L'objectif de cette thèse est l'étude des conséquences de la thermo-oxydation sur la structure chimique et le comportement mécanique d'un Ethylène Propylène Diène Monomère (EPDM). Afin de déterminer les modifications à différentes échelles structurales, quatre formulations modèles sont étudiées : la gomme pure, les matrices vulcanisées stabilisée et non stabilisée et l'élastomère industriel. L'ensemble des échantillons est vieilli entre 70 et 170°C dans l'air ou sous vide puis caractérisé par divers outils analytiques. La thermogravimétrie donne accès aux variations de masse résultant de l'incorporation d'oxygène et l'émission de composés volatils. L'analyse infrarouge permet de suivre les évolutions des espèces chimiques. Les essais de gonflement, de chromatographie et de spectrométrie mécanique permettent de calculer les nombres de coupures de chaînes et d'actes de réticulation à chaque instant. Sur la base de ces résultats, un modèle cinétique général de thermo-oxydation de la matrice EPDM est proposé et en partie validé. Les conséquences du vieillissement thermique sur le comportement mécanique de l'élastomère industriel sont mises en évidence par des essais de traction uniaxiale et de multi-relaxation à température ambiante et vitesse de déformation initiale de 10-3 s-1. L'impact du vieillissement thermique sur les propriétés ultimes et les réponses à l'équilibre et hors équilibre est examiné. Un critère prédictif de rupture basé sur la mécanique de la rupture est proposé. Enfin, le couplage vieillissement thermique - contrainte mécanique est étudié par des essais relaxation de contraintes continues entre 130 et 170°C dans l'air. Les modifications de la microstructure pendant le vieillissement thermique sont intégrées dans les équations constitutives du modèle mécanique macroscopique afin de proposer un outil de prédiction du comportement à long terme de l'élastomère industriel. La simulation numérique montre une bonne adéquation avec les résultats expérimentaux. / The aim of this work is to study the consequences of the thermal oxidation on the chemical structure and mechanical behavior of an Ethylene-Propylene-Diene Monomer (EPDM). In order to determine the structural changes at different scales, four model formulations have been considered: free additive gum, stabilized and unstabilized vulcanized matrix and industrial rubber. All samples were aged between 70 and 170°C in air or vacuum and characterized by several analytical tools. Thermogravimetry gives access to weight variations due to oxygen grafting and volatile compounds release. Infrared analysis is used to follow chemical species evolutions. Swelling tests, chromatographic and mechanical spectrometry tests allow calculating the number of chain scission and cross-linking events at any time. Based on these results, a general kinetic model is proposed and partially validated for EPDM matrix thermal oxidation. The consequences of thermal ageing on the mechanical behavior of the industrial rubber are pointed out by monotonic tensile and stress relaxation tests at room temperature and a 10-3 s-1- initial strain rate. The impact of thermal ageing on ultimate properties and equilibrium and non-equilibrium response are examined. Finally, the coupling between thermal ageing and mechanical stress is studied by continuous stress relaxation tests between 130 et 170°C in air. The microstructural modifications during thermal ageing are introduced into the constitutive equations of the macroscopic mechanical model in order to propose a predictif tool of the long time behavior of the industrial rubber. The numerical simulation is in good agreement with experimental results.

The main focus of this work lies in the simulation of the deformation of mechanical components which consist of nonlinear elastic, incompressible material and that are subject to large deformations. Starting from a nonlinear formulation one can derive a discrete problem by using linearisation techniques and an adaptive mixed finite element method. This turns out to be a saddle point problem that can be solved via a Bramble-Pasciak conjugate gradient method. With some modifications the simulation can be improved.:1. Introduction 2. Basics 3. Mixed variational formulation 4. Solution method 5. Error estimation 6. LBB conditions 7. Improvement suggestions

