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La courbe S-N est le moyen le plus courant d'analyse et de prédiction de la durée de vie d'un matériau, d'un composant ou d'une structure. Cependant, les modèles standards, qu'ils soient basés sur la théorie de la rupture ou sur des modèles probabilistes n'ajustent pas la courbe dans la totalité sans information sur la microstructure du matériau. Or, cette information provient d'analyses fractographiques souvent coûteuses et rarement disponibles dans le cadre d'une production industrielle. D'un autre côté, les modèles statistiques ne proposent pas d'interprétation matériau et ne peuvent pas être utilisées pour réaliser des prévisions. Les résultats d'un test de fatigue sont par ailleurs très dispersés, plus particulièrement pour les fortes durées de vie, lieu d'apparition d'un phénomène de bi-modalité. Ces constats sont la raison de la proposition d'un nouveau modèle probabiliste. Celui-ci est composé d'un modèle de mélange spécifique, prenant en compte l'approche apportée par la mécanique de la rupture sans nécessiter de d'information supplémentaire sur la microstructure du matériau. Il utilise le fait que la fatigue peut être vue comme la somme d'un amorçage de fissure suivi de sa propagation. Les paramètres du modèle sont estimés à l'aide d'un algorithme EM, où la phase de maximisation combine une méthode d'optimisation de Newton-Raphson et une intégration de type Monte-Carlo. Le modèle "amorçage-propagation" offre une représentation parcimonieuse des courbes $S-N$ dont les paramètres peuvent être facilement interprétés par des ingénieurs matériau. Ce modèle a été testé à l'aide de simulations et appliqué à des données réelles (données sur l'Inconel 718). Ceci nous a permis de mettre en évidence le bon ajustement du modèle à nos données, et ce, pour toutes les déformations disponibles. / S-N curve is the main tool to analyze and predict fatigue lifetime of a material, component or structure. But, standard models based on mechanic of rupture theory or standard probabilistic models for analyzing S-N curves could not fit S-N curve on the whole range of cycles without microstructure information. This information is obtained from costly fractography investigation rarely available in the framework of industrial production. On the other hand, statistical models for fatigue lifetime do not need microstructure information but they could not be used to service life predictions because they have no material interpretation. Moreover, fatigue test results are widely scattered, especially for High Cycle Fatigue region where split $S-N$ curves appear. This is the motivation to propose a new probabilistic model. This model is a specific mixture model based on a fracture mechanic approach, and does not require microstructure information. It makes use of the fact that the fatigue lifetime can be regarded as the sum of the crack initiation and propagation lifes. The model parameters are estimated with an EM algorithm for which the maximisation step combines Newton-Raphson optimisation method and Monte Carlo integrations. The resulting model provides a parsimonious representation of S-N curves with parameters easily interpreted by mechanic or material engineers. This model has been applied to simulated and real fatigue test data sets. These numerical experiments highlight its ability to produce a good fit of the S-N curves on the whole range of cycles.

Vem se tornando cada vez mais importante o conhecimento e avaliação da incerteza de medição em todos areas de ensaios experimentais. Este trabalho visa estudar a incerteza de medição no levantamento do comportamento em fadiga de materiais metálicos utilizando-se de curvas S-N. Embora existam diversas normas e códigos sobre a análise estatística dos resultados obtidos em fadiga, eles avaliam apenas a dispersão no número de ciclos para a falha, não considerando fatores como as fontes incerteza das tensões aplicadas, da máquina de ensaios utilizada, entre outros. / The knowledge and evaluation of measurement uncertainty is becoming more and more important in all areas of experimental tests. The goal of this work is to study the measurement uncertainty in the fatigue tests of metalic materials using the S-N curve approach. Although there are various standards and codes on statistical analysis of the fatigue results, they only assess the dispersion in the number of cycles to failure, not taking into account uncertainty sources of aplied load, test machine, among others.

Vem se tornando cada vez mais importante o conhecimento e avaliação da incerteza de medição em todos areas de ensaios experimentais. Este trabalho visa estudar a incerteza de medição no levantamento do comportamento em fadiga de materiais metálicos utilizando-se de curvas S-N. Embora existam diversas normas e códigos sobre a análise estatística dos resultados obtidos em fadiga, eles avaliam apenas a dispersão no número de ciclos para a falha, não considerando fatores como as fontes incerteza das tensões aplicadas, da máquina de ensaios utilizada, entre outros. / The knowledge and evaluation of measurement uncertainty is becoming more and more important in all areas of experimental tests. The goal of this work is to study the measurement uncertainty in the fatigue tests of metalic materials using the S-N curve approach. Although there are various standards and codes on statistical analysis of the fatigue results, they only assess the dispersion in the number of cycles to failure, not taking into account uncertainty sources of aplied load, test machine, among others.

