Literatura académica sobre el tema "Bulge Theory"

A long tube with elastic walls containing water is immersed in the sea aligned in the direction of wave travel. The waves generate bulges that propagate at a speed determined by the distensibility of the tube. If the bulge speed is close to the phase velocity of the waves, there is a resonant transfer of energy from the sea wave to the bulge. At the end of the tube, useful energy can be extracted. This paper sets out the theory of bulge tubes in the sea, and describes some experiments on the model scale and practical problems. The potential of a full-scale device is assessed.

Abstract 1. When rubber bulges through an aperture, the bulge height varies linearly with applied pressure. It also varies linearly with radius or width of the aperture when the dimensions of the rubber block are much larger than the aperture, in good agreement with linear elasticity theory. When the block is not much larger than the radius or width of the aperture, a simple empirical factor provides a satisfactory correction. 2. FEM results were in good agreement with experiment in all cases and confirmed the empirical correction for relatively large apertures. 3. Bulge profiles were calculated to be elliptical in all cases. 4. Results for an elastic solid are wholly consistent with Roscoe's results for a viscous liquid. 5. Changing slip conditions at the interface had a surprisingly small effect. The exact theory, Equations (5) and (7), is based upon a nonslip condition. When a fully lubricated condition was employed instead, so that free sliding was allowed at the interface, the maximum bulge heights predicted by FEM were only about 5% higher than before for a circular aperture and about 12% higher for a slit. Experimental observations of bulge heights with dry and lubricated interfaces were in good agreement with these predictions. 6. Bulge heights through small apertures provide a simple means of measuring pressure at contact surfaces.

In the hydraulic bulge test, flow curves are determined by applying a hydrostatic pressure to one side of a clamped sheet metal specimen, which bulges freely into a circular cavity under the pressure. The pressure and various data such as bulge height, curvature and equivalent strain at the pole are recorded and used to calculate the flow curve of the specimen material using analytical equations based on membrane theory. In the determination of the flow curve, the elastic behavior of the specimen, the elastic-plastic transition and bending effects are neglected, and the flow curves calculated this way are affected by these simplifications. An alternative to this procedure is an inverse analysis, which proceeds by searching for a flow curve that minimizes the difference between computed and measured data, e.g. bulge height vs. pressure. An inverse analysis based on a finite element model takes into account elastic and bending effects but since it involves the solution of an optimization problem, it is not clear whether it yields more accurate results than membrane theory. The objective of this paper is to compare the ‘identifiability’ of a given flow curve from the bulge test by direct identification based on membrane theory and by inverse analysis with different objective functions to be minimized. Using a re-identification procedure, it is shown that an inverse analysis can improve the results of the direct identification if a suitable objective function is chosen.

Abstract For decades ‘youth bulge’ theory has dominated understandings of youth in mainstream International Relations. Youth bulge theory has also become part of some public media analyses, mainstream political rhetoric, and even officially enshrined in the foreign policy of some states. Through the ‘youth bulge’ lens, youth—especially males—have been presented as current or future perpetrators of violence. However, this article argues that the youth bulge thesis postulated in mainstream IR is based on flawed theoretical assumptions. In particular, supporters of youth bulge theory fail to engage with existing research by feminist IR scholars and thus take on a biological essentialist approach. This has led to theoretical and practical misunderstandings of the roles youth play in relation to conflict, peace and security. These partial and biased understandings have also resulted in less effective policy-making. In critically reflecting on the ‘youth bulge’ thesis, this article argues that applying gender analysis is crucial to understanding the involvement of young people in general—and young men in particular—in conflict. Doing so will contribute to advancing more accurate analysis in scholarship and policy-making.

In recent years, hot stamping of sheet metal parts has emerged to satisfy the contrary demands of the automotive industry for components with increased strength at reduced weight. To analyse the material behaviour during these processes, a hot gas bulge test at high temperatures and high strain rates is promising, since the bulge test at room temperature has already proven itself as a useful test for the material characterization of sheet metals up to high strains. Therefore, a hot gas bulge test at elevated temperatures and high strain rates is being developed at the Institute of Metal Forming (IBF) in cooperation with the Institute for Fluid Power Drives and Controls (IFAS) at the RWTH Aachen. To verify if the concepts of the membrane theory, which are used for the evaluation of bulge tests at room temperature, are adaptable to such a hot gas bulge test, a simulation study using finite element calculations was conducted. The purpose of this simulation study is is to estimate the errors which occur if the equivalent stress at the bulge pole is calculated by using the membrane theory. In addition to this study several approaches were examined to obtain the sheet thickness at the bulge pole by measuring the bulge height. The study showed that a hot gas bulge test can be described very well by the membrane theory if the sheet thickness, the curvature at the bulge pole and the pressure inside the bulge are exactly known. However, substantial errors can occur if the sheet thickness at the bulge pole is determined by measuring the height of the bulge pole.

