1,720,961 research outputs found
Fracture Mechanics Approach to compare Laser Sintered parts and Injection Mouldings of Nylon-12
Get PDFIn comparison to equivalent parts made by injection moulding, components manufactured by laser sintering are often perceived to offer inferior mechanical properties, yet the evidence for this is rarely based upon systematic research studies. In this paper, attempts have been made to conduct a fundamental study of the fracture behaviour of both injection moulded and laser sintered parts, based upon a modification of a standard technique used to determine linear elastic fracture mechanics parameters. The influence of specimen thickness (in the range 2–10 mm) was also included in the experimental plan, which concentrated upon the testing of single-edge notch bending (SENB) beam specimens.
Force-displacement characteristics demonstrated significant plastic deformation in nylon (PA12) specimens, so that the J-integral method was used to obtain quantitative fracture parameters, including the energy requirements for crack growth. Comparisons of this parameter showed thickness-dependent ‘geometry-sensitive’ data for each set of samples. For the injection moulded SENB specimens, energy absorption decreased with increasing thickness, a result attributed to the influence of plane-strain-dominated conditions. In contrast, laser sintered samples exhibited increased toughness as specimen thickness increased towards 10 mm; this could not be explained by density or particle melting data and may be interpreted by changes in molecular structure that occur during the additive manufacturing process
Methods for quantifying the stable sintering region in laser sintered polyamide-12
Get PDFManufacturing complex parts by the laser sintering process requires a minimum amount of energy input for consolidation of polymer particles to occur; however too much energy can result in a decline in mechanical properties. This decrease is thought to be the result of polymer chain degradation. A stable sintering region (SSR) has been proposed to describe the optimum temperature range for successful laser sintering. This article will aim to quantify the SSR for polyamide-12 by using thermogravimetric analysis (TGA) to provide a framework for identifying key laser sintering processing parameters. Weight loss with respect to temperature is the main measurement output of the TGA procedure. However, the precise temperature and thermal history of a material is difficult to quantify during the laser sintering process; instead an energy input approach has been developed. A degradation energy was calculated from the TGA data and was used in conjunction with a laser sintering formula called energy melt ratio to prescribe build parameters for laser sintered parts. The mechanical properties of these parts illustrated the effect of degradation at various levels of energy input. Implications for this work include optimizing the material selection process for polymer laser sintering materials beyond polyamide-12. © 2012 Society of Plastics Engineers
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
Optimum sintering region for laser sintered nylon-12
Get PDF It is well known that the mechanical properties of laser sintered Nylon-12 improve with increased applied energy. However properties can reach a maximum after which, the application of additional energy can a lead to a decline in part properties. It is thought that the reason for this decline is that the additional energy causes polymer chain degradation or other changes in molecular structure. This paper aims to use thermogravimetric analysis (TGA) to investigate the thermal degradation of nylon-12 and explain the deterioration of mechanical properties when high energy density conditions are applied during processing. The key findings are the application of modelling methods to predict the temperatures achieved during laser sintering of nylon-12. It is shown that temperatures in the laser sintering machine can achieve levels above 300°C. At these temperatures, TGA data show that mass loss occurs and could cause mechanical property breakdown. This practical work coupled differential scanning calorimetry and TGA as a means of identifying thermal transitions in the material. The term ‘stable sintering region’ is proposed as a novel concept for the laser sintering community, and can have implications for better understanding of how process parameters can affect parts built in the machine. In addition, the concept could be used in the material selection process when screening potential new polymers for the process. One limitation of laser sintering, compared to other polymer processes such as injection moulding, is the limited understanding of the connection between machine parameters and part properties. This work aims to improve that understanding by discussing the pattern of thermal behaviour, including degradation, seen in polyamide exposed to high laser parameters. </jats:p
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