The thesis examines the fatigue life of weld ends, where very little usable research previously has been conducted, and often the weld ends are the critical parts of the weld. It is essential knowing the fatigue life of welds to be able to use them most efficiently.The report is divided into two parts; in the first the different calculation methods used today at Toyota Material Handling are examined and compared. Based on the results from the analysis and what is used mostly today, the effective notch approach is the method used in part two.To validate the calculation methods and models used, fatigue testing of the welded test specimens was conducted together with a stress test. New modelling methods of the weld ends that coincide with the test results were made in the finite element software Abaqus. A new way of modelling the weld ends for the effective notch method is also proposed. By using a notch radius of 0.2 mm and rounded weld ends the calculated fatigue life better matches the life of the real weld ends.

Inconel 738, which is a nickel base superalloy used for hot section components of aircraft and industrial turbines is difficult to fabricate and repair by fusion welding due to its susceptibility to heat affected zone (HAZ) intergranular cracking. Crack-free joining of the difficult-to-weld alloy is currently achieved by using linear friction welding (LFW). Nevertheless, oxidation along the joint during LFW is a major problem. Information about the effect of process parameters on the microstructural evolution of linear friction welded nickel base alloys is very limited. In this work, the effect of forging pressure on the microstructure of linear friction welded Inconel 738 was studied. The results as elucidated in this work showed that increased forging pressure caused strain-induced rapid solidification of metastable liquid, which resulted in complete elimination of deleterious liquid phase oxides in bonded material contrasting the generally accepted view that assumes extrusion of solid state oxides during LFW.

Ce travail de thèse s’inscrit dans le contexte de la sûreté nucléaire, et plus précisément, de l’intégrité des circuits secondaires des Réacteurs à eau pressurisée (REP). L’étude porte donc sur le comportement à rupture de structures minces soudées dans le domaine haut de la transition fragile/ductile. Elle a pour objectif de développer le modèle en contrainte seuil initialement développé par Chapuliot, qui permet de prédire la non-rupture par clivage de cette structure soudée. Le modèle est identifié pour la soudure de l’acier au C-Mn de construction nucléaire, en s’intéressant plus particulièrement à la limite supérieure du domaine de transition.Une contrainte seuil, en-dessous de laquelle le clivage ne peut avoir lieu, est identifiée à partir d’essais de traction à basses températures sur éprouvettes axisymétriques entaillées prélevées dans le joint soudé. Cette contrainte seuil permet de définir le volume seuil, ou volume dans lequel les contraintes principales maximales dépassent la contrainte seuil au cours de l’essai.L’analyse au MEB des faciès des éprouvettes rompues montre que la zone fondue brute de solidification dans la ZAT est la zone la plus susceptible de cliver. La relation entre la probabilité de rupture fragile et le volume seuil dans cette zone est établie via une fonction de sensibilité, grâce à des essais sur éprouvettes CT et à leur simulation multi-matériaux. Le modèle ainsi identifié est testé pour prévoir la non rupture par clivage d’éprouvettes SENT prélevées dans le joint soudé et sollicitées en traction. Les résultats obtenus sont encourageants relativement à la transférabilité du modèle à la structure réelle / This work concerns the nuclear safety, specifically the secondary circuit integrity of pressurized water reactors (PWR). Therefore, the present study focuses on the fracture behaviour of welded thin structures in brittle/ductile transition. It aims at developing the threshold stress model initially proposed by Chapuliot, to predict the non-brittle-fracture of this welded structure. The model is identified for the welded joint in C-Mn steel for nuclear construction, specifically in the upper part of the transition.A threshold