Escoamentos viscoelásticos não estacionários com superfícies livres são comuns em muitos processos industriais e diversas técnicas numéricas têm sido empregadas para reproduzir computacionalmente estes processos. A maioria dos modelos empregados utiliza equações diferenciais na definição do tensor de tensões. Porém, para alguns grupos de fluidos complexos, por exemplo, fluidos de Boger, os modelos integrais mostram-se mais capacitados em fornecer uma boa aproximação para os comportamentos não lineares desses fluidos. Este trabalho trata da solução numérica do modelo constitutivo integral KBKZ-PSM para escoamentos transientes bidimensionais com superfícies livres. O método numérico proposto é uma técnica numérica que utiliza diferenças finitas para simular escoamentos com superfícies livres na presença de paredes sólidas. As principais características do método numérico proposto são: solução das equações de conservação de quantidade de movimento e massa utilizando um método semi-implícito; a condição de contorno na superfície livre é acoplada à equação de Poisson, o que garante conservação de massa; a discretização do tempo t é realizada por uma nova técnica numérica; o tensor de Finger é calculado pelo método dos campos de deformação e avançado no tempo pelo método de Euler modificado. Essa nova técnica é verificada em escoamentos cisalhantes e elongacionais. Adicionalmente, uma solução analítica desenvolvida para escoamentos em canais bidimensionais é empregada para verificar e analisar a convergência do método proposto. Com relação a escoamentos com superfícies livres, a convergência é verificada por meio de refinamento de malha nas simulações de um jato incidindo sobre placa rígida e no problema do inchamento do extrudado. Finalmente, o método é aplicado para investigar os problemas jet buckling e inchamento do extrudado de fluidos KBKZ-PSM. / Unsteady viscoelastic free surface flows are common in many industrial processes and a variety of numerical techniques have been employed to simulate these flows. The majority of constitutive models employed are based on differential equations to define the extra stress tensor. However, for some complex fluids, for instance, Boger fluids, integral models are more adequate to approximate the nonlinear behaviour of these fluids. This work deals with the numerical solution of the integral constitutive model KBKZ-PSM for two-dimensional unsteady free surface flows. The proposed numerical method is a numerical technique that employs finite differences to simulate moving free surface flows that interact with solid walls. The main features of the method are: numerical solution of the momentum and mass equations by an implicit method; the pressure condition on the free surface is implicitly coupled with the Poisson equation for obtaining the pressure field from mass conservation; a novel scheme for defining the past times t is employed; the Finger tensor is calculated by the deformation fields method and is advanced in time by the modified Euler method. This new technique is verified by solving shear and uniaxial elongational flows. Moreover, an analytic solution for channel flows is obtained that is used in the verification and convergence analysis of the proposed methodology. For free surface flows, the assessment of convergence lies on the mesh refinement on the simulation of a jet impinging on a flat surface and the extrudade swell problem. Finally, the new method is applied to investigate the jet buckling phenomenon and extrudate swell of KBKZ-PSM fluids.

