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Les aciers à effet TWIP (TWinning Induced Plasticity) suscitent un regain d'intérêt au niveau de la sidérurgie mondiale car ils combinent simultanément très haute résistance mécanique et très grande ductilité. Ces excellentes propriétés mécaniques sont liées à la présence de maclage mécanique, mécanisme connu sous le nom d'effet TWIP. L'objectif majeur de cette thèse est d'étudier l'effet TWIP sur plusieurs nuances d'aciers Fe-Mn (entièrement austénitiques, austéno-ferritiques duplex) afin de développer une loi de comportement prédictive des aciers à effet TWIP. La première partie de cette thèse fut donc consacrée à la détermination du comportement des aciers austénitiques Fe-Mn-C à effet TWIP. Pour ce faire, un modèle micromécanique par transition d'échelle en élastoviscoplasticité a été développé en se basant sur une description physique des mécanismes de déformation considérés dans cette étude: glissement cristallographique et maclage mécanique. Les interactions macle-glissement et macle-macle en relation avec le comportement de l'écrouissage à l'échelle du polycristal et à l'échelle du grain ont été finement analysé. La seconde partie de ce travail a été consacrée à la caractérisation du comportement d'aciers duplex Fe-Mn-Al-C par la Diffraction des Rayons X afin d'évaluer les contraintes internes initiales dans les deux phases ainsi que leur évolution avec la déformation au cours d'un essai mécaniques in situ. Une modélisation du comportement d'aciers duplex a été établie dans le but de développer un outil d'optimisation de la microstructure (proportion de la phase ferritique/austénitique) dans une approche "Alloy design". Puis, des essais de traitement thermique ont été faits afin de favoriser le maclage dans les aciers duplex / Steels having TWIP effect (TWinning Induced Plasticity) are very interesting for the worldwide siderurgy, because they simultaneously combine very high mechanical strength and ductility. These excellent mechanical properties are related to the presence of mechanical twinning, the so-called TWIP effect. The major objective of this thesis is to study the TWIP effect on several grades of Fe-Mn steels (entirely austenitic, austeno-ferritic duplex) in order to develop a predictive behavior law of steels with TWIP effect. The first part of this work consisted of the modelling of the behavior of Fe-Mn-C austenitic steels having TWIP effect. A micromechanical model using the scale transition method in elastoviscoplasticity has been developed. It is based on a physical description of the deformation mechanisms considered in this study: crystallographic slip and mechanical twinning. The twin-slip and twin-twin interactions in relation with the hardening behaviour at the polycrystal scale and the grain scale have been finely analyzed.The second part of this work is concentrated on the characterization of the behavior of Fe-Mn-Al-C duplex steels by X-rays diffraction in order to evaluate the initial internal stresses in the two phases as well as their evolution with the deformation during an in situ tensile test. A modeling of the duplex steel behavior was established in order to develop an optimization tool of the microstructure (proportion of the ferritic/austenitic phase) in an approach "Alloy design". Then, tests of heat treatment were made in order to generate the TWIP effect in the duplex steels

[pt] Atualmente, o escoamento de fluidos não Newtonianos está presente em diversos processos industriais e também no dia- a-dia de todos. Na presente dissertação, inicialmente, é apresentada uma nova equação constitutiva capaz de modelar fluidos que possuam tanto elasticidade como viscoplasticidade, sendo este novo modelo definido como elasto-viscoplástico. Para a melhor compreensão do modelo, anteriormente, é realizada, uma breve revisão dos fluidos não Newtonianos, com maior ênfase para o modelo viscoplástico SMD e o modelo viscoelástico de Oldroyd-B, que possuem grande influência no novo modelo constitutivo. Em seguida é apresentada uma nova metodologia de adimensionalização levando-se em conta apenas os parâmetros reológicos neste processo, garantindo a independência das equações com relação a vazão. Por fim, é realizada a simulação deste novo modelo em um escoamento com uma expansão e contração abrupta. Nesta simulação, é analisado o comportamento do fluido ao passar por esta cavidade com relação às principais variáveis da equação constitutiva. A simulação foi realizada pelo método dos elementos finitos e os resultados mostram a influência do número de Deborah reológico, da velocidade, do expoente power-law e da razão entre os tempos de retardo e de relaxamento, na perda de carga e no padrão de escoamento. / [en] Currently, the flow of non-Newtonian fluids is present in many industrial processes and also in day-to-day of all. In this dissertation, initially it is exposed a new constitutive equation capable of modeling fluids that present as much elasticity as viscoplasticity, and this new model is called as Elasto-viscoplastic. For better understanding of this model, previously, a brief review of non- Newtonian fluids is done, with a focus on the SMD viscoplastic model and on the Oldroyd-B viscoelastic model, both which have a great influence in this new constitution model.Afterward, a new methodology of non- dimensionalization is presented, taking into account only the rheological parameters in this process and ensuring the independence of equations with respect to flow. Finally, the simulation of this new model is performed in a flow within a abrupt expansioncontraction geometry. In this simulation, it is studied the behavior of the fluid through this cavity with respect to key variables of the constitutive equation. The simulation was carried out by the finite element method and, by the analysis of the results, it is shown the influence of the rheological Deborah, flow speed, the power-law exponent and the ratio of the time of retardation and relaxation on the head loss and the flow pattern.

