1,721,011 research outputs found
Cyclic Fatigue-Crack Propagation Behavior in Silicon Carbide: Long- and Small-Crack Behavior
No full textCyclic fatigue properties of high-toughness SiC with additives of Al2O3 and Y2O3 were examined, with a focus on differences between long- (>3 mm) and small-crack (<200 <mu>m) behavior. Small cracks were initiated with Vickers indents placed on the tensile surfaces of beams, and crack extension was monitored optically under cyclic load. For small cracks, high growth rates which exhibited a negative dependence on the far-field driving force were observed. Such behavior was explained by both indent-induced residual stresses and the relative size of cracks compared with bridging zone lengths
Anomalous cyclic fatigue-crack propagation behavior of small cracks in monolithic, grain-bridging ceramics
No full textCyclic fatigue properties of two monolithic, high-toughness SIC ceramics were examined, with emphasis placed on differences between long- (>3 mm) and small-crack (<250 mu m) behavior. Studies were performed on two microstructures in which sintering additives were systematically varied. Small cracks were initiated with Vickers indents placed on the tensile surfaces of beams, and crack extension was monitored optically under an applied cyclic load. For small cracks, high growth rates which exhibited a negative dependence on the farfield driving force were observed. Such behavior was rationalized both in terms of indent-induced residual stresses and the relative size of cracks compared to bridging zone lengths. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.Work on the Al, B, C-based SiC was supported by the
Director, Oce of Energy Research, Oce of Basic
Energy Sciences, Materials Sciences Division of the US
Department of Energy under Contract No. DE-AC03-
76SF00098. Additional support to facilitate collaboration
between the Korean and U.S. groups on the Al2O3/
Y2O3-based SiC was provided by the U.S. National
Science Foundation through their Division of Interna-
tional Programs under Grant No. INT-9507653. Thanks
are also due to Mr. Q. Tran for experimental assistance
Indentation techniques for evaluating the fracture toughness of biomaterials and hard tissues
No full textIndentation techniques for assessing fracture toughness are attractive due to the simplicity and expediency of experiments, and because they potentially allow the characterization of both local and bulk fracture properties. Unfortunately, rarely have such techniques been proven to give accurate fracture toughness values. This is a concern, as such techniques are seeing increasing usage in the study of biomaterials and biological hard tissues. Four available indentation techniques are considered in the present article: the Vickers indentation fracture (VIF) test, the cube corner indentation fracture (CCIF) test, the Vickers crack opening displacement (VCOD) test and the interface indentation fracture (IIF) test. Each technique is discussed in terms of its suitability for assessing the absolute and relative toughness of materials or material interfaces based on the published literature on the topic. In general, the VIF and CCIF techniques are found to be poor for quantitatively evaluating toughness of any brittle material, and the large errors involved (similar to +/- 50%) make their applicability as comparative techniques limited. Indeed, indentation toughness values must differ by at least by a factor of three to conclude a significant difference in actual toughness. Additionally, new experimental results are presented on using the CCIF test to evaluate the fracture resistance of human cortical bone. Those new results indicate that inducing cracking is difficult, and that the cracks that do form are embedded in the plastic zone of the indent, invalidating the use of linear elastic fracture mechanics based techniques for evaluating the toughness associated with those cracks. The VCOD test appears to be a good quantitative method for some glasses, but initial results suggest there may be problems associated with applying this technique to other brittle materials. Finally, the IIF technique should only be considered a comparative or semi-quantitative technique for comparing material interfaces and/or the neighboring materials. (C) 2008 Elsevier Ltd. All rights reserved.ROR acknowledges support from the Director, Office of
Science, Office of Basic Energy Science, Division of Materials
Sciences and Engineering of the Department of Energy under
Contract No. DEAC0205CH11231. DKK would like to thank
the SBS Foundation and Korea Research Foundation (a/c#
KRF2005005J09701) for supporting his sabbatical leave in
Berkeley where the experimental part of this study was
performed
Ultra-strong tungsten refractory high-entropy alloy via stepwise controllable coherent nanoprecipitations
Full text linkHigh-performance refractory alloys with ultrahigh strength and ductility are in demand for a wide range of critical applications, such as plasma-facing components. However, it remains challenging to increase the strength of these alloys without seriously compromising their tensile ductility. Here, we put forward a strategy to defeat this trade-off in tungsten refractory high-entropy alloys by stepwise controllable coherent nanoprecipitations (SCCPs). The coherent interfaces of SCCPs facilitate the dislocation transmission and relieve the stress concentrations that can lead to premature crack initiation. As a consequence, our alloy displays an ultrahigh strength of 2.15 GPa with a tensile ductility of 15% at ambient temperature, with a high yield strength of 1.05 GPa at 800 degrees C. The SCCPs design concept may afford a means to develop a wide range of ultrahigh-strength metallic materials by providing a pathway for alloy design
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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