Le présent travail concerne l’étude de l’usinage de l’alliage de titane Ti-6Al-4V, matériau très apprécié par les industries aéronautique, biomédicale et de l’énergie. Les qualités des alliages de titane sont nombreuses : haute résistance aux températures élevées et à la corrosion, haute résistance mécanique, biocompatibilité, etc. Cependant, certaines propriétés physiques de ces matériaux, comme leur faible conductivité thermique, conduisent à des difficultés lors de leur mise en forme par usinage. Des études ont été et sont toujours conduites afin de comprendre le comportement de ces matériaux lors de leur mise en forme. Peu de travaux portent sur la prise en compte de la microstructure dans le comportement des alliages de titane lors du procédé d’usinage. Cette dimension constitue l’une des originalités de ce travail de thèse. Les phénomènes microstructuraux sont caractérisés à travers une étude expérimentale en coupe orthogonale de l’alliage Ti-6Al-4V. Les efforts, la température, la morphologie des copeaux et la microstructure sont analysés et interprétés. Une étude numérique du processus de coupe par simulation éléments finis est employée pour comprendre le rôle de l’endommagement et de la recristallisation. A partir des conclusions de ces différentes études, la construction d’un nouveau modèle de comportement est proposée. Ce modèle est appliqué à une modélisation élément fini pour différentes conditions de coupe afin d’étudier l’influence des paramètres d’usinage. Le modèle est validé par comparaison aux résultats expérimentaux. Il est ensuite exploité afin de proposer une analyse du processus de la coupe et notamment de la formation du copeau. / The present work concerns the study of the machining of titanium alloy Ti-6Al-4V. This material is much appreciated by the aerospace, biomedical and energy industries for its advantageous properties: high resistance to high temperatures and corrosion, high mechanical strength, biocompatibility, etc. However, certain physical properties of these materials, such as their low thermal conductivity, lead to difficulties during the machining process. Studies have been and are still conducted to understand the behavior of these materials during their shaping. Few studies consider the influence of microstructure on the behavior of titanium alloys during the machining process. This is one of the originalities of the present work. The microstructural phenomena are characterized through an experimental study of orthogonal cutting of the Ti-6Al-4V alloy. Machining forces, temperature, chip morphology and microstructure are analyzed and discussed. A numerical study of the finite element simulation process is used to understand the role of damage and recrystallization. From the conclusions of these different studies, the construction of a new model of behavior is proposed. This model is applied to finite element modeling for different cutting conditions to study the influence of machining parameters. The model is validated by comparison with the experimental results. It is then used to propose an analysis of the microstructural phenomena during the cutting process and the formation of the chip.

Sabe-se que na Engenharia há uma larga utilização de uma gama de materiais (concreto, aço, compósitos, solos etc.), os quais, de forma prática são analisados macroscopicamente naquilo que diz respeito a diversos fatores que influem no seu comportamento, como por exemplo, resistência, módulo de elasticidade, rigidez, dentre outras características. No entanto, estes materiais, em sua maioria heterogêneos, possuem tais comportamentos intrinsicamente relacionados à sua estrutura microscópica, a qual nos mostra que um material é o resultado de uma grande combinação de elementos dentro de sua composição, os quais irão reger tais propriedades. Os materiais podem ser estudados em diversas escalas, a qual dependerá do nível de detalhamento a ser atingido, de tal modo que a mesma pode variar desde o meio particulado até seu meio atômico. Uma das principais vantagens dos modelos multi-escala é a visualização, por parte do analista, das interações entre os constituintes do compósito, o que permite um melhor entendimento do comportamento do material e dos fenômenos de deterioração que ocorrem nas escalas menores e que determinam o comportamento da estrutura na escala maior. O objetivo do presente trabalho é fornecer uma revisão da aplicação de tais modelos, bem como estudar tais elementos diferenciais do material, em sua individualidade (como um meio contínuo), para então, através de um volume representativo, determinar as propriedades do material heterogêneo através de um modelo, representando assim o comportamento do conjunto de tais elementos, de tal modo a se tornar possível a avaliação dos impactos de eventuais mudanças em cada elemento no comportamento do material. / It is known that in Engineering there is a wide use of a range of materials (concrete, steel, composites, soils, etc.), which are practically analyzed macroscopically with respect to several factors that influence their behavior, such as for example, strength, modulus of elasticity, rigidity, among other characteristics. However, these materials, mostly heterogeneous, possess such behaviors intrinsically related to their microscopic structure, which shows us that a material is the result of a great combination of elements within its composition, which will govern such properties. The materials can be studied at various scales, which will depend on the level of detail being reached, such that it can vary from the particulate medium to its atomic medium. One of the main advantages of multi-scale models is the analyst\'s visualization of the interactions between the constituents of the composite, which allows a better understanding of the behavior of the material and of the deterioration phenomena occurring in the smaller scales that determine the behavior on the larger scale. The objective of the present work is to provide a review of the application of such models, as well as to study such differential elements of the material, in their individuality (as a continuous medium), to then, through a representative volume, determine the properties of the heterogeneous material through of a model, thus representing the behavior of the set of such elements, so as to make possible the evaluation of the impacts of eventual changes in each element in the behavior of the material.