Vem se tornando cada vez mais importante o conhecimento e avaliação da incerteza de medição em todos areas de ensaios experimentais. Este trabalho visa estudar a incerteza de medição no levantamento do comportamento em fadiga de materiais metálicos utilizando-se de curvas S-N. Embora existam diversas normas e códigos sobre a análise estatística dos resultados obtidos em fadiga, eles avaliam apenas a dispersão no número de ciclos para a falha, não considerando fatores como as fontes incerteza das tensões aplicadas, da máquina de ensaios utilizada, entre outros. / The knowledge and evaluation of measurement uncertainty is becoming more and more important in all areas of experimental tests. The goal of this work is to study the measurement uncertainty in the fatigue tests of metalic materials using the S-N curve approach. Although there are various standards and codes on statistical analysis of the fatigue results, they only assess the dispersion in the number of cycles to failure, not taking into account uncertainty sources of aplied load, test machine, among others.

The improvement of static properties of combined rivet and adhesive bonded joints have been proven by several authors [1, 2]. On the other side, dynamic properties of joints (for example fatigue and corrosion) significantly affect final function of structures during their service life. In this thesis, the combine joints created by blind rivets and hyper elastic sealant are solved. Complex description of dynamic properties of this particular combined joining technology has not been publicised, yet. Description of sealant layer influence on stress concentration in rivet hole regions is one of the main goal of this work. The next stage of the thesis is focused on the influence of above mentioned sealant layer on fatigue properties of combined blind rivet and solid countersunk rivet joints. Stress strain analysis of rivet and combined joints done by FE analysis and by experimental optical measurement of strain field proved that hyper elastic sealant layer has a positive effect on decreasing of stress peaks in rivet hole regions. This findings are in direct compliance with fatigue measurement of combined joint (AAPL). The influence of applied sealant in this combined joints improved fatigue properties by twenty percentage increasing of stress to failure in comparison with rivet joints.

[pt] Esta pesquisa teve como objetivos promover variações microestruturais em um ferro fundido nodular ferrítico tipo ASTM A536 60-40-18, pelo do uso de resfriadores durante a solidificação do material e pela adoção de tratamentos térmicos pós-fundição, bem como avaliar a influência de tais variações microestruturais sobre as propriedades mecânicas e vida em fadiga do material. Inicialmente, amostras do material foram fundidas em areia com e sem o uso de resfriadores. Após a fundição, algumas amostras de ambas as condições de resfriamento sofreram normalização, enquanto outras foram recozidas, perfazendo seis diferentes condições microestruturais: sem resfriador bruta de fundição (SRB); sem resfriador normalizada (SRN); sem resfriador recozida (SRR); com resfriador bruta de fundição (CRB); com resfriador normalizada (CRN) e com resfriador recozida (CRR). Em seqüência, corpos de prova de todas as condições mencionadas acima foram ensaiados em tração e, posteriormente, sofreram análises metalográficas qualitativas e quantitativas. Dando continuação a etapa experimental, levantaramse as curvas tensão versus número de ciclos para a falha das condições microestruturais SRB, SRR, CRB e CRR, por meio de ensaios de fadiga em flexão rotativa. A vida em fadiga do material também foi relacionada com às características metalúrgicas de cada condição. / [en] The objectives of the present work were to promote microstructural variations in an ASTM A 536 60-40-18 ferritic nodular cast iron, making use of cast coolers during and adopting heat treatments after casting, as well as to evaluate the influence of the microstructural variations on the mechanical properties and fatigue life of the material. Initially, samples of the material were cast in sand moulds with and without internal coolers. After casting, a number of samples in both cooling conditions were subjected to normalizing and annealing heat treatments and, therefore, six different microstructural conditions were obtained: as- cast without cooler (SRB), normalized without cooler (SRN), annealed without cooler (SRR), as-cast with cooler (CRB), normalized with cooler (CRN) and annealed with cooler (CRR). Tensile test were carried out on specimens representing the above mentioned conditions and their microstructures were analysed by qualitative and quantitative metallography. In the sequence of the experimental procedure, rotating bend fadigue test were performed in order to establish the stress-life curves for the SRB, SRR, CRB and CRR microstructural conditions. The fadigue life of the material was also related to the metallurgical characteristics of each condition. The metallographic analysis has indicated that the use of coolers increases the number of graphite nodules, reduces the graphite nodule size and otimizes the spherical morphology. However, these microstructural modifications seam to have no significant influence on the mechanical properties of the material. As to the effect of normalizing annealing, boht treatments not imply in significant changes in the mechanical properties of the as-cast conditions. Regarding the fadigue resistance of the material in the as-cast conditions, the CRB sample showed a longer fatigue life than the SRB samples and this performance under cyclic loading was attributed to the fact that the CRB condition is characterized by a higher number of graphite nodules of class VI. A comparison between the as-cast and annealed conditions indicated that the microstructural conditions SRR and CRR presented a lower fatigue resistance than the conditions SRB and CRB, respectively. This behaviour was associated with the microstructural features of the as-cast conditions, namely the smaller graphite nodule size, the higher microhardness of the matrix and the presence of the bull`s-eye structure. Finally, the experimental stress-life curves were modelled by means of Coffin-Manson law, which was considered efficient in the fadigue life data of ferritic nodular cast iron.

