituel : coup de bélier, un phénomène de surpression. Depuis les années 80, le polyéthylène prend une part de plus en plus importante dans la fabrication des canalisations d'eau potable. Les jonctions sont les zones les plus dangereuses dans les réseaux. D'où l'importance d'étudier la résistance à la rupture des conduites coudées en PEHD. Pour résoudre ce problème, une étude est abordée par une approche expérimentale et une approche numérique par éléments finis pour caractériserle comportement à la fissuration des conduites coudées en PE100. Deux méthodologies sont proposées pour déterminer la ténacité du PEHD : la méthode de l'intégrale J et la méthode du déplacement d'ouverture en pointe de fissure ''CTOD''.La combinaison de ces outils permet de choisir la valeur critique de l'intégrale J comme valeur de la ténacité du PEHD.Ensuite, nous proposons une formule simplifiée basée sur la détermination de l'intégrale J en fonction de la pression dans les réseaux d'adduction d'eau potable en présence d'un défaut superficiel. Enfin, nous étudions le phénomène de coup de bélier pour déterminer la surpression avec un modèle mathématique développé dans cette thèse. Nous démontrons l'importance de l'interaction fluide-structure pour définir la pression au niveau des coudes / Water scarcity will be threatening more than 40% of the world population by 2050, more than 240 million people will not have a source of improved water. In fact, to ensure a sustainable management of this resource, the minimization of the leakages in drinking-water supply network is vital. Pipe rupture, a frequent phenomenon in urban zones, starts with a defect, under the effect of constraints caused by an unusual over pressure: Water Hammer. Since the 80s, polyethylene is being widely considered in manufacturing the pipelines water supply networks. Nevertheless, junctions are the most dangerous zones in the networks. As a result, it is vital to study the tear resistance of the angled conducts in PEHD. To solve this problem, a study is approached with an experimental investigation and a digital approach by fine elements in order to characterize the behavior in the fissuring of pipe bends PE100. Two methodologies are proposed to determine the tenacity of the PEHD: the method of the J-integral and the method of the sharp's movement opening of crack "CTOD ". The combination of these tools permits to choose the critical value of the integral J as a value of the tenacity of the HDPE. In addition, a simplified formula was proposed based on the calculation of the J-integral as a function of the pressure in water supply networks in the presence of a superficial defect. Finally, the water hammer phenomenon was investigated in order to determine the overpressure with a mathematical model which was developed in this thesis. The fluid-structure interaction was found to be important in defining the pressure at elbow pipe

[pt] Este trabalho teve como objetivo o estudo do comportamento à fratura do aço estrutural DIN 42CrMo4 através da determinação experimental de curvas de resistência (curvas R) à propagação estável de trincas. Inicialmente, conduziram-se ensaios de tração para a determinação das propriedades mecânicas do material. Os ensaios de tenacidade à fratura foram realizados em espécimes do tipo SE(B) entalhados, submetidos à flexão e com 3 geometrias distintas. Os corpos de prova foram pré-trincados por fadiga de maneira a atender a relação a/W equivalente a 0,5. Nos ensaios de propagação de trinca, adotou-se a técnica de corpo de prova único com a utilização do método das descargas parciais (Unloading Compliance Method) para a obtenção das curvas carga (P) versus deslocamento da boca do entalhe (CMOD - Crack Mouth Opening Displacement). A cada ponto de descarregamento, relacionando a inclinação da linha de carga com as medidas da flexibilidade elástica do corpo de prova, pôde-se calcular o comprimento da trinca e, consequentemente, valores do parâmetro elasto-plástico J. Em sequência, com base nos valores de J e propagação de trinca, foram levantadas as curvas R do material. Os resultados experimentais mostraram que a geometria dos corpos de prova influenciou a estabilidade da propagação das trincas durante o ensaio, sendo possível a obtenção de curvas R somente para os corpos de prova com geometria mais robusta. Além disso, percebeu-se que os valores de propagação de trinca calculados pelo método Compliance foram superestimados. / [en] This work aimed the study of the fracture behavior of the structural steel DIN 42CrMo4 through the experimental determination of resistance curves (R curves) to the stable spread of cracks. Traction tests were initially conducted to determine the mechanical properties of the material. The fracture tenacity tests were carried out in specimens of the type SE(B) notched, subjected to flexion and with 3 distinct geometries. The samples were precracked by fatigue in order to meet the a/W ratio equivalent to 0.5. In the crack propagation tests, the single specimen technique was adopted with the use of the partial discharge method for obtaining the curves load (P) versus displacement of the notch mouth (CMODCrack mouth Opening Displacement). At each point of unloading, relating the inclination of the load line with the measurements of the elastic flexibility of the sample, it was possible to calculate the length of the crack and consequently the values of the elasto-plastic parameter J. In sequence, based in the values of J and crack propagation, the R curves of the material were raised. The experimental results showed that the geometry of the specimens influenced the stability of crack propagation during the test, and it was possible to obtain R curves only for the most robust specimens. In addition, it was noticed that the crack propagation values calculated by the compliance method were overestimated.

