Many computational methodologies have been developed over the years with the goal of characterizing damage presence in structural components. In this thesis two approached were investigated. The first approach covered in this thesis is the modeling of damage presence through the reduction of the modulus of elasticity. This approach was mainly applied to a cantilevered beam of uniform cross-section. Various crack configurations/orientations were investigated, and from this data equations relating modulus as a function of crack length were derived. The second approach deals with modifying the local flexibility at the location of damage through modification of the element stiffness matrix. This approach has certain advantages in that it can adequately capture the global modal and displacement effects of damage without the added computational effort of mesh refinement that is required for physically modeled cracks.

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Understanding failure mechanics of mechanical equipment is one of the most important aspects of structural and aerospace engineering. Crack growth being one of the major forms of failure in structural components has been studied for several decades to achieve greater reliability and guarantee higher safety standards. Conventional approaches using the finite element framework provides accurate solutions, yet they require extremely complicated numerical approaches or highly fine mesh densities which is computationally expensive and yet suffers from several numerical instabilities such as element entanglement or overly soften element behavior. The eXtended Finite Element Method (XFEM) is a relatively recent concept developed for modeling geometric discontinuities and singularities by introducing the addition of new terms to the classical shape functions in order to allow the finite element formulation to remain the same. XFEM does not require the necessity of computationally expensive numerical schemes such as active remeshing and allows for easier crack representation. In this work, verifies the validity of this new concept for quasi-static crack growth in tension with Abaqus' XFEM is employed. In the course of the work, the effect of various parameters that are involved in the modelling of the crack are parametrically analyzed. The load-displacement data and crack growth were used as the comparison criterion. It was found that XFEM is unable to accurately represent crack growth in the models in the elastic region without direct manipulation of the material properties. The crack growth in the plastic region is found to be affected by certain parameters allowing us to tailor the model to a small degree. This thesis attempts to provide a greater understanding into the parametric dependencies of XFEM crack growth. / Master of Science

Finite Element Analysis (FEA) is proposed to simulate the connection response of practical in-service conditions and test the performance of Oil Country Tubular Goods (OCTG) premium threaded connections. A plug-in is developed in Abaqus/CAE for creating the 360-degree full 3D parametric finite element model with helical threads as an effective design and analysis tool. All size, position and material data of the model are parameterized. The premium connection plug-in accepts input from the Graphical User Interface (GUI) for further modification. Each premium connection component is programed as a collection of single-purpose independent functions organized as an independent module in order to allow users to modify specific function behavior conveniently. A main program is designed as an Abaqus kernel plug-in to achieve all the functions by calling these independent functions, making the plug-in flexible. Each single script file is not too long to jeopardize readability. The GUI of the plug-in is designed with proper layout arrangement and illustrations to make the plug-in user-friendly and easy to use. The premium connection FE model is used in a virtual test to validate the model against the ISO 13679 test protocol and is used to develop the seal metrics for points on the ISO 13679 sealability envelope. The plug-in can be used to develop and evaluate the design envelope of the premium connection. / Master of Science

Ce travail de thèse contribue à étudier le comportement élasto-plastique au rayage du verre métallique massif Zr55Cu30Al10Ni5 par la méthode des éléments finis (MEF) et expérimentaux. Le critère de plasticité de type Drucker-Prager est utilisé, une méthode de remaillage est proposée afin d'éviter le problème de convergence qui vient de la grand contrainte cisaillement. Pour cela, le comportement au rayage est étudié par le changement de l'angle d'attaque, du coefficient de frottement local entre le matériau et l'indenteur. Ces influences sont valorisés par l'évolution des forces rayures, par la morphologie de l'échantillon, et ils montrent le mécanisme de changement des modes de rayage : du labourage à l'usinage avec la formation des copeaux. Les essais sont réalisés à l'aide de l'équipement du LARMAUR : Un nano-triboindenteur de type Hysitron Ti-950. La comparaison des résultats simulés et expérimentaux nous permettre d'évaluer la loi comportement utilisé et d'estimer la valeur de coefficient de frottement entre le matériau et l'indenteur. / This thesis contributes to modeling of the elasto-plastic behavior in scratch test of a Zr55Cu30Al10Ni5 Bulk Metallic Glasses (BMG) by the finite element method and by experimental testing. The Drucker-Prager criterion is used and dedicated re-meshing method is proposed in order to solve the numerical problems classically encountered when modeling such a test and this with a controlled element population. The influence of friction coefficient as well as the angle of attack are investigated to understand the occurrence of two deformation mechanisms : plowing and cutting. The test is realized by using the LARMAUR's equipment : nano triboindenter Hysitron Ti-950. The result of experimental and simulation are confronted the finite element simulations.

