Made available in DSpace on 2016-06-02T20:15:30Z (GMT). No. of bitstreams: 1 5592.pdf: 31266949 bytes, checksum: 2b640b435377cc433450c874294869e3 (MD5) Previous issue date: 2013-11-14 / Financiadora de Estudos e Projetos / In recent decades the study of β-Titanium alloys are attracting the interest to the biomaterials science community in general, since have improved properties as compared with current commercial biomedical alloys which present problems of both mechanical and chemical compatibility. In this sense, the determination and optimization of the mechanical properties, in particular of the elastic modulus, through of control the phases present that are of great importance. In this study was determined the dynamic elastic modulus (E), their relative variation ( ΔE/E) and internal friction (Q-1) as function of temperature by mechanical spectroscopy technique, being that the information provided by these parameters, associated with complementary characterization techniques and theoretical parameters of the literature provided relevant information on the phases stability in some alloys of the Ti-Nb-Zr and Ti- Nb-systems. Thus, complex anelastic relaxation processes were observed which through cyclic heat treatment and aging was possible to dissociate into their component of phase transformations, which highlighted in the temperature range between 300 K and 700 K the sequence β → β + ω → β + ω + α → β + α, and once these transformations are developed, in a joint manner are also present relaxation processes that include interactions of elements containing alloys with interstitial atoms. At low temperature (130 K-300 K), a process of relaxation was observed, which may be related to processes such as β → ω (athermic) transformation and/or H-O interactions. However by the behavior of the elastic modulus this process may be linked in part to the reverse martensitic transformation β→α" being possible to identify Ms and Af temperatures. In addition was characterized a low modulus of elasticity, yielding values between 67 and 54 GPa, which are related to the greater stability of the β phase, being these suitable values regarding the mechanical compatibility as compared with commercial alloys used as biomaterials. / Nas últimas décadas, o estudo de ligas de titânio do tipo β tem despertado o interesse da comunidade científica na área de biomateriais por apresentarem propriedades superiores se comparadas com as atuais ligas biomédicas comerciais, uma vez que, estas últimas apresentam problemas de compatibilidade tanto mecânica como química. Neste sentido, a determinação e otimização das propriedades mecânicas, principalmente através do controle das fases presentes são de grande importância, em especial objetivando obter o módulo de elasticidade próximo ao do osso humano (10-30 GPa). Assim, neste trabalho foram determinados, o módulo de elasticidade dinâmico (E), sua variação relativa (ΔE/E) e o atrito interno (Q-1) em função da temperatura, por meio da técnica de espectroscopia mecânica. A informação proporcionada por estas grandezas, associada a técnicas de caraterização complementares e a parâmetros teóricos da literatura, forneceram informações relevantes sobre a estabilidade das fases em algumas ligas de Ti-β dos sistemas Ti-Nb-Zr e Ti-Nb-Fe. Desta forma, processos de relaxação anelástica complexos foram observados, sendo que, através de tratamentos cíclicos e de envelhecimento foi possível dissociá-los em suas componentes de transformações de fase. Nestes espectros foi evidenciada, na faixa de temperatura entre 300 K e 700 K, a sequência de transformações β→β+ω→β+ω+α→β+α e, uma vez que, estas transformações se desenvolvem, de maneira conjunta, estão presentes processos de relaxação que incluem interações dos elementos que contém as ligas com átomos intersticiais. Em baixa temperatura (130 K a 300 K) foi observado um processo de relaxação, que pode estar relacionado a transformações β→ω (atérmica) e/ou interações H-O, no entanto, devido ao comportamento do módulo de elasticidade este processo pode estar associado em parte à transformação martensitíca reversa β→α , sendo possível identificar as temperaturas Ms e Af. Por outro lado, foi caracterizado um baixo módulo de elasticidade, obtendo-se valores entre 67 e 54 GPa, que estão relacionados com a maior estabilidade da fase β. Estes valores são adequados quanto a compatibilidade mecânica se comparados com as ligas comerciais empregadas como biomateriais.