Les milieux poreux sont omniprésents dans le quotidien des hommes du 21ème siècle que ce soit par hasard ou par nécessité. Certains permettent le transport d’une ou plusieurs phases fluides immiscibles, une situation à la fois courante et critique dans de nombreuses applications industrielles. Le transport d’une phase mouillante, l’imbibition, a été largement étudiée mais un certain nombre de problèmes restent ouverts. Dans cette thèse, nous nous sommes concentrés sur trois d’entre eux. La fragmentation de phase induite par la gravité dans une jonction asymétrique a été étudiée. La dynamique et un critère d’apparition ont été prédits analytiquement puis confirmés expérimentalement. Ensuite, l’évolution de l’épaisseur d’un front d’imbibition dans un réseau de capillaires a été simulée numériquement. Les résultats ont permis de lever une controverse de la littérature. Enfin, l’imbibition dans un milieu constitué de lames flexibles déformables a été explorée numériquement et expérimentalement. Il a été montré que la déformabilité des lames induit leur coalescence et agit sur la dynamique de l'imbibition. / Porous media are ubiquitous in today’s society due to chance or necessity. Some of them allow the transportation of one or several immiscible fluid phases simultaneously. This property is both usual and critical in many industrial processes. The transport of a wetting phase, imbibition, has been widely studied but lots of issues remain opened. In this manuscript, three of them are addressed. Gravity induced phase fragmentation has been studied in an asymmetric pore junction. Fragmentation criterion and dynamic are predicted analytically and confirmed experimentally. Then, the broadening of an imbibition front in a capillary network has been investigated numerically. Results resolved a controversy in the literature. Finally, imbibition in a medium made of flexible sheets has been studied both numerically and experimentally. It showed that sheets flexibility induces their clustering and influences the imbibition dynamic.

The purpose of this study is to compare two possible methods of computational modeling of straightening long profiles. The study presents fundamentals of the straightening process, basic principles of the finite element method and the principle of fast algorithm based on Eulerian description of motion of continuum. The study investigates how the two methods are computationally demanding and precise. Finally, the acquired results are summarised and the effectiveness of both algorithms is assessed.

