1,720,967 research outputs found
Experimental analysis of toughness in 6156 Al-alloy sheet for aerospace application
No full textAnalysis of toughness in 6156 Al-Mg-Si-Cu sheet has been performed using enhanced Kahn tear tests on samples quenched at different rates, whilst microstructures of the samples have been assessed using differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Crack initiation energies were unaffected by changing water quench temperature from 20°C to 60°C, however a significant reduction was evident on air cooling. Crack propagation resistance was reduced for both 60°C water quenched and air cooled materials. The failure morphology of the air cooled material appears consistent with classical intergranular ductile failure. Coarse voiding and shear decohesion was prevalent in the 20°C water quenched material, whilst the 60°C water quenched material showed a mixture of transgranular and intergranular fracture modes. Changes in microstructure and precipitation behaviour resulting from reduced quenching rate were identified and related to the observed fracture behaviour, particularly in terms of precipitate free zone formation and the simultaneous presence of coarse particles at grain boundaries
Evolution of voids during ductile crack propagation in an aluminium alloy sheet toughness test studied by synchrotron radiation computed tomography
No full textThe anisotropy of fracture toughness in AA2139 (Al-Cu-Mg) alloy sheet has been investigated via synchrotron radiation computed tomography of arrested cracks in Kahn tear test pieces for different loading cases. The three dimensional distribution and morphology of pores and defects in the as-received state are seen to be anisotropic, with chains of voids and void elongation in the L (longitudinal) direction. For toughness testing in L-T orientation (T is transverse), voids ahead of the crack grow and link in the L direction. In T-L tests, voids ahead of the crack tip also grow in the loading direction, although a high degree of alignment is retained in the L direction. The present work provides quantitative microstructural data that can be used as input for and validation of recent idealised model formulations, and it is shown that the measured void dimensions and evolution are consistent with measured toughness anisotropy
Quench sensitivity of toughness in an Al alloy: direct observation and analysis of failure initiation at the precipitate free zone
Get PDFAnalysis of toughness in 6156 Al-Mg-Si-Cu sheet has been performed using enhanced Kahn tear tests on samples quenched at different rates. Crack initiation energies were hardly affected by changing water quench temperature from 20°C to 60°C; however a significant reduction was evident on air cooling. Crack propagation energy was reduced for both 60°C water quenched and air cooled materials. Observation of failure initiation through synchrotron radiation computed tomography (SRCT), for the 60°C water quenched material revealed failure ahead of the crack tip of grain boundaries oriented at 45° to the main loading axis and crack “tongues” extending into the material ahead of the main crack. Failure was predominantly intergranular. Fractographic assessment revealed predominantly voiding and shear decohesion in the 20°C water quenched material. With the aid of the new findings past models on the influence of precipitate free zone parameters on toughness have been revise
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
Direct observation and analysis of failure initiation and crack progression in tear toughness of two Al sheet alloys
No full textThe failure initiation and crack progression in tear toughness tests on 2 sheet alloys have been analysed through synchrotron radiation computed tomography (SRCT), supported by TEM, SEM and DSC studies. For the quench sensitive 6156 Al-Mg-Si-Cu alloy propagation energy was reduced by changing water quench temperature from 20°C to 60°C. Observation of failure initiation for a 60°C water quenched sample revealed failure ahead of the crack tip of grain boundaries oriented at 45° to the main loading axis and crack “tongues” extending into the material ahead of the main crack. The fracture toughness of AA2139 (Al-Cu-Mg-Ag) is anisotropic. SRCT reveals that three-dimensional distribution and morphology of pores and defects in the as-received state are anisotropic, with chains of voids and void elongation in the L (longitudinal) direction. For toughness testing in L-T orientation (T is transverse), voids ahead of the crack grow and link in the L direction. In T-L tests, voids ahead of the crack tip also grow in the loading direction. New models for crack propagation and toughness have been derived on the basis of the quantitative microstructural data
- …