Os aços de alta resistência e baixa liga (ARBL) utilizados em tubos para linhas de transmissão, ou seja, transferência e transporte de petróleo e gás, são especificados pela American Petroleum Institute (API) através da norma API 5L. Neste trabalho foi realizado um estudo da influência da têmpera e da nitretação no comportamento mecânico do aço API 5L X56. A microestrutura, os compostos formados com a nitretação e os mecanismos de fratura foram analisadas usando microscopia óptica, difração de raios X e microscopia eletrônica de varredura respectivamente. As amostras foram caracterizadas mecanicamente por testes de microdureza, tração, impacto e fadiga. Os resultados revelaram que apenas a têmpera promoveu modificações severas na microestrutura em relação à como recebida, formando bainita, martensita e constituinte M-A. A camada nitretada apresentou profundidade de 25 ?m e formação dos nitretos Fe3N e Fe4N. Houve aumento da microdureza, resistência mecânica com os tratamentos, juntamente com a diminuição da tenacidade e também houve um melhoramento na vida em fadiga para as duas amostras tratadas termicamente e superficialmente. Os mecanismos de fratura variaram de dúctil à frágil e em fadiga foi observado que as trincas nuclearam a partir da superfície para todas as amostras. / The high strength and low alloy steel (HSLA) used in pipeline for line transmission, there is transference and transportation of oil and gas, they are specified by American Petroleum Institute (API) through norm API 5L. In this work it was conducted a study of the nitriding and quenching influence on the mechanical behavior of API 5L X56. The microstructure, compounds made with the nitriding and the mechanisms failure were analyzed using optical microscopy, X-ray diffraction and scanning electron microscopy respectively. The samples were mechanical characterized by microhardness, tensile, impact and fatigue test. The results revealed that only quenching treatment promoted severe modifications in microstructure in relation to as received, making up bainite, martensite and M-A constituent. The nitriding layer showed depth of 25 ?m and formation of Fe3N e Fe4N nitrides. There was an increasing of microhardness and mechanical strength with the treatments, along with the decreasing of toughness and there was also an improvement in fatigue life for the two samples heat e surface treated. The failure mechanisms varied from ductile to brittle and in fatigue was observed that the cracks nuclear from the surface to all samples.