Afin de participer à l’émergence de technologies innovantes et contribuer aux objectifs de développement durable, un consortium composé de 13 partenaires (3 laboratoires académiques et 10 entreprises industrielles) a été formé. Le projet Thermofluid-RT consiste à développer un système de refroidissement à boucle de fluide diphasique à pompage mécanique. Le LMT-Cachan contribue à la conception de l'élément essentiel de la pompe, à savoir, le soufflet. Celui-ci est obtenu en soudant des feuilles d’acier inoxydable à durcissement structural très mince (70 µm) et doit fonctionner sans défaillance pendant 20 ans. Un dimensionnement fiabiliste du soufflet basé sur la théorie du maillon le plus faible est réalisé. Une méthode d'optimisation basée sur la technique d’identification intégrée à la corrélation d'images numériques aboutit à une géométrie d’éprouvette qui minimise l'incertitude des paramètres recherchés. Toutes les données brutes sont combinées à leur juste valeur grâce à une formulation Bayésienne basée sur l’hypothèse de bruits blanc gaussiens. La géométrie optimisée est testée sur Mini-Astrée, la nouvelle machine biaxiale du LMT. Plusieurs lois de comportements sont étudiées et testées sur le matériau étudié. De très fines feuilles du même acier, sont de même testées à l’aide d’essais uni-axiaux et multiaxiaux. Une analyse microscopique est conduite au travers d’un micro-essai de traction sur 2 grains et l’identification de paramètres d’une loi de plasticité cristalline. Enfin, le dimensionnement probabiliste du soufflet est validé à partir de plusieurs mesures expérimentales infra-rouges sur un nouveau banc d’essai. Un modèle probabiliste à deux échelles permet la caractérisation des phénomènes observés relatifs au matériau d’étude et au composant lui-même. / In the context of leveraging and accelerating innovative technological solutions that contribute to meeting sustainable goals, a consortium composed of 13 partners (3 academic laboratories and 10 industrial companies) has been formed. The THERMOFLUID-RT project consists in developing a two-phase fluid loop driven by a mechanical pump. LMT-Cachan contributes to the design of the critical component of the pump, i.e., bellows. This component obtained by welding very thin (70 µm) pre-deformed sheets made of precipitation-hardened stainless steel is expected to operate without failure for 20 years. First, a new probabilistic design methodology allows for the fatigue design of the component. Second, an optimization methodology based on full field measurements and Integrated Digital Image Correlation (IDIC) allows the sample geometry to be designed with the least uncertainty of the sought parameters. All data account for the latter thanks to a Bayesian foundation that equitably weights all measurements. Third, the optimized cruciform geometry has been tested in a new compact biaxial machine, mini-Astrée that allows for a fast, yet robust identification. Several elasto-plastic models with increasing complexity are investigated to probe the material behavior. Ultra-thin sheets are also tested in uniaxial and biaxial experiments thanks to an anti-wrinkling setup. Fourth, a microscopic analysis is also performed via quasi-3D IDIC and a uniaxial micro-specimen allow a crystal plasticity law to be characterized. Last, the probabilistic fatigue design of the bellows based on the weakest link theory and a two-scale probabilistic model is validated with infrared measurements in the high cycle fatigue regime.

[pt] Sendo a exploração de petróleo cada vez mais profunda, atingindo vários quilômetros abaixo dos leitos marítimos, uma simulação numérica adequada para prever o comportamento de rochas antes da perfuração está se tornando cada vez mais importante para a indústria de petróleo, devido aos altos custos operacionais para garantir a estabilidade do poço. Um dos problemas típicos que os engenheiros de petróleo enfrentam é a instabilidade de poços em rochas evaporíticas, que geralmente são sujeitas a deformações excessivas e possuem características de comportamento mecânico dependentes do tempo. Grandes reservas de petróleo que foram encontradas ao redor do mundo em rochas evaporíticas encorajaram aos engenheiros a investigar mais profundamente essa resposta mecânica dependente do tempo (creep). Por outro lado, a concentração de tensões em torno dos furos pode torná-lo um projeto de engenharia inviável. A desestabilização devido a grandes deformações pode levar a problemas como colapso e fechamento do poço. Assim, para estudar a estabilidade de poços e projetar um sistema de produção de petróleo adequado, a influência do creep deve ser considerada adequadamente no comportamento esperado do material. Nesta pesquisa, as equações que definem o modelo elásto-viscoplástico de Sterpi e Gioda (2007) são implementadas no programa computacional FLAC 3D - ITASCA, código baseado no método das diferenças finitas. O procedimento de implementação consiste em gerar uma DLL (Dynamic Link Library) escrita em linguagem de programação C (mais mais) e integrar as tensões ao longo de um incremento de deformações usando um algoritmo de integração explícito. O modelo elásto-viscoplástico foi validado com resultados experimentais envolvendo rochas salinas disponíveis na literatura. Finalmente, é realizada uma simulação numérica com o programa FLAC 3D, considerando o modelo de Sterpi e Gioda, com o objetivo de estudar o fechamento de um poço no pré-sal brasileiro. / [en] Since oil exploration is reaching several kilometers below seafloor, an adequate numerical simulation for prediction of rock behavior prior to drilling is becoming increasingly important for the oil industry due to the high operating costs to ensure well stability. One of the typical problems that oil engineers face is the instability of wells in evaporitic rocks, which are often subject to excessive deformation and have time-dependent mechanical behavior characteristics. Huge oil reserves that were found around the world in evaporitic reservoirs encouraged engineers to further investigate this mechanical time-dependent response (creep). On the other hand, the concentration of stresses around the well can make it an unviable engineering project. Destabilization due to large deformations may be involved, leading to problems such as collapse and well closure. Thus, in order to study the stability of the boreholes and design an appropriate oil production system, creep must be properly considered in the expected behavior of the material. In this research, the equations that define the elasto-viscoplastic model of Sterpi and Gioda (2007) will be implemented in the computer program FLAC 3D - Itasca, code based on the finite difference method. The implementation procedure consists of generating a Dynamic Link Library (DLL) written in C (plus plus) programming language and integrating the stress along a strain increment by using an explicit integration algorithm. The elasto-viscoplastic model has been validated with experimental results from triaxial creep tests in salt rocks available in the literature, indicating a successful implementation. Finally, a numerical simulation in FLAC 3D considering the model of Sterpi and Gioda is performed in order to study a pre-salt wellbore closure.