Les réarrangements chromosomiques affectant la région d'hétérochromatine constitutive du chromosome 1 humain (bande cytogénétique 1q12) sont remarquablement fréquents dans les lymphomes, les myélomes, les leucémies aiguës et dans certaines tumeurs solides. Ceci suggère fortement l'existence de mécanismes oncogéniques dépendant de l'hétérochromatine constitutive dans ces maladies. Mes travaux de thèse montrent que ces réarrangements induisent des altérations profondes de l'organisation et de la fonction de la chromatine dans des cellules de lymphome B. Les conséquences majeures sont la formation de foyers hétérochromatiques aberrants résultant d'appariements intra-chromosomiques ‘longue distance' entre le domaine d'hétérochromatine 1q12 réarrangé et le domaine centromérique. Ces foyers sont associés à un enrichissement de l'euchromatine adjacente en marques épigénétiques répressives, et à la répression de l'expression de gènes, parmi lesquels GMCL1 et MXD1 qui codent pour des protéines impliquées dans le contrôle de la signalisation P53 et MYC, respectivement. D'autre part, l'étude pilote de profiling transcriptionnel par puces Affymetrix dans des cas de lymphome avec ou sans anomalie de l'hétérochromatine 1q12 confirme et identifie de nouvelles cibles de dérégulation liées à l'hétérochromatine dans les lymphomes B non-Hodgkiniens. La compréhension du rôle de ces foyers hétérochromatiques aberrants présenterait un intérêt majeur pour les tumeurs hématologiques ou solides, puisque ces anomalies sont observées de manière fréquente et non-aléatoire dans un large spectre de tumeurs humaines, et sont associées à la progression tumorale et à un mauvais pronostic.

Contrary to elastic deformation, plastic deformation of crystalline materials, such as metals, is size-dependent. Most commonly, this phenomenon is present but unnoticed, such as the effect of microstructural length scales. The grain size in metallic materials is a length scale that affects material parameters such as yield stress and hardening moduli. In addition, several experiments performed in recent years on specimens with geometrical dimensions on the micron scale have shown that these dimensions also influence the mechanical behaviour. The work presented in this thesis involves continuum modelling and simulation of size-dependent plastic deformation, with emphasis on thin films and the formulation of interface conditions. A recently published strain gradient plasticity framework for isotropic materials [Gudmundson, P., 2004. A unified treatment of strain gradient plasticity. Journal of the Mechanics and Physics of Solids 52, 1379-1406] is used as a basis for the work. The theory is higher-order in the sense that additional boundary conditions are required and, as a consequence, higher-order stresses appear in the theory. For dimensional consistency, length scale parameters enter the theory, which is not the case for conventional plasticity theory. In Paper A and B, interface conditions are formulated in terms of a surface energy. The surface energy is assumed to depend on the plastic strain state at the interface and different functional forms are investigated. Numerical results are generated with the finite element method and it is found that this type of interface condition can capture the boundary layers that develop at the substrate interface in thin films. Size-effects are captured in the hardening behaviour as well as the yield strength. In addition, it is shown that there is an equivalence between a surface energy varying linearly in plastic strain and a viscoplastic interface law for monotonous loading. In paper C, a framework of finite element equations is formulated, of which a plane strain version is implemented in a commercial finite element program. Results are presented for an idealized problem of a metal matrix composite and several element types are examined numerically. In paper D, the implementation is used in a numerical study of wedge indentation of a thin film on an elastic substrate. Several trends that have been observed experimentally are captured in the theoretical predictions. Increased hardness at shallow depths due to gradient effects as well as increased hardness at more significant depths due to the presence of the substrate are found. It is shown that the hardening behaviour of the film has a large impact on the substrate effect and that either pile-up or sink-in deformation modes may be obtained depending on the material length scale parameter. Finally, it is qualitatively demonstrated that the substrate compliance has a significant effect on the calculated hardness of the film. / QC 20100723

ABSTRACT 3-D SOIL STRUCTURE INTERACTION ANALYSES OF THREE IDENTICAL BUILDINGS IN SAKARYA CITY AFTER 17 AUGUST 1999 KOCAELI EARTHQUAKE &Uuml / nal,Orhan M.S., Department of Civil Engineering, Supervisor: Assist. Prof. Dr Kemal &Ouml / nder &Ccedil / etin October 2003, 116 Pages The aim of this study is to analyze the soil structure interaction of three identical buildings on &ordf / ahinler Street of Sakarya city which had no damage to heavy damage after the Kocaeli (1999) earthquake. For the purpose of 3-D dynamic nonlinear analysis of the soil site and the overlying structures, Flac3D software was chosen as the numerical modeling framework. Soil properties were determined by using the results of available site investigation studies. A three dimensional mesh was created to represent the topographic and geometric constraints of the problem. Linearly elastic perfectly plastic constitutive model was implemented to model the soil behavior. The results of 3-D dynamic numerical analyses in the forms of acceleration, displacement, strain, stress and pore pressure were presented. The higher acceleration, strain and stress levels calculated under the collapsed building can be attributed as the major cause of poor performance of the structure.

