Este trabalho aborda o estudo de modelos constitutivos a fim de analisar o comportamento mecânico de um biopolímero derivado de óleo de mamona (Ricinus communis). A importância deste trabalho se dá ao fato de: servir como roteiro de ensaio de materiais poliméricos; completar caracterização do material estudado além do regime viscoelástico, bem como aplicação da análise do comportamento do material além do regime viscoelástico linear. A aplicação dos modelos avaliados via Método dos Elementos Finitos (MEF) exigiu o levantamento das propriedades e do comportamento mecânico do biopolímero, bem como a preparação dos ensaios, com as devidas especificações sugeridas pela ASTM (American Society for Testing and Materials) para cada tipo de ensaio. Assim, foram obtidos os corposde- prova (CDP) para a realização dos ensaios mecânicos quase-estáticos de tração, compressão e flexão (monotônicos e cíclicos), bem como, ensaio para análise dinâmicomecânica (Dynamic Mechanical Analysis - DMA) para a obtenção de propriedades associada às parcelas viscosas do material. Com estes foram obtidos parâmetros inerentes a cada tipo de ensaio, permeados com uma cuidadosa revisão bibliográfica sobre as implicações para a realização de cada ensaio. Uma outra etapa foi a verificação de modelos de plastificação baseados na teoria de von Mises, Drucker-Prager e de viscoelasticidade implementados no programa comercial ABAQUS®. Sendo que o objetivo maior foi a comparação dos resultados experimentais obtidos com os modelos em MEF. Os resultados para tração monotônica obtiveram erro de 0,61%, os resultados de compressão monotônica apresentaram erro de 1,5% e as simulações para os carregamentos cíclicos de tração e compressão não foram tão bons quanto os anteriores. Por isso se justifica a criação do modelo fenomenológico utilizando os parâmetros do material que foram identificados. / This work develops the study involving constitutive models with the objective to analyze the mechanical behavior of a biopolymer obtained from the Castor Oil Polyurethane (Ricinus communis). The importance of this work is due to the fact that: serves as a test script for the use of polymer materials; complete the characterization of the material studied beyond the viscoelastic realm, as well as the application of the analysis of the behavior of the material beyond the linear viscoelastic domain. The application of the evaluated models by way of the Finite Element Method (FEM), required the gathering of the properties and mechanical behavior of the biopolymer, as well as the preparation of the tests, with the required specifications suggested by the ASTM (American Society for Testing and Materials) for each type of test. Therefore, there were obtained the body-tests in order to run the mechanical quasi-static traction tests, tensile, compression and flexion (monotonic and cyclical) dynamicmechanical analysis (DMA) in order to obtain the properties associated with the viscous parts of the material. With these the inherent parameters were obtained for each specimen, permeated with a careful biographical revision of the implications for the experimenting of each specimen. Another phase was the verification of laminated models based on the theory by Von Mises, Drucker-Prager and of the viscoelasticity implemented in the commercial program ABAQUS®. The main objective being the comparison of the experimental results obtained with the models in FEM. The results for the monotonic traction obtained a error of 0,61%, the results of monotonic comparison presented an error of 1,5% and the simulations for the cyclical charges of traction and compression were not as good as the former. Therefore it justifies the creation of the phenomenological model utilizing the parameters of the materials that were identified.

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Die Arbeit beschreibt die skalenübergreifende Modellierung und Simulation des Werkstoffverhaltens von Faser-Kunststoff-Verbunden mit textiler Verstärkungsstruktur, die ausgehend von den konstitutiven Eigenschaften der Verbundbestandteile (Mikroskala) und ihrer geometrischen Anordnung im Verbund (Mesoskala) die rechnerische Vorhersage des effektiven Materialverhaltens des Verbundes (Makroskala) ermöglicht. Neben Schädigungsprozessen beeinflusst insbesondere das dehnratenabhängige Materialverhalten der polymeren Matrix das mechanische Verhalten des Verbundes. Dieser Einfluss wird anhand verschiedener Glasfaser-Polypropylen-Verbunde numerisch untersucht. Ein viskoplastisches Materialmodell bildet dabei das nichtlineare Materialverhalten von Polypropylen ab. Die Modellierung der textilen Verstärkungsstruktur erfolgt durch Anwendung der erweiterten Finiten-Elemente-Methode (XFEM). Anhand des Vergleichs von rechnerisch und experimentell gewonnenen Ergebnissen erfolgt schließlich die Verifikation der vorgeschlagenen Modellierungsstrategie. / This contribution covers the trans-scale modelling and simulation of the mechanical behaviour of textile-reinforced polymers. Starting from the material properties of the individual constituents (micro-scale) and their geometrical arrangement (meso-scale), the effective material behaviour of the composite (macro-scale) is numerically predicted. In addition to damage processes, the inelastic deformation behaviour of the composite is influenced by the strain-rate dependent material behaviour of the polymeric matrix. This influence is numerically investigated for different glass-fibre-polypropylene composites. A viscoplastic material model accounts for the nonlinear mechanical behaviour of polypropylene. The complex textile reinforcement is modelled by the eXtended finite element method (XFEM). A comparison of computed and experimental results allows for the verification of the proposed modelling strategy.