stress, below which the cleavage cannot take place, is identified using tensile tests at low temperature on axis-symmetrical notched specimens taken in welded joint. This threshold stress is used to define the threshold volume where the maximum principal stress exceeds the threshold stress during the test.The analysis by SEM of specimen fracture surfaces shows that the gross solidification molten zone in the weld is the most likely to cleave. The relation between the brittle fracture probability and the threshold volume in the gross solidification molten zone is established via a sensitivity function, using multi-materials simulations. The model thus identified is tested for the prediction of non-brittle-fracture of SENT specimens taken in the welded joint and tested in tension. The results obtained are encouraging with regards to the transferability of the model to the actual structure

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-10-27Bitstream added on 2014-06-13T19:35:05Z : No. of bitstreams: 1 musardo_gb_me_ilha.pdf: 3996445 bytes, checksum: ce4f6124da4b6648c41885a10eb3e368 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No Brasil, a maior parte da energia elétrica disponível é gerada por usinas hidrelétricas as quais contam com grande número de turbinas hidráulicas. Durante sua operação estas turbinas sofrem sérios danos provenientes tanto de natureza mecânica como também hidráulica. Fenômenos de perda de massa e também trincas e rachaduras são alguns dos principais problemas que ocorrem devido a um fenômeno chamado de erosão cavitacional, que comumente é recuperado por soldagem. Sendo assim, grandes níveis de resistência à cavitação vêm sendo obtidos com a deposição de aços inoxidáveis com a presença de cobalto pelo processo de soldagem a arco com proteção gasosa. Neste trabalho, seis amostras feitas de aço-carbono ASTM A36, as quais foram extraídas de retalhos de turbinas, foram usadas como metal de base para as amostras. Usando um processo a arco elétrico com proteção gasosa (GMAW) em posição plana, duas camadas de aço AWS E70-S6 (1,2 mm de diâmetro) foi depositada em todas as amostras, e, somente em três das amostras foram depositadas duas camadas de amanteigamento com o arame de aço inoxidável AWS E309-T1 (1,6 mm de diâmetro) usando o mesmo processo, onde foi utilizado como proteção gasosa uma mistura de 75% de dióxido de carbono e 25% de argônio. A energia de soldagem nominal nestes casos foi de 0,5 kJ/mm. Por final, mais duas camadas de aço inoxidável com cobalto, liga resistente à cavitação foram depositadas por arco pulsado, com energia de soldagem nominal de 0,5 a 0,8kJ/mm, com uma mistura de gases de 98% de argônio e 2% de oxigênio como proteção. Secções transversais das amostras foram preparadas, devidamente lixadas e depois polidas com alumina 1,0μm, seguido de ataque químico moderado com Villela para observação de microestruturas. Foi feito o estudo de microdureza Vickers com carga padrão de 0,4 N e espaçamento regular (0,4 mm)... / Nowadays most of the power supply used in Brazil is provided for a large number of hydraulic turbines. During its operation in hydroelectric power plants, these turbines usually have been damaged either mechanical or hydraulic reasons. So, catastrophic cracking and loss-of-mass due to cavitation erosion are main problems which are commonly repaired by welding. Higher levels of resistance to cavitation erosion have been attained with surface deposition of a cobalt-alloyed stainless steel coating by gas-protected arc welding techniques. In the present work six plates, which were machined from blades of hydraulic turbines made with ASTM A36 carbon steel grade, were used as base metal. Using manual gas-metal arc welding (GMAW) in flat weld position two layers of AWS E70-S6 carbon steel (1.2 mm diameter) were deposited on all samples. Only 3 samples two buttering layers were deposited with AWS E309-T1 flux-cored wire (1.6 mm diameter) using same processing, where were applied a 75% carbon dioxide - 25% argon mixture as protection gas. The nominal heat input used in all layers was approximately 0.5 kJ/mm. At the last welding deposition another two cobalt-alloyed, cavitation resistant, stainless steel cladding layers were