The mechanical behavior of the arterial wall is determined by the composition and structure of its internal constituents as well as the applied traction-forces, such as pressure and axial stretch. The purpose of this work is to develop new theoretical frameworks and experimental methodologies to further the understanding of arterial mechanics and role of the various intrinsic and extrinsic mechanically motivating factors. Specifically, residual deformation, matrix organization, and perivascular support are investigated in the context of their effects on the overall and local mechanical behavior of the artery. We propose new kinematic frameworks to determine the displacement field due to residual deformations previously unknown, which include longitudinal and shearing residual deformations. This allows for improved predictions of the local, intramural stresses of the artery. We found distinct microstructural differences between the femoral and carotid arteries from non-human primates. These arteries are functionally and mechanically different, but are geometrically and compositionally similar, thereby suggesting differences in their microstructural alignments, particularly of their collagen fibers. Finally, we quantified the mechanical constraint of perivascular support on the coronary artery by mechanically testing the artery in-situ before and after surgical exposure.

This thesis presents a whole-embryo finite element model of neurulation -- the first of its kind. An advanced, multiscale finite element approach is used to capture the mechanical interactions that occur across cellular, tissue and whole-embryo scales. Cell-based simulations are used to construct a system of constitutive equations for embryonic tissue fabric evolution under different scenarios including bulk deformation, cell annealing, mitosis, and Lamellipodia effect. Experimental data are used to determine the parameters in these equations. Techniques for obtaining images of live embryos, serial sections of fixed embryo fabric parameters, and material properties of embryonic tissues are used. Also a spatial-temporal correlation system is introduced to organize and correlate the data and to construct the finite element model. Biological experiments have been conducted to verify the validity of this constitutive model. A full functional finite element analysis package has been written and is used to conduct computational simulations. A simplified contact algorithm is introduced to address the element permeability issue. Computational simulations of different cases have been conducted to investigate possible causes of neural tube defects. Defect cases including neural plate defect, non-neural epidermis defect, apical constriction defect, and convergent extension defect are compared with the case of normal embryonic development. Corresponding biological experiments are included to support these defect cases. A case with biomechanical feedbacks on non-neural epidermis is also discussed in detail with biological experiments and computational simulations. Its comparison with the normal case indicates that the introduction of biomechanical feedbacks can yield more realistic simulation results.

This thesis presents a whole-embryo finite element model of neurulation -- the first of its kind. An advanced, multiscale finite element approach is used to capture the mechanical interactions that occur across cellular, tissue and whole-embryo scales. Cell-based simulations are used to construct a system of constitutive equations for embryonic tissue fabric evolution under different scenarios including bulk deformation, cell annealing, mitosis, and Lamellipodia effect. Experimental data are used to determine the parameters in these equations. Techniques for obtaining images of live embryos, serial sections of fixed embryo fabric parameters, and material properties of embryonic tissues are used. Also a spatial-temporal correlation system is introduced to organize and correlate the data and to construct the finite element model. Biological experiments have been conducted to verify the validity of this constitutive model. A full functional finite element analysis package has been written and is used to conduct computational simulations. A simplified contact algorithm is introduced to address the element permeability issue. Computational simulations of different cases have been conducted to investigate possible causes of neural tube defects. Defect cases including neural plate defect, non-neural epidermis defect, apical constriction defect, and convergent extension defect are compared with the case of normal embryonic development. Corresponding biological experiments are included to support these defect cases. A case with biomechanical feedbacks on non-neural epidermis is also discussed in detail with biological experiments and computational simulations. Its comparison with the normal case indicates that the introduction of biomechanical feedbacks can yield more realistic simulation results.

The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.