Ce travail de recherche donc concerne l'étude du système ultrasonique de fatigue en torsion de type indirect pouvoir étudier le comportement des matériaux métalliques à haute résistance, essentiellement au domaine de fatigue gigacyclique. Il existe actuellement deux types de système ultrasonique de torsion : un système qualifié de "direct" dans lequel le convertisseur délivre une rotation permettant, de manière simple et directe, la mise en vibration de torsion du système ; un système qualifié de "indirect" qui utilise un convertisseur longitudinal et nécessite une transformation en rotation pour créer la vibration en résonance de torsion. Premièrement, la présente d'étude sur le système indirect permet de comprendre son comportement de fatigue et ses propriétés. Cette étude est présentée à partir des calculs analytiques et numériques afin de dimensionner et modéliser ce système. Ensuite, l'optimisation du système à l'aide de la méthode des éléments finis est réalisée et un système plus effectif et plus robuste est obtenu. Des comparaisons entre les résultats numériques et les résultats de calibration sont proposées et une interprétation des écarts constatés est proposée avec les nouvelles simulations numériques. Deuxièmement, une campagne expérimentale à 20 kHz au-delà de 10⁸ cycles est menée en utilisant le système optimisé sur les aciers 16MnCr5 et 50CrV4 du projet FreqTigue. La méthode de l'escalier est utilisé dans les essais afin de décrire la courbe S-N, d'estimer la résistance à la fatigue et d'obtenir la durée de vie en fatigue. Des comparaisons des courbes S-N à différentes fréquences et sollicitations sont présentées. Les surfaces de rupture des éprouvettes sont analysées pour tenter d'identifier les causes de la rupture. / This research work concerns the study of the torsional ultrasonic fatigue system of indirect type which is able to study the behavior of high-strength metallic materials, mainly in the domain of gigacyclic fatigue. With the developments of technique, there are currently two types of ultrasonic torsional system: the first one is described as "direct" and its converter delivers a rotation which allows the system vibrate in torsion; the second one is described as "indirect", which uses a longitudinal converter and requires the transformation of a translation into a rotation to create a desired torsional resonant vibration in the specimen. Firstly, the study of the indirect system could understand the fatigue behavior and the properties of this system. This study is presented with the analytical and numerical calculations in order to determine and model the indirect system. Then, the optimization of this system by using the finite element method is performed and a more efficient and robust system is developed. Some comparisons between the numerical results and calibration’s results are proposed and an interpretation of differences is proposed by using new numerical simulations. Secondly, the tests of the 16MnCr5 and 50CrV4 steels of the FreqTigue project are carried out at 20 kHz and beyond 10⁸ cycles by using this optimized system. The staircase method is used in the tests to describe the S-N curve, to estimate the fatigue strength and to obtain the fatigue life. Then, the comparisons of the S-N curves at different vibration frequencies and stresses are presented, and the ruptured surfaces of the specimen are also analyzed to identify the causes of the rupture.

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.

This diploma thesis describes properties of ultra-fine grain Cu prepared via ECAP procedure. The influence of fatigue loading with positive mean stress on S-N curve (i.e. fatigue life), cyclic plastic behaviour and grain size was investigated. It was found that tensile mean stress leads to shorter lifetime in comparison with fatigue loading with zero mean stress. During main part of the lifetime, significant hardening of UFG Cu was observed. There is no distinct effect on microstructural orientation and stability.

As traffic demand on bridges increases, loading cycles on critical components will increase, reducing their service life. Modular bridge expansion joints, which are imperative to allowing the bridge superstructure to move, are susceptible to fatigue damage at their field splice. These splices are used to connect segments of the total joint, during staged construction. Current splice designs are either bolted or welded connections, which allow stress concentrations to induce pre-mature fatigue failure. This thesis examines the use of a hybrid FRP/steel design under fatigue loading for use as a splice detail. The splice detail consists of steel plates bolted to steel beam webs and CFRP pultruded plates adhesively bonded to the underside of the steel beam flanges. Two different moduli of CFRP were examined: Normal Modulus and Ultra High Modulus. Two beams of each modulus were tested under static conditions and six under constant amplitude fatigue loading. A testing rig was used to simulate similar bending moments experienced in bridge joints. In the static tests, slippage of the web plates caused considerable stiffness loss and the slippage load varied drastically between CFRP moduli. For the fatigue tests, the intention was to reach two million cycles at the different constant load ranges. Stiffness degradation was noticed during the fatigue process, and was likely due to bolt pre-tension loss and/or plastic deformation of the adhesive. Specimens that reached two million cycles were monotonically loaded to failure. Once the CFRP had failed, a secondary mechanism was observed for reserve load capacity. Simple beam mechanics were used to create prediction models for the initial spliced beam stiffness and peak CFRP load. Flexural and shear deformations of the spliced system were considered for beam stiffness. For the CFRP failure load prediction, a design peak strain in the CFRP was used to account for shear lag effects in the material and variability of the splice detail. While the model was inaccurate for beam stiffness, it provided a good approximate of the peak CFRP load. Based on the presented test data, the Normal Modulus CFRP hybrid splice detail showed better fatigue performance than conventional steel connection details. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-07-24 11:28:19.728

