1,720,974 research outputs found
Precipitation hardening in Al-Cu-Mg alloys: analysis of precipitates, modelling of kinetics, strength predictions
No full textIn Al-Cu-Mg with compositions in the theta+S phase field, precipitation hardening is a two-stage process. Experimental evidence shows that the main precipitation sequence in alloys with Cu contents in excess of 1wt% is involves Cu-Mg co-clusters, GPBII/S'' and S. The first stage of the age hardening is due to the formation of Cu-Mg co-clusters, and the hardening can be modelled well by a modulus hardening mechanism. The appearance of the orthorhombic GPBII/S'' does not influence the hardness. The second stage of the hardening is due to the precipitation of S phase, which strengthens the alloy predominantly through the Orowan looping mechanism. These findings are incorporated into a multi-phase, multi mechanism model for yield strength of Al-Cu-Mg based alloys. The model is applied to a range of alloys with Cu:Mg ratios between 0.1 and 1 and to heat treatments ranging from room temperature ageing and artificial isothermal ageing to rapid heating to the solution treatment temperature. The predictive capabilities of this model are reviewed and its constitutive components are compared and contrasted with a range of other methods, such as the Kampmann-Wagner and JMAK models for precipitation as well as the LSW model for coarsening
The origins of room temperature hardening of Al–Cu–Mg alloys
No full textThe most commonly cited mechanisms for the rapid age hardening of Al–Cu–Mg alloys at about 100–200 °C are hardening by Guinier–Preston B zone formation, formation of Cu–Mg co-clusters and a dislocation–solute interaction mechanism. New experiments on ageing–deformation–ageing cycles at room temperature indicate that no substantial additional age hardening occurs with the addition of deformation to the cycle, and hence, a dislocation–solute interaction mechanism appears unlikely. Instead, strengthening due to modulus hardening generated by the difference in shear modulus of Cu–Mg co-clusters and matrix is proposed as the main strengthening mechanism for room temperature hardening
VPPA welds of Al-2024 alloys: analysis and modelling of local microstructure and strength
Get PDFThe microstructural features of variable polarity plasma arc welded Al-Cu-Mg 2024-T351 with 2319 filler have been studied by TEM, SEM and DSC. Fusion zone, partial melting zone, re-solutionising zone, overageing (for S phase), peak ageing (for S phase) and under ageing zones (for S phase) have been identified. The omega phase has been observed between re-solutionising zone and peak ageing zone. The hardness profile contains two peaks. The microstructure development, and resulting hardness and yield strength profiles are modelled using a model which combines primary precipitation, resolution, partial/full melting and resolidification (Scheil type) and re-precipitation, in a two precipitate – two mechanism approach. Hardness profiles and microstructures are accurately predicted. The hardness peak in the re-solutionising zone is due to re-solutionising and subsequent Cu-Mg co-cluster formation; and the second hardness peak is caused by S phase strengthening
A model for precipitation kinetics and hardening in Al-Cu-Mg alloys
No full textA physically-based numerical model is developed to predict the microstructural evolution and strengthening in Al Cu Mg alloys during isothermal treatments. The modelling of the formation kinetics of the precipitates is based on the Kampmann and Wagner model. The strengthening by the shearable Cu:Mg co clusters is modelled on the basis of modulus strengthening mechanism and the strengthening by the non-shearable S phase precipitates is based on the Orowan looping mechanism. The model predictions are verified by comparing with the strength and differential isothermal calorimetery data on 2024-T351 aluminium alloys. The microstructural development and strength predictions of the model are generally in good agreement with the experimental data
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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