Thermal conductivity of textile reinforcements for composites

Thermal conductivity data for dry carbon fibre fabrics are required for modelling heat transfer during composites manufacturing processes; however, very few published data are available. This article reports in-plane and through-thickness thermal conductivities measured as a function of fibre volume fraction ( Vf) for non-crimp and twill carbon reinforcement fabrics, three-dimensional weaves and reinforcement stacks assembled with one-sided carbon stitch. Composites made from these reinforcements and glass fibre fabrics are also measured. Clear trends are observed and the effects of Vf, de-bulking and vacuum are quantified along with orthotropy ratios. Limited differences between the conductivity of dry glass and carbon fibre fabrics in the through-thickness direction are reported. An unexpected trend in the relationship between that quantity and Vf is explained summarily through simple simulations

Analyse métrique de structures HI dans le plan galactique

Je présente une version améliorée de la technique d'analyse par espace métrique introduite pour la première fois par Adams (1992). Cette technique est basée sur la comparaison de "fonctions de sortie" à une dimension qui analyse la topologie de cartes astrophysiques. Le nouvel espace métrique inclut de nouvelles fonctions de sortie, une meilleure réduction des données ainsi qu'une augmentation significative du nombre de structures isolées. A partir des données du "Canadian Galactic Plane Survey", la complexité de structures HI associées à 27 régions de formation d'étoiles, 13 étoiles Wolf-Rayet et 12 restes de supernova a pu être évaluée. Suite à ces calculs, une étude de corrélation a été réalisée entre le degré de complexité des structures HI et certaines caractéristiques intrinsèques associées aux objets, telles leur âge, la vitesse des vents stellaires et le paramètre d'excitation

Investigation Of Fraying In Textile Reinforcements For Composites

This paper discusses the fraying of textile reinforcements upon preforming. The paper also introduces a method for quantifying the fraying characteristics of fabrics. Six different fabrics including three carbon fabrics and three glass fabrics were tested. Digital microscopy was also used for measuring the structures of the fabrics tested. The relation between the structures and fraying is discussed

Comparative study of microlaser excitation thermography and microultrasonic excitation thermography for submillimeter porosity in carbon fiber reinforced polymer composites

Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Thermographic approaches including microvibrothermography, microlaser line thermography, and microlaser spot thermography on the basis of pulsed and lock-in techniques were proposed. These techniques are used to detect the submillimeter porosities in a stitched T-joint carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to validate the thermographic results. Finally an experimental comparison of microlaser excitation thermography and microultrasonic excitation thermography was conducte

Optical excitation thermography for twill / plain weaves and stitched fabric dry carbon fibre preform inspection

Carbon fibres have become the natural choice as reinforcements for polymer composite materials (PMCs). The non-destructive inspection of dry carbon fibre preforms has the potential to increase the reproducibility and reduce the cost of PMC manufacturing, by identifying defects in dry multilayer preforms prior to resin injection. However, use of optical excitation thermography for inspecting dry carbon fibre preforms that constitute the structural reinforcement precursor in the manufacturing of PMCs is poorly documented in the open literature. In this work, optical excitation thermography was used for inspecting six dry multilayer carbon fibre preforms featuring different textile structures, thicknesses and defects, for the first time. Advanced image processing techniques were used in processing the thermographic data for comparative purposes. In particular, partial least square thermography, as a recently proposed technique, was studied in detail. Finally, the performance of different thermography techniques was analysed in terms of: 1) summarizing the capabilities of image diagnosis/processing techniques by signal-to-noise ratio analysis, and 2) identifying the monitoring modalities most suitable to industrial manufacturing

Étude sur les obstacles à la mise en place d’activités d’engagement civique en milieu scolaire au Québec

This study surveyed 46 school workers in order to investigate factors that can impede youths’ engagement in civic activities at school in the Province of Quebec. The results confirmed that structural impediments and the lack of information represent hurdles to the development of civic engagement activities. Other barriers related to employees and work conditions emerged. Moreover, school workers’ justification of the system can havean indirect effect on their own civic behaviour, thus potentially diminishing their civic mobilization in school settings. These results suggest courses of action to promote civic activities to youths within school settings.La présente étude a sondé 46 intervenants scolaires afin d’examiner les facteurs pouvant entraver la participation des jeunes à des activités civiques dans le milieu scolaire québécois. Les résultats montrent que les contraintes structurelles et le manque d’information représentent des obstacles au développement d’activités civiques. D’autres obstacles concernant le personnel et les conditions de travail ont émergé. De plus, la justification du système par les intervenants agirait indirectement sur leurs comportements civiques, risquant de diminuer leur mobilisation civique dans le cadre scolaire. Ces résultats suggèrent des pistes d’intervention afin d’encourager l’offre