[pt] Desenvolveu-se estudo teórico e numérico para simular o comportamento tensão-deformação de solos e rochas. Procurou-se estabelecer modelagem constitutiva apta a representar as peculiaridades inerentes ao comportamento destes materiais sob grandes deformações e degradação da estrutura. Dentro do contexto geotécnico brasileiro, o objetivo da pesquisa foi, também, investigar uma nova abordagem constitutiva para modelar o comportamento de solos moles, solos residuais e rochas sedimentares. O trabalho está dividido nos seguintes tópicos: revisão bibliográfica; estudo de medidas de deformações e taxas objetivas de tensões; definição e desenvolvimento dos modelos constitutivos a serem testados; definição dos algoritmos de retorno para integração das equações constitutivas; implementação em elementos finitos; simulação do comportamento observado em ensaios de laboratório. Os resultados da pesquisa indicam que o comportamento viscoso da argila mole do Sarapuí pode ser reproduzido corretamente adotando-se modelo constitutivo viscoplástico. A abordagem de solo estruturado está condizente com o comportamento do arenito de Vila Velha. Por fim, para modelar o comportamento de solos residuais dentro de um novo quadro constitutivo, foi proposta uma separação das deformações irreversíveis. / [en] A theoretical and numerical study was developed to simulate the stressstrain behavior of soils and rocks, formulating constitutive models able to catch the peculiarities inherent to the behavior of these materials under large strains and structure degradation. Within the Brazilian geotechnical context, the objective of the research was also to investigate constitutive approaches to model the behavior of soft soils, residual soils and sedimentary rocks. The work is divided into the following topics: literature review; study of strain measurements and objective stress rates; definition and development of the constitutive models to be tested; definition of the return mapping algorithms for integrating the constitutive equations; finite element implementation; and simulation of the behavior observed in laboratory tests. Results indicate that the viscous behavior of the Sarapuí soft clay can be correctly reproduced by adopting a viscoplastic constitutive model. The structured soil approach appears to be consistent with the behavior of Vila Velha sandstone. Finally, a decomposition of irreversible strains was proposed to model the behavior of residual soils within a novel constitutive framework.

In the combustion zone of industrial- and aero- gas turbines, thermomechanical fatigue (TMF) is the dominant damage mechanism. Thermomechanical fatigue is a coupling of independent creep, fatigue, and oxidation damage mechanisms that interact and accelerate microstructural degradation. A mixture of intergranular cracking due to creep, transgranular cracking due to fatigue, and surface embrittlement due to oxidation is often observed in gas turbine components removed from service. The current maintenance scheme for gas turbines is to remove components from service when any criteria (elongation, stress-rupture, crack length, etc.) exceed the designed maximum allowable. Experimental, theoretical, and numerical analyses are performed to determine the state of the component as it relates to each criterion (a time consuming process). While calculating these metrics individually has been successful in the past, a better approach would be to develop a unified mechanical modeling that incorporates the constitutive response, microstructural degradation, and rupture of the subject material via a damage variable used to predict the cumulative “damage state” within a component. This would allow for a priori predictions of microstructural degradation, crack propagation/arrest, and component-level lifing. In this study, a unified mechanical model for creep-fatigue (deformation, cracking, and rupture) is proposed. It is hypothesized that damage quantification techniques can be used to develop accurate creep, fatigue, and plastic/ductile cumulative- nonlinear- damage laws within the continuum damage mechanics principle. These damage laws when coupled with appropriate constitutive equations and a degrading stiffness tensor can be used to predict the mechanical state of a component. A series of monotonic, creep, fatigue, and tensile-hold creepfatigue tests are obtained from literature for 304 stainless steel at 600°C (1112°F) in an air. iv Cumulative- nonlinear- creep, fatigue, and a coupled creep-fatigue damage laws are developed. The individual damage variables are incorporated as an internal state variable within a novel unified viscoplasticity constitutive model (zero yield surface) and degrading stiffness tensor. These equations are implemented as a custom material model within a custom FORTRAN onedimensional finite element code. The radial return mapping technique is used with the updated stress vector solved by Newton-Raphson iteration. A consistent tangent stiffness matrix is derived based on the inelastic strain increment. All available experimental data is compared to finite element results to determine the ability of the unified mechanical model to predict deformation, damage evolution, crack growth, and rupture under a creep-fatigue environment.