Made available in DSpace on 2014-12-17T14:57:55Z (GMT). No. of bitstreams: 1 AdrianoSB_TESE.pdf: 4047692 bytes, checksum: 5b0ec3af1fa350ee85a33e2b05f88fc7 (MD5) Previous issue date: 2012-11-30 / The static and cyclic assays are common to test materials in structures.. For cycling assays to assess the fatigue behavior of the material and thereby obtain the S-N curves and these are used to construct the diagrams of living constant. However, these diagrams, when constructed with small amounts of S-N curves underestimate or overestimate the actual behavior of the composite, there is increasing need for more testing to obtain more accurate results. Therewith, , a way of reducing costs is the statistical analysis of the fatigue behavior. The aim of this research was evaluate the probabilistic fatigue behavior of composite materials. The research was conducted in three parts. The first part consists of associating the equation of probability Weilbull equations commonly used in modeling of composite materials S-N curve, namely the exponential equation and power law and their generalizations. The second part was used the results obtained by the equation which best represents the S-N curves of probability and trained a network to the modular 5% failure. In the third part, we carried out a comparative study of the results obtained using the nonlinear model by parts (PNL) with the results of a modular network architecture (MN) in the analysis of fatigue behavior. For this we used a database of ten materials obtained from the literature to assess the ability of generalization of the modular network as well as its robustness. From the results it was found that the power law of probability generalized probabilistic behavior better represents the fatigue and composites that although the generalization ability of the MN that was not robust training with 5% failure rate, but for values mean the MN showed more accurate results than the PNL model / Quando da utiliza??o de materiais em estruturas ? comum ? realiza??o de ensaios est?ticos e c?clicos. Para os ensaios c?clicos avalia-se o comportamento ? fadiga do material e com isso obt?m-se as curvas S-N e estas s?o utilizadas para construir os diagramas de vida constante. Por?m, estes diagramas, quando constru?dos com pequenas quantidades de curvas S-N, subestimam ou sobrestimam o comportamento real do comp?sito, havendo necessidade crescente de se fazer mais ensaios para a obten??o de maior precis?o nos resultados. Pensando assim, uma forma de diminuir custos ? a an?lise estat?stica do comportamento ? fadiga. Assim, este trabalho possui o intuito de avaliar o comportamento probabil?stico ? fadiga de materiais comp?sitos e foi dividido em tr?s partes. A primeira parte consiste em como associar a equa??o de probabilidade de Weilbull ?s equa??es comumente utilizadas no modelamento da curva S-N de mat?rias comp?sitos, quais sejam, a equa??o exponencial e a lei de pot?ncia e suas respectivas generaliza??es. Na segunda parte utilizou-se os resultados obtidos pela equa??o que melhor representa as curvas S-N de probabilidade e treinou-se uma rede modular ? 5% de falha. Na terceira parte, realizou-se um estudo comparativo dos resultados obtidos usando o modelo n?o linear por partes (PNL) com os resultados de uma arquitetura de rede modular (MN) na an?lise do comportamento ? fadiga. Para tanto utilizouse uma base de dados com dez materiais obtidos da literatura para se avaliar a capacidade de generaliza??o da rede modular, bem como sua robustez. A partir dos resultados verificou-se que a lei de pot?ncia generalizada de probabilidade representa melhor o comportamento probabil?stico ? fadiga de comp?sitos e que apesar da capacidade de generaliza??o da MN esta n?o se mostrou robusta para um treinamento com 5% de falha, por?m para valores m?dios a MN apresentou resultados mais precisos que o modelo PNL

Os aços de alta resistência e baixa liga (ARBL) utilizados em tubos para linhas de transmissão, ou seja, transferência e transporte de petróleo e gás, são especificados pela American Petroleum Institute (API) através da norma API 5L. Neste trabalho foi realizado um estudo da influência da têmpera e da nitretação no comportamento mecânico do aço API 5L X56. A microestrutura, os compostos formados com a nitretação e os mecanismos de fratura foram analisadas usando microscopia óptica, difração de raios X e microscopia eletrônica de varredura respectivamente. As amostras foram caracterizadas mecanicamente por testes de microdureza, tração, impacto e fadiga. Os resultados revelaram que apenas a têmpera promoveu modificações severas na microestrutura em relação à como recebida, formando bainita, martensita e constituinte M-A. A camada nitretada apresentou profundidade de 25 ?m e formação dos nitretos Fe3N e Fe4N. Houve aumento da microdureza, resistência mecânica com os tratamentos, juntamente com a diminuição da tenacidade e também houve um melhoramento na vida em fadiga para as duas amostras tratadas termicamente e superficialmente. Os mecanismos de fratura variaram de dúctil à frágil e em fadiga foi observado que as trincas nuclearam a partir da superfície para todas as amostras. / The high strength and low alloy steel (HSLA) used in pipeline for line transmission, there is transference and transportation of oil and gas, they are specified by American Petroleum Institute (API) through norm API 5L. In this work it was conducted a study of the nitriding and quenching influence on the mechanical behavior of API 5L X56. The microstructure, compounds made with the nitriding and the mechanisms failure were analyzed using optical microscopy, X-ray diffraction and scanning electron microscopy respectively. The samples were mechanical characterized by microhardness, tensile, impact and fatigue test. The results revealed that only quenching treatment promoted severe modifications in microstructure in relation to as received, making up bainite, martensite and M-A constituent. The nitriding layer showed depth of 25 ?m and formation of Fe3N e Fe4N nitrides. There was an increasing of microhardness and mechanical strength with the treatments, along with the decreasing of toughness and there was also an improvement in fatigue life for the two samples heat e surface treated. The failure mechanisms varied from ductile to brittle and in fatigue was observed that the cracks nuclear from the surface to all samples.