This paper aims to evaluate the stress-strain characteristics of tubular materials considering their anisotropic effects by hydraulic bulge tests and a proposed analytical model. In this analytical model, Hill’s orthogonal anisotropic theory was adopted for deriving the effective stresses and effective strains under a biaxial stress state. Annealed AA6011 aluminum tubes and SUS409 stainless-steel tubes were used for the bulge test. The tube thickness at the pole, bulge height, and the internal forming pressure were measured simultaneously during the bulge test. The effective stress-effective strain relations could be determined by those measured values and this proposed analytical model. The flow stress curves of the tubular materials obtained by this approach were compared with those obtained by the tensile test with consideration of the anisotropic effect. The finite element method was also adopted to conduct the simulations of hydraulic bulge forming with the flow stress curves obtained by the bulge tests and tensile tests. The analytical forming pressures versus bulge heights were compared with the experimental results to validate the approach proposed in this paper.

The vacuum hot bulge forming has been used in aerospace industry to manufacture cylindrical workpiece with improved mechanical properties and reduced fabrication cost. Vacuum hot bulge forming is based on the material soften and the stress relaxation theory. Different from other metal forming techniques, deformation of the workpiece takes place well below yield point and the amount of plastic deformation is directly relaxed to heating temperature and holding time. In this paper, a two-dimension thermo-mechanical coupled finite element model was developed. In this model, nonlinear radiation heat transfer and thermal physical properties of material depending on temperature were considered. This paper carried out numerical simulation of vacuum hot bulge forming of BT20 Ti-alloy cylindrical workpiece by using finite element software MSC.Marc. The temperature field, deformation field and stress field of hot bulge forming of BT20 Ti-alloy cylindrical workpiece were calculated. Numerical simulation results were accorded with experimental ones, which provided for the practice production as theory bases.

We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity Galactic bulge. The sample abundances are also contrasted with the abundances found for PN in the Galactic disk. The mean C/O ratio for the bulge PN is significantly lower than that found for Galactic disk PN. Further, we present an abundance analysis of the very metal-poor bulge PN M2-29. From an analysis of the differential extinction found from the observed ratios of the He ii 1640,4686Å lines, we find that the ultraviolet reddening law towards the bulge is steeper than in the solar neighbourhood.

In plasticity theory, the effective stress–strain curve of a metal is independent of the loading path. The simplest loading path to obtain the effective stress–strain curve is a uniaxial tensile test. In order to demonstrate in a plasticity laboratory that the stress–strain curve is independent of the loading path, the hydrostatic bulge test has been used to provide a balanced biaxial tensile stress state. In our plasticity laboratory we compared several different theories for the hydrostatic bulge test for the determination of the effective stress–strain curve for two representative metals, brass and aluminium alloy. Finite element analysis (FEA) was performed based on the uniaxial tension test data. It was shown that the effective stress–strain curve obtained from the biaxial tensile test (hydrostatic bulge test) had a good correlation with that obtained in the uniaxial tensile test and agreed well with the analytical and FEA results. This paper may be used to support an experimental and numerical laboratory in teaching the concepts of effective stress and strain in plasticity theory.

This thesis addresses the question of whether Saudi Arabia’s youth bulge presents a threat to domestic and international security. Youth bulge theory informs us that if countries are home to large youth populations whilst experiencing high levels of unemployment they are susceptible to civil unrest, terrorism or civil war. It is irrefutable that Saudi Arabia has a youth bulge, high unemployment and -- in spite of its perceived prosperity -- it has experienced both domestic and global terrorism, with 15 of the hijackers on September 11, 2001 coming from the Kingdom. Consequently, following 9/11 Saudi Arabia was criticized by the West for having a religious education system that turned out terrorists, an allegation it strongly refuted. Given the recent resurgence in domestic and international terrorism by young Saudi members of DAESH (Islamic State), both within Saudi Arabia and the Levant, after a decade of relative calm, there would appear to be a strong case to support the theory. However, in Arabia, things are not always as they may seem. It is argued that youth bulge theory is overly focused on civil war and needs to be recalibrated to take account of Saudi exceptionalism. Built upon a foundation of Social Movement Theory, this thesis is supported by the three pillars of youth bulge, terrorism and feminist theory; the latter because half the population has to date been ignored by the academy in the discussion on youth bulge. Drawing from Durkheim’s work on religion, education and suicide, and Habermas for his public sphere, administrative power, education and crisis in society, the theory is reinforced by exhaustive ethnographic research and data drawn from primary and secondary sources. This process to recalibrate youth bulge theory will lead us to a better understanding of Saudi youth and an explanation for why when a few young Saudis embraced terrorism, the vast majority did not.

Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed June 7, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 172-178).

For 20 years now, gravitational microlensing observations towards the Galactic bulge have provided us with a wealth of information about the stellar and planetary content of our Galaxy, which is inaccessible via other current methods. This thesis summarises work on two research topics that arose in the context of exoplanetary microlensing, but we take a step back and consider ways of increasing our understanding of more fundamental phenomena: firstly, stellar microlenses in our Galaxy that were stereoscopically observed and, secondly, the morphological variety of binary-lens light curves. In autumn 2008, the ESA Rosetta spacecraft surveyed the Galactic bulge for microlensing events. With a baseline of ∼1.6 AU between the spacecraft and ground observations, significant parallax effects can be expected. We develop a photometry pipeline to deal with a severely undersampled point spread function in the crowded fields of the Galactic bulge, making use of complementary ground observations. Comparison of Rosetta and OGLE light curves provides the microlens parallax π[subscript{E}] , which constrains the mass and distance of the observed lenses. The lens mass could be fully determined if future proper motion measurements were obtained, whereas the lens distance additionally requires the determination of the source distance. In the second project, we present a detailed study of microlensing light curve morphologies. We provide a complete morphological classification for the case of the equal-mass binary lens, which makes use of the realisation that any microlensing peak can be categorised as one of only four types: cusp-grazing, cusp-crossing, fold-crossing or fold-grazing. As a means for this classification, we develop a caustic feature notation, which can be universally applied to binary lens caustics. Ultimately, this study aims to refine light curve modelling approaches by providing an optimal choice of initial parameter sets, while ensuring complete coverage of the relevant parameter space.