deposited under pulsed arc with a nominal heat input of 0.5 to 0.8kJ/mm, being used for them a protective gas mixture of 98% argon - 2% oxygen. Transverse sections of weld deposit were prepared according standard grinding method (up to 1200-grit SiC paper) and final mechanical polishing using 1.0μm alumina, followed by moderate etching in Villela reagent for microstructural observation. Vickers microhardness measurements were carried out at standard load (0.4 N) and regular spacings (0,4mm) from surface to base metal. Light microscopy (LM) was used to determine average size of inclusions, which was measured from digitalized images using a freeware image analysis ...(Complete abstract, click electronic access below)

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-08-17T15:03:40Z No. of bitstreams: 1 JAIME MATIAS DA SILVA NETO- DISSERTAÇÃO (PPGEM) 2018.pdf: 3496418 bytes, checksum: 6c6b6ae8738da4d0e77cbcedcb6bb9d6 (MD5) / Made available in DSpace on 2018-08-17T15:03:40Z (GMT). No. of bitstreams: 1 JAIME MATIAS DA SILVA NETO- DISSERTAÇÃO (PPGEM) 2018.pdf: 3496418 bytes, checksum: 6c6b6ae8738da4d0e77cbcedcb6bb9d6 (MD5) Previous issue date: 2018-02-27 / CNPq / O presente trabalho teve como objetivo avaliar a influência da aplicação de vibração mecânica durante o processo da soldagem sobre o refino de grãos em metais de solda obtidos na soldagem do aço ASTM A516 Gr.60, aplicado em caldeiras e vasos de pressão. Para o tratamento de vibração mecânica foi utilizado o processo VWC (Condicionamento de Soldagem Vibratória), e para a soldagem foram empregados dois tipos de processos: SMAW (Arco Elétrico com Eletrodo Revestido) e GMAW (Soldagem ao arco elétrico com proteção gasosa). Os consumíveis utilizados foram o arame AWS ER 70S-6 com 1,2 mm de diâmetro protegido com CO2 no processo GMAW e o eletrodo AWS E7018 com 2,25 mm de diâmetro no processo SMAW. Foi projetada e desenvolvida uma bancada vibratória para realização dos experimentos. As juntas foram executadas sem e com vibração, submetidas a amplitudes que variaram de 7,2 a 51,2 m/s2 e frequências de 205 a 220 Hz. A vibração promoveu uma melhor distribuição da microestrutura no metal de solda, promovendo um refino de até 113% para uma amplitude de 51,2 m/s2 e frequência de 220 Hz no processo GMAW, em relação a condição sem vibração. Já no processo SMAW a redução chegou a 25% com amplitude de 7,2 m/s2 e frequência de 205 Hz. As reduções nos desvios padrões médios de dureza chegaram a 71% para uma amplitude de 48,9 m/s2 e frequência de 215 Hz, no processo GMAW. Enquanto que no processo SMAW, o desvio padrão médio de microdureza reduziu 27%, com amplitude 7,2 m/s2 e frequência de 205 Hz, em relação a condição sem vibração. / The present work had the objective of evaluating the influence of mechanical vibration during the welding process on grain refining in brazing metals obtained in the welding of steel ASTM A516 Gr.60, applied in boilers and pressure vessels. For the mechanical vibration treatment VWC (Vibration Welding Conditioning) process was used.. , The welds were done using the SMAW (Electric Arc with Coated Electrode) and GMAW (Electric Arc Welding with Gaseous Protection) process. AWS ER 70S-6 wire with 1.2 mm of diameter protected with CO2 in the GMAW process and the electrode E7018 with 2.25 mm of diameter in the process SMAW were used as consumable. A vibratory bed was designed and developed to perform the experiments. The joints were performed without and with vibration, subjected to amplitudes ranging from 7.2 to 51.2 m/s2 and frequencies from 205 to 220 Hz. The vibration promoted a better distribution of the microstructure in the weld metal, promoting a refining of up to 113% for an amplitude of 51.2 m/s2 and a frequency of 220 Hz in the GMAW process, in relation to the condition without vibration. In the SMAW process the reduction reached 25% with amplitude 7.2 m/s2 and frequency of 205 Hz. The reductions in the average hardness standard deviations reached 71% for a range of 48.9 m/s2 and a frequency of 215 Hz, in the GMAW process. Using the SMAW process, the mean standard deviation of microhardness value decreased by 27%, with amplitude 7.2 m/s2 and a frequency of 205 Hz, in relation to the condition without vibration.

