Orientadores: David de Carvalho, Heraldo Luiz Giacheti / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-03T20:52:34Z (GMT). No. of bitstreams: 1 BeiraFontaine_Eduardo_D.pdf: 3663857 bytes, checksum: 2b1520fd0d5ae83e782045ee6301b199 (MD5) Previous issue date: 2004 / Doutorado

Orientador : Paulo Jose Rocha de Albuquerque / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-03T23:09:07Z (GMT). No. of bitstreams: 1 Nogueira_RogerioCarvalhoRibeiro_M.pdf: 10041706 bytes, checksum: 87fb0f1801f18159edc6d8cafcdd6bc7 (MD5) Previous issue date: 2004 / Mestrado

Le développement de machines à forte vitesse spécifique et de taille réduite en régime subsonique suscite actuellement une forte demande dans de nombreux domaines industriels. Les machins à rotors contrarotatifs largement étudiées en aéronautique constituent une alternative efficace aux machines conventionnelles offrant de nombreux avantages : réduction de la vitesse de rotation, de l'encombrement radial et une grande flexibilité d'utilisation. Cependant, leur utilisation dans des applications subsoniques courantes nécessite une meilleure compréhension de leur fonctionnement et notamment de l'interaction inter-rotors pour mieux les concevoir. Ce travail a pour objectif d'étudier et de caractériser expérimentalement un étage contrarotatif fonctionnant en conduit, conçu avec le code de conception et d'analyse pour rotor et rotor-stator, MFT auquel on a implémenté une méthode de conception simple et rapide pour dessiner le rotor aval. On analyse en particulier l'effet de la distance axiale entre les rotors et l'effet du rapport de leur vitesse. Il met en évidence une nette amélioration des caractéristiques et du rendement global par rapport à une machine conventionnelle. Par ailleurs, plusieurs aspects de l'interaction entre les rotors sont constatés à travers des mesures locales à proximité des rotors. Le présent mémoire s'articule autour de quatre parties : conception d'un étage rotor-stator et d'un étage contrarotatif ; conception du dispositif expérimental normalisé, AERO²FANS pour les mesures de performances globales et locales instationnaires ; caractérisation et comparaison des deux étages et validation de la conception de MFT; enfin, étude des effets de la distance axiale et du rapport des vitesses sur les performances globales et locales. / Recently, the need for smaller axial fans with high specific speeds lead to the design of counter-rotating axial fans. The design of this kind of machines, which have promising aerodynamic performances, suffers from a lack of knowledge about their aerodynamics. Counter-rotating rotors, widely studied in aeronautics, are an effective alternative to conventional machines and offer many advantages: rotation ratio and diameter reduction, and high flexibility in use. However, a better understanding of their working and of the rotors interaction is required to enhance their design and to make them widely integrated in current applications. This experimental research work investigates on a ducted counter-rotating stage designed with a home code, MFT based on an inverse design method for rotors and rotor-stator stages, and to which a rapid and simple method is implemented to design the rear rotor. The study focuses on the effects of the rotation ratio and on the axial spacing between rotors. It highlights several aspects of the rotors interaction through global performance and local unsteady measurements. This dissertation is organized in four parts: rotor-stator and rotor-rotor stages design; design of the experimental facility, AERO²FANS allowing global performance and local unsteady measurements; comparison between the two stages and design validation; investigation on the effects of the rotation ratio and the axial spacing on the global and the local performances.

