1,720,958 research outputs found
Low Cycle Fatigue behaviour and anisotropy of two steels for turbogenerator coil retaining rings and rotors
No full textTurbogenerator rotors and coil retaining rings (CRR) are typically subjected to low cycle fatigue (LCF). The rotor contains uniformly spaced longitudinal slots, where copper conductors are packed: at the nominal speed of 3000 rpm a great centrifugal force acts on the copper conductors that must be restrained by CRRs, shrunk fitted onto the body over the coils. Thus, at each on-off transitory (10,000 – 15,000 in the whole machine life) both the rotor and the CRR are subjected to a cyclic load. Several contributions report the mechanical properties of the typically used steels for rotor and CRR manufacturing, but none deals with their characterization under LCF in strain controlled conditions, while investigations on the anisotropy were performed just on CRR steels in load controlled conditions. This research aims at determining the main parameters describing the LCF performance of two widely applied steels for rotors and CRRs, investigating also the anisotropy in the dynamic behaviour: for this purpose an extensive experimental campaign was carried out on specimens machined (in the tangential and radial directions) from prolongations of trial rotors and CRRs. An original approach was used for misalignment compensation, strain control and data recording, sensitivity analyses were finally performed on results
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
A new loading-constraining device for mechanical testing with misalignment auto-compensation
No full textExperimental testing represents the basic approach for mechanical characterization. Due to the high costs for test execution, the research is often developed with the collaboration of several laboratories, finally collating al the results. At this stage problems may arise due to data scattering, often due to (lateral or angular) misalignments between the fixed and the moving machine crossheads. The object of this work is to manufacture and experimentally validate a novel loading-constraining device for misalignment compensation. Conceptual design is applied to investigate on the optimal technical solution. The developed device achieves misalignment reduction with the use of a thrust bearing with sphered housing washers. The bearing is mounted under one of the specimen heads: the inverted orientation of the upper ring, allowing relative lateral displacement between the two rings, and the spherical shape of the washer compensate for offset and angular misalignments. Experimental results showed that such misalignments are respectively reduced to less than 0.02 mm and 0.05°, while the bending strain is lowered to just 6% of the nominal one, so that requirements in different standards for mechanical testing can be fulfilled
The AISI H11 creep-fatigue behaviour: an innovative experimental design
No full textDuring the hot-extrusion manufacturing process, a number of damage and deformation mechanisms act
simultaneously to produce cumulative damage to the tools, thus causing the increasing deviations from the
original geometry or the final breaking [1-3]. Due to the severe cyclic thermo-mechanical loads, mandrel, i.e. the
part of the hollow die that defines the internal shape of the profile, is the most critical component in the extrusion of an
hollow profile. Indeed, the high pressure generated during the process creates severe friction conditions that results in
longitudinal tensile stress and significant bending stresses can arise in the bridges of the mandrel during extrusion. In
addition to the mechanical cyclic load, the total loading/unloading time for the whole batch and the temperature that the
die is exposed to are great enough to necessitate the consideration on the creep behaviour of the die material, particularly
for hollow dies. Hence, the combination of dynamic, heavy loading and high temperature determines a hostile working
condition for the mandrel that is normally designed on the basis of static loading at elevated temperatures on hot-work
tool steels that are tempered to reach an adequate balance of hot hardness and toughness. Premature failure may occur
after a certain number of loading and unloading cycles as a result of creep-fatigue interaction. The new technologies
developed for aluminium extrusion aim to minimize the tool system-material flow interference and optimize the
mechanical performance of the die that is related both to design and tool steel.
Aim of the present work is to illustrate the steps followed to design an innovative experimental test purposely developed
to investigate the deforming mechanisms of the AISI H11 tool steel in the creep-fatigue regime. The specimens replicate
the geometry and the loading scheme of a mandrel on a smaller scale and are manufactured following the same working
scheme. In such a way the test is able to account for realistic stress and strain distributions and superficial roughness of a
real mandrel as well as to investigate different material and heat treatments
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
Prevalence of allergy and asthma in a rural community of children and adults in Bolivian Chaco
No full text- …
