1,720,957 research outputs found
Damage in CFRP composites subjected to simulated lighting strikes - Assessment of thermal and mechanical responses
Get PDFDamage is inflicted upon Carbon Fiber Reinforced Polymer (CFRP) composite laminates using simulated lightning strikes to investigate the resulting residual mechanical properties. Seven different CFRP laminate specimens were exposed to simulated lightning strikes using three different electric waveforms. The three waveforms imposed were the 10/350 μs waveform, which simulates the first return stroke during a direct strike according to IEC 61400–24 Ed1.0. The second was a unipolar long stroke component, and the third was a combination of the first return stroke and the long stroke. After exposure to lightning, coupon specimens were prepared for mechanical testing. The test specimens were subsequently subjected to compression and shear loading to determine the post-strike mechanical properties. The compression tests were conducted using uniaxial coupons in accordance with ASTM standard D6641. The shear tests were conducted using V-notch specimens utilizing an Iosipescu test rig in accordance with ASTM standard D5379. Digital Image Correlation was used to capture the strain fields on the surface of the specimens. The results of the material coupon tests are compared with test results from pristine CFRP coupon samples that were not exposed to any electrical current. The shear and compression strengths, compressive and shear stress-strain curves, compressive and shear moduli, and the maximum temperature on the CFRP specimens during lightning tests are presented and discussed. Key results include that the largest reduction of strength occurred in the specimens that were subjected to the largest current and specific energy. The specific energy correlated more closely to the observed reduction of residual strength than the charge, and the damaged specimens displayed a higher degree of nonlinear stress-strain behavior than the pristine specimens
Heat response of unipolar lightning impulse and DC current component conducted through CFRP samples used for wind turbine sparcaps
No full textLightning protection of wind turbine blades has reached much attention due to the increased number of blade manufacturers now featuring blade designs that include conductive Carbon Fiber Reinforced Polymers (CFRP) composites for structural components. CFRP materials are stiff and lightweight, but exhibit material properties different from other conductive materials like metals, making them more susceptible to lightning damage. The weaknesses observed is governed by the limited electrical and thermal conductivity, transverse to the fibers, the anisotropic material properties, and the integration of the CFRP into the overall WT blade or aerospace structure. This study investigates in detail the heat response on CFRP material exposed to two different components of a lightning strike; the unipolar impulse current and the direct current (DC). The first waveform examined is a unipolar 10/350µs waveform simulating the first return stroke during a direct strike according to IEC 61400-24 Ed1.0 , the second being a unipolar long stroke component also defined by the IEC standards. Both current components are tested using the conducted current test method provided in Annex D3.4 of IEC 61400-24 Ed1.01.CFRP strips made with vacuum assisted liquid resin infusion were exposed to conducting currents as defined above using the two different waveforms. A PYROVIEW 640L IR camera was used to monitor the heat response of each sample. The data from the center of the sample was used to collect the heat response and the results can be seen in Figure 1 and Figure 2. This data helps determine thermal response models to help determine damage from thermal degradation due to electric current
Lightning protection of CFRP wind turbine blades - What is the dominant cause of failure: Specific energy or charge?
No full textThis paper investigated which component of a lightning strike is responsible for the majority of damage in Carbon Fiber Reinforced Plastic (CFRP) by investigating the strength loss induced by the exposure to two different electric current waveforms. The two waveforms used were the 10/350μs waveform simulating the first return stroke during a direct strike according to IEC 61400-24 Ed1.0 and the second was a unipolar long stroke component. CFRP strip specimens were manufactured and subjected to the two waveforms of electric current to simulate a lightning strike event. After exposure, specimens were extracted from the CFRP strips, and then loaded in compression and shear to determine the residual strength remaining. The compression tests were conducted on uniaxial coupons and loaded in accordance to ASTM standard D6641. Shear tests were conducted on V-notch specimens and loaded in an Iosipescu test rig in accordance to ASTM standard D5379. The results of the tests were compared to CFRP coupons, which were not exposed to any electrical current. A comparison between undamaged specimens and damaged specimens was made to determine which has more effect on the strength degradation; electric charge from the long stroke component or specific energy from the first return stroke. The results show that impulse current has more impact on strength degradation than a unipolar long stroke current
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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