Les composites SiC/SiC sont envisagés comme matériaux pour des composants de cœur de réacteurs nucléaires du futur. Le dimensionnement de ces structures par la simulation numérique repose sur une modélisation du comportement mécanique de ces matériaux. Ces travaux visent à améliorer la compréhension de leurs mécanismes de déformation afin de construire une loi de comportement à même de prédire la réponse du matériau sous chargements complexes. Une caractérisation approfondie du comportement macroscopique de tubes SiC/SiC multicouches - similaires aux concepts de gaines de combustibles - a été entreprise, par des essais de traction-pression interne, traction-torsion et flexion multi-instrumentés, et a permis de constituer une importante base expérimentale pour la compréhension des mécanismes d'endommagement et l'identification de modèles. Des observations in-situ et après rupture ont permis de quantifier l'orientation des fissures matricielles observées en surface en fonction du type de chargement appliqué. Des mesures de champs de déplacement par Corrélation d'Images Numériques à l'échelle d'un motif du textile ont permis d'apporter des informations fines sur la cinématique de la surface du composite, telles que l'ouverture des fissures ou la déformation des fragments matriciels. Ces mesures ont également permis de mettre en évidence l'importance de la réorientation des torons dans la direction de chargement, mécanisme pouvant expliquer certaines spécificités du comportement macroscopique du fait de son couplage avec la fissuration matricielle. Enfin, ces différentes données expérimentales ont permis de construire un modèle phénoménologique, identifiable sur quatre essais uniaxiaux, permettant de prédire de manière satisfaisante le comportement macroscopique sous divers chargements bi-axés. L'accord de certaines quantités locales, telles que les caractéristiques de la fissuration en traction, ont également été vérifiées. / SiC/SiC composites are candidate materials for in-core components of future nuclear reactors. The analysis of these structures using numerical simulations requires material constitutive laws. The present work focuses on understanding the deformation mechanisms of these materials in order to build a constitutive model able to predict their stress-strain response under complex loadings. An extensive characterization of the mechanical behaviour of SiC/SiC multi-layered tubes – similar to fuel cladding concepts - was carried out, using tension-internal pressure, tension-torsion and bending tests, that allowed to build an important experimental basis for the understanding of the mechanisms and the identification of constitutive laws. In-situ and post-failure observations have allowed quantifying the orientation of surface matrix cracks as a function of the loading type. Full-field measurements using Digital Image Correlation at the tow scale brought precise information on the composite surface kinematics, such as the crack opening or the deformation of the matrix fragments. These measurements also evidence the importance of the tow reorientation, that could explain specific features of the macroscopic behaviour because of its coupling with matrix cracking. Finally, these experimental data allowed to build a constitutive model, identified on only four uniaxial tests, able to predict satisfactorily the macroscopic behaviour under several biaxial loadings. The correct prediction of local quantities, such as the characteristics of the matrix cracking in tension, has also been verified.

This thesis presents the results of a research programme to investigate the behaviour and robustness of reinforced concrete (RC) frames in fire. The research was carried out through numerical simulations using the commercial finite element analysis package TNO DIANA. The main focus of the project is the large deflection behaviour of restrained reinforced concrete beams, in particular the development of catenary action, because this behaviour is the most important factor that influences the frame response under accidental loading. This research includes four main parts as follows: (1) validation of the simulation model; (2) behaviour of axially and rotationally restrained RC beams at elevated temperatures; (3) derivation of an analytical method to estimate the key quantities of restrained RC beam behaviour at elevated temperatures; (4) response and robustness of RC frame structures with different extents of damage at elevated temperatures. The analytical method has been developed to estimate the following three quantities: when the axial compression force in the restrained beam reaches the maximum; when the RC beams reach bending limits (axial force = 0) and when the beams finally fail. To estimate the time to failure, which is initiated by the fracture of reinforcement steel at the catenary action stage, a regression equation is proposed to calculate the maximum deflections of RC beams, based on an analysis of the reinforcement steel strain distributions at failure for a large number of parametric study results. A comparison between the analytical and simulation results indicates that the analytical method gives reasonably good approximations to the numerical simulation results. Based on the frame simulation results, it has been found that if a member is completely removed from the structure, the structure is unlikely to be able to develop an alternative load carrying mechanism to ensure robustness of the structure. This problem is particularly severe when a corner column is removed. However, it is possible for frames with partially damaged columns to achieve the required robustness in fire, provided the columns still have sufficient resistance to allow the beams to develop some catenary action. This may be possible if the columns are designed as simply supported columns, but have some reserves of strength in the frame due to continuity. Merely increasing the reinforcement steel area or ductility (which is difficult to do) would not be sufficient. However, increasing the cover thickness of the reinforcement steel to slow down the temperature increase is necessary.