La corrosion des canalisations métalliques pour le transport de gaz ou d’hydrocarbures est un problème critique qui peut avoir des répercussions financières et environnementales très importantes. Les revêtements polyoléfines tricouches sont largement utilisés pour préserver l’intégrité des structures. Ils sont constitués d’une sous couche mince époxy, d’une couche mince d’adhésif et d’une couche épaisse le plus souvent en polyéthylène. Ce système de revêtement bénéficie de très bonnes qualités d'adhérence. Néanmoins, des cas de décollements de ces revêtements à l’interface époxy/acier ont été constatés sur des pipelines en service depuis quelques années seulement, alors que la durée minimale de vie escomptée des tubes dans le sol est de quelques dizaines d’années. Ces décollements pourraient être dus à une dégradation progressive des liaisons interfaciales entre le primaire époxy et la surface métallique, associée à la présence de contraintes interfaciales importantes entre les différentes couches de l'assemblage. Cette étude vise alors d'une part à proposer des solutions permettant d’aboutir à la meilleure performance en vieillissement de la liaison adhésive, et d'autre part à quantifier les niveaux de contraintes au sein de la canalisation en acier revêtue depuis sa mise en œuvre, jusqu'à sa mise en service.Les liaisons interfaciales dépendant nécessairement de la préparation de surface de l’acier, des procédés de nettoyage ont été testés afin d’évaluer leur influence sur l’adhérence initiale et la durabilité des assemblages. Les préparations de surface permettent d'obtenir un degré de propreté et une rugosité. Ces deux éléments maximisent les forces de liaison et donc l'adhérence du revêtement. Le revêtement résiste alors mieux dans des environnements agressifs. Tous les procédés de nettoyage testés ont conduits à des niveaux de propreté équivalents du substrat en acier. Les essais effectués sur substrats polis miroir ont mis en évidence qu’une rugosité est nécessaire pour améliorer la durabilité des assemblages. La rugosité permet d'obtenir des adhérences supérieures à celles sur substrats polis miroir, de ralentir les effets du vieillissement humide et donc de prolonger la durée de vie du système. Il a été mis en évidence que les fortes rugosités étaient particulièrement bénéfiques pour les adhérences sèches. Par contre, au-delà d’une certaine rugosité, l’augmentation de la rugosité ne s’accompagne pas d’une amélioration significative de l’adhérence humide. Une étude sur l’apport des traitements de surface a aussi été menée. L’addition d’un traitement de surface a peu d’impact sur les adhérences initiales des assemblages, en comparaison avec une préparation de surface classique. Par contre les traitements de surfaces améliorent considérablement les adhérences humides, et donc la durabilité des assemblages. Notre travail prouve que le traitement aminosilane est un candidat potentiel en vue du remplacement du traitement toxique de chromatation, référence en matière de traitements de surface dans l'industrie des pipelines et dont l'utilisation sera interdite dans un futur proche compte tenu de l'évolution de la réglementation. Dans de bonnes conditions d'application et associé avec des primaires époxy appropriés, les adhérences sèches et humides obtenues avec les silanes sont comparables (voire supérieures) à celles de la chromatation.Par ailleurs, la modélisation par éléments finis du système tricouches a permis de préciser les niveaux de contraintes aux interfaces résultant de la mise en œuvre et de prévoir leur évolution au cours du temps et du vieillissement humide. / External Corrosion can weaken underground steel pipelines and render them unsafe for transporting oil or gas. Premature damage of this network could lead to dramatic financial and environmental consequences. Three layers polyolefin coatings composed by a fusion bonded epoxy, a modified polyolefin adhesive and a thick polyolefin topcoat, are the most widely systems used to preserve the structure integrity. This protective coating system presents excellent adhesion. Nevertheless, in some specific cases, loss of adhesion has been observed at steel/epoxy interface on operating pipelines on shorter period than their expected lifetime of about fifty years. This disbonding can be assigned to the progressive degradation of interfacial bonds between the epoxy primer and the metallic surface combined to substantial interfacial stresses between the different layers of the assembly. This study thus aims both to provide solutions to achieve the best ageing performance of the adhesive bond, and secondly to quantify the stress levels in a coated steel pipe since coating manufacturing to pipeline commissioning.Given that interfacial bonds depend necessarily on steel surface preparation, cleaning methods were compared to appraise their influence on assemblies dry and wet adhesion. Surface preparations allow to achieve a level of cleanness and to create a surface roughness. These two elements maximize binding forces and therefore the adhesion of the coating. The coating is thus more resistant to aggressive environments. All cleaning process have led to equivalent level of cleanness of steel substrate. Experiments carried out on mirror polished steel substrates highlighted that a surface roughness is necessary to improve joints durability. Roughness allows to obtain higher adhesion compared to mirror polished steel substrates, slows the effects of humid ageing and thus contributes to extend the durability of the system. It has been demonstrated that a high roughness is particularly beneficial for dry adhesion. By cons, beyond a certain roughness, increasing the surface roughness does not lead to significant improvement of wet adhesion. The benefits of surface treatments were also investigated. The addition of a surface treatment has little impact on dry adhesion in comparison with a conventional surface preparation. However, surface treatments substantially enhance the adhesion strength in wet stage, and therefore increase the durability of the assemblies. We also demonstrate that aminosilane surface treatments are competitive alternatives to traditional chromate conversion, which is the surface treatment of reference in pipeline industry, and whose use will be prohibited in a near future considering changes in legislation. Under good conditions of application and associated with appropriate fusion bonded epoxy, dry and wet adhesion obtained with silane surface treatments are comparable (or even higher ) than those obtained with chromate surface treatments.Furthermore, finite element modeling has allowed to specify interfacial stresses levels inside the assembly resulting from coating's manufacturing process and to predict their evolution over time and during wet ageing.