This thesis offers an account of children's lived experiences in Rwanda (1930s-2016) in four key domains: kinship, education, economic transitions, and marriage. Based on historical and ethnographic fieldwork in rural and urban Rwanda from 2012 to 2014, this work explores how three generations of young people have experienced and navigated childhood and coming of age at the interface of 'traditional' and 'modern' institutional systems. Rather than focusing narrowly on 'crisis' childhoods, individual agency, or exogenous forces, as studies of young Africans and social change tend to, this work examines young people's 'everyday' actions - intentional and unintentional, individual and collective, compliant and non-compliant - and locates them within their broader historical, relational, and institutional environment. By focusing on the intensely reproductive period of childhood and coming of age, on Rwanda's unexceptional majority rather than its exceptionally vulnerable minority, and on children's everyday actions rather than the strategic actions of elites, this thesis shows us how children shape the institutions of childhood and marriage and, in so doing, influence how society is reproduced and changed. Theoretically, this thesis explains how children and their institutional environment are mutually constituting: it examines how and why young people experience rapid change and structural violence differently and it traces how they reproduce and change these structural conditions as they engage with institutional mechanisms in (un)intended ways. The research reveals that children in central Rwanda navigate constraints and opportunities by drawing on established kinship relationships and institutions while also opportunistically engaging with modern institutions and their actors. However, in this context of 'institutional multiplicity', traditional and modern institutional systems each need Rwanda's young majority to reproduce their institutions over others', and as intended, to achieve their power-distributional goals. This makes children's actions particularly consequential and demands that we redefine what political action - and political actors - look like.

In recent years, much attention has been given to the question of whether content externalism is compatible with an account of self-knowledge maintaining that we have an epistemically privileged access to the content of our propositional mental states. Philosophers who maintain the two are incompatible (incompatibilists) have put forward two majors types of challenge, which I call - following Martin Davies - the Achievement and Consequence Problems, which aim to demonstrate that self-knowledge cannot be reconciled with externalism. These challenges have spawned a great deal of literature, and a diverse range of arguments and positions have emerged in response. In this dissertation, I intend to focus on examples of these different avenues of response, and show how none of them are adequate. In the first chapter, I lay the groundwork for the debate, setting up how externalism and self-knowledge are to be understood, and outlining both the incompatibilist challenges as well as the available responses to them. In the second chapter I examine these responses in more detail, concluding finally that the best available response is Tyler Burge's. Burge has two arguments that together establish his compatibilist position. First, he shows that even if externalism is true, our judgements about our occurrent thoughts are immunejrom error. This establishes that our judgements about our thoughts must be true. Second, he offers a transcendental argument for self-knowledge, arguing that our access to our mental states must be not only true, but non-accidentally true, in a way sufficient for genuine knowledge. This establishes that we possess the correct epistemic entitlement to our thoughts. In the third chapter, I argue Burge's arguments do not, in fact, give us good reason to suppose externalism and self-knowledge to be compatible. This, I argue, is because B urge relies upon a transcendental argument, which, in this context, cannot establish that we have self-knowledge if externalism is true. All it establishes, I argue, is that we do possess self-knowledge. And this is insufficient to establish that externalism and self-knowledge are compatible.
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Revêtir une surface d’un film mince permet de lui conférer de nouvelles propriétés, comme en réduire les reflets ou améliorer sa résistance aux rayures. Une méthode pour produire ces revêtements est le dépôt par voie liquide : elle consiste à couvrir la surface avec un matériau dispersé dans un liquide puis à le sécher. Cette méthode permet de fonctionnaliser efficacement et rapidement de grandes surfaces. Bien qu'attrayante pour l’industrie verrière, la perspective d'une fonctionnalisation par voie liquide se heurte actuellement à l'apparition de défauts dans le film lors de son séchage, notamment des variations d'épaisseurs sur de grandes distances. Ces imperfections détériorent l'esthétique et les propriétés optiques de la surface. Dans cette thèse, nous apportons un éclairage sur l’apparition de ces défauts, en étudiant les écoulements générés lors du séchage de films liquides de mélanges binaires. En effet, l'évaporation du solvant peut induire des variations de composition qui génèrent en retour des gradients de tension à la surface du film qui le déstabilisent. La combinaison d'expériences modèles, de modélisations théoriques et de simulations numériques ont permis de mettre en évidence et de décrire quantitativement plusieurs régimes, qui correspondent aux différents effets limitant l’instabilité : la pesanteur, la pression de Laplace, l’homogénéisation latérale par diffusion des composées dans le film ou au contraire la stratification verticale de ces composés, causée par l’évaporation. Une étude indépendante a été menée sur la génération de trains de bulles lorsque de l’air est lentement injecté dans un bain
Coating processes allow functionalizing a surface to obtain new properties, as anti-glare or anti-scratch. Amongst the various methods, wet coating, the process of spreading then drying a liquid layer containing a material of interest, is particularly appealing because of its efficiency and low cost. One key hurdle, however, is the possible apparition of defects in the film during the drying process, notably, thickness variations over large areas. These imperfections degrade the aspect and the optical properties of the surface. In this Ph.D. thesis, we shed light on the apparition of these defects, by studying the flows triggered by the evaporation in liquid films of binary mixtures. Indeed, the evaporation of the solvent can induce variations of composition which generate in return gradients of tension at the film surface which destabilize it. The combination of model experiments, theoretical modeling and numerical simulations allowed us to reveal and describe quantitatively several regimes, which correspond to the factor limiting the instability: gravity, Laplace pressure, lateral homogenization by diffusion of the compounds or by their vertical stratification due to the evaporation. An independent study has been lead on the generation of bubble trains when air is slowly injected in a bath

