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Le besoin de prédire le comportement mécanique des structures industrielles en béton armé et d’évaluer leur niveau d’endommagement en conditions extrêmes sous l’action de chargements dynamiques violents nécessite de faire appel à la simulation numérique utilisant des modèles de matériaux fiables et robustes. Dans cette thèse, le modèle d’endommagement anisotrope induit utilisant une variable tensorielle d’ordre 2 est étendu aux cas de chargements peu confinés à l’aide d’un nouveau critère modulaire formulé en contraintes. Grâce au mécanisme de visco-endommagement, le modèle traite toute la gamme de vitesses de sollicitation envisagée pour des structures en béton armé. Le comportement cyclique avec refermeture des fissures est pris en compte et l’endommagement peut atteindre 1 exactement dans une ou plusieurs directions grâce à une nouvelle gestion de la rupture. Le calcul d’un tirant a montré que cette procédure est indispensable pour plastifier l’acier et éviter un endommagement généralisé du béton. Lors du volet expérimental de la thèse, des essais de caractérisation du béton et des essais d’arrachement ont été réalisés en coopération avec le Département Génie Civil de l’ENS Cachan, suivis des essais d’impact sur poutres sur la tour de chute Orion au laboratoire DYN du CEA à Saclay. Avec une prise en compte pragmatique de l'interface acier-béton, la comparaison des calculs et des essais a montré qu'il était nécessaire de disposer d’un modèle de liaison acier-béton pour éviter un endommagement trop important du béton au voisinage des armatures, de réduire les temps de calcul, d’améliorer la méthode de régularisation et de prendre en compte les déformations permanentes. / The need to predict the mechanical behavior of reinforced concrete industrial structures and assess their level of damage in extreme conditions under the action of dynamic loads requires the use of numerical simulations and develop reliable and robust material models. In this thesis, the model of induced anisotropic damage using a tensor variable of order 2 is extended to the case of low-level confined loads using a new modular criterion written with stresses. Through the mechanism of visco-damage, the model treats the entire solicitation rate range considered for reinforced concrete structures. The cyclic behavior with reclosing of cracks is taken into account and the damage can reach 1 exactly in one or more directions due to a new rupture management. The calculation of a tie-beam showed that this procedure is necessary to plasticize steel and prevent widespread damage concrete. During the experimental part of the thesis, characterization tests for concrete and pullout tests were conducted in cooperation with the Civil Engineering Department at ENS Cachan, followed by impact tests on beams on the Orion drop tower of DYN CEA Saclay laboratory. With a pragmatic consideration of steel-concrete interface, the comparison of calculations and tests showed that it was necessary to have a model of steel-concrete connection to avoid excessive concrete damage in the vicinity of reinforcements, as well as to reduce computing time, improve the regularization method, and take into account permanent deformations.

