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The effects of microstructure and environment on high temperature fatigue and creep-fatigue mechanisms in a nickel base superalloy
No full textA comparison of high temperature fatigue crack propagation in sub-solvus heat treated turbine disc alloys
No full textThis paper presents the results of high temperature fatigue tests carried out in air at 725°C on four different materials: N18, RR1000, Udimet 720Li (U720Li) and U720Li Large Grain (U720Li LG) variant. The influence of composition, sub-solvus heat treatments, together with varied cooling rates on grain size and gamma prime size and distribution on fatigue crack propagation behaviour are compared and contrasted
Effects of grain and precipitate size variation on creep-fatigue behaviour of Udimet 720Li
No full textHigh temperature fatigue crack growth in powder processed nickel based superalloy U720Li
No full textFatigue crack propagation at elevated temperatures (650 and 725°C) has been studied in a powder processed high strength nickel based superalloy, U720Li, in air and vacuum environments, using trapezoidal loading waveforms. Constant load (increasing ?K) tests were used to generate da/dN-?K curves, while interrupted constant ?K tests were used to study crack propagation paths and mechanisms. At 650°C in air there is little effect of any dwell at maximum load while at 725°C such a dwell causes a significant increase in the crack growth rate coupled with a transition from mixed mode to fully intergranular crack growth. In vacuum the growth rates were significantly lower, and the dwell caused little or no change in crack growth rate at 650°C, but an increase at 725°C. The crack path in vacuum changed from fully transgranular at 650°C to incorporate increasingly mixed mode growth at 725°C with dwell. The intergranular failure in vacuum was through creep cavitation of grain boundaries, while in air, static failure of oxygen embrittled boundaries dominated
Effects of grain and precipitate size variation on creep-fatigue behaviour of Udimet 720Li in both air and vacuum
No full textThe high temperature fatigue characteristics of U720Li have been investigated over the temperature range 650°C to 725°C under imposed dwell times (at maximum load) of 1 and 20 seconds in vacuum and air conditions. The effect of varying grain size and coherent precipitate size under these conditions has been assessed.Testing in air resulted in oxidation dominated intergranular crack growth at all temperatures and dwell times with the slope (m-values) of the crack growth rate curves remaining constant. Increased crack growth rates are seen at the higher temperatures and at longer dwells, although no effect of dwell was observed at 650?C in the as-received fine grained variant. In vacuum crack growth rates were much lower than in air and a purely cyclic dependent regime was evident at 650°C. As temperature and dwell time at maximum load was increased, m-values increased and were accompanied by a change in crack growth mechanism from transgranular to intergranular cracking. This indicated that true, time-dependent, creep-fatigue processes were occurring.The large grain variant of the U720Li showed little advantage in crack growth rates within the cyclic dependent and creep-fatigue regime, but did show a significant increase in resistance to crack growth in the time dependent (oxidation-fatigue) regime. The effect of the large precipitate variant was to give similar or worse crack growth resistance than the baseline U720Li at temperatures up to 725°C (1 second dwell) but improved crack growth resistance when oxidation processes predominated at 725°C in air with an imposed 20 second dwell
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
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