Ingeniero Civil / Los muros de hormigón armado con discontinuidades a nivel basal son bastante comunes en edificaciones chilenas. Estas discontinuidades afectan directamente en cómo se traspasan los esfuerzos ante eventuales solicitaciones, al no tener una sección transversal regular, la hipótesis de bernoulli de secciones planas no es apropiadas, ya que la discontinuidad genera una variación en el flujo de cargas la cual invalida la hipótesis; es por esto que surge la necesidad de estudiar el comportamiento de este tipo de muros frente a acciones sísmicas con más detalle. La presente memoria tiene por objetivo principal la construcción y ensayo de cuatro probetas de muros a escala de hormigón armado con una abertura en su base, tres de ellos son muros rectangulares y uno tiene además losas en el sector de la abertura, de manera de aumentar la rigidez en esa zona y considerar este efecto en futuros análisis. Adicionalmente se realiza un modelo tipo puntal-tensor de una de las probetas y se realiza una comparación respecto a los resultados que se obtienen experimentalmente del ensayo. El ensayo consiste en inducir sobre cada muro a través de un actuador hidráulico una carga pseudocíclica en su parte superior, así como también una carga axial constante del 10% de la resistencia nominal a compresión del hormigón, y observar cual es su comportamiento en cuanto a deformaciones y esfuerzos resultantes dado el tamaño de la abertura presente en su base. Se compara la respuesta de los muros y sus capacidades de deformación respecto a una probeta base sin discontinuidades. El muro con la abertura más pequeña es la que menor impacto genera en la respuesta de la probeta, así mismo, la abertura más grande es la que mayor impacto genera, disminuyendo considerablemente las capacidades de carga y deformación de la probeta respecto a la probeta base. Además se logra que las tensiones registradas experimentalmente sean consistentes con las teóricas obtenidas con un modelo tipo puntal-tensor.

Magíster en Ciencias de la Ingeniería, Mención Ingeniería Sísmica. Ingeniero Civil / Este estudio resume los resultados de un estudio analítico de Muros de Hormigón Armado (MHA) chatos y esbeltos, con y sin aberturas. El objetivo principal de este estudio es evaluar el efecto de aberturas y del pandeo de las barras longitudinales en MHA, modelando probetas experimentales disponibles en la literatura, y realizando variaciones paramétricas relevantes. Para lograr este objetivo, el presente estudio mejora la representación uniaxial de la curva tensión-deformación del acero en el elemento de membrana propuesto por Rojas [1], incorporando el modelo del pandeo en barras longitudinales propuesto por Massone y Moroder [2]. La exactitud de la técnica del modelamiento del elemento mejorado es corroborada, comparando simulaciones con datos experimentales de MHA disponibles en la literatura. Finalmente, se incorporan a nivel paramétrico diferentes aspectos como tipo de muro (sólido o con abertura), razón de aspecto, nivel de carga axial, cuantía de borde, deriva inicio de techo, y razón entre longitud libre y diámetro de la barra (relación L/d), de manera de ampliar el espectro de resultados. Resultados indicaron que el elemento mejorado fue capaz de reproducir los resultados y formas de falla experimentales, incluso en los casos con abertura. En general, el efecto del pandeo no causó mayor impacto en la respuesta global de muro para una relación L/d menor a 6, tanto en muros sólidos como en muros con abertura en el borde. Sin embargo, para L/d > 6 el pandeo produjo un impacto significativo en la ductilidad global de muro. Por otra parte, los resultados del modelo mostraron que la abertura, localizada en el borde sobre la base de muro, causó un impacto en la pérdida de capacidad por desplazamiento global de muro. Sin embargo, la pérdida de la capacidad por desplazamiento causada por la abertura está condicionada por dos parámetros: razón altura y largo de muro (hw/lw), y razón largo y espesor de muro (lw/tw). En la medida que la razón hw/lw disminuye, y la razón lw/tw aumenta, la abertura causa un impacto menor en la capacidad por desplazamiento global de muro, ya que el comportamiento inelástico de muros muy chatos (hw/tw < 2) está limitado por poseer una elevada resistencia a la flexión, por lo cual, la ductilidad está restringida; mientras que muros delgados (lw/tw > 12) tienen poca resistencia a las tensiones de corte, por lo cual, la ductilidad también está restringida.

Pattern formation is the process by which undifferentiated cells divide and differentiate to generate complex tissues and organs. In plants, pattern formation begins in embryogenesis and continues post-embryonically with the function of the meristems. microRNAs (miRNAs), which are small regulatory RNAs that repress gene expression, are involved in a variety of patterning processes in plants, including the formation and function of the meristems and establishment of polarity. For example, regulation of the class III HOMEODOMAIN-LEUCINE ZIPPER (HD-ZIP III) transcription factors by miR165/6 is not only involved in the formation and function of the meristems, but also in polarity establishment in the leaf, and in axial patterning during embryogenesis. To gain a better understanding of the role of miRNAs in embryonic patterning, I investigated the tissue-specific functions of the miRNA biogenesis protein SERRATE (SE), which is required for the regulation of the HD-ZIP IIIs via miR165/6. By expressing SE in various domains in se-5 null mutant embryos, I revealed that although SE is expressed throughout the embryonic body, tissue-specific expression of SE from either the upper or lower tier of the embryo is sufficient for correct patterning. This observation suggests a SE-dependent non-cell autonomous and bi-directional mechanism that influences patterning in Arabidopsis embryos. Furthermore, through a suppressor screen of a se-3 loss-of-function mutant allele, I identified mutants in genes that likely function upstream of SE, and downstream or in parallel of the HD-ZIP IIIs. One of those se-3 suppressors is likely to be a mutant in the BELL homeobox gene POUND-FOOLISH (PNF).