Cette étude s’inscrit dans le cadre de l’inspection en service des soudures des réacteurs nucléaires de génération IV, en vue de contribuer à la démonstration de sûreté. La structure anisotrope et hétérogène des soudures multipasses en acier inoxydable austénitique rend leur contrôle ultrasonore difficile. Ainsi, afin d'interpréter correctement les signaux mesurés et de caractériser les défauts potentiels, une description de la soudure est utilisée. Elle constitue la connaissance a priori introduite dans la méthode de l'Energie Topologique. L’étude réalisée se décline en deux temps : le développement de la méthode en milieu borné et sa comparaison avec le Matched Field Processing, puis son application au cas de soudures réelles. L'extension de la méthode de l'Energie Topologique aux milieux bornés isotropes et homogènes vise à tirer parti des réflexions multiples. Plusieurs solutions du problème numérique de propagation, obtenues pour différentes conditions aux frontières, sont judicieusement associées afin de sélectionner les échos de diffraction porteurs d'information. Selon le type de défaut à imager des énergies topologiques spécifiques sont définies. La technique est introduite analytiquement avant d'être validée numériquement puis expérimentalement.Dans un second temps, la méthode est appliquée au milieu complexe de la soudure. La procédure est testée expérimentalement sur des soudures réelles afin d'évaluer les performances en localisation. Cependant, en raison de la variabilité de la structure, la qualité de l'image peut se dégrader selon les cas d'étude. La possibilité de générer des sources arbitraires permet de pallier en grande partie cette difficulté. / The present study has been done as part of the in-service inspection of weld structure belonging to generation IV nuclear reactors. It aims at checking both the safety and integrity of these components. The anisotropic and heterogeneous structure of austenitic stainless steel welds disturbs the ultrasonic non destructive testing. Thus, a weld description model is necessary to properly analyze the ultrasonic measured signals and to characterize potential flaws. The weld model makes a priori knowledge up in the Topological Energy method. The study is divided into two parts: development of the method in a bounded medium and comparison with the Matched Field Processing method, and then its application to real weld structures.The work firstly focuses on expanding the Topological Energy method to isotropic and homogeneous bounded medium to take advantage of multiple reflections between the flaw and edges. For that, different conditions are numerically applied to boundaries. By adding up these conditions it becomes possible to select the appropriate scattering signal. Modified topological energies are defined according to the type of analyzed flaws. The approach is analytically demonstrated before being validated firstly from synthetical data and then from experimental data.The second part deals with the application of the method to the complex weld structure. The process is experimentally tested on welds in order to evaluate efficiency of flaws localization. However, the image's quality can be deteriorated because of variability of the structure. By generating arbitrary ultrasonic source this difficulty is mostly overcame.

Les liaisons bimétalliques entre acier faiblement allié et acier inoxydable sont nombreuses au sein des réacteurs nucléaires français où elles assurent la connexion entre les principaux composants et les tuyauteries du circuit primaire. Le revêtement interne de cuve réalisé par soudage feuillard-flux est un autre cas de soudure dissimilaire dont le rôle est d'assurer une bonne protection contre la corrosion. Ce travail de thèse a notamment pour but de comprendre la genèse des microstructures complexes se formant à l'interface entre les deux aciers pendant le soudage. Il étudie d'autre part leur évolution durant le traitement thermique post-soudage à 610°C ainsi que les conséquences de ces transformations sur le comportement mécanique du joint soudé. Partant du métal de base, on rencontre successivement une fine bande de martensite, une zone purement austénitique puis la microstructure biphasée δ/γ de l'acier inoxydable. Des techniques de microscopie (MEB, EDS, EBSD) combinées à des calculs thermo-cinétiques (modèle de Scheil-Gulliver, surfusion en pointe de dendrite) ont permis d'expliquer le gradient de microstructure et les raisons des transitions de phases observées. Au cours du traitement thermique de détensionnement à 610°C, le gradient de potentiel chimique du carbone à travers l'interface de fusion cause la dissolution de la cémentite et la croissance des grains du côté faiblement allié. On observe également la diffusion du carbone à travers l'interface et la précipitation de carbures riches en Cr dans le liseré martensitique et la zone austénitique. Une caractérisation détaillée des profils de composition et de la précipitation a été réalisée à différentes échelles (depuis le millimètre jusqu'au niveau atomique). Un modèle mésoscopique, s'appuyant sur des bases de données thermodynamiques et cinétiques, a été développé