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23176号 / 工博第4820号 / 新制||工||1753(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 林 為人, 教授 福山 英一, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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<p>The superior high-temperature elastic-plastic properties coupled with greater damage tolerance when compared with monolithic ceramics make ceramic matrix composites, CMCs, promising candidates for challenging applications such as engine components, rocket nozzles, cutting tools and nuclear energy reactor core components. Anelastic recovery is the time-dependent back strain observed upon the load removal following creep. In whisker-reinforced CMCs this can be a factor limiting operating conditions. Plastic strain misfit between two phases is thought to be the main driver in terms of the interactions within a percolating network. However, the network deformation mechanisms are still unclear and a previous neutron diffraction study showed an unexpected decrease of peak width after creep contradicting the theoretical predictions.</p> <p>In this contribution, the finite element method (FEM) is applied to a representative volume element (RVE) with proper boundary conditions in order to simulate the creep deformation and hot pressing processes. Three geometries have been generated and studied: a 3D randomly-oriented short-fiber unit cell without fiber to fiber contact, generated by a random sequential adsorption algorithm; 3D regularly aligned single fiber unit cells; and 2D regularly aligned percolating unit cells. Deformation mechanism has been studied from an energy point of view and compared with a modified analytical model. Then a virtual diffraction model has been developed providing a framework to transfer information between the FEM simulations (strain fields) and the diffraction pattern in terms of the peak width (full width at half maximum: <strong><em>FWHM</em></strong>) and peak position as a measure of stress distribution and mean stress state respectively. Furthermore, the coupling effects of external stress, deformation mode, and thermal stress on the diffraction patterns have been studied.</p> <p>The critical importance of a percolating whisker network for the anelastic recovery is demonstrated based on the 3D multi-whisker random unit cell. Whisker bending is shown to be the dominant mechanism over contact effects during the creep deformation of a composite containing a well aligned percolating whisker network based on the 2D unit cell model. Good qualitative agreement was found between our FEM simulations and the analytical model of Wilkinson and Pompe with regards to the maximum recoverable strain and the characteristic relaxation time. The analytical model captures all the critical factors characterizing the strain recovery, e.g., the effect of creep pre-exponent constant, whisker Young’s modulus and aspect ratio. Furthermore, it is found that the deformation from an initial stress-free state inevitably introduces peak broadening of whiskers inside the matrix. Several factors determine the peak-width and -shift, i.e., creep strain, applied stress, aspect ratio and geometry. However, thermal stress from the cooling stages following creep and hot pressing processes shelters this broadening effect and complicates the trends. Wide-ranging peak-width changes from narrowing to broadening are predicted depending on the geometry and applied stress. The peak position is shifted to a lower angle due to this thermal effect. This clearly explains the contradicting phenomena motivating this work and leads to that recommendation that a diffraction source with high angular resolution is needed to detect the subtle change of peak profile during creep.</p> / Doctor of Philosophy (PhD)

Dans le contexte industriel de la mise en forme des matériaux composites à renforts fibreux, l’outil de simulation est devenu partie intégrante de l’amélioration des procédés. Aujourd’hui, les simulations numériques de la mise en forme des renforts fibreux sont pour la plupart basées sur une approche macroscopique et des modèles de matériaux continus dont on suppose que le comportement est non linéaire élastique, donc réversible. Or on sait que sous chargement non-monotones (charges et décharges), les renforts fibreux montrent d’importantes irréversibilités, liées notamment aux glissements entre mèches et entre fibres. La première partie de ce travail consiste à caractériser l’importance des irréversibilités par des tests de charges/décharges à l’échelle macroscopique en différents modes de déformation (flexion, cisaillement, compression) réalisés sur des renforts tissés. La seconde partie consiste à chercher des modèles de comportement qui décrivent l’anélasticité en flexion et en cisaillement et à les implémenter dans un code éléments finis. Une validation de ces modèles obtenus est faite par comparaison simulation-expérimentation des essais d’identification de flexion et de cisaillement plan. Cette partie est réalisée sur le logiciel PlasFib développé par l’INSA de Lyon, un code éléments-finis explicite en grande transformation proposant une approche macroscopique semi-discrète des renforts fibreux. La troisième partie consiste à simuler différents cas de mises en forme inspirées de pièces industrielles pour mettre en évidence les zones du renfort qui subissent des chargements non monotones (en flexion et en cisaillement) lors d’une mise en forme. Cela vise également à