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No description available.

Fatigue failure plays an important role in engineering applications, especially when structural components experience significant cyclic thermal loading and complex force loading simultaneously. During the last decades, several post-processing techniques have been developed based on empirical investigations of experimental evidence to predict the fatigue life of materials. The work at hand postulates a conventional continuum damage theory for thermomechanical fatigue failure modeling. In particular, an implicit gradient-enhanced approach is employed to address the ill-posedness of the partial differential equation system when the damage onsets. An internal fatigue variable is phenomenologically defined based on the accumulation of viscoplasticity. In the sequel, a regularized fatigue variable is obtained to further yield the damagesoftening function, which straightforwardly applies to the stress, material tangent, and viscoplastic dissipation. A multi-field problem, consisting of the strain field, the temperature, and the non-local variable, is taken into consideration, leading to a fully coupled system. This numerical methodology is consistently derived and implemented into the context of the finite element method. Several representative and demonstrative examples are performed, which yield good numerical stability and agreement with experimental data. Conclusive findings and further perspectives close this article.

Les durées de vie classiques des pièces en aéronautique sont de plusieurs dizaines d’années. Cependant, certaines applications en marge impliquent des durées de vie bien plus courtes, sans réparation ou récupération des pièces. Les modèles de conception classiques doivent être adaptés et la démarche du choix matériau se faire « au juste besoin », autorisant l’utilisation des matériaux aux conditions limites de leur intégrité. Afin d’estimer ces limites, la caractérisation à plus hautes températures d’alliages existants est entreprise. C’est dans cette optique que se placent les travaux de thèse présentés dans ce manuscrit. L’alliage étudié est le Ti-6Al-4V (TA6V) forgé qui possède à l’issu du traitement thermomécanique une microstructure duplex. Il est actuellement l’alliage de titane le plus couramment utilisé en aéronautique et son utilisation est généralement limitée aux environs de 350°C pour des durées de vie classiques. Dans le but d’utiliser cet alliage pendant une dizaine d’heure, l’étude menée consiste à caractériser le TA6V de 20°C à 600°C. La caractérisation se centre, dans un premier temps, sur l’état métallurgique de la matière initiale issue du galet forgé et sur sa stabilité en température. Ensuite, le comportement mécanique du TA6V est étudié de 20°C à 600°C en traction, mettant en évidence une sensibilité de la contrainte d’écoulement à la vitesse de déformation dépendant de la température. Ce comportement est mis en lien avec le phénomène de vieillissement dynamique. La caractérisation du comportement mécanique est poursuivie par une campagne étendue de fluage de 20°C à 600°C pour différents niveaux de contraintes (de 0,3 à 1 fois la limite d’élasticité en traction). Ces essais montrent différents comportements en fonction de la température. La matière déformée en traction et en fluage est analysée en microscopie électronique en transmission afin d’apporter des informations sur les mécanismes de déformation gouvernant les différents comportements de l’alliage. Les campagnes de caractérisation en traction et en fluage ont permis d’établir un modèle de comportement viscoplastique du TA6V de 20°C à 600°C validé par l’ajustement des résultats obtenus à l’issue d’essais thermomécaniques complexes avec la simulation de ces essais par éléments finis. La corrélation des résultats en traction et en fluage et la détermination des mécanismes de déformation conduit à une discussion sur le comportement viscoplastique du TA6V, pour finalement aboutir à une proposition de modélisation du fluage du TA6V de 20°C à 600°C. Le modèle permet de reproduire qualitativement des courbes de fluage à partir de la sensibilité à la vitesse de déformation mesurée au cours d’essais de traction. / Classical life time of aeronautic parts lasts several decades. However, for some special applications with short life time and without repairs or recovery of parts, material design is tailored “close to real needs”. This justifies characterization at higher temperatures of well-known alloys and not developing new alloys. The study presented in this manuscript is included within this frame of short life applications. Forged Ti-6Al-4V (Ti-64) alloy with a bimodal microstructure is the most common titanium alloy in aeronautic and is usually limited below 350°C applications during classical life time. In order to use this alloy during a ten hour application, this thesis consists in characterizing Ti-64 from 20°C to 600°C. In a first time, characterization is focused on initial metallurgical state coming from a forged billet and on its thermal stability. Then, mechanical behavior of Ti-64 is studied by tensile testing from 20°C to 600°C, highlighting strain rate sensitivity (SRS) of flow stress. SRS is depending on temperature. This dependency is usually due to dynamic strain ageing phenomenon. Mechanical behavior characterization continues with creep testing from 20°C to 600°C for several stress levels (from 0.3 to 1 time yield stress values). Different behaviors versus temperature are revealed. Deformed samples by tensile testing and creep testing are analyzed by transmission electronic microscopy to bring information about deformation mechanisms controlling the different behaviors of the alloy. Thanks to tensile and creep testing, a viscoplastic modeling of Ti-64 from 20°C to 600°C has been performed and validated by fitting results from complex thermo mechanical tests with finite elements simulations. Comparison of mechanical behavior with deformation mechanisms leads to a discussion about viscoplasticity of Ti-64, and finally results in a proposal modeling creep behavior of Ti-64 from 20°C to 600°C. The model is able to estimate qualitatively creep curves using strain rate sensitivity measured during tensile tests.