pour coupler la diffusion à longue distance dans un milieu multi-constitué à la germination et croissance des précipités (approche de type Kampmann-Wagner). Il a permis de prévoir la teneur en carbone ainsi que la fraction volumique et la distribution de taille des précipités en fonction de la distance à l'interface. Les conséquences de la forte variabilité de microstructure sur le comportement mécanique local ont été analysées dans la dernière partie de ce travail, en particulier les aspects de déformation localisée et de rupture ductile. Des lois de comportement élasto-plastique ont été déterminées pour chacune des régions de l'assemblage à l'état détensionné. L'étude des mécanismes de rupture ductile dans les zones les plus faibles de la soudure, c'est-à-dire le métal de base décarburé et les couches de revêtement austénitique a donné lieu à des observations in-situ et une modélisation de l'endommagement. / Dissimilar welds between low-alloy steel and stainless steel are numerous within the French nuclear power plants where they enable connecting the main components to the primary circuit pipes. The internal cladding (in stainless steel) of the pressure vessel (in bainitic steel) made by submerged arc welding is another case of dissimilar weld whose goal is the protection against corrosion. This PhD work aims at understanding the complex microstructures which form at the interface between both steels during welding together with their evolution during the post-weld heat-treatment at 610°C and their consequences on the mechanical behavior of the welded assembly. Starting from the base metal, one meets successively a thin layer of martensite, a fully austenitic zone and the two-phase δ/γ microstructure of the stainless steel. Microscopy techniques (SEM, EDS, EBSD) combined with thermo-kinetics calculations (Scheil-Gulliver model, dendrite tip undercooling) have allowed explaining the graded microstructure and the reasons for the observed phase transitions. During the post-weld heat-treatment, the large gradient of carbon chemical potential across the fusion line leads to cementite dissolution and grain growth on the low-alloyed side. Carbon diffusion through the interface and Cr-rich carbides precipitation in both the martensitic layer and the austenitic weld have also been observed. An in-depth characterization has been performed at different scales (from the millimeter to the atomic level) to quantify the extent of carbon diffusion and carbides precipitation during the phase transformations. A mesoscopic thermodynamic and kinetic model based on Calphad databases has been developed to fully couple long-range diffusion in a multi-component system with precipitates nucleation and growth (Numerical Kampmann-Wagner approach). It allowed a prediction of the carbon content, volume fraction and size distribution of the precipitates at any distance from the fusion line. The consequences of the high variability of microstructures on the local mechanical behavior have been examined in the last part of this work, in particular the localization of deformation and the ductile failure. Elasto-plastic constitutive laws were determined for each region of the dissimilar weld in the heat-treated state. Ductile failure mechanisms in the weak zones of the weld, namely the decarburized base metal and the stainless steel cladding layers, were investigated through in-situ observations and damage modeling.

Made available in DSpace on 2016-12-08T17:19:29Z (GMT). No. of bitstreams: 1 Elementos pre-textuais.pdf: 356258 bytes, checksum: 9fa8daf60f02856f1b21e1882468c798 (MD5) Previous issue date: 2006-12-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The weld line is a common phenomenon in molded plastic articles and its consequences can be evaluated by several manners. This study treat weld line as a sharp crack, which length can be estimated based on the self-diffusion of molecular chains across the polymer-polymer interface. The temperature gradient from the contact surface mold/polymer up to the centre of the thickness was determined by simple heat transfer analyses equations. By combining the temperature gradient behavior through the part thickness with the polymer properties it is possible to determine the diffusion value across the interface and the interpenetration as a result of that. Above a critical interpenetration value, the weld line crack length will fall below a critical crack length, whereby the weld line will no longer initiate brittle fracture. The critical interpenetration is a function of the melt temperature and it is determined by strength tests for samples molded in several temperatures in the polymer manufacture recommended range. The results from strength tests, by which were possible analyze the weak area generated by weld line, were compared with theoretical results. It was evident, by comparing experimental and theoretical results, that weld lines are determined to be near-surface flaws, which embrittle notch sensitive materials such as most amorphous polymers. A software was developed to become possible to determine very quickly the crack length calculations as a function of the melt temperature