Cyber attacks by domestic and foreign threat actors are increasing in frequency and sophistication. Cyber adversaries exploit a cybersecurity skill/knowledge gap and an open society, undermining the information security/privacy of citizens and businesses and eroding trust in governments, thus threatening social and political stability. The use of open digital hacking technologies in ethical hacking in higher education and within broader society raises ethical, technical, social, and political challenges for liberal democracies. Programs teaching ethical hacking in higher education are steadily growing but there is a concern that teaching students hacking skills increases crime risk to society by drawing students toward criminal acts. A cybersecurity skill gap undermines the security/viability of business and government institutions. The thesis presents an examination of opportunities and risks involved in using AI powered intelligence gathering/surveillance technologies in ethical hacking teaching practices in Canada. Taking a qualitative exploratory case study approach, technoethical inquiry theory (Bunge-Luppicini) and Weick’s sensemaking model were applied as a sociotechnical theory (STEI-KW) to explore ethical hacking teaching practices in two Canadian universities. In-depth interviews with ethical hacking university experts, industry practitioners, and policy experts, and a document review were conducted. Findings pointed to a skill/knowledge gap in ethical hacking literature regarding the meanings, ethics, values, skills/knowledge, roles and responsibilities, and practices of ethical hacking and ethical hackers which underlies an identity and legitimacy crisis for professional ethical hacking practitioners; and a Teaching vs Practice cybersecurity skill gap in ethical hacking curricula. Two main S&T innovation risk mitigation initiatives were explored: An OSINT Analyst cybersecurity role and associated body of knowledge foundation framework as an interdisciplinary research area, and a networked centre of excellence of ethical hacking communities of practice as a knowledge management and governance/policy innovation approach focusing on the systematization and standardization of an ethical hacking body of knowledge.