Doctor of Philosophy / Department of Civil Engineering / Hayder A. Rasheed / The use of laminated composites in aerospace, automotive, and civil engineering applications is ever growing due to their distinguished properties (High stiffness-to-weight ratio, high strength-to-weight ratio, fatigue and corrosion resistance). This growth has resulted in increasing the demand for better understanding the mechanics of laminated composites. Composite columns and wide plates, like any traditional members subjected to axial compression, undergo stability issues prior to failure. Limited amount of research studies has focused on the buckling of laminated anisotropic composite members. Analytical formula for the buckling load of generally anisotropic laminated composite simply supported thin columns and wide plates is derived using the Rayleigh Ritz approximation and bifurcation approach. The effective axial, coupling and flexural stiffness coefficients of the anisotropic layup is determined from the generalized constitutive relationship using dimensional reduction by static condensation of the 6x6 composite stiffness matrix. The resulting explicit formula is expressed in terms of the generally anisotropic material properties as well as the member geometry. The developed formula may be considered an extension to Euler buckling formula using Rayleigh-Ritz approximation and the first of its kind since Euler. This formula reduces down to Euler buckling formula once the effective coupling stiffness term vanishes for isotropic and certain classes of laminated composites. The analytical results are verified against finite element Eigen value solutions for a wide range of anisotropic laminated layups yielding high accuracy. Comparisons with experiments; conducted at Kansas State University for the simply supported case, are also performed showing good correspondence. A brief parametric study is then conducted to examine the effect of ply orientations and material properties including hybrid carbon/glass fiber composites, element thickness, and element type in FE analysis. Relevance of the numerical and analytical results is discussed for all these cases.