étudier l’importance de l’utilisation des modèles irréversibles pour simuler ces mises en forme en comparant les résultats des simulations obtenus avec des modèles de comportement réversibles avec ceux obtenus pour des modèles irréversibles. / In the industrial context of shaping composite materials with fibrous reinforcements, the numerical simulation tool has become an integral part of process improvement. Today, numerical simulations of shaping fibrous reinforcements are mostly based on a macroscopic approach and continuous material models that have been assumed to be nonlinear elastic, thus reversible. However, under non-monotonous loading paths, the fibrous reinforcement shows significant irreversibility, particularly related to sliding between yarns and between fibers. First of all, we will try to characterize the importance of irreversibilities by cyclic tests (bending, in-plan shearing, compression) carried out on woven reinforcements. The second part consists in looking for behavior models that describe bending and in-plane shear irreversibilities to implement them in a finite element code. A validation of these behavior models is made by comparing simulation and experimental results of bending and in-plane shear identification tests. This part is realized on PlasFib, a software developed by INSA Lyon, based on finite element code in large deformation, proposing a macroscopic semi-discrete approach of fibrous reinforcements. The third part of the study will consist in simulating the shaping process of different industrial parts (or inspired by industrial parts). This will aim first at identifying loading cases apt to produce non-monotonous loading paths (in bending and in-plane shear) during the shaping process ; and second, at studying the importance of using irreversible models to simulate these shaping processes by comparing the results of simulations obtained with reversible behavior models with those obtained for irreversible behavior models.

L’approximation dite « anélastique » permet de filtrer les ondes acoustiques grâce à un développement asymptotique deséquations de Navier-Stokes, réduisant ainsi le pas en temps moyen, lors de la simulation numérique du développement d’instabilités hydrodynamiques. Ainsi, les équations anélastiques sont établies pour un mélange de deux fluides pour l’instabilité de Rayleigh-Taylor. La stabilité linéaire de l’écoulement est étudiée pour la première fois pour des fluides parfaits, par la méthode des modes normaux, dans le cadre de l’approximation anélastique. Le problème de Stokes issu des équations de Navier-Stokes sans les termes non linéaires (une partie de la poussée d’Archiméde est prise en compte) est défini ; l’éllipticité est démontrée, l’étude des modes propres et l’invariance liée à la pression sont détaillés. La méthode d’Uzawa est étendue à l’anélastique en mettant en évidence le découplage des vitesses en 3D, le cas particulier k = 0 et les modes parasites de pression. Le passage au multidomaine a permis d’établir les conditions de raccord (raccord Co de la pression sans condition aux limites physiques). Les algorithmes et l’implantation dans le code AMENOPHIS sont validés par les comparaisons de l’opérateur d’Uzawa développé en Fortran et à l’aide de Mathematica. De plus des résultats numériques ont été comparés à une expérience avec des fluides incompressibles. Finalement, une étude des solutions numériques obtenues avec les options anélastique et compressible a été menée. L’étude de l’influence de la stratification initiale des deux fluides sur le développement de l’instabilité de Rayleigh-Taylor est amorcée. / The « anelastic » approximation allows us to filter the acoustic waves thanks to an asymptotic development of the Navier-Stokes equations, so increasing the averaged time step, during the numerical simulation of hydrodynamic instabilitiesdevelopment. So, the anelastic equations for a two fluid mixture in case of Rayleigh-Taylor instability are established.The linear stability of Rayleigh-Taylor flow is studied, for the first time, for perfect fluids in the anelastic approximation.We define the Stokes problem resulting from Navier-Stokes equations without the non linear terms (a part of the buoyancyis considered) ; the ellipticity is demonstrated, the eigenmodes and the invariance related to the pressure are detailed.The Uzawa’s method is extended to the anelastic approximation and shows the decoupling speeds in 3D, the particular casek = 0 and the spurius modes of pressure. Passing to multidomain allowed to establish the transmission conditions.The algorithms and the implementation in the existing program are validated by comparing the Uzawa’s operator inFortran and Mathematica langages, to an experiment with incompressible fluids and results from anelastic and compressiblenumerical simulations. The study of the influence of the initial stratification of both fluids on the development of the Rayleigh-Taylor instability is initiated.