Tese de doutoramento em Engenharia Mecânica, na especialidade de Produção Tecnologica, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
O ensaio de expansão biaxial sob pressão hidráulica continua a ser hoje em dia uma ferramenta importante de caracterização do comportamento plástico de chapas metálicas quando sujeitas a grandes deformações plásticas. A informação retirada deste ensaio não só faculta dados adicionais aos da curva tensão-deformação em tração, mas também desempenha um papel importante como informação necessária para a identificação dos parâmetros dos critérios de plasticidade mais avançados. Este trabalho foi realizado recorrendo a simulações numéricas do ensaio de expansão biaxial em matriz circular, com recurso ao programa DD3IMP. Tem como objetivo contribuir para a determinação da curva tensão-deformação de chapas metálicas em tração biaxial, de modo simples e preciso. Durante o ensaio foram analisadas a geometria e outras variáveis do ensaio, tais como, a evolução de pressão, o raio de curvatura e as trajetórias de tensão e de deformação no pólo da calote. Isto permitiu delinear algumas recomendações, de modo a melhorar o procedimento tradicional experimental de determinação da curva de encruamento, e desenvolver novos métodos diretos e inversos com o intuito de simplificar a sua avaliação. O procedimento tradicional de obtenção da curva de encruamento do ensaio de expansão biaxial em matriz circular não toma em consideração a anisotropia do material. Neste estudo analisam-se em pormenor algumas questões, tais como a geometria da calote esférica e as trajetórias de tensão e de deformação no pólo, de modo a compreender as relações entre as diferentes variáveis do ensaio em função da anisotropia do material e para diferentes comportamentos de encruamento. Isto permite uma compreensão aprofundada sobre a precisão na determinação do raio de curvatura e na espessura da chapa no pólo da calote esférica durante o ensaio, com impacto na determinação experimental da curva de encruamento do material. Foram propostos modelos analíticos para que descrevem a evolução do raio de curvatura e da espessura de chapa em função da altura de pólo. Estes modelos são baseados numa ampla análise de comportamentos de materiais, ou seja, para diferentes valores de tensão limite de elasticidade, coeficiente de encruamento, anisotropia, e também para diferentes valores de espessura inicial da chapa e geometrias circulares de matriz. As variáveis analisadas, respeitantes à geometria da matriz, são o raio da matriz e o raio de concordância da matriz. A validação dos modelos analíticos propostos foi realizada com resultados gerados numericamente e experimentais; neste último caso, foram utilizados os existentes na literatura, para várias geometrias de matriz, e os obtidos no âmbito da presente tese, com uma geometria de matriz específica. Esta formulação mostra-se adequada para simplificar a determinação experimental da curva de encruamento recorrendo ao ensaio de expansão biaxial sob pressão hidráulica. Nomeadamente, é possível evitar o procedimento experimental complexo para determinar os valores de tensão e de deformação durante o ensaio, que requer dispositivos específicos para a análise do raio de curvatura e da espessura da chapa no pólo da calote. Por fim, os presentes resultados também mostram que é possível sobrepor as curvas da evolução da pressão em função da altura de pólo e este conhecimento foi utilizado de modo a conceber uma estratégia de análise inversa para identificar os parâmetros da lei encruamento de Swift, baseada no ensaio de expansão biaxial. A sobreposição das curvas de pressão em função da altura de pólo é possível de obter com a utilização de fatores de multiplicação para a pressão e para a altura de pólo, no caso de materiais com o mesmo coeficiente de encruamento independentemente dos restantes parâmetros da lei de encruamento de Swift, da anisotropia e da espessura inicial da chapa. Além disso, a análise da evolução da pressão durante o ensaio mostrou que os valores desses fatores são sensíveis aos parâmetros da lei de Swift e à espessura inicial da chapa, sendo apenas ligeiramente dependentes da anisotropia do material. A metodologia proposta consiste em definir a melhor sobreposição entre os resultados experimentais e de referência, obtidos numericamente para materiais isotrópicos com diferentes valores de coeficiente de encruamento. Esta metodologia foi validada utilizando resultados gerados numericamente e resultados experimentais. Ela permite simplificar o procedimento experimental e não está exposta a erros relacionados com a determinação experimental da deformação no pólo da calote e a utilização da teoria de membrana na avaliação da tensão a partir da análise do raio de curvatura, que é normalmente a principal fonte de erro. The hydraulic bulge test remains nowadays an important tool for characterizing the behaviour of sheet materials submitted to large plastic deformation. Data from this test, not only provides additional information to the tensile stress-strain curve, but also plays an important role as input information when identifying the parameters of the current most advanced yield criteria. The circular hydraulic bulge test is studied by means of finite element simulations, using the in-house code DD3IMP. This work aims to contribute to the easy and accurate evaluation of stress-strain curve of sheet metals in biaxial tension. The geometry and other variables of the test, such as pressure evolution during the test, radius of curvature, strain and stress paths at the pole of the cap, were analysed. This allows to make recommendations in order to improve the traditional experimental procedure for determining the hardening curve, but also the development of new direct and inverse methodologies for simplifying its evaluation. The traditional procedure for obtaining the hardening curve from the circular bulge test does not takes into account the anisotropy of the material. This study analyses in detail issues such as the geometry of the spherical cap and the stress and strain paths at the pole, in order to understand the relationships between different variables of the test as a function of the anisotropy and for different hardening behaviours of the material. This allows the in-depth understanding about the accuracy of the assessment of thickness and radius of curvature at the pole of the spherical cap during the test, with repercussions on the experimental determination of the hardening curve of the material. Analytical models for the radius of curvature and the sheet thickness evolutions with the pole bulge height were proposed. These models are based in an extensive analysis of material Abstract vi behaviours, i.e. different values of yield stress, hardening coefficient, anisotropy, and also different values of initial sheet thickness and geometry of the circular bulge test. The geometric variables analysed are the bulge die radius and the fillet radius of the die. The validation of the proposed analytical models is performed with numerically generated and experimental results; in the latter case, results from literature, with various die geometries, and those obtained in the framework of this thesis, with a specific die geometry, were used. This formulation shows to be appropriate for simplifying the experimental assessment of the hardening curve from the hydraulic bulge test. Namely, it is possible to avoid the complex experimental procedure to determine the stress and strain values during the test, which requires specific devices for evaluating the radius of curvature and the sheet thickness at the pole of the cap. Finally, the current results also showed that it is possible to overlap the curves concerning the evolution of the pressure with the pole height, and this insight was explored in order to build an inverse strategy for identifying the parameters of the Swift hardening law, from the bulge test. The overlapping of these curves can be accomplished by using multiplying factors for the pressure and the pole height, in case of materials with the same hardening coefficient regardless of the remaining parameters of the Swift law, anisotropy and initial thickness of the sheet. Moreover, analysis of the pressure evolution during the test has shown that the values of these factors are sensitive to the parameters of Swift law and the initial sheet thickness, being only slightly dependent of the anisotropy of the material. The proposed methodology consists on choosing the best overlap between the experimental and reference results, numerically obtained for isotropic materials with various values of the hardening coefficient. It was validated using numerical generated and experimental results. The methodology allows simplifying the experimental procedure and additionally is not exposed to experimental errors related to the experimental evaluation of strain at the pole of the bulge and the use of membrane theory approach for assessment of the stress from the radius of curvature, which is usually the major source of error.
The hydraulic bulge test remains nowadays an important tool for characterizing the behaviour of sheet materials submitted to large plastic deformation. Data from this test, not only provides additional information to the tensile stress vs. strain curve, but also plays an important role as input information for identifying the parameters of the current most advanced yield criteria. The circular hydraulic bulge test is studied by means of finite element simulations, using the in-house code DD3IMP. This work aims to contribute to the easy and accurate evaluation of stress vs. strain curve of sheet metals in biaxial tension. Variables of the test, such as pressure evolution during the test, geometry of the cap, including radius of curvature and sheet thickness, strain and stress paths at the pole of the cap, were analysed. This allows to make recommendations in order to improve the traditional experimental procedure for determining the stress vs. strain curve, but also to develop new direct and inverse methodologies for simplifying its evaluation. The traditional procedure for obtaining the stress vs. strain curve from the circular bulge test does not takes into account the anisotropy of the material. The detailed analysis of issues such as the geometry of the spherical cap and the stress and strain paths at the pole, allowed to understand the relationships between such variables of the test, the sheet anisotropy and the different hardening behaviours of the material. The in-depth understanding of these relationships has repercussions on the experimental evaluation of the stress vs. strain curve of materials when using the bulge test, for which recommendations are made. Analytical models for the radius of curvature and the sheet thickness evolutions with the pole bulge height were proposed. These models are based in an extensive analysis of material behaviours, i.e. different values of yield stress, hardening coefficient, anisotropy, and also different values of initial sheet thickness and geometry of the circular bulge test. The analysed geometric variables include the bulge die radius and the fillet radius of the die. The validation of the proposed analytical models is performed both by numerically generated results and experimental results; in the latter case, results were considered not only from literature, having various die geometries, but also from an experimental equipment in the framework of this thesis, having a specific die geometry. This formulation shows to be appropriate for simplifying the experimental assessment of the hardening curve from the hydraulic bulge test. Namely, it is possible to avoid the complex experimental procedure to determine the stress and strain values during the test, which requires specific devices for evaluating the radius of curvature and the sheet thickness at the pole of the cap. Finally, the current results also showed that it is possible to overlap the curves concerning the evolution of the pressure with the pole height, and this insight was explored in order to build an inverse strategy for identifying the parameters of the Swift hardening law, from the bulge test. The overlapping of these curves can be accomplished by using multiplying factors for the pressure and the pole height, which in case of materials with the same hardening coefficient it is independent of the remaining parameters of the Swift law, anisotropy and initial thickness of the sheet. Moreover, the analysis of the pressure evolution during the test has shown that corresponding values of these factors are sensitive to the parameters of Swift law and the initial sheet thickness, being only slightly dependent of the anisotropy of the material. The proposed methodology consisted on choosing the best overlap between the experimental and reference results, which were numerically obtained for isotropic materials with various values of the hardening coefficient. Validation was performed using numerical generated results and experimental results. The methodology allows simplifying the experimental procedure and in addition is not exposed to experimental errors related to the experimental evaluation of strain at the pole and the use of membrane theory approach, for assessment of the stress from the radius of curvature, which is usually the major source of error.
FCT - Pest-C/EME/UI0285/2013

