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Microstructural Changes in Brazing Sheet due to Solid-Liquid Interaction
No full textAluminium brazing sheet is the material of choice to produce automotive heat exchangers. Although in Dutch the official translation of aluminium brazing sheet is “aluminium hardsoldeerplaat” the English name is used in the industry. Aluminium brazing sheet is basically a sandwich material and consists of an aluminium core alloy, typically an AA3XXX alloy (containing Mn) or an AA6XXX alloy (containing Mg and Si) with a clad alloy of the AA4XXX (containing Si) series. The core alloy gives the final product the desired properties after brazing. The core alloys are designed in such a way that after the brazing cycle, the condition is reached where the core has its optimum properties. Properties like strength and corrosion resistance are the main engineering parameters. Typically the core alloy is single side or both side clad and the thickness of the clad alloy ranges between 5 and 20% of the total thickness. The AA4XXX alloy used for aluminium brazing sheet has a melting range between 570°C and 610°C while the melting range of a typical AA3XXX core alloy lies above 610°C. This difference in temperature between the two alloys is used to join complex shaped products in “one shot”. At the brazing temperature, typically around 600°C, the AA4XXX clad alloy is completely molten. Due to capillary forces and surface tension differences, the molten clad alloy will flow to connect adjacent pieces. The process by which joining is taking place is called the brazing process. During this brazing process liquid metal from the clad alloy is in close contact with the solid core alloy. At this stage an interaction between the two phases can take place. Several types of interaction between the two phases can take place but the interaction that is referred to as Liquid Film Migration is the topic of study in this thesis. Liquid Film Migration is, however, not the only name given in literature to what seems to be the same interaction. Liquid Film Migration is causing a significant change in microstructure and element distribution of the core alloy. These changes are detrimental to the corrosion resistance of the final product. Although the name Liquid Film Migration was given to the process responsible for the observed changes no conclusive evidence has been presented to confirm the existence of a liquid film in aluminium brazing sheet. The literature available on Liquid Film Migration in aluminium brazing sheet has given some information on the conditions favourable for Liquid Film Migration to occur. These conditions are residual strain in the core alloy present at the peak brazing temperature and a small grain size of the core alloy. This thesis focussed on the occurrence of LFM in brazing sheet and the possible mechanism and driving forces behind it. Two different core alloys with the same clad alloy were processed and studied for their susceptibility to Liquid Film Migration. Conditions were created that according to literature should result in different degrees of Liquid Film Migration. Brazing took place in a standard brazing furnace or in a salt bath. The salt bath would enable a kinetic study since time and temperature are well controlled. The study of the samples after brazing indeed showed a different response to the applied processing. The main observation was that the onset of recrystallization of the core alloy plays a major role in the occurrence of Liquid Film Migration. A detailed study of the liquid film showed the accumulation of constituents and dispersoids which were originally present in the core alloy. The measured diffusion profiles of silicon in front of the liquid film coincide with theoretical diffusion profiles as if they originated from a moving boundary. From the diffusion profiles of silicon, the kinetics of the moving liquid film was extracted resulting in an inverse square root dependence of the velocity with time. An estimation of the energies available in the system showed that the coherency strain energy could not be the driving force for Liquid Film Migration in aluminium brazing sheet. Most likely the energy is supplied by the reduction of the (sub)grain size. This is supported by the fact that strained samples that do not recrystallize during brazing are the ones showing the highest degree of Liquid Film Migration. Based on these findings, the residual strain present in the form of sub-grains or dislocations is considered to provide the energy for the movement of the liquid film. A qualitative assessment of the residual strain present in samples after brazing supported the hypothesis that indeed this residual strain is the energy source needed for the movement of the liquid film. The mechanism behind liquid film migration has been found to be similar to the recrystallization process caused by Strain Induced Boundary Migration. It was presented that lowering the surface energy between grains by a liquid film would allow the boundary to move at lower dislocation densities compared to a non liquid infiltrated grain boundary. Recrystallization would reduce the dislocation density taking away the driving force to spport liquid film migration. Liquid film migration and strain induced boundary migration are both in competition for the same energy. Strain induced boundary migration can take place during the whole brazing cycle while liquid film migration only can occur in the presence of a liquid. This means that the clad alloy has to be at least partly molten to allow wetting of the grain boundaries. When recrystallization by strain induced boundary migration takes place no liquid film migration will occur. A theoretical approach to determine the velocity of the liquid film was in reasonable agreement with the observations. The main obstacle to completely quantify liquid film migration is the uncertainty of the development of the film thickness in time. As demonstrated, recrystallization plays a critical role in the onset of liquid film migration. A through Process Model was used to determine if such model could be used to predict recrystallization based on thermal mechanical process input parameters and alloy chemistry. Unfortunately the model lacks sensitivity to predict the onset of recrystallization in this study. However the model contains all necessary modules to ensure that after fine tuning for this application, more predictive power can be expected.Light Metal ProcessingMechanical, Maritime and Materials Engineerin
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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