La méditation Vipassana est une méthode de contemplation du corps et de l'esprit qui vise la cessation de la souffrance et, ultimement, la réalisation de l'Éveil. Issue de la modernisation du bouddhisme theravada, elle se pratique désormais de manière fortement déritualisée et connaît depuis les années soixante une popularité croissante, comme d'autres thérapeutiques spirituelles orientales. Parmi les plus influentes écoles du mouvement Vipassana figure la tradition du maître indien Satya Narayan Goenka, dont les centres internationaux offrent des retraites où la méditation s'apprend en silence selon un protocole rigoureusement codifié. Au terme des retraites, les participants sont encouragés à méditer tous les jours, à suivre d'autres cours et à vivre en harmonie avec le Dhamma, l'enseignement du Bouddha. À ce jour, près de deux millions de personnes auraient été initiées dans cette tradition. Pour saisir ce qu'un tel phénomène signifie dans la société moderne actuelle, cette étude socio-anthropologique se penche sur la pratique de la méditation Vipassana au Québec. L'auteur s'appuie sur une enquête ethnographique dans les centres de la tradition de Goenka, l'analyse des discours du maître, des entrevues avec des méditants et sa propre expérimentation méthodologique de la méditation Vipassana. L'étude commence par proposer une description critique et détaillée de ce en quoi consiste cette « technique », pour expliquer ensuite l'efficacité thérapeutique que les méditants lui attribuent, moteur de leur pratique. La recherche va pour ce faire au-delà de l'interprétation traditionnelle du pouvoir salvifique de la méditation. Combinant une position constructiviste avec des contributions complémentaires issues de l'étude du bouddhisme, de l'ethnopsychiatrie, de l'anthropologie et de la sociologie, elle identifie les conséquences implicites de sa pratique et les modalités de la « guérison » qu'elle produit. Sans nier ses effets réels, l'argument mis de l'avant est que la pratique méditative rituelle est indissociable d'un vaste processus rhétorique qui construit une nouvelle réalité symbolique et valorise une forme d'individualité en consonance avec le contexte actuel de la modernité avancée. L'étude conclut avec un retour critique sur la méthodologie d'une enquête reposant sur la participation expérientielle du chercheur à son objet. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : méditation Vipassana, efficacité thérapeutique, rhétorique, bouddhisme, modernité avancée, soi

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.

DIN 35NiCrMoV125 (equivalent to AISI 4340), which is a high strength low alloy steel (HSLA), is mainly used at military applications in the production of gun barrels. The main aim of this study was to determine the low cycle fatigue (LCF) behaviour and the influence of temperature on low cycle fatigue failure properties of that steel. Three different temperatures (room temperature, 2500C and 4000C) were used in the experiments in order to analyze the effect of temperature. For each temperature, five strain amplitudes (in the range of 0.2% offset yield point to 2% strain) were applied and the duplicates of each experiment were performed to obtain more accurate results. Strain amplitudes and the corresponding stresses were calculated from tension tests performed at each temperature. Strain amplitude versus fatigue life (e- N) curves for three different temperatures predicted that fatigue life at a given strain increases with increasing temperature. The transition lives of those three curves were observed at 1 % strain amplitude and no significant effect of temperature on transition lives was observed. For stress based analysis, stress versus fatigue life (S-N) curves were drawn. These curves pointed that fatigue strength at a given number of cycle decreases with increasing temperature. Fractographic analyses of the fracture surfaces were performed to examine the effects of load and temperature on the specimens. It was observed that the number of crack initiation sites increases with increasing strain.

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.