The report aims to describe the austenitic stainless steel Sanicro 25 from a thermomechanical point of view. The thermal and mechanical properties of the material make it suitable for use in coal – and thermal power plants. By the use of Sanicro 25 it would be possible to bring the efficiency of these plants up while bringing the carbon emissions down.A material model is created from material testing and validated through simulation in the finite element software Abaqus. The model that has been derived describes the material behavior during loading and stress relaxation for the first cycle in a thermomechanical fatigue test well. The unloading part of the cycle however cannot be described correctly by the use of this model. / Rostfritt

This work describes the implementation of the eXtended Finite Element Method (XFEM) in the Abaqus software package. A user-defined element was developed containing the analytical functions relating to homogeneous and interface fracture mechanics. The long-term goal of such work is to increase the ability to analyze fractures and other imperfections in multimaterial systems containing large elastic mismatches, such as flexible electronics. A review of XFEM-related literature is presented, as well as an overview of fracture mechanics for both homogeneous and interface systems. The theoretical basis of the XFEM is then covered, including the concepts of Partition of Unity and stress intensity factor evaluation. Finally, numerical results of the implementation are compared to several benchmark cases, along with conclusions and suggestions for future work.

Made available in DSpace on 2016-12-12T20:25:12Z (GMT). No. of bitstreams: 1 Caroline Zanini Bressan.pdf: 4091231 bytes, checksum: 0de27c28e4c845db49e9a2081c0c7b93 (MD5) Previous issue date: 2015-06-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Numerical methods have received a substantial attention from Engineering Professionals especially due their capacity to provide solutions for a wide range of problems in many areas. In the last years, numerical simulation has become increasingly common and has turned into a key factor for solving numerous engineering problems in the industry as well in academia. This, however, requires the development of suitable methodological strategies to determinate constitutive law able to best describe the material behavior in the simulation. The present work is inserted within the context of metal forming, aiming to simulate 2D and 3D geometrical models of the simple tensile test and three-point bending test of a notched plate, both using the material properties of an Interstitial Free Steel, IF. For both cases, it was used a modified Gurson model available in the ABAQUS ® software, which is based on the finite elements method. Numerical modelling of the elasto-plastic process used to simulate the three-point bending and simple tensile test was discretised using structured meshes with an appropriate refinement. The experimental results for tensile tests used smooth cylindrical specimens with dimensions defined according to ASTM E 8M-01. The three point bending test was qualitatively compared with the results reported by Mashayeshi, et al (MASHAYEKHI, ZIAEI-RAD, et al., 2005). The strain hardening law used in this work was the Holomon or modified Swift law coupled with the damage evolution of the Gurson s model. The geometrical models for the tensile specimens account for axisymmetry, so that only one-quarter part of the 2D and 3D specimens was modelled. An appropriate mesh refinement in the necking