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Strain rate dependence of compressive behavior in an Al-Zn-Mg alloy processed by ECAP
No full text
Experiments were conducted to study the compressive mechanical properties of an Al-Zn-Mg alloy after solid solution treatment and equal-channel angular pressing (SS-ECAP) using strain rates ranging from 1.0 × 10
−3
to 3.0 × 10
3
s
−1
. The results show that SS-ECAP processing enhances the compressive strength due to the high dislocation density, large numbers of fine precipitates and grain refinement. The alloy in both the peak-aged (as-received) and the SS-ECAP states shows a strain rate strengthening effect such that the strain rate sensitivity increases with increasing strain rate. The high volume fraction of fine precipitates in the SS-ECAP alloy decreases the strain rate sensitivity. The coarse precipitates in the peak-aged alloy are fragmented while their sizes increase in the SS-ECAP alloy due to dynamic precipitation assisted by the high density of dislocations during compressive testing. With increasing strain rate, the size of the precipitates further increases for the SS-ECAP alloy and this is influenced by accelerated dislocation motion. During compression, the T (Al
20
Cu
2
Mn
3
) and E (Al
18
Mg
3
Cr
2
) phases evolve into a new tetragonal phase containing Mg, Mn, Cr and Zn with Al.
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Effect of ECAP processing on microstructure evolution and dynamic compressive behavior at different temperatures in an Al-Zn-Mg alloy
Get PDFAn artificially aged Al-Zn-Mg alloy with a grain size of ~ 1.3 µm was processed by equal-channel angular pressing (ECAP) and then subjected to dynamic compression at a strain rate of 4000 s-1 in the range from room temperature to 673 K. The results show the n' phase is refined and a n phase is formed during the first pass of ECAP and after further processing 8 passes the GP zones are removed. An ultrafine-grained (UFG) structure with an average grain size of ~200 nm was obtained after 4 passes. It is shown that dynamic compressive deformation assists the precipitation process through precipitate coalescence and by changing the precipitate orientations. The dynamic compressive yield strengths and flow stresses decrease gradually to different degrees with increasing temperature except after ECAP processing for 4 passes where there is thermal stability up to 473 K. The ECAP processing significantly improves the strength of the alloy at elevated temperatures by comparison with the as-received material
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
Temperature and strain rate dependence of microstructural evolution and dynamic mechanical behavior in nanocrystalline Ti
Get PDFThe mechanical behavior of commercial purity titanium with a nanocrystalline (NC) grain size was investigated using split Hopkinson pressure bar tests at high strain rates and over a range of temperatures. The study was accompanied by detailed microstructural investigations before and after compression testing. The results show that rotary dynamic recrystallization operates during compressive deformation at strain rates of ~3000 and ~4500 s?1 at temperatures from 298 to 573 K but cells form at 673 K. The dynamic mechanical behavior of NC Ti shows a strong dependence on temperature and strain rate such that the flow stress and the strain hardening rate both increase with increasing strain and decreasing temperature. A constitutive equation is derived to relate the flow stress to the temperature, strain rate and true strain and to predict the yield strength and the peak stress of NC Ti subjected to dynamic deformation at elevated temperatures
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
An evaluation of the microstructure and microhardness in an Al–Zn–Mg alloy processed by ECAP and post‐ECAP heat treatments
No full textHerein the microstructure evolution and microhardness variations in a peak‐aged Al–Zn–Mg alloy after equal‐channel angular pressing (ECAP) for 1–8 passes followed by heat treatments at temperatures of 393–473 K for 5–20 h are examined. The results show that ECAP processing hardens the alloy, and the hardness increases with each pass due to grain refinement, the formation of large numbers of fine precipitates, and the introduction of a high dislocation density. Post‐ECAP annealing at 393 K up to 20 h after 1 and 4 passes of ECAP leads to a further increase in microhardness and this increase is substantial for an annealing time of 20 h after 1 pass due primarily to the extensive formation of a nano‐sized η′ phase. After ECAP for 8 passes, post‐ECAP annealing at 393 K for 5 h or more leads to softening due to the occurrence of recrystallization and the transformation of fine η′ to coarse η. Post‐ECAP anneals at the higher temperatures of 423 and 473 K are not capable of producing high hardness values
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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