This chapter develops two-dimensional membrane theory as a leading order small-thickness approximation to the three-dimensional theory for thin sheets. Applications to axisymmetric equilibria are developed in detail, and applied to describe the phenomenon of bulge propagation in cylinders.

In the 1930s the US Air Corps Tactical School (ACTS) articulated the concept of high-altitude daylight precision bombing (HADPB), a coherent yet controversial theory for victory through the independent employment of air forces. The ACTS lectures present a uniquely American theory of strategic bombing later tested in World War II. These lectures, never before published, introduce Air Corps thinking on strategic bombing during the interwar period. Their originality is found in the causal logic for how HADPB operations would lead to victory by the direct attack of vital and vulnerable economic targets. The ACTS instructors and students would later be responsible for translating theory into practice. In so doing, the logic of HADPB was tested and in many ways found wanting. Though the US Army Air Force fell short of independently achieving decisive victory, the ACTS prewar rationale for the construction of heavy bombers offered the United States the offensive capability to conduct long-range air campaigns. HADPB proved to be a key component to the Allies gaining air superiority over western Europe. Finally, HADPB raids starved the German military of fuel such that it no longer had the means to maintain its desperate counteroffensive at the Battle of the Bulge. American air power did prove critical to the Allied victory, not in the independent and decisive way envisioned by ACTS but as a crucial component of a combined arms strategy.

Following Descartes, philosophers like Shoemaker and Burge argue that only self-conscious creatures can exercise rational control over their mental lives. In particular, they urge that reflective rationality requires possession of the I-concept, the first-person concept. These philosophers maintain that rational creatures like ourselves can exercise reflective control over belief as well as action. This chapter agrees that we have this reflective control over our own actions and that this form of practical freedom presupposes self-consciousness, but denies that anything like this is true of belief. The chapter endorses Williams’ claims that the first-person concept is indispensible only to practical reasoning.

AbstractMandible, a horseshoe shaped bone of the facial skeleton, is one of the sturdy bones in humans. Prominent chin is a unique feature of anatomically modern man in comparison with his anthropological ancestors. The simian shelf has reduced to two genial tubercles to which two muscles are attached. The neck of the condyle has narrowed and acts as a buffer to budge by fracture if there is a severe force on the prominent chin. These evolutionary changes facilitated increased space for the tongue as men started articulation. It articulates with the temporal bone by two inter-dependent Temporo-mandibular joints. Mandible is important in both function and aesthetics.Mandible can be cut into multiple pieces and re-arranged and fixed to achieve aesthetic and functional changes. Facial bones have a tremendous capacity to regenerate and heal provided proper blood supply is ensured to the cut segments. Ostoetomies of the mandible can be done on ramus, body, chin, dento-alveolar region, inferior border, etc. Most of these procedures are done intraorally. Technological advancements have aided orthognathic surgery at large. This chapter envisages to elaborate different techniques of osteotomy of mandible.

