1,721,015 research outputs found
Influence of interphase properties on the macroscopic response of single- and double-walled CNT/epoxy nanocomposites : a numerical study
No full textA concept for improving the impact resistance of carbon fibre reinforced plastic (CFRP) laminates by using a carbon nanotube (CNT)/epoxy surface coating is presented. An initial parametric numerical study shows the effects of interphase properties on the macroscopic stressstrain behaviour of carbon nanotube/epoxy nanocomposites. Finite element (FE) simulations carried out for fully aligned single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs) investigated the influence of properties of the polymer/CNT interphase and the interwall phase of DWCNTs. They reveal that a high shear stiffness of the CNT/polymer interphase is essential to take the full advantage of the load-bearing ability of the inner wall of the DWCNT, and thus enhance the mechanical performance of the nanocomposite. Furthermore the interphase shear stress distributions in interwall and CNT/polymer interphase of a DWCNT point out the relationship between CNT/epoxy interphase damage propagation and shear stress in the interwall phase
Hygrothermal behaviour of cementitious mortars containing bio-based phase change materials (PCMs) and/or miscanthus fibres : material and wall-scale studies
No full textCette thèse s'inscrit dans le contexte de l'amélioration des performances thermo-hydriques des matériaux d'enveloppe dans le bâtiment, en vue de réduire la consommation d'énergie et d'optimiser le confort des occupants. Elle propose une comparaison du comportement thermo-hydrique aux échelles du matériau et de la paroi de trois solutions différentes de mortiers cimentaires incorporant : soit des matériaux à changement de phase (MCP) microencapsulés d'origine biosourcée ou des fibres de miscanthus micronisées, soit une combinaison de ces deux types d'inclusions. La dernière solution, qualifiée de mortier hybride, explore la possibilité de combiner les avantages des deux inclusions en un composite présentant à la fois des propriétés d'isolant thermique, une bonne régulation d'humidité et une capacité de stockage d'énergie par chaleur latente.A l'échelle du matériau, une première étape a consisté à définir des protocoles de formulation adaptés aux 3 différents mortiers, pour compenser la perte d'ouvrabilité due à l'introduction des inclusions. Ensuite, une caractérisation microstructurale, mécanique et thermo-hydrique a été appliquée à 28 jours aux mortiers contenant des teneurs variables en MCP et/ou en fibres végétales. Globalement, le mortier avec les MCP et le composite hybride présentent des propriétés d'isolation thermique nettement supérieures à celle du mortier de référence, mais leur hygroscopicité n'est pas significativement améliorée car la présence des MCP tend à limiter les transferts hydriques au sein de ces matériaux. L'introduction des fibres de miscanthus conduit en revanche à une amélioration conjointe des performances thermiques et hygriques. Par ailleurs, quel que soit le type d'inclusion utilisé, la porosité augmente significativement et les propriétés mécaniques chutent par rapport à la référence. Pour chacune des solutions, une teneur « optimale » en inclusions offrant un compromis entre gains de propriétés thermo-hydriques et perte de résistance mécanique est sélectionnée pour l'investigation à l'échelle supérieure. Pour simuler les différents scénarios climatiques à l'échelle de la paroi, un dispositif bi-climatique spécifique a été conçu au laboratoire. Des murs réalisés avec les 3 mortiers sélectionnées, ont ensuite été instrumentés de capteurs et exposés à des sollicitations cycliques de température (entre 15°C et 40°C) et d'humidité relative (entre 33 et 75% HR). Les réponses thermiques des différents murs ont été comparées à celles du mur en mortier de référence, afin de quantifier les gains de performance liés à l'incorporation des inclusions. Pour la paroi contenant les MCP, un léger amortissement de l'ordre de 1°C de la température est mesuré à différentes profondeurs pendant la phase de chauffage (la face extérieure est chauffée à 40°C), comparé à la référence. Des simulations numériques du transfert thermique menées à l'échelle du bâtiment en intégrant l'influence du changement de phase des MCP, prédisent des gains énergétiques significatifs pour le chauffage hivernal (33%) et la climatisation (27-31%) sous différents climats. La paroi de mortier hybride a montré une réduction plus importante de la température ressentie dans l'environnement intérieur pendant la phase de chauffage, avec un écart d'environ 4°C par rapport à la référence, cependant elle présente un effet limitant sur les transferts d'humidité, ce qui peut compromettre le confort intérieur. La paroi contenant les fibres de miscanthus, permet de réduire de l'ordre de 4°C de la température ressentie dans l'environnement intérieur pendant la phase de chauffage, et aussi d'amortir les variations d'humidité extérieures. Elle offre donc les meilleures performances thermo-hydrique et constitue une solution prometteuse comme matériau d'enveloppe. Globalement, les données expérimentales collectées dans le cadre de cette thèse aux échelles du matériau et de la paroi constituent une base précieuse pour des travaux de modélisation futuresThis doctoral work addresses the general issue of improving the thermo-hygric performance of building envelope materials, with the aim of reducing energy consumption and optimizing occupant comfort. More specifically, it is proposed to compare the thermo-hygric behavior of three different solutions at both the material and wall scales: cementitious mortars incorporating either bio-sourced microencapsulated phase change materials (PCM), micronized miscanthus fibers, or a combination of these two types of inclusions. This latter solution, referred to as a hybrid mortar, explores the possibility of combining the advantages of both inclusions in a composite with thermal insulation properties, good moisture regulation and latent heat energy storage capacity.At the