Magnesium is the lightest metal that can be used for structural applications. For the reasons of weight saving, there has been an increasing demand for magnesium from the automotive industry. However, poor formability at room temperature, due to a limited number of slip systems available owing to its hexagonal close packed crystal structure, imposes severe limitations on the application of Mg and its alloys in the wrought form. One possibility for improving formability is to form the components superplastically. For this, it is necessary to refine the grain structure. A fine-grained material is also stronger than its coarse grain counterpart because of grain size strengthening. Moreover, fine-grained magnesium alloys have better ductility as well as a low ductile to brittle transition temperature, thus their formability at room temperature could be improved. In addition to grain refinement, the issues pertaining to poor formability or limited ductility of Mg alloys can be addressed by controlling the crystallographic texture. Recently, it has been shown that warm equal channel angular extrusion (ECAE) of magnesium led to reduction in average grain size and shear texture formation, by virtue of which subsequent room temperature rolling was possible. Based on the literature, it was also certain that, in order to make magnesium alloys amenable for processing, grain refinement needs to be carried out and the role of shear texture needs to be explored. Since processing at higher temperature would lead to relatively coarser grain size, large strain deformation at lower temperatures is desirable. The present thesis is an attempt to address these issues. The thesis has been divided in to eight chapters. The chapters 1 and 2 are dedicated to introduction and literature review on the subject that provides the foundation and motivation to the present work. Subsequent chapters deal with the research methodology, experimental and simulation results, discussion, summary and conclusion. In the present investigation, two single phase alloys were chosen, the commercially pure magnesium and the magnesium alloy AM30. These materials were subjected to suitable processing techniques, detailed posteriori. A systematic analysis of microstructure and texture for each of the as-processed materials was performed by electron backscattered diffraction (EBSD) using a field emission gun scanning electron microscope (FEG-SEM). Bulk texture measurement by X-ray diffraction, neutron diffraction and local texture measurement by synchrotron X-rays were also carried out. In addition, dislocation density was measured using X-Ray diffraction line profile analysis (XRDLPA). The experimental textures were validated by using Visco-Plastic Self Consistent (VPSC) simulation. The details of experimental as well simulation techniques used in the present investigation is described in chapter 3. To understand the philosophy of large strain deformation by shear in magnesium and its alloy, free end torsion tests could provide a guide line. Based on the understanding developed from these tests, further processing strategy could be planned. Therefore, a rigorous study of deformation behaviour under torsion was carried out. In chapter 4, the results of free end torsion tests carried out at different temperatures, 250⁰C, 200⁰C and 150⁰C and strain rates, 0.01 rad.s-1, 0.1 rad.s-1, 1 rad.s-1 are presented for both the alloys. In addition to the analysis of stress-strain behaviour, a thorough microstructural characterization including texture analyses pertaining to deformation and dynamic recrystallization was performed. Both pure Mg and the AM30 alloy exhibit similar ductility under the same deformation condition, while the strength of AM30 was more. The strain hardening rate decreased with temperature and increased with strain rate for both the materials. However, the strain hardening rate was always higher in case of the alloy AM30. Large amount of dynamic recrystallization (DRX) was observed for both the alloys. The initial texture had an influence on the deformation behaviour under torsion and the resulting final texture. The initial non-axisymmetric texture of pure Mg samples led to nonaxisymmetric deformation producing ear and faces along the axial direction, and the final texture was also non-axisymmetric. An examination of the texture heterogeneity was carried out in one of the pure Mg torsion tested samples by subjecting it to EBSD examination at different locations of the surface along the axial direction. The strain induced on the ear portion was maximum, and in the face was lower. This has been attributed to the orientation of basal planes in the two regions. The axisymmetric initial texture in case of the alloy AM30 led to the formation of axisymmetric texture with no change in the shape of the material. Owing to this simplicity, the occurrence of dynamic recrystallization (DRX) was studied in more detail for this alloy. The mechanism of texture development due to deformation as well as dynamic recrystallization could be tracked at every stage of deformation. A typical shear texture was observed with respect to the strain in each case. Very low fraction of twins was observed for all the cases indicating slip dominated deformation, which was validated by VPSC simulation. It was found that with the increase in strain during torsion, the fraction of dynamically recrystallized grains increased. The recrystallization mechanism was classified as “continuous dynamic recovery and recrystallization” (CDRR) and is characterized by a rotation of the deformed grains by ~30⁰ along c-axis. After developing an understanding of large strain deformation behaviour of pure Mg and the alloy AM30 through torsion tests, the possibility of low temperature severe plastic deformation for both the materials by equal channel angular extrusion (ECAE) was explored. The outcome of this investigation has been presented in chapter 5. At first, ECAE of pure magnesium was conducted at 250⁰C up to 4 passes and then the temperature was reduced by 50⁰C in each subsequent pass. In this way, ECAE could be carried out successfully up to 8th pass with the last pass at room temperature. A grain size ~250 nm and characteristic ECAE texture with the fibres B and C2 were achieved. The AM30 alloy subjected to similar processing schedule as pure Mg, however, could be deformed only up to 6th pass (TECAE=150⁰C) without fracture. An average grain size ~ 420 nm and a texture similar to ECAE processed pure Mg was observed for this alloy. The difference in the deformation behaviour of the two alloys has been explained on the basis of the anisotropy in the stacking fault energy (SFE) in the case of pure Mg. Neutron diffraction was carried out to confirm and validate the microtexture results obtained from the EBSD data, while the local texture measurement by synchrotron radiation was carried out at different locations of the ECAE samples to give a proper account of the heterogeneity in texture. The effect of grain refinement was examined, deconvoluting the effect of shear in improving the strength and ductility using another severe plastic deformation technique, namely multi axial forging (MAF). In this process, the material was plastically deformed by a combination of uniaxial compression and plane strain compression subsequently along all the three axes. The details of this investigation has been presented in chapter 6. By this method, the alloy AM30 could be deformed without fracture up to a minimum temperature of 150⁰C leading to ultra-fine grain size (~400 nm) with very weak texture. A room temperature ductility ~55% was observed for this material. Finally, a comparison of room temperature mechanical properties of the alloy AM30 was carried out for the ECAE and MAF processed conditions having similar grain size in order to observe the effect of texture formed during both the processes. A similar strength and ductility for both the cases was attributed to the orientation obtained from both the ECAE and MAF, which is away from the ideal end orientation for tensile tests. The final outcomes of the thesis has been summarized in chapter 7.