Ces travaux exposent et analysent les performances d’un composite à matrice thermoplastique semi-cristallin au passage et au-delà de la transition vitreuse. Il est nécessaire de donner des éléments objectifs afin d’évaluer et discuter dans quelles mesures ce matériau peut être utilisé de manière innovante. L’objectif visé est de donner des perspectives en termes de plage de températures d’utilisation des matériaux composites à matrice thermoplastique et plus spécifiquement pour des applications à hautes températures. Le composite à fibres continues de carbone et matrice polyétheréthercétone PEEK a ainsi été étudié sur une large gamme de température, avant et après sa température de transition vitreuse (Tg = 143°C).La phase de caractérisation quasi-statique a mis en évidence l’importance du renfort et le bon transfert de charge de la matrice au-delà de la Tg pour les différentes sollicitations. En particulier, la résistance à la rupture en compression s’est avérée intéressante dans l’optique d’une application structurelle. De plus, les observations fractographiques ont mis en évidence des comportements radicalement différents au passage de la transition vitreuse. Le caractère plus ductile de la matrice permet de limiter la propagation de fissures au travers des plis par dissipation de l’énergie : la plastification de la matrice augmente la capacité du composite à dissiper de l’énergie en limitant ainsi la fissuration. Cependant pour des chargements où la matrice pilote la réponse mécanique du composite tels que des efforts de cisaillement, les comportements non linéaires sont fortement accentués. Des mécanismes de déformations dépendant du temps ont été observés à travers des essais de charge-décharge et de fluage au-delà de la Tg : le caractère visqueux de la matrice joue un rôle prépondérant.Ces mécanismes non linéaires étant identifiables sur des temps longs, il était intéressant de proposer des méthodes de modélisation pour prédire le comportement du composite. C’est pourquoi des modèles à l’échelle du pli ont été adaptés en fonction de la température et de la prépondérance des caractères viscoélastique et viscoplastique. Différents essais de fluage-recouvrance en torsion rectangulaire menés sur un rhéomètre ont permis d’évaluer les composantes viscoélastiques et viscoplastiques de la déformation à des températures inférieures et supérieures à la Tg. / The present study shows and analyses the specifications of a semi-crystalline thermoplastic composite as function of temperature, below and above the glass transition. In order to assess and discuss about what extent this material could be innovately use, objective facts must be necessary exposed: the main target is to give the outlooks about the temperature range, in particular the high temperatures. The studied material is a continuous carbon fibre composite with a polyetheretherketone (PEEK) matrix. Its glass transition temperature is around 143°C. It has been characterized throughout a wide temperature range.For several kinds of quasi-static loadings, the load transfer from the matrix to the fibre reinforcement is good even above the glass transition temperature. The compression strength is indeed very interesting for an aeronautical application. In addition, the fracture surface analysis have significantly revealed a different behaviour above the glass transition temperature: the matrix is more ductile and thus the crack propagation is limited thanks to the energy dissipation. However when the mechanical response is driven by the matrix behaviour such as shear loadings, the nonlinear mechanical behaviour of the composite are highly increased. Therefore the time-dependent behaviours have been characterized by using creep experiments and loading-unloading tensile tests as function of the temperature.In order to predict those non-linear behaviours, meso-models have been developed as function of the temperature. Thus viscoelasticity and viscoplasticity have been taken into account to model the nonlinear mechanical behaviour of the composite material, thanks to creep-recovery tests which have been carried out with a torsion rheometer.