and other properties related to diffusion. The software can be used to the calculations of any amorphous polymer, process condition and part thickness, obviously by the use of proper adjust equations. / A linha de solda é um fenômeno muito comum em produtos plásticos injetados e as conseqüências da mesma podem ser analisadas de várias maneiras. Este trabalho considerou a linha de solda como sendo uma trinca, cujo comprimento foi estimado a partir da difusão molecular na interface entre as duas frentes convergentes de fluxo. Um gradiente de temperatura desde a superfície de contato molde/polímero até o centro da espessura da peça foi determinado com equações para análise de troca térmica. E o comportamento deste gradiente de temperatura ao longo da espessura do produto somado as propriedades do polímero determinaram valores para a difusão molecular na interface e a conseqüente interpenetração. Acima de um determinado valor crítico de interpenetração, o comprimento da trinca da linha de solda cai para valores abaixo de um determinado valor crítico, pelo qual a linha de solda não mais será responsável por uma fratura frágil. A interpenetração crítica é função da temperatura de injeção e foi determinada via ensaios de tração para amostras injetadas em várias temperaturas dentro da faixa recomendada pelo fabricante da matéria-prima. Os resultados dos ensaios de tração, que possibilitaram a análise da perda de resistência à tração devido à trinca gerada pela linha de solda, foram comparados com os resultados obtidos teoricamente. Ficou evidente, devido a convergência dos resultados teóricos e experimentais, que a linha de solda é um fenômeno que produz um defeito superficial que fragiliza de maneira mais acentuada os materiais poliméricos amorfos, devido a sensibilidade dos mesmos ao entalhe. Um aplicativo foi desenvolvido para proporcionar o cálculo do comprimento da trinca em função da temperatura de injeção e demais propriedades. O aplicativo pode ser utilizado para o cálculo de qualquer polímero de estrutura amorfa, em qualquer condição de processo e espessura, mediante a utilização das adequadas equações de ajuste.

Made available in DSpace on 2016-12-08T17:19:31Z (GMT). No. of bitstreams: 1 Cap 9 .pdf: 34438 bytes, checksum: 74e72b9773d5bd61697450a6994d08cc (MD5) Previous issue date: 2008-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The use of steel tubes with seam in the industry is growing every year. Advantages as the low cost and the reduced weight of the tubular pieces do the first option of this product in the moment of the conception of the projects. But the competition in the automotive industry submits the manufacturers of steel tubes to new challenges, once the demand of characteristics as high conformability and mechanical resistance is becoming more and more common for this product, which already was considered a commodity. In this context, the processes of thermal treatment and the drawing it has been efficient methods to modify the mechanical properties, consolidating as important tools of technology aggregation and value to the steel tubes with seam. The search of great properties picks on continuous improvement in the production processes and improvement of steel tubes with seam, and this study evaluates the main variables of control of the process, welding and thermal treatment of these products. Those variables include the type of used steel, the microstructure of the heat affected zone (HAZ), mechanical properties, austenitizing temperature and the time of thermal treatment. This work also exposes the state of art and relative concepts to production of steel tubes with seam, beyond a detailed description of the methods, materials and processes involved in the research. / O emprego de tubos de aço com costura na indústria vem crescendo a cada ano. Vantagens como o baixo custo e o peso reduzido das peças tubulares fazem deste produto a primeira opção no momento da concepção dos projetos. Mas a concorrência acirrada na indústria automotiva submete os fabricantes de tubos de aço a novos desafios, uma vez que a exigência de características como elevadas conformabilidade e resistência mecânica estão se tornando cada vez mais comuns para este produto, que já foi considerado um commodity. Neste contexto, os processos de tratamento térmico e a trefilação tem sido métodos eficientes para modificar as propriedades mecânicas, consolidando-se como importantes ferramentas de agregação de tecnologia e valor aos tubos de aço com costura. A busca de propriedades ótimas implica em melhoria contínua nos processos de fabricação e beneficiamento de tubos de aço com costura, e este estudo avalia as principais variáveis de controle do processo de conformação, solda e tratamento térmico destes produtos. Essas variáveis incluem o tipo de aço utilizado, a microestrutura da zona afetada pela temperatura da solda (ZAT), propriedades mecânicas, temperatura de austenitização e o tempo de tratamento térmico. Este trabalho também expõe o estado da arte e conceitos relativos à fabricação de tubos de aço com costura, além uma detalhada descrição dos métodos, materiais e processos envolvidos na pesquisa.