Common explanations of why the Arab region erupted in 2011 are only partly accurate and have glaring omissions. The youth bulge is real butsuch bulges do not automatically lead to upheavals.Socio-economic conditions in Egypt or Yemen were dismal, but no more so in 2011 than in the previous decades. Tunisia, where the uprisings started, is a middle-income country, and Gulf monarchies are incredibly rich but still fearful of unrest. Artificial borders explain even less about countries’ stability. Syria and Iraq have borders drawn on maps by colonial powers after World War I, but Egypt’s date back millennia.A crucial factor in causing the disaffection of Arab citizens toward their government is the absence of “state projects,” a vision of what the country could and should be, and of inspiring leaders to embody that vision. Egypt had a project and a leader that inspired the entire Arab world in the days of Gamal Abdel Nasser, but that is no longer the case.

Producing fuel cells bipolar plates and other devices such as microscale heat exchangers for electronics requires both macroscale and microscale forming processes. At the macroscale, typically, mechanical properties of sheet metal are determined by performing tensile tests. In addition, it has long been recognized that bi-axial tension tests, dome tests, and hydroforming or viscous bulge tests provide the basis for improved understanding of the mechanics of sheet metal forming. At the microscale strain gauges are too large for measuring strains in small regions and membrane theory is only valid at the poles of the bulge. Continuum mechanics models are useful but require tedious thickness measurements for multiple work pieces, requiring extensive sample preparation and analysis. In this paper experimental results from hydroforming tests for 0.2-mm thick annealed ASTM 304 stainless steel sheet in 11 mm, 5 mm, and 1 mm diameter open dies at various pressures were evaluated. The height of the bulge at the pole and strains based upon measurements of 127 micron strain grids were determined. These dies represent the transition from a small macroscale process to a microscale forming process. Two methods were used to estimate material properties: an analytical model and an iterative method which compared experimental strain results with the strains from a finite element model where the Holloman constitutive properties of the sheet were varied. The problems estimating material properties based upon grid strain measurement, membrane theory, and the iterative finite element approaches were investigated and the results were compared. This study indicates that membrane theory will provide adequate predictions for Holloman constructive properties provided the assumptions for membrane theory are not violated. However, using measured microscale grid deformation strains does not produce very good agreement estimates of the Holloman constitutive model when comparing experimental results with FEA strains. It is believed that while the grid strain measurement method used results in strain measurement errors of less than 1.5% of strain, this error is sufficient to result in enough uncertainty to produce results that are inconsistent with other methods.

The mechanical properties of compliant materials such as biological tissues and biocompatible soft polymers are essential in medical research and engineering applications. These properties are often determined using techniques that require costly instrumentation (e.g. pull test machines). Alternative and more accessible methods can significantly aid the characterization process. The bulge test determines a material elastic modulus by analyzing the pressure-deflection response of thin samples made of this material. The technique has been extensively employed in the characterization of metals and semiconductors (modulus ∼ 100 GPa). By employing plate rather than membrane mechanics, the present study extends bulge testing to characterize materials with a modulus that is five orders of magnitude lower (∼ 1 MPa). The novel method is demonstrated analytically using plate theory, numerically using finite element modeling and experimentally by successfully applying it to polydimethylsiloxane (modulus ∼ 1.33 MPa). The introduced technique does not require costly equipment, is simple to implement and presents an appealing alternative to current characterization approaches.

The objective of this study is to simulate the shaking test of a condensate storage tank (CST). In this test, the typical failure mode was an elephant-foot bulge (EFB) or a shear buckling. It is difficult to reproduce such buckling modes. However, at last, an analytical model which describes those modes with enough accuracy was achieved. The comparison between simulation results and experiments is explained. Acoustic theory and classical plasticity theory were used in the FEM simulation. The phase and magnitude of the response acceleration and hydraulic pressure obtained from the FEM simulation are well corresponded to those from the experiments. In addition, asymmetrical distribution of maximum and minimum hydraulic pressure is described.

Several studies recognized that cracks in delayed coke drums resulted from low cycle fatigue induced by cyclic thermal stress [1], [2], [3]. According to a coke drum survey coordinated by API in 1996 [1], there are two different areas where cracks are produced. The first zone is located at the shell to skirt weld, and the second at the bulged areas found in the cylindrical section. In the second case, from 145 coke drums 57% reported that had shell bulging problems. Of the drums that bulged, 87 % also showed cracks. Recently, it has been reported the use of a novel weld repair procedure on bulged sections of a drum. In this repair, the bulge is overlaid with weld metal on the inside or outside on the bulge depending on the bulge shape. It has been reported that this repair procedure can stop further bulging on the shell, but detailed information about its influence has not yet been published. Finite element analysis of several bulged patterns that were identified from some laser mappings are used to compare the level of the stress after a weld overlay repair is made. The study was carried out running a sequentially-coupled thermo-mechanical analysis. The assessment shows the influence of the thickness and the extent of the weld overlay on the level of stress on bulged coke drums. The results indicated that depending on the initial bulged shape this repair method either reduces or increases the level of the stress. When an inward deformation pattern is observed, an external reinforcement is recommended; however, when an outward deformation pattern is developed in a coke drum, an external weld overlay repair is not recommended.