[pt] Neste trabalho um estudo de estruturas pneumáticas considerando acoplamento pressão–volume e modelos constitutivos plásticos e viscoplásticos são desenvolvidos. Estruturas pneumáticas são estruturas de membrana sobre as quais atuam pressão de gases estabilizadas por tensões de tração. Essas estruturas são mais leves que estruturas convencionais resultando em soluções mais econômicas. Elas possuem ainda algumas características que contribuem para um desenvolvimento sustentável, como a utilização de luz natural e ventilação e a possibilidade de reutilização. Quando as estruturas pneumáticas são submetidas a cargas externas, essas estruturas apresentam variação da pressão internal e do volume. Este acoplamento é um dos objetos de estudo do presente trabalho. Soluções analíticas são desenvolvidas para descrever este acoplamento. Em programas convencionais de elementos finitos esse acoplamento não é considerado. Uma formulação para o acoplamento pressão–volume para câmaras fechadas é incluído no modelo de elementos finitos com grandes deformações. A variedade de modelos de material implementados tem a finalidade de abranger o comportamento de muitos tipos de materiais de membrana usados em estruturas pneumáticas. Na literatura o estudo dos materiais de membrana para estruturas pneumáticas tem foco na análise experimental. Modelos para material de membrana são incorporados no modelo de elementos finitos para pequenas e grandes deformações. Os modelos constitutivos considerados neste trabalho são hiperelástico, elastoplástico e elastoviscoplástico. A ocorrência de grandes deformações é incluída. Um novo material baseado em superfícies NURBS é proposto e validado com base em resultados experimentais e modelos clássicos de materiais. Neste trabalho ênfase é dada ao material ETFE (Etileno tetrafluoretileno), o qual é amplamente usado em estruturas pneumáticas. Os modelos desenvolvidos aqui, como o acoplamento pressão–volume e os modelos de materiais são implementados em elementos finitos no programa usado na cadeira de estática das construções da TUM (Technische Universitat Munchen), chamado CARAT++ (Computer Aided Research Analysis Tool). / [en] In this work a study of pneumatic structures considering pressure–volume coupling under plastic and viscoplastic material behavior is developed. Pneumatic structures are membrane structures acted on by air or gases stabilized by tension. These structures are lighter than conventional structures resulting in economic structural solutions. They present also some characteristics that contribute to the sustainable development, such as the utilization of natural lighting and ventilation and its possibility of reuse. When pneumatic structures are subjected to external loads these structures present both internal pressure and volume variation. This coupling is one of the objects of the present work. Analytical solutions are developed to describe this coupling. In conventional finite element systems this coupling is not considered. A formulation for pressure–volume coupling by closed chambers is included in the framework of a finite element large strain model. The variety of material models implemented has the purpose to cover the behavior of the many kinds of membrane materials used in pneumatic structures. In the literature the study of the membrane materials for pneumatic structures focuses on experimental analysis. Membrane material models are incorporated in the finite element model for small and large strains. The constitutivematerial models considered in this work are hyperelastic, elastoplastic and elastoviscoplastic. The onset of large strains is enclosed. A new material model based on NURBS surfaces is proposed an validated on hand of experimental results and classic material models. In this work emphasis is given to the material ETFE (Ethylene tetrafluoroethylene), which is widely used in pneumatic structures. The models developed here, such as the pressure-volume coupling and the material models, are implemented in finite elements on the program used in the Static Chair at TUM (Technische Universitat Munchen), which is called CARAT++ (Computer Aided Research Analysis Tool).

[pt] Os problemas geotécnicos e geológicos envolvem a descrição do comportamento de materiais tais como solo e rocha e sua eventual interação com fluidos e estruturas. Em geral, a evolução desses problemas é caracterizada por grandes deformações e deslocamentos, descontinuidades, heterogeneidades e um comportamento constitutivo complexo. A abordagem deste tipo de problemas requer técnicas numéricas que levem em conta essas características, sem apresentar inconvenientes numéricos associados à distorção dos elementos como acontece no método dos elementos finitos (FEM). A presente tese desenvolve um algoritmo computacional baseado no método do ponto material (MPM) para aproximar a solução das equações governantes dos fenômenos mencionados. O algoritmo é baseado numa formulação dinâmica tridimensional do contínuo, considerando grandes deformações. Os amortecimentos de Rayleigh o local não viscoso são incorporados para modelar problemas dinâmicos e quase-estáticos. A geração dinâmica das poro-pressões é formulada assumindo o meio poroso saturado e um ponto material para discretizar a mistura. Diversas técnicas de suavização das pressões são avaliadas em problemas de impacto sobre meios saturados. Diferentes modelos constitutivos são implementados para modelar tanto a formação da superfície de ruptura e o processo de escoamento da massa de solo durante as instabilidades, quanto a gênese, evolução e quantificação de zona de falhas nos processos geológicos. Para a abordagem da discretização de problemas de escala geológica de grande número de partículas usando o MPM, uma metodologia é proposta e verificada com a discretização do deslizamento do Daguangbao, na China. Visando à diminuição do tempo computacional, o algoritmo é implementado segundo o paradigma de programação paralela. / [en] Geotechnical and geological problems involve the description of the behavior of materials such as soil and rock, and their eventual interaction with fluids and structures. In general, the evolution of these problems is characterized by large deformations and displacements, discontinuities, heterogeneities and complex constitutive behavior. Addressing these problems requires numerical techniques that take these characteristics into account, without numerical drawbacks associated with element distortion as occurs in the finite element method (FEM). In this thesis is developed a computational algorithm based on the material point method (MPM) to approximate the solution of the governing equations to the mentioned phenomena. The algorithm is based on a three-dimensional dynamic formulation of the continuum considering large deformations. Rayleigh damping and non-viscous local damping are incorporated to model dynamic and quasi-static problems. The dynamic generation of pore pressures is formulated assuming the saturated porous medium and a single material point to discretize the mixture. Different techniques are evaluated to mitigate spurious pressure in impact problems on saturated media. Different constitutive models are implemented to model the failure surface and the soil mass flow process during slope instabilities, as well as the genesis, evolution and failure zone quantification in geological processes. To address the discretization of large-scale geological problems using MPM, a methodology is proposed and validated with the discretization of the Daguangbao landslide, in China. In order to decrease the computational time, the algorithm is implemented according to the parallel programming paradigm.