Este trabalho apresenta uma avaliação dos efeitos de juntas soldadas dissimilares sobre forças motrizes de trinca e o desenvolvimento de procedimentos adaptados baseados em critérios mecânicos e micromecânicos para avaliação de defeitos em juntas soldadas incorporando efeitos de dissimilaridades mecânicas. A motivação central reside na forte expansão da indústria nacional de petróleo e a crescente demanda por aumento de produtividade aliado ao aumento na segurança operacional de sistemas dutoviários e estruturas correlatas. Para que tal intento seja atingido, é inicialmente apresentada uma descrição detalhada dos parâmetros de interesse da mecânica da fratura, fundamentos da metalurgia da soldagem e efeitos microestruturais e mecânicos oriundos da presença de soldas dissimilares. São então descritos os principais métodos experimentais de determinação de tenacidade à fratura, detalhados os procedimentos correntes de avaliação de integridade por meio de diagramas FAD e é estudada a teoria da tensão de Weibull. Tais estudos configuram o arcabouço conceitual necessário para o desenvolvimento de uma extensa variedade de ensaios experimentais em juntas soldadas e proposição de correções aos procedimentos correntes de determinação experimental de tenacidade, refinamentos na determinação de cargas limite e o desenvolvimento de um modelo de transferabilidade de tenacidades baseado em tensão de Weibull aplicável a juntas soldadas. Por fim, todas as contribuições são compiladas e incorporadas em um procedimento adaptado do tipo FAD especificamente adaptado à avaliação de estruturas soldadas constituídas de materiais dissimilares. Os resultados experimentais revelam forte e deletéria influência das juntas soldadas na tenacidade e capacidade de carga de estruturas. Por outro lado, o extenso compêndio de fatores eta e rotacionais plásticos rp desenvolvido permite a determinação experimental acurada de tenacidade à fratura para espécimes SE(B) homogêneos e bimateriais. Adicionalmente, a metodologia proposta de determinação de cargas limite incorpora o encruamento dos respectivos materiais e o modelo de transferabilidade baseado em tensão de Weibull permite a estimação acurada da tenacidade de componentes soldados dissimilares a partir dos dados do metal de base e poucas calibrações experimentais. Resultados de uma aplicação exploratória real indicam elevado grau de precisão e corroboram a validade das propostas apresentadas. Assim, os desenvolvimentos do presente trabalho mostram-se como potenciais ferramentas de projeto e avaliação de integridade estrutural. / This work presents an evaluation of weld strength mismatch effects on crack driving forces and proposes an extension of defect assessment procedures for welded structures to include effects of weld strength mismatch. The main motivation is based on the strong expansion of Brazilian petroleum industry and the increasing demand for productivity, safety and reliability of pipelines and correlated structures. In this context, it is initially presented a detailed description of fracture mechanics parameters, welding metallurgy fundamentals and mechanic and microestructural effects due to mismatched welds. Next, the main procedures for experimental evaluation of fracture toughness are addressed followed by a discussion on current integrity assessment standards based on FAD and the Weibull stress methodology. These studies provide the necessary background to conduct a wide variety of experimental tests in welded joints and the proposal of corrections for experimental fracture toughness evaluation in welded joints, corrections for limit load estimation schemes in mismatched structures and a new toughness scaling model based on Weibull stress applicable to welded mismatched joints. Finally, the resulting framework is incorporated into a modified FAD-based procedure specifically designed for integrity assessment of welded mismatched structures. The experimental results reveal strong deleterious effects of mismatched welds on loading capacity and fracture toughness of the analyzed specimens. However, the extensive body of calibrated eta and plastic rotational rp factors allows accurate experimental determination of fracture toughness for homogeneous and bimaterial SE(B) specimens. Additionally, the limit load estimation scheme proposed incorporates the materials hardening capacity while the Weibull-based toughness scaling model incorporating mismatch effects allows accurate estimation of the weldment toughness from base metal data and a simple experimental calibration. Results from an exploratory application indicate a high degree of accuracy and confirm the validity of the proposed methodology as a potential tool for design and integrity assessments of cracked weldments.