1,720,958 research outputs found
Elevated temperature short crack fatigue behaviour in near eutectic Al-Si alloys
No full textThis paper considers two candidate automotive piston alloys and highlights the influence of microstructural features on fatigue behaviour. Fatigue initiation and subsequent short crack growth was assessed at 20, 200 and 350 °C. It is shown that both temperature and test frequency have a strong influence on the fatigue performance of the materials tested. The microstructure was quantitatively characterised in terms of the primary Si distribution. Together with post failure analysis, this allowed identification of critical microstructural features affecting both fatigue crack initiation and early growth. Large primary Si particles were found to act as preferential initiation sites by cracking or decohesion (dependent on test temperature) and are also sought out preferentially during short crack growth
Fatigue of an Al-Si gravity die casting alloy
No full textFatigue crack initiation, short crack and long crack growth studies were performed on a high performance cast piston type alloy (Al-Si-Cu-Ni-Mg). Crack initiation was mainly associated with large blocky Si particles although a few cracks were initiated at clusters of FeNiAls intermetallics. Classical short crack growth was shown with crack arrest for up to 15000 fatigue cycles at second phase particles. Long crack growth showed no evidence of Stage I like facets near threshold or ductile striations in the mid Delta K region. A large number of fractured Si particles were, however, observed on the fracture sur faces and crack profiles the incidence of which increased with Delta K. The findings of this study suggest this alloy is brittle in nature with the Si particle content generally controlling fatigue crack initiation and growth
Elevated temperature fatigue of Al-Si piston alloys
No full textLong crack fatigue tests were carried out on two cast Al-Si alloys used in the manufacture of pistons for small automotive engines. These were performed at a frequency of 15Hz at room temperature, 200 degreesC and 350 degreesC, in addition further tests were performed at 50Hz at the highest temperature. The fatigue performance of both alloys was found to improve with increasing temperature. This was linked to a change in fatigue crack propagation mechanism in both alloys with respect to the primary Si phase. It was seen that the transition between a given Si phase decohering or fracturing ahead of a fatigue crack occurred at a temperature and strain rate dependent critical stress intensity factor. The relation between critical stress intensity factor, temperature and strain rate differentiated the two materials studied
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
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