region was also adopted. The numerical simulation was able to predict with success the stress-strain curve behaviour of the IF steel comparing with the experimental results. Both 2D and 3D simulation results of the simple tensile test were very similar. The prediction of porosity evolution with the applied displacement was analysed and the results indicated that the necking region in the central zone of the specimen presented the largest micro-void concentration, as expected. For the three-point bending test of a notched plate, the simulation provided a good qualitative agreement with the Mashayekhi´s numerical results, which have shown that the largest concentration of micro-voids was in the central region of the notch where the crack initiation occurs. / Métodos numéricos tem recebido uma grande atenção dos profissionais da área da engenharia em especial principalmente pelo seu caráter facilitador na solução de problemas em diversas áreas. Nos últimos tempos, a simulação numérica está se tornando cada vez mais comum e se transformando em uma peça chave para a resolução de inúmeros problemas de engenharia encontrados tanto nas indústrias quanto nas linhas de pesquisa científica das universidades. Isso, porém, exige desenvolvimento de estratégias de metodologias científicas adequadas o suficiente para determinar as leis que descrevam melhor o comportamento dos materiais a serem simulados. O presente trabalho está inserido no contexto da conformação de metais, tendo por objetivo simular, com malhas tipo 2D e 3D, os ensaios de tração simples e de flexão de três pontos de uma placa com entalhe de um aço livre de interstícios, aço IF (interstitial free steel), utilizando o modelo de Gurson modificado no programa ABAQUS ®, que utiliza o Método dos Elementos Finitos. Para o modelamento numérico do processo de deformação elasto-plástica dos ensaios de tração simples e flexão foi utilizada a lei de Gurson modificado de materiais porosos e uma malha com refinamento adequado. Os corpos de prova ensaiados experimentalmente em tração simples foram de aço IF cilíndricos preparados de acordo com a norma ASTM E 8M-01. Já o ensaio de flexão de três pontos foi simulado com o intuito de fazer uma comparação qualitativa com o resultado apresentado por Mashayekhi, Ziaei-Rad, et al. (MASHAYEKHI, ZIAEI-RAD, et al., 2005). A lei de encruamento plástico utilizada neste trabalho foi a Lei de Holomon ou Swift modificado acoplado com o modelo de evolução do dano de Gurson modificado. Após a escolha da geometria de somente quarta parte do corpo de prova, devido à simetria axissimétrica e do refinamento adequado da malha na região da estricção local, a simulação numérica foi capaz de prever com sucesso o comportamento da curva de tensãodeformação do aço IF comparando-se com os resultados experimentais. Os resultados da simulação 2D e 3D do ensaio de tração simples foram iguais. Portanto, a simulação 2D do ensaio de tração simples é mais conveniente pois é mais rápida e igualmente precisa que a simulação 3D para o presente caso de material dúctil e isotrópico. A previsão da evolução da porosidade com a deformação e a região de maior concentração de vazios foi analisada: ocorreu na região da estricção local e na zona central do corpo de prova como esperado. No caso do ensaio de flexão da placa com entalhe central, os resultados da simulação numérica mostraram uma boa concordância com os resultados de Mashayekhi, Ziaei-Rad et al. (2005), que apresentaram a maior concentração de vazios na região central do entalhe onde ocorrerá o aparecimento de trincas.