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Propriedades mecânicas e de fadiga de ligas de alumínio-silício com gradação funcional
No full textTese de doutoramento em Engenharia Mecânica (ramo de conhecimento em Mecânica de Materiais)Many structural components encounter service conditions and, hence, required
materials performance, which vary with location within the component.
It is well known that abrupt transitions in materials composition and properties
within a component often result in sharp local concentrations of stress, whether the stress
is internal or applied externally. It is also known that these stress concentrations are
greatly reduced if the transition from one material to the other is made gradual. By
definition, functionally graded materials are used to produce components featuring
engineered gradual transitions in microstructure and/or composition, the presence of
which is motivated by functional performance requirements that vary with location within
a part. With functionally graded materials, these requirements are met in a manner that
optimizes the overall performance of the component.
The research on functionally graded materials (FGMs) is encouraged by the need for
properties that are unavailable in any single material and the need for graded properties to
offset adverse effects of discontinuities for layered materials. Centrifugal casting is a very
common method for obtaining functionally graded materials, mainly composite materials
or metallic materials which has high differences of density and low solubility on different
phases or different materials of the same alloy. The present work is emphasizing the fact
that the centrifugal process could be successfully used for obtaining functionally graded
materials also for metallic materials (alloys) with moderate solubility and small
differences of density of the different phases, as is the case of most aluminum alloys.
The first approach of the problem was to isolate the effects of the centrifugal casting
technique (the centrifugal pressure effect, the fluid dynamics and the inherent vibration
effects) in order to identify the reason of mechanical properties improving. To have a
reference for comparison, castings obtained by both centrifugal casting technique and
gravity casting technique were tested. To isolate the vibration effect, experimental equipment was designed and constructed
in order to be able to cast within a certain level of vibration equivalent with the vibration
level of the centrifugal casting equipment. The results are confirming that there is a
correlation of improving mechanical properties with the vibration of the melt during
solidification.
The difference of the mechanical properties of castings obtained by gravity casting
technique and by centrifugal casting technique could be explained by the fact that, the
vibration due to the inherently vibration of the equipment, the fluid dynamics and the
centrifugal pressure make the melt, during solidification, to initiate more nuclei of
solidification. Then, the centrifugal pressure moves the nuclei of solidification to the
furthest point of the mould (where the pressure is higher) fact that explains the obtained
results which are higher on one side of the ingots which corresponds with the side of the
mould where the pressure is higher and smaller on the other side where the pressure is
smaller. This causes several differences in microstructures in both sides of the ingot.
The mechanical and fatigue properties are largely influenced by microstructure and
the presence of material inhomogeneities. Pores, inclusions or secondary phase particles
are common sites for fatigue crack nucleation in aluminium alloys. The constituent
particle’s size and shape are also important characteristics that influence crack nucleation.
This study intends to assess also the problem of fatigue life prediction by
establishing a relation within some of the characteristics of the micro structural features
of studied aluminium silicon alloys such as: micropores, secondary dendrites arm spacing
(SDAS), volume fractions of phases (α-Al phase, eutectic and intermetallic phases), the
size of silicon lamellas in interdendritic eutectic regions and the size and shape of silicon
particles. This evaluation was performed along the ingots gradients for different
aluminum alloys.Muitos componentes estruturais, nas suas condições de serviço, requerem
desempenhos que variam com a localização dentro do componente.
É sabido que transições bruscas de composição química dos materiais no
componente muitas vezes resultam em acentuadas concentrações de tensão locais. É
também sabido que estas concentrações de tensões são muito reduzidas/atenuadas se a
transição de um material para outro é feita gradualmente. Por definição, materiais com
gradiente funcional de propriedades são usados para produzir componentes de engenharia
com transições graduais na microestrutura e / ou composição química, cuja presença é
motivada por exigências de desempenho funcional, que variam com a localização de cada
parte do componente. Com materiais com gradiente funcional, estes requisitos são
cumpridos de uma forma que otimiza o desempenho geral do componente.
A pesquisa sobre materiais com gradiente funcional (FGMs) é incentivada pela
necessidade de propriedades que não estão disponíveis em qualquer material único ou em
componentes obtidos pelas junção de partes diferentes materiais onde existe o efeito
negativo da sua junção.
A fundição centrífuga é um método muito comum para a obtenção de materiais com
gradiente funcional, principalmente materiais compósitos ou materiais metálicos, que tem
grandes diferenças de densidade e baixa solubilidade em diferentes fases ou em diferentes
materiais da mesma liga. O presente trabalho visa enfatizar o fato de que o processo de
fundição centrifuga pode ser utilizada com sucesso para a obtenção de materiais com
gradiente funcional também para materiais metálicos (ligas) com solubilidade moderada e
pequenas diferenças de densidade das diferentes fases, como é o caso da maioria das ligas
de alumínio. A primeira abordagem do problema foi isolar os efeitos da técnica de
fundição centrífuga (o efeito das pressões centrífugas, a dinâmica dos fluidos e os efeitos
da vibração inerente), a fim de identificar o motivo da melhoria das propriedades mecânicas. Para ter uma referência para comparação, foram obtidos e testados provetes de
vazamentos por ambas as técnicas, quer de fundição centrífuga quer de fundição por
gravidade. Para isolar o efeito da vibração, um equipamento experimental foi projetado e
construído de modo a ser capaz de reproduzir um determinado nível de vibração
equivalente ao nível de vibração do equipamento de fundição centrífuga. Os resultados
confirmam que há uma correlação entre a melhoria das propriedades mecânicas com a
vibração da liga durante a solidificação. A diferença das propriedades mecânicas de peças
fundidas obtidas pela técnica da gravidade e pela técnica de fundição centrífuga poderia
ser explicada pela vibração inerente do sitema, pela dinâmica dos fluidos e pel pressão
centrífuga, que originam, durante a solidificação, mais núcleos/germens de solidificação.
A pressão centrífuga move os núcleos de solidificação para o ponto mais afastado do eixo
de rotação (onde a pressão é maior) que explica que os resultados obtidos são mais
elevados nessa zona do que do lado mais próximo do eixo de rotação, que corresponde ao
lado do molde em que a pressão é menor. Isto causa substanciais diferenças de
microestrutura e mambos os lados dos lingotes.
As propriedades mecânicas e de fadiga são grandemente influenciadas pela
microestrutura assim como pela presença de inomogeneidades no material. Poros,
inclusões ou partículas de fases secundárias são responsáveis pela nucleação de fendas de
fadiga em ligas de alumínio. O tamanho das partículas e a sua forma são também
características importantes que influenciam a nucleação da fenda. Este estudo pretende
avaliar a previsão da vida à fadiga através de correlações com características
microestruturais das ligas de alumínio-silício estudadas tais como: microporos,
espaçamento entre braços das dendrites (SDAS), frações volumicas de fases ou
constituintes( α primária, eutético e intermetálicos), a espessura das lamelas do silicio
eutéctico e dimensões de partículas de silicio eutéctico. Esta avaliação é feita para
diferentes diferentes zonas ao longo do gradiente de propriedades dos lingotes das
diferentes ligas de alumínio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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