A study was conducted to evaluate the properties and processes influencing the rate and magnitude of volume decrease and strength gain for oil sand fine tailings resulting from a change in bitumen extraction process (caustic versus non-caustic) and the effect of adding a coagulant to caustic fine tailings. Laboratory flume deposition tests were carried out with the objective to hydraulically deposit oil sand tailings and compare the effects of extraction processes on the nature of beach deposits in terms of geometry, particle size distribution, and density. A good correlation exists between flume deposition tests results using oil sand tailings and the various other tailings materials. These comparisons show the reliability and effectiveness of flume deposition tests in terms of establishing general relationships and can serve as a guide to predict beach slopes. Fine tailings were collected from the various flume tests and a comprehensive description of physical and chemical characteristics of the different fine tailings was carried out. The characteristics of the fine tailings is presented in terms of index properties, mineralogy, specific surface area, water chemistry, liquid limits, particle size distribution and structure. The influence of these fundamental properties on the compressibility, hydraulic conductivity and shear strength properties of the fine tailings was assessed. Fourteen two meter and one meter high standpipe tests were instrumented to monitor the rate and magnitude of self-weight consolidation of the different fine tailings materials. Consolidation tests using slurry consolidometers were carried out to determine consolidation properties, namely compressibility and hydraulic conductivity, as well as the effect of adding a coagulant (calcium sulphate [CaSO4]) to caustic fine tailings. The thixotropic strength of the fine tailings was examined by measuring shear strength over time using a vane shear apparatus. A difference in water chemistry during bitumen extraction was concluded to be the cause of substantial differences in particle size distributions and degree of dispersion of the comparable caustic and non-caustic fine tailings. The degree of dispersion was consistent with predictions for dispersed clays established by the sodium adsorption ratio (SAR) values for these materials. The biggest advantage of non-caustic fine tailings and treating caustic fine tailings with coagulant is an increased initial settlement rate and slightly increased hydraulic conductivity at higher void ratios. Thereafter, compressibility and hydraulic conductivity are governed by effective stress. The chemical characteristics of fine tailings (water chemistry, degree of dispersion) do not have a significant impact on their compressibility behaviour and have only a small influence at high void ratio (low effective stress). Fine tailings from a caustic based extraction process had relatively higher shear strengths than comparable non-caustic fine tailings at equivalent void ratios. However, shear strength differences were small and the overall impact on consolidation behaviour, which also depends on compressibility and hydraulic conductivity, is not expected to be significant.

No description available.

The thesis is devoted to study of continuum mechanics and thermodynamics and the related mathematical analysis. It consists of four self-contained chapters dealing with different aspects. The first chapter focuses on peridynamics, a non-local theory of continuum mechanics, and its relation to conventional local theory of Cauchy-Green elasticity. Similar compar- isons has been used for proving consistency and for determining some of the material coefficients in peridynamics, provided the material parameters in the local theory are known. In this chapter the formula for the non-local force-flux is computed in terms of the peridynamic interaction, relating the fundamental concepts of these two theories and establishing hence a new connection, not present in the previous works. The second and third chapters are both devoted to Rate-Independent Systems (RIS) and their applications to continuum mechanics. RIS represents a suitable approximation when the internal, viscous, and thermal effects can be neglected. RIS has been proven to be useful in modeling hysteresis, phase transitions in solids, elastoplasticity, damage, or fracture in both small and large strain regimes. In the second chapter the existence of solutions to an evolutionary rate-independ- ent model of Shape Memory Alloys (SMAs) is proven. The model...