Abstract In recent years the understanding of the relationship between drum damage and bulge sharpness has improved significantly. The authors of this paper developed a new parameter called bulge sharpness and have previously shown the relationship between sharpness and observed damage. Further to this study, the authors have exhaustively studied the evolution of stress cracking (elephant skin) on mid-course bulges and have estimated the likelihood of finding a particular type of surface damage based on the observed sharpness levels. This correlation has led to a proposed scale to categorize stress cracking into three levels: minor, intermediate, and significant. In addition, the progression of bulge sharpness over time was analyzed and it was determined through statistical modeling that bulge sharpness can have a range of rates of change or sharpness growth rates: low, medium, and high. These sharpness growth rates were subsequently studied and their relationship with overall cycle times analyzed. The study also shows that individual coke drums can experience different sharpness growth rates and there can be a distribution of these rates. To determine when repairs should be conducted, coke drum operators must consider the expected operational run. While the random nature of coke drum damage can defy such targets, bulge sharpness growth assessments can be used to better define when repairs should be conducted. Understanding current bulge sharpness levels, year-over-year sharpness growth rates and their distribution, can significantly assist in targeting areas of concern for optimized repair strategies and can also be used to avoid unnecessary repairs.

Coke drums are thin-walled pressure vessels that experience low cycle fatigue due to thermal loadings. The delayed coking process is comprised by three major stages: heating, coking and cooling, which repeat at intervals between 20 and 48 hours. The cyclic changes of temperature increase the growth of bulges and cracks which with the passing of time, propagate and eventually cause failures due to the loss of containment. A better understanding of the phenomena of the thermal gradients and their influence on the generated stresses would reduce the effects of the damage mechanisms afflicting coke drums, for example; a continuous monitoring system could be implemented in order to control the cooling ramp to obtain a more homogeneous quenching around the cylinder of the coke drum and consequently increase its lifetime. It is been widely accepted that there is a relationship between high cooling rates in isolated zones and high axial stresses. However, this relationship has not been fully validated, since there are also been reported events of low cooling rates and high stresses. This study shows a predictable behavior (trend) that relates the spatial thermal gradients and the axial and circumferential stresses generated. A coke drum in an upgrader facility was instrumented with two arrays or grids, each of them having 24 thermocouples and 2 strain gauges in zones with distinct bulges. One arrangement was located at an inward bulge while the other was located at an outward bulge. Computational models were carried out to reproduce the behavior of the instrumented zones with their actual deformations obtained from laser scanning. Finite element models were developed using a sequentially coupled thermo-mechanical analysis to determine the transient temperature and stress distributions. The effect of the circumferential thermal gradients on the stress levels in the instrumented cylindrical sections were analyzed, considering two cases; the first of them a perfect cylinder (without deformation) and the second one considering the presence of bulges in the area of interest. The results indicate that there is a relationship between the circumferential thermal gradients [°C/m] or [°F/ft] and the axial stress levels, i.e., cold zones generate axial tensile stresses, and hot zones produce compressive axial stresses. This relationship is affected — exacerbated or counteracted — by the presence of the bulges. Additionally, the results obtained in this paper confirm those of previous investigations showing that outward bulges subject to pressure and thermal loading generate high stresses on its internal surface and low stresses on its external face whereas inward bulges produce the opposite effect.

The frequency and extent of vessel bulging and cracking being registered in delayed coke drums throughout the global coking industry has accelerated significantly as refinery operators reduce their cycle times. Several theoretical approaches have been developed to identify how a bulged area may lead to drum damage; however, limited information has been presented to match the theoretical predictions with actual surface damage reported by coke drum operators. The results of hundreds of laser scans spanning the last 25 years have been analyzed to correlate vessel bulging with observed surface damage. Specific categorizations of bulge profiles, and the proximity of these to circumferential weld seams (circs), have been calibrated against hundreds of real-world examples of drum damage and failure, including through wall cracking and stress cracking of the cladding, and further associated with the triggers for repair strategies implemented by industry leading refiners. Strong correlations between specific aspects of bulge profiles and the presence of surface damage were found resulting in an assessment tool that can rank and prioritize coke drum distortions on the likelihood of damage, and can serve as a useful guide for planning future coke drum maintenance.

This paper presents results from a recent combined experimental-analytical study of the inelastic response and the sequence of events that lead to collapse of pipes bent under internal pressure. Experimental results from stainless steel 321 seamless tubes with D/t of 52 are reported. The tubes were loaded by pure bending at fixed values of pressure ranging from zero to a value that corresponds to 0.75 times the yield pressure. The moment-curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure in the form of an outward bulge. Pressure increases the wavelength of the wrinkles as well as the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated using a FE shell model. The material is represented as an anisotropic elastic-plastic solid using the flow theory, while the models are assigned initial geometric imperfections that correspond to the wrinkling bifurcation mode. It will be shown that all aspects of the observed behavior including the failure by localized bulging can be successful reproduced by the models developed.