material scale, the first step involved defining formulation protocols suitable for the 3 considered mortars, allowing for compensation of the loss of workability due to the introduction of inclusions. A comprehensive program of microstructural, mechanical, and thermo-hydric characterization was then conducted on mortar formulations containing varying amounts of PCM and/or plant fibers, after 28 days of curing. Overall, it was found that the mortar with PCM and the hybrid composite exhibit higher thermal insulation properties compared to the reference mortar, but their hygroscopicity is not significantly improved as the presence of PCM tends to restrict moisture transfers within these materials. The introduction of miscanthus fibers, on the other hand, leads to a simultaneous improvement in both thermal and hygric performance. Furthermore, regardless of the type of inclusion used, a significant increase in porosity and a significant drop in the mechanical properties of the mortar are observed compared to the reference. For each of the solutions, an "optimal" content of inclusions, offering a compromise between gains in thermo-hygric properties and loss of mechanical strength, is then selected for investigation at the larger scale.For the purposes of the study at the wall scale, a specific bi-climatic setup was designed in the laboratory to simulate different climate scenarios. Walls made from the three selected mortars were then equipped with sensors and subjected to cyclic temperature (between 15°C and 40°C) and relative humidity (between 33% and 75% RH) fluctuations. The thermal responses of these different walls were compared to that of the reference mortar wall in order to quantify the performance gains associated with the incorporation of inclusions. For the wall containing PCMs, a relatively modest damping effect of approximately 1°C in temperature was measured at various depths during the heating phase (exterior face subjected to 40°C) compared to the reference. However, numerical simulations conducted at the building scale, taking into account the influence of PCM phase change on heat transfer, predict significant energy savings for winter heating (33%) and air conditioning requirements (27-31%) under different climates. The hybrid mortar wall exhibits a higher reduction in the perceived temperature in the interior face during the heating phase with a reduction of around 4°C compared with the reference, however it has a limiting effect on moisture transfer, which may compromise indoor comfort. The wall containing miscanthus fibers resulted in a greater damping of temperature variation at the interior environment during the heating phase, with a difference of approximately 4°C compared to the reference, and also effectively dampened humidity variations. It therefore emerges as the most promising choice among the three considered solutions, demonstrating superior thermo-hygric performance for potential use as an envelope material. Besides, the comprehensive experimental data gathered in this thesis, at both material and wall scales, forms a valuable foundation for future modeling wor
Recycling and Reuse of Materials and Their Products
No full textInternational audienceThis important book is an overall analysis of different innovative methods and ways of recycling in connection with various types of materials. It aims to provide a basic understanding about polymer recycling and its reuse as well as presents an in-depth look at various recycling methods. It provides a thorough knowledge about the work being done in recycling in different parts of the world and throws light on areas that need to be further explored. Emphasizing eco-friendly methods and recovery of useful materials
Recent Advances in Flame Retardancy of Textile Related Products
No full textInternational audienceReplacement of existing flame retardants (FR) with sustainable and environmentally friendly alternatives for textiles, polymers, and composite materials in domestic, transport (automotive, rail, aerospace, and marine), civil emergency and military, construction and other industries requires a multidisciplinary approach from textile technology to the physics and chemistry of fire. This Special Issue of Polymers is the result of the scientific work and subsequent discussions and collaborations that took place during four years (May 2012–May 2016) of the COST Action MP1105 "FLARETEX: Sustainable flame retardancy for textiles and related materials based on nanoparticles substituting conventional chemicals". The Action involved 30 countries and more than 850 participants attended the 20 organized events up to December 2015; four events including the final conference are planned for 2016. The participants included post graduate students, early career researchers, established academics, engineers, and researchers/technologists from industry. The work done by the members of this Action from 2012 until 2016 is an important source of information regarding recent developments in the area of fire safety, and environmentally friendly flame retardant solutions for textiles and related materials.This Special Issue of Polymers is devoted to the “Recent Advances in Flame Retardancy of Textile Related Products", the theme of the COST Action MP 1105. This Special Issue will include papers with the most recent advances on Thermal Stability and Fire Retardancy of Textiles, Polymer Blends and Composite Materials. The publication will respect all rules and procedures requested by the journal and by the Editorial Office of MDPI. On behalf of the Guest Editors, we would like to invite you to submit your unpublished and original results which may be part of this Special Issu
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
Nouveaux matériaux biosourcés à base de bois de palmier dattier pour l'isolation thermique dans l'habitat
Get PDFInternational audienceNouveaux matériaux biosourcés à base de bois de palmier dattier pour l'isolation thermique dans l'habita
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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