A associação entre epilepsia e transtornos psicóticos é amplamente relatada na literatura. Características clínicas e do seu impacto, tais como suicídio, tentativas de suicídio, homicídio e alterações cognitivas são evidenciados em poucos estudos que associam epilepsia e psicose. Este estudo comparou o impacto clínico e funcionamento psicossocial dos pacientes com epilepsia e transtornos psicóticos, analisando ainda as diferenças entre pacientes com psicose interictal e pós-ictal. O estudo consiste de uma revisão de prontuário de todos os pacientes atendidos no PRONEPSI com epilepsia e transtornos mentais. Foram estudados 143 indivíduos, divididos em dois grupos: 82 pacientes com diagnóstico de epilepsia e transtornos psicóticos e 61 pacientes com epilepsia e outro transtorno mental. O grupo de pacientes psicóticos foi estudado comparando dados entre pacientes com psicose interictal (53) e pós-ictal (17). O grupo de pacientes com transtornos psicóticos apresentou menor escolaridade, mais história familiar de psicose, maior número de tentativas de homicídio, mais estados de mal epiléptico, mais internações psiquiátricas, história pregressa de insulto ao SNC e retardo mental. Além disso, a epilepsia foi considerada um fator causal importante para desenvolvimento da psicose. O grupo de pacientes com transtornos psicóticos também se diferenciou, revelando maior impacto na esfera cognitiva, vocacional e pessoal. Os pacientes com psicose interictal tiveram mais história familiar para psicose e a epilepsia foi considerada um fator causal importante para seu desenvolvimento. Pacientes com epilepsia e transtornos psicóticos apresentam um maior comprometimento clínico geral o que interfere diretamente no seu comprometimento funcional e na gravidade do impacto. Os pacientes com epilepsias mais graves e algum tipo de insulto ao SNC parecem ser mais vulneráveis ao desenvolvimento de transtornos psicóticos em comparação aos pacientes com formas menos graves de epilepsia / The association between epilepsy and psychotic disorders has been well documented in literature. Although this association is well-known, few studies regarding psychosis and epilepsy investigated the clinical characteristics of these patients and its impact on psychosocial function, suicide and suicide attempts, homicide attempts and cognitive deficits. The aim of this chart review was to compare the clinical impact and the psychosocial function between patients with epilepsy and psychotic disorders and patients with epilepsy and other psychiatric disorders. We also compared the clinical characteristics and psychosocial function between patients with postictal psychosis and interictal psychosis. We reviewed 143 charts, divided in two groups: 82 charts of patients with epilepsy and psychotic disorders and 61 charts of patients with epilepsy and other psychiatric disorders. In the group of patients with epilepsy and psychosis, 53 had a diagnosis of interictal psychosis and 17 of postictal psychosis. Patients with psychotic disorders had fewer years of education, more family history of psychotic disorders and higher number of homicide attempts, status epilepticus, psychiatric admissions and history of central nervous system insults. They also presented more impact on cognitive, vocational and interpersonal scales. Epilepsy was considered a major cause to the development of psychosis. Regarding the differences between patients with interictal and postictal psychosis, the only difference found was that the patients with interictal psychosis presented more family history of psychosis. Also, in both groups epilepsy was considered a major cause to the development of psychosis. Patients with psychotic disorders had a more severe clinical impairment in comparison with patients with other psychiatric disorders, which may have interfered in psychosocial functioning and severity of impact. Patients with central nervous system\'s insults and severe epilepsy may be likely more prone to psychosis\'s development than other patients with less severe forms of epilepsy