Made available in DSpace on 2014-06-12T17:37:46Z (GMT). No. of bitstreams: 2 arquivo2408_1.pdf: 3478641 bytes, checksum: eb0a9acd07c63f1148e729cf12fd792a (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2010 / Agência Nacional do Petróleo, Gás Natural e Biocombustíveis / O comportamento de solos e rochas pode ser descrito através de modelos constitutivos que associam estados de tensões com estados de deformações. Trata-se de um problema de valor inicial cuja solução é obtida empregando de técnicas numéricas. Neste problema, a partir de um estado de tensão inicial e de um incremento de deformações, obtém-se um novo estado de tensões resultante da integração da lei constitutiva ao longo do passo de tempo. As relações constitutivas usadas são do tipo elastoplástica e visco-plástica com regularização viscosa de Perzina. Os critérios de plastificação adotados foram os de Mohr-Coulomb e o de Drucker-Prager, ambos com suavização da superfície de fluência. Foram analisados problemas mecânicos e hidro-mecânicos. Para representar o acoplamento hidro-mecânico foram adotadas leis que relacionam variáveis mecânicas a deformação do meio. Na dissertação foram implementados, no programa de elementos finitos CODE_BRIGHT, o método explícito de integrações de tensões de Euler Modificado e o de Runge-Kutta-Dormand-Price, ambos com controle de erro. As implementações foram verificadas através de um problema de expansão de cavidade cilíndrica e as análises de desempenho dos esquemas de integração foram feitas tomando como critério o número de passos e o tempo total de CPU. Esta mesma análise também foi realizada para os casos de escavação do túnel de Brasília e o de reativação de falha selante, mostrando que os algoritmos implementados funcionam satisfatoriamente para problemas geomecânicos com e sem acoplamento de fluxo de fluidos

Tese de mestrado. Faculdade de Engenharia. Universidade do Porto. 1998

In this study, Reometer AR2000 is used to investigate the effect of shear rate on viscosity of emulsion. And a model for the effective viscosity of emulsion is established. Moreover, another model for the hydrodynamic lubrication with binary mixtures of non-Newton fluids is developed. The coupled modified Reynolds are solved by combining the advanced multilevel method with the Newton-Raphson method. The effect of shear rate on lubrication characteristics of hydrodynamic lubrication of emulsion is investigated in cold rolling process. Research results show that the viscosity of emulsion is decreased with increasing the shear rate. Hence,the oil film thickness, oil preasure and oil concentration under hydrodynamic lubrication are increased with decreasing the slide-to roll ratio. Emulsion will be Newton fluid under high shear rate. In the cold rolling process, the emulsion shows the high shear rate, and the elastic deformation of roller and strip are considersd. Hence the end point of plastic zone of strip is moved to oulet zone due to the lubricated zone is increased, so that the film thickness is higher than that for rigid body. When roller radius is increased, the effective elastic modulus and the thickness reduction of strip are decreased, then the lubrication characteristics in cold rolling process are influenced by elastic deformation. When the rolling speed is increased , the inlet film thickness is increased, and the roll torque is slightly increased, but the rolling force and peak preasure are almost not influenced.