O trabalho apresenta uma análise do desempenho de vários métodos de extração de fatores de intensidade de tensão a partir de soluções numéricas obtidas com o método dos elementos finitos generalizados (MEFG). A convergência dos fatores de intensidade de tensão é comparada com a da energia de deformação a fim de investigar a superconvergência dos métodos. Para extração dos fatores de intensidade de tensão e o cálculo da taxa de energia disponibilizada para propagação da fissura, implementam-se os métodos da integral de contorno (MIC), da função cutoff (MFC) e da integral-J no contexto do MEFG. Desenvolve-se a formulação dos métodos de extração de forma a obter uma implementação independente da malha utilizada na modelagem do problema. Aplica-se a extração dos fatores de intensidade de tensão, para modos puros e mistos, em problemas clássicos da mecânica da fratura. Verifica-se a convergência dos fatores de intensidade de tensão e da taxa de energia disponibilizada para a propagação da fissura, obtidos com cada método de extração, com o enriquecimento da ordem polinomial da solução do MEFG. Investiga-se a robustez dos métodos com relação ao tamanho dos domínios de extração / The performance of several techniques to extract stress intensity factors (SIF) from numerical solutions computed with the generalized finite element method (GFEM) is investigated. The convergence of the stress intensity factors is compared with the convergence of strain energy with the aim of investigate the superconvergence of the methods. The contour integral (CIM), the cutoff function (CFM) and the J-integral methods are considered to compute stress intensity factors and energy release rate. The proposed implementation of the extraction techniques is completely independent of the discretization used. Several numerical examples demonstrating the convergence of the computed stress intensity factors and the energy release rate, with the increasing of p order of the GFEM solution, are presented

Orientador: Itamar Ferreira / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T11:42:58Z (GMT). No. of bitstreams: 1 AguirreTorrico_IvanFelix_D.pdf: 3675970 bytes, checksum: 89da868d1276d05e3f5f216b82efb029 (MD5) Previous issue date: 2006 / Resumo: O gasoduto Bolívia-Brasil foi fabricado com dutos de aços API 5L X65 e X70. Existem relatos na literatura especializada de que o campo de tensões nas vizinhanças da ponta da trinca e a tenacidade à fratura são similares entre os corpos de prova não normalizados do tipo tração com entalhe lateral [SE(T)] e dutos. Neste trabalho realizou-se um estudo numérico e experimental da tenacidade à fratura em condições elasto-plásticas, com corpos de prova do tipo SE(T), dos aços API 5L X65 e API 5L X70. A determinação dos parâmetros da mecânica da fratura elástica linear foi feita pelos Métodos dos Elementos Finitos (MEF) e dos Elementos de Contorno (MEC) e a determinação do parâmetro elasto-plástico integral J por MEF. O fator eta plástico obtido numericamente, pelo MEF e com dados fornecidos pelo método EPRI, foi de 1,0, para medições do deslocamento de abertura da boca da trinca (CMOD). Com este fator eta plástico, foram realizados ensaios experimentais de tenacidade à fratura com corpos de prova do tipo SE(T), com espessura de 5 mm, e esses valores foram comparados com os resultados de ensaios em corpos de prova de flexão em três pontos [SE(B)], também com espessura de 5 mm. Houve um boa concordância entre os resultados numéricos e experimentais da integral J. Verificou-se que as curvas J-R obtidas com ensaios SE(T) são próximas das obtidas com ensaios SE(B), tendo em vista que a espessura dos corpos de prova utilizada, de 5 mm, não pôde ser modelada no estado plano de tensão ou de deformação / Abstract: The gas pipeline Bolivia-Brazil was manufactured with pipes of API 5L X65 and X70 steels. Specialized literature report that the stress field in the neighborhood of the crack tip and the fracture toughness are similar between not standard single edge notch tensile specimens - SE(T) - and pipes. In this work numerical and experimental study were made of the elastic-plastic fracture toughness using SE(T) specimens for API 5L X65 and X70 steels. The determination of the parameters of the linear elastic fracture mechanics was performed by the methods of the Finite Elements (FEM) and Boundary Elements (BEM). The J-integral parameter was determined by FEM. The plastic eta factor was obtained by FEM and with data supplied by the EPRI method. In both cases for measurements of the crack mouth opening displacement (CMOD) the determined plastic eta factor is 1.0. With this plastic eta factor, experimental tests of fracture toughness were accomplished using SE(T) specimens with thickness of 5 mm, and those values were compared with the test results obtained with standard single edge bend -SE (B)- specimens also with thickness of 5 mm. There was a good agreement between the numeric and experimental results of J-integral. Was verified that the J-R curves obtained with SE(T) specimens are close to the obtained with SE(B) specimens / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

No description available.

Polyethylene is a widely-used material in package industries. The fracture behavior of this material has not been studied in the plastic region in many years. In this thesis work, the J-Integral which is one material property used to represent the plastic material strength is calculated through the numerical analysis. To build a correct numerical model, the material behavior is summarized from previous uniaxial tensile test. The result from the fracture experiment for variable initial crack length is used to validate the reliability of the numerical model. The numerical analysis is done by the software ABAQUS which has the function to get the value of J-Integral directly. The final result contains the comparison between experiments and numerical analysis and the value of J-Integral at the crack initiation.

The primary objective of this masters thesis is to assess the eects of the length of crack and the angle, of which is this crack inclined on the stress and strain states at its front for the test sample loaded under shear. The rst part of this thesis will analyze the individual approaches that lead to the description of the aforementioned conditions. The second part deals with the FEM model assembly, which will lead to the fracture parameters, the values of which will be compared in part three.

The presented master’s thesis deals with description of short fatigue cracks and can be divided to the several parts. In the first part, theoretical background of fatigue of materials and fracture mechanics parameters which can describe fatigue cracks is presented. Following part describes how to determine fracture mechanics parameters by finite elements method. Due to the shape of propagated fatigue crack, numerical model was established as a three-dimensional. Results obtained based on this model, was compared with literature with very good agreement. Than real shape of propagated short crack was used for description of the experimental data. It was shown, that plastic part of J-integral is suitable parameter for description of the short cracks.

Abstract The objective of this study was a values evaluation of fracture toughness of fiber-metal laminates (FML) compounded from carbon fibers in epoxy matrix and aluminium plates of lay-up 6/5. Samples with unidirectional and bidirectional orientation were tested experimentally. In the case of unidirectionally oriented samples an effect of moisture absorption to epoxy matrix on the values of fracture toughness was reviewed. A fracture toughness calculation was realized by COD method firstly. A bigger pop-ins in F – COD diagram as critical moments for "delta"c evaluation were considered; it was determined by 5% tangential line. It was found out, that results of this measurement weren’t in agreement with plane deformation condition and for this the results couldn’t be rated as fracture toughness "delta"Ic. A method of J integral for fracture toughness evaluation was used consequently. A test of elastic compliance changes before J integral calculation by all of samples was performed. Beginning of stable grow of crack was determined by this method. A critical forces Fc from beginnings were established, which were used for calculation of Jc. A functional dependence of elastic compliance on crack opening had specific waved shape before its linear (up to exponential) grow. It was observed in all cases. The critical forces Fc from the end of “wave” preceding the continual grow of compliance were determined. Equations stated in standards for J integral calculation were used, which are for metal materials normally used. Despite this was found out all of results of Jc were in good agreement with plane deformation condition and could be rated as fracture toughness JIc. In this study were found out these pieces of knowledge about fracture toughness of FML CARE: Unidirectional CARE had fracture toughness JIc about 76 kJ/m^2 and the same type but with bigger amount of absorbed moisture had JIc about 4 % higher. In this case negative moisture influences on CARE weren’t found. Bidirectional CARE had fracture toughness JIc about 31 kJ/m^2; it was about 65 % less then in the case of unidirectional CARE