A associação entre epilepsia e transtornos psicóticos é amplamente relatada na literatura. Características clínicas e do seu impacto, tais como suicídio, tentativas de suicídio, homicídio e alterações cognitivas são evidenciados em poucos estudos que associam epilepsia e psicose. Este estudo comparou o impacto clínico e funcionamento psicossocial dos pacientes com epilepsia e transtornos psicóticos, analisando ainda as diferenças entre pacientes com psicose interictal e pós-ictal. O estudo consiste de uma revisão de prontuário de todos os pacientes atendidos no PRONEPSI com epilepsia e transtornos mentais. Foram estudados 143 indivíduos, divididos em dois grupos: 82 pacientes com diagnóstico de epilepsia e transtornos psicóticos e 61 pacientes com epilepsia e outro transtorno mental. O grupo de pacientes psicóticos foi estudado comparando dados entre pacientes com psicose interictal (53) e pós-ictal (17). O grupo de pacientes com transtornos psicóticos apresentou menor escolaridade, mais história familiar de psicose, maior número de tentativas de homicídio, mais estados de mal epiléptico, mais internações psiquiátricas, história pregressa de insulto ao SNC e retardo mental. Além disso, a epilepsia foi considerada um fator causal importante para desenvolvimento da psicose. O grupo de pacientes com transtornos psicóticos também se diferenciou, revelando maior impacto na esfera cognitiva, vocacional e pessoal. Os pacientes com psicose interictal tiveram mais história familiar para psicose e a epilepsia foi considerada um fator causal importante para seu desenvolvimento. Pacientes com epilepsia e transtornos psicóticos apresentam um maior comprometimento clínico geral o que interfere diretamente no seu comprometimento funcional e na gravidade do impacto. Os pacientes com epilepsias mais graves e algum tipo de insulto ao SNC parecem ser mais vulneráveis ao desenvolvimento de transtornos psicóticos em comparação aos pacientes com formas menos graves de epilepsia / The association between epilepsy and psychotic disorders has been well documented in literature. Although this association is well-known, few studies regarding psychosis and epilepsy investigated the clinical characteristics of these patients and its impact on psychosocial function, suicide and suicide attempts, homicide attempts and cognitive deficits. The aim of this chart review was to compare the clinical impact and the psychosocial function between patients with epilepsy and psychotic disorders and patients with epilepsy and other psychiatric disorders. We also compared the clinical characteristics and psychosocial function between patients with postictal psychosis and interictal psychosis. We reviewed 143 charts, divided in two groups: 82 charts of patients with epilepsy and psychotic disorders and 61 charts of patients with epilepsy and other psychiatric disorders. In the group of patients with epilepsy and psychosis, 53 had a diagnosis of interictal psychosis and 17 of postictal psychosis. Patients with psychotic disorders had fewer years of education, more family history of psychotic disorders and higher number of homicide attempts, status epilepticus, psychiatric admissions and history of central nervous system insults. They also presented more impact on cognitive, vocational and interpersonal scales. Epilepsy was considered a major cause to the development of psychosis. Regarding the differences between patients with interictal and postictal psychosis, the only difference found was that the patients with interictal psychosis presented more family history of psychosis. Also, in both groups epilepsy was considered a major cause to the development of psychosis. Patients with psychotic disorders had a more severe clinical impairment in comparison with patients with other psychiatric disorders, which may have interfered in psychosocial functioning and severity of impact. Patients with central nervous system\'s insults and severe epilepsy may be likely more prone to psychosis\'s development than other patients with less severe forms of epilepsy

Le phénomène de défaillance par fatigue peut apparaitre à des niveaux de contraintes éloignés du seuil de dimensionnement statique de mécanique des milieux continus, tout simplement du fait que l’endommagement suit un processus complexe et de longue haleine. Disposer d’outils performants de prévision de durée de vie en fatigue est donc une nécessité de conception pour le dimensionnement des machines, composants, structures, par natures soumises à des sollicitations variables dans le temps, liée à leur utilisation en service. Pour contribuer à cet objectif nous nous sommes attachés à une conception concernant les outils les plus fréquemment utilisés pour ces prévisions en fatigue : les critères multiaxiaux de fatigue et les lois d’endommagement et de cumul en fatigue. La première partie du travail effectué a consisté en une étude de validité et d’analyse de nouveaux critères de fatigue multiaxiaux proposés depuis une dizaine d’années. Cette validité est comparée vis-à-vis de celle des critères implantés dans l’industrie. L’approche intégrale dont le principe est l’établissement du caractère endommageant d’un cycle multiaxial par la contribution des sollicitations présentes sur tous les plans physiques et non un seul comme le cas de l’approche « plan critique », est la plus efficace en règle générale pour traduire correctement le comportement en fatigue sous chargement multiaxial. L’intégration d’une démarche probabiliste proposée permet d’associer la probabilité de survie aux résultats de calcul d’un critère. La seconde partie de cette thèse a conduit à proposer de nouveaux modèles différentiels d’endommagement permettant de retrouver, dans le cas d’un chargement d’amplitude constante, le formalisme classique des courbes S-N des matériaux (Wöhler, Basquin, Bastenaire et Stromeyer). L’influence de l’ordre d’apparition des cycles de contraintes, les valeurs moyennes, l’évolution non linéaire du dommage par fatigue sont ainsi prises en compte. Le problème de sensibilité du modèle et donc ses prévisions de durée de vie en fatigue uniaxiale d’amplitude variable, comme cela est rencontré dans le modèle de Chaboche, est ainsi écarté. La confrontation du modèle proposé pour les courbes S-N de Basquin et Bastenaire est prometteuse en terme de prévision de duré de vie. Une étude comparative par rapport à la loi de Miner, prise comme référence, avec celles proposée et de Mesmacque & Amrouche à donnée des résultats concluants pour les lois à évolution non linéaire. / The phenomenon of failure by fatigue can apparaitre at levels of stress remote from the threshold of static dimensinnaly of mechanics of the continuous medium, simply because the damage follows a complex and longterm process. Have successful tools of forecast of life expectancy in fatigue is thus a necessity of conception forthe dimensionnly of machines, components, structures, by natures subjected to requests time-varying, connected to their use in service. To contribute to this objective we became attached to a conception concerning tools most frequently used for these forecasts in fatigue: The multiaxial criteria of fatigue and the laws of damage and of cumul in fatigue. The first part of the made work consisted of a study of validity and analysis of new multiaxial criteria of fatigue proposed since around ten years. This validity is compared towards that of the criteria implanted in the industry. The integral approach the principle of which is the establishment of the character damaging of a multiaxial cycle by the contribution of the sollicitation on all the physical plans and not the only one as the case of the approach " critical plan", is the most effective as a general rule to translate correctly the behavior into fatigue under multiaxial load. The integration of a proposed probability approach allows to associate the probability of survival with the results of calculation of a criterion. The second part of this thesis led to propose new differential models of damage allowing to find, in the case of a load of constant amplitude, the classic formalism of the curves S-N of materials (Wöhler, Basquin, Bastenaire and Stromeyer). The influence of the order of appearance of cycles of stress, the mean values, the not linear evolution of the damage by fatigue are so taken into account. The problem of sensibility of the model and thus its forecasts of life in fatigue uniaxiale of variable amplitude, as it is met in the model of Chaboche, is so pushed aside. The confrontation of the model proposed for the curves S-N of Basquin and Bastenaire is promising in term of forecast of the life. A comparative study with regard to the law of Miner, taken as reference, with those proposed and of Mesmacque and Amrouche with datum of the decisive results for the laws with not linear evolution.

The master’s thesis deals with the fatigue life prediction under multiaxial cyclic loading. First, the fatigue process is discussed and the methods for fatigue life prediction under uniaxial and multiaxial loading are described. In the practical part, the accuracy of selected criteria is assessed based on experimental data obtained on cylindrical samples made of 1.2210 steel that were tested under synchronous symmetric axial-torsion loading. Application of criteria requires to determine the fatigue strength under pure axial and torsional loading.

O uso das ligas de alumínio em aplicações estruturais tem crescido consideravelmente nas últimas décadas. Nos transportes, a baixa massa específica do alumínio resulta em uma alta razão resistência/ peso, favorecendo a fabricação de aviões, trens e automóveis. Com a crescente preocupação em reduzir a emissão de gases poluentes, vem tornando-se promissora a alternativa de reduzir o peso dos veículos substituindo peças convencionalmente produzidas com outros materiais por peças de alumínio. As ligas tratáveis termicamente da série 6xxx são frequentemente escolhidas para estas aplicações. Assim, para que o emprego dessas ligas seja otimizado, é importante um estudo mais detalhado de suas propriedades mecânicas, principalmente sob solicitações cíclicas. Neste trabalho foram estudadas ligas de Al-Si-Mg que são amplamente utilizadas nas indústrias automotivas, em especial na fabricação de componentes de carroçarias para caminhões e ônibus. Foi realizado o estudo do comportamento em fadiga de baixo ciclo e fadiga multiaxial das ligas AA6005 T6, AA6063 T6 e AA6351 T6, fornecidas pela CBA (Companhia Brasileira de Alumínio) visando caracterizar e comparar essas ligas em sua microestrutura, propriedades de tração e fadiga. As propriedades básicas de fadiga foram determinadas por meio do método ε-N (fadiga de baixo ciclo) e os ensaios foram realizados com controle de deformação total, onda triangular e taxa de deformação 0,005 seg-1. As análises dos laços de histerese elasto-plástica permitiram inferir sobre aspectos microestruturais relacionados às propriedades mecânicas das ligas estudadas. O comportamento em fadiga multiaxial foi avaliado por meio de carregamentos combinados axial-torcional em fase e fora de fase. Para ajustar os dados experimentais obtidos, foram testados alguns dos modelos encontrados na literatura. Os cálculos baseados no modelo de plano crítico, proposto por Fatemi e Socie, apresentaram resultados satisfatórios. Também foram realizadas análises microestruturais e fractográficas para as três ligas. As superfícies de fratura dos ensaios de fadiga multiaxial mostraram resultados diferentes de acordo com o carregamento adotado. A avaliação comparativa das três ligas estudadas fornece subsídios para fundamentar a seleção de materiais para a fabricação de componentes estruturais para o setor automotivo. / The use of aluminum alloys in structural applications has grown considerably in recent decades. In transportation, the low density of aluminum results in a high strength-to weight ratio, proving attractive for production of aircrafts, trains and automobiles. With a growing concern for the reduction of pollutant gas emissions, aluminum alloys are becoming a promising alternative to diminish vehicle weight through the replacement of conventionally produced parts made from other heavier materials for aluminum parts. The heat treatable alloys from the 6xxx series are often chosen for these applications. Therefore, to optimize the employment of these alloys, a detailed study of their mechanical properties, primary under cyclic solicitations is necessary For the present study Al-Mg-Si alloys were chosen, which are widely used in automotive industries, particularly in the manufacturing of components for trucks and bus bodies. The low-cycle fatigue behavior and multiaxial fatigue of the three following aluminum alloys: AA6005 T6, AA6063 T6 and AA6351 T6, provided by CBA (Brazilian Aluminum Company), were assessed, with the aim of characterizing and comparing these alloys in their microstructure, tensile properties and fatigue. The basic properties of fatigue were studied by ε-N method (low cycle fatigue) and the experiments were performed with total strain control, triangular waveform and with a constant deformation rate of 5.0x10-3 s-1. The analyses of hysteresis loops elasto-plastic provided insight about microstructural aspects, related to mechanical properties of the studied alloys. Multiaxial fatigue behavior was assessed in combined axial-torsion loading in phase and out of phase. To adjust the experimental data, some models found in the literature were tested. Calculations based on critical plane model, proposed by Fatemi Socie, presented satisfactory results. Furthermore, microstructure analyses and fractography were performed for these three alloys. The fracture surface of multiaxial fatigue assays demonstrated different results according to the adopted loading. Comparative evaluation of the three studied alloys provides support for the selection of materials for manufacturing structural components of the automotive sector.

Made available in DSpace on 2014-12-17T15:38:52Z (GMT). No. of bitstreams: 1 HanniaRRPR_DISSERT.pdf: 2137181 bytes, checksum: ae4af965fe56dad2f3f8c2d06548931d (MD5) Previous issue date: 2011-05-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Millon describes the normal personality by means of adaptation styles that are effective in normal environments and personality disorders such as unadapted operating styles. To operacionalize his theoretical model, Millon has built several instruments, including the Millon Clinical Multiaxial Inventory III (MCMI-III), wich consists of a self report inventory composed by 175 true or false response items, containing four verification scales, and others scales wich evaluates 14 personality patterns and 10 clinical syndromes. The Substance Dependence scale (T) is placed along with Clinical Syndromes scales. This research is justified by the lack of a Brazilian instrument to assess personality psychopathological aspects, and aims to translate and semantically adapt the MCMI-III to the Brazilian context, checking validity elements of the Substance Dependence scale, and developing a computer application for assisting the evaluation of assessment results. To this intent, 2.588 individuals data was collected, male and female, aged between 18 and 85 years, characterized as belonging to a clinical or non-clinical group, who took part in the survey via the internet or in person. Respondents completed the MCMI-III, a socio-demographic questionnaire and a subgroup also answered to the Goldberg General Health Questionnaire (GHQ). Besides descriptive statistics, we performed the analysis using the Student t test, principal components analysis and internal consistency. Despite difficulties related to translating very specific English terms, the assessment by judges, experts on Millon?s theory, and the back translation, attested the adequacy of the Brazilian version. Factorial analysis indicated the grouping of translated T scale items into three factors (social activities prejudice, lack of impulse control, and oppositional behavior), by presenting a single item on a fourth factor (apparently related to seeking pleasurable stimuli). The Cronbach alpha for this set of items was 0,82, indicating an acceptable scale reliability. The data analysis resulted in distinction of scores between clinical and non-clinical groups and between men and women; the relationship between high scores on the scale T and the other scales; scores of drug users according to the declared used substance; and the relationship between high scores on T and the verification of disorder or risk on GHQ mental health factor, indicating the instrument?s adequate sensistivity in identifying psychopathologies and the relationship between the different disorders or psychopathological personality patterns. Although further studies are necessary to develop the scores transformation factors, the computerized correction tool was adequate. / Millon descreve a personalidade normal em termos de estilos de adapta??o que s?o eficazes em meios normais e transtornos de personalidade como os estilos de funcionamento desadaptados. Para operacionalizar seu modelo te?rico, Millon construiu diversos instrumentos, entre eles o Millon Clinical Multiaxial Inventory III (MCMI-III), que consiste num invent?rio de auto-relato de 175 itens com resposta falso ou verdadeiro, que avalia 14 padr?es de personalidade e 10 s?ndromes cl?nicas, al?m de conter 4 escalas de verifica??o. Entre as escalas de S?ndromes Cl?nicas encontra-se a escala de Depend?ncia de Subst?ncia (T). A presente pesquisa justifica-se pela inexist?ncia de instrumentos no pa?s que avaliem os aspectos psicopatol?gicos da personalidade, e tem como objetivos traduzir e adaptar semanticamente o MCMI-III para o Brasil, verificando elementos de validade da escala de Depend?ncia de Subst?ncias, e elaborar um aplicativo informatizado que assessore a avalia??o dos resultados desse instrumento. Para tal, foram coletados dados junto a 2.588 pessoas, dos sexos masculino e feminino, com idades entre 18 e 85 anos, caracterizados como pertencentes a um grupo cl?nico ou n?o-cl?nico, que participaram da pesquisa presencialmente ou via internet. Os participantes responderam ao MCMI-III, a um question?rio s?cio-demogr?fico e um subgrupo tamb?m respondeu ao Question?rio de Sa?de Geral de Goldberg (QSG). Al?m das estat?sticas descritivas, foram efetuadas an?lises por meio do teste t de Student, an?lises de componentes principais e de consist?ncia interna. Apesar de dificuldades relacionadas ? tradu??o de termos muito espec?ficos da l?ngua inglesa, a avalia??o por ju?zes conhecedores da teoria de Millon e o procedimento de back translation atestaram a adequa??o da vers?o brasileira. A an?lise fatorial indicou o agrupamento dos itens da escala T em 3 fatores (comprometimento das atividades sociais, aus?ncia de controle dos impulsos e condutas opositivas), com a apresenta??o de um item isolado em um quarto fator (aparentemente relacionado ? busca de est?mulos prazerosos). O alfa de Cronbach para este grupo de itens foi de 0,82, indicando aceit?vel confiabilidade da escala. A an?lise dos dados obtidos resultou em diferencia??o nas pontua??es de grupos cl?nico e n?o cl?nico e entre homens e mulheres; rela??o entre pontua??es altas na escala T com as demais escalas do instrumento; diferencia??o nas pontua??es dos usu?rios de drogas de acordo com a subst?ncia declarada como utilizada; e rela??o entre as altas pontua??es em T e a verifica??o de dist?rbio ou risco no fator Sa?de Geral do QSG, indicando adequada sensibilidade do instrumento na identifica??o de quadros psicopatol?gicos e na rela??o entre os diferentes transtornos ou padr?es psicopatol?gicos de personalidade. O aplicativo de corre??o informatizado se mostrou adequado, embora ainda sejam necess?rios estudos para o desenvolvimento dos fatores de transforma??o dos escores

O uso das ligas de alumínio em aplicações estruturais tem crescido consideravelmente nas últimas décadas. Nos transportes, a baixa massa específica do alumínio resulta em uma alta razão resistência/ peso, favorecendo a fabricação de aviões, trens e automóveis. Com a crescente preocupação em reduzir a emissão de gases poluentes, vem tornando-se promissora a alternativa de reduzir o peso dos veículos substituindo peças convencionalmente produzidas com outros materiais por peças de alumínio. As ligas tratáveis termicamente da série 6xxx são frequentemente escolhidas para estas aplicações. Assim, para que o emprego dessas ligas seja otimizado, é importante um estudo mais detalhado de suas propriedades mecânicas, principalmente sob solicitações cíclicas. Neste trabalho foram estudadas ligas de Al-Si-Mg que são amplamente utilizadas nas indústrias automotivas, em especial na fabricação de componentes de carroçarias para caminhões e ônibus. Foi realizado o estudo do comportamento em fadiga de baixo ciclo e fadiga multiaxial das ligas AA6005 T6, AA6063 T6 e AA6351 T6, fornecidas pela CBA (Companhia Brasileira de Alumínio) visando caracterizar e comparar essas ligas em sua microestrutura, propriedades de tração e fadiga. As propriedades básicas de fadiga foram determinadas por meio do método ε-N (fadiga de baixo ciclo) e os ensaios foram realizados com controle de deformação total, onda triangular e taxa de deformação 0,005 seg-1. As análises dos laços de histerese elasto-plástica permitiram inferir sobre aspectos microestruturais relacionados às propriedades mecânicas das ligas estudadas. O comportamento em fadiga multiaxial foi avaliado por meio de carregamentos combinados axial-torcional em fase e fora de fase. Para ajustar os dados experimentais obtidos, foram testados alguns dos modelos encontrados na literatura. Os cálculos baseados no modelo de plano crítico, proposto por Fatemi e Socie, apresentaram resultados satisfatórios. Também foram realizadas análises microestruturais e fractográficas para as três ligas. As superfícies de fratura dos ensaios de fadiga multiaxial mostraram resultados diferentes de acordo com o carregamento adotado. A avaliação comparativa das três ligas estudadas fornece subsídios para fundamentar a seleção de materiais para a fabricação de componentes estruturais para o setor automotivo. / The use of aluminum alloys in structural applications has grown considerably in recent decades. In transportation, the low density of aluminum results in a high strength-to weight ratio, proving attractive for production of aircrafts, trains and automobiles. With a growing concern for the reduction of pollutant gas emissions, aluminum alloys are becoming a promising alternative to diminish vehicle weight through the replacement of conventionally produced parts made from other heavier materials for aluminum parts. The heat treatable alloys from the 6xxx series are often chosen for these applications. Therefore, to optimize the employment of these alloys, a detailed study of their mechanical properties, primary under cyclic solicitations is necessary For the present study Al-Mg-Si alloys were chosen, which are widely used in automotive industries, particularly in the manufacturing of components for trucks and bus bodies. The low-cycle fatigue behavior and multiaxial fatigue of the three following aluminum alloys: AA6005 T6, AA6063 T6 and AA6351 T6, provided by CBA (Brazilian Aluminum Company), were assessed, with the aim of characterizing and comparing these alloys in their microstructure, tensile properties and fatigue. The basic properties of fatigue were studied by ε-N method (low cycle fatigue) and the experiments were performed with total strain control, triangular waveform and with a constant deformation rate of 5.0x10-3 s-1. The analyses of hysteresis loops elasto-plastic provided insight about microstructural aspects, related to mechanical properties of the studied alloys. Multiaxial fatigue behavior was assessed in combined axial-torsion loading in phase and out of phase. To adjust the experimental data, some models found in the literature were tested. Calculations based on critical plane model, proposed by Fatemi Socie, presented satisfactory results. Furthermore, microstructure analyses and fractography were performed for these three alloys. The fracture surface of multiaxial fatigue assays demonstrated different results according to the adopted loading. Comparative evaluation of the three studied alloys provides support for the selection of materials for manufacturing structural components of the automotive sector.

Les travaux présentés concernent le développement d'un modèle de prévision de durée de vie unifié pour traiter les problématiques de fatigue à faible et grand nombre de cycles. Le modèle est basé sur une approche à deux échelles et un endommagement de type Lemaitre. Le caractère "en vitesse" de la loi d'endommagement permet de traiter des chargements complexes, non proportionnels et aléatoires. Une campagne expérimentale de fatigue sur 12 éprouvettes cruciformes en alliage TA6V pour application aérospatiale est présentée. Elle comporte des essais biaxiaux proportionnels et non proportionnels ainsi que des cas de chargement pseudo-aléatoires. L'utilisation de la corrélation d'images numériques prises dans la zone utile permet d'évaluer les déformations locales en réponse aux sollicitations appliquées. Les cas de chargements sont simulés afin de confronter les déformations de surface et les durées de vie obtenues par calcul, aux résultats expérimentaux. Parmi les contributions théoriques présentées dans le manuscrit, sont à noter : - La proposition d'une nouvelle loi d'évolution pour écrouissage cinématique adaptée au comportement élastoplastique du TA6V sous chargement cyclique; - L'utilisation d'une correction élastoplastique locale permettant d'évaluer les déformations plastiques en surface à partir de calculs de structures linéaires; - L'amélioration d'un critère de micro-plasticité pour la prise en compte des effets de contrainte moyenne et de triaxialité en fatigue à grand nombre de cycles; - L'unification de deux lois d'endommagement afin d'étendre le domaine de validité du modèle initial vers les durées de vie à faible nombre de cycles. La démarche s'appuyant sur le cadre thermodynamique de la mécanique des milieux continus, de nombreuses perspectives d'amélioration du modèle sont discutées. / This work presents the proposal of a unifying predictive model to deal with LCF and HCF problems. It is based on a two-scale approach initially developed by Lemaitre. As the damage evolution law is rate written, complexity due to non proportional and random loadings may also be treated. An experimental fatigue campaign of 12 cross shaped samples made of TA6V alloy for aerospace applications is presented. It includes not only proportional and non proportional biaxial tests but also pseudo random loadings. Digital Image Correlation is used to evaluate the local strains from pictures taken in the zone of interest. Loadings are the simulated and both strains and lifetimes are compared to experimental observations. Among the theoretical contributions presented in this work, the main are: - A new kinematic hardening evolution law for the modeling of elasto-plasticity of TA6V alloy under cyclic loadings; - Use of local elastoplastic correction from linear Finite Element Calculation to estimate plastic strains in the structure zone of interests; - Improvements of the micro-plastic yield function to take into account mean stress effect and triaxiality effects in the lifetime prediction in HCF domain; - A unifying method of two damage variables in order to extend the validity domain of the initial model to shorter lifetimes (LCF). As the model is based on a thermodunamical framework for continuum mechanics, several extension are mentioned as future propects.