1,720,964 research outputs found
Effect of Thermal Ageing on the Mechanical Strength of Carbon Fibre Reinforced Epoxy Composites
Full text linkApplications of Carbon Fibre Reinforced Polymers (CFRP) at temperatures over 150–200 ◦C are becoming common in aerospace and automotive applications. Exposure of CFRP to these temperatures can lead to permanent changes in their mechanical properties. In this work, we investigated the effect of thermal ageing in air on the strength of carbon fabric/epoxy composites. To this end, accelerated artificial ageing at different temperatures was performed on carbon fabric/epoxy specimens. The flexural and interlaminar shear strengths of the aged specimens were assessed by three-point bending and short beam shear tests, respectively, and compared to those of unaged samples. For ageing at temperatures below the glass transition temperature of the resin, Tg, a moderate reduction of strength was found, with a maximum decrease of 25% for 2160 h at 75% Tg. On the other hand, a rapid strength decrease was observed for ageing temperatures above Tg. This was attributed to degradation of the epoxy matrix and of the fibre/epoxy interface. In particular, a 30% strength decrease was found for less than 6 h at 145% Tg. Therefore, it was concluded that even a short exposure to operating temperatures above Tg could substantially impair the load-carrying capability of CFRP components
Damage Tolerance in CFRP Structures - Numerical and Experimental Analysis of Low Energy Near Edge Impacts
No full textThis work aims towards contributing to the better understanding of the behaviour of the primary composite aeronautical structure after near-edge impacts which are inevitable during the service life of an aircraft.
Following the experimental work on near edge impacted CFRP specimens, presented by the authors at ICAF2015, a numerical model relative to near edge impacts was developed and calibrated using the obtained experimental data.
The size and the shape of near-edge impacted zone (dent) in the thin specimen was considered to be in direct correlation with the delaminated area of the specimen and this assumption is made based on data presented in open literature.
The FEM model relative to the tested specimens has been developed and tuned for near edge impacts of CFRP structure, based on material data for CFRP pre-preg and lamina interface available in the literature, and on experimental measurement of size and shape of the impacted zone in the tested specimens.
By correlating the numerical model for the thin specimens with the size and shape of the impacted area, it is possible, for different configurations and energy levels, to predict the extension of a delamination in a CFRP structure and to estimate its residual static strength using a very simple but robust technique
SIMULATION OF CRACK GROWTH IN ADHESIVELY BONDED JOINTS VIA COHESIVE ZONE MODELS
Full text linkAdhesively bonded joints have shown great advantages in the aerospace industry when compared with traditional mechanical fastening methods. These types of joints allow to reduce the overall structural weight, improve the fatigue life characteristics due to reduction of stress concentrations (uniform stress distribution), smooth external finish, sealed surfaces, and many others. However, one of the main concerns with these joints is their characterization under fatigue loading, i.e., a comprehensive study of crack growth which will allow the development of standardized tests and certification in the aerospace sector. At the moment, their certification for primary structures requires that critical disbond be prevented by proper design. To this end, Disbond Arrest Features (DAFs) have been tested as a mean to improve the fatigue resistance of bonded joints. In this work, the authors developed a numerical model to assess fatigue disbonding under mixed-mode loading, a condition which is frequently encountered in adhesive joints. The model was based on a cohesive zone formulation, which was implemented via userdefined subroutines UMAT in the finite element software Abaqus. Mixed mode disbonding was modelled through the Bürger’s modification of Paris’ law. Two test cases were simulated: a double cantilever beam (DCB) specimen and a modified cracked-lap shear specimen with a bolted DAF. The results of the simulations were compared with experimental data from previous tests, showing that the model is able to reproduce the observed fatigue disbonding and capture the disbond arrest provided by the DAF
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
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
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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