1,720,994 research outputs found
Effect of temperature on hydrogen assisted fatigue crack growth rate of a gaseous hydrogen precharged austenitic stainless steel
No full textThe fatigue crack growth rate (FCGR) of austenitic stainless steel 1.4404 was measured as a function of temperature in both, uncharged and in gaseous hydrogen precharged conditions. At room temperature, the FCGR of precharged 1.4404 specimens is by a factor of about 5 higher compared to uncharged specimens. The related FCGR at ΔK = 22–25 MPa m0.5 as a function of temperature revealed a maximum at temperatures between 250 and 270 K. This is about 50 K higher than the temperature of minimum tensile relative reduction of area (RRA), which is about 220 K. An interpretation based on the respective governing embrittlement mechanism, HEDE and/or HELP, is proposed. For the interpretation of the experimental findings, a phenomenological model is developed, based on the mechanics of metals and on the thermodynamic defactant concept, which incorporates the two prominent mechanisms for hydrogen embrittlement, HEDE and HELP. From the comparison of our theoretical and experimental results we conclude that the experimentally observed temperature dependence of hydrogen effects on the mechanical properties of the studied steel can be explained quite well by HELP but not by HEDE.20
Relationship between hydrogen embrittlement and Md30 temperature: Prediction of low-nickel austenitic stainless steel's resistance
No full textHydrogen embrittlement (HE) of several low-nickel austenitic stainless steels (AISI 300 series) was studied with special attention to the impact of strain induced α′-martensite. The susceptibility of the steels to HE is judged with respect to the relative reduction of area (RRA): The HE susceptibility is lower for larger RRA-values. Strain-induced martensite formation was evaluated within in the framework of the Olson-Cohen model, revealing a linear relationship between RRA and the probability β of martensite nucleus formation in the steels. In order to widen the scope of data evaluation to literature data, the consideration of a parameter alternative to β is required. It is demonstrated that among other parameters the Md30 temperature (Nohara), which assesses the stability against martensitic transformation, can serve as an indicator to predict HE of AISI 300 series steels. Regarding the Md30 temperature (Nohara), a trend-line with respect to the RRA-values is found. Thereby, the RRA-values of low-nickel austenitic stainless steels group into three distinct regimes; (1) for Md30 > −80 °C, where RRA-values decrease with increasing Md30 temperature, (2) at Md30 ≈ −80 °C, where RRA-values show a large variation (‘threshold band’), and (3) for Md30 < −80 °C, showing constant RRA-values of nearly 100%. Some RRA data points that deviate from the trend line can be explained by the special microstructure of the investigated samples.Fil: Izawa, Chika. Universität Göttingen; AlemaniaFil: Wagner, Stefan. Karlsruher Institut für Technologie; AlemaniaFil: Deutges, Martin. Universität Göttingen; AlemaniaFil: Martín, Mauro Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Weber, Sebastian. Bergische Universität Wuppertal; AlemaniaFil: Pargeter, Richard. The Welding Institute; Reino UnidoFil: Michler, Thorsten. Opel Automobile; AlemaniaFil: Uchida, Haru Hisa. Tokai University; JapónFil: Gemma, Ryota. Tokai University; JapónFil: Pundt, Astrid. Universität Göttingen; Alemania. Karlsruher Institut für Technologie; Alemani
Effect of Hydrogen on the Mechanical Properties of Stainless Steels
No full textFuel cell vehicles running on hydrogen are seen as the long term solution to enable sustainable mobility. Compressed hydrogen gas storage systems are a promising route for storing hydrogen on board of vehicles, provided that a reliable and cheap material capable of withstanding hydrogen embrittlement is found. In this paper, the physicochemical behaviour of stainless steel in the presence of hydrogen with special focus on a ductility minimum near room temperature is reviewed
SIMS analysis on austenitic stainless steel: The influence of type of oxide surface layer on hydrogen embrittlement
No full textThe surface oxide layer on nine different types of solution-annealed austenitic stainless steel (ASS) was evaluated by Secondary Ion Mass Spectrometry (SIMS). Tensile tests were conducted at 25 degrees C and -50 degrees C in hydrogen at 40 MPa and in air at atmospheric pressure. Relative reduction of area (RRA) was calculated accordingly. Additionally the martensite transformation curves were measured in air at -50 degrees C to evaluate the probability of the formation of alpha' martensite nuclei. A linear relationship between RRA and the calculated probability of the nucleation of alpha' martensite nuclei was found on samples represented by the following three oxides types; (a) thick oxide, (b) decaying sub-surface oxide and (c) thin surface oxides. However, type (d) with high constant oxide level down to 60 nm depth does not follow the trend. The observed variation of the oxide layer is linked to the variability of tensile test results. (C) 2013 Elsevier B.V. All rights reserved
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
SIMS study on the surface chemistry of stainless steel AISI 304 cylindrical tensile test samples showing hydrogen embrittlement
No full textThe local surface chemistry of a low-Ni austenitic stainless steel AISI type 304 used for tensile testing in hydrogen atmosphere is characterized by secondary ion mass spectrometry (SIMS). A chemical map on cylindrical austenitic stainless steel samples can be obtained even after a tensile test. In an effort to obtain the proper chemical element distribution on the samples, the influence of contamination and sample orientation is discussed. An iron oxide on top of a chromium oxide layer is present and Si segregation at grain boundaries is detected. Oxides are judged to reduce the initial hydrogen attack but to be of minor importance for crack propagation during the embrittlement process. (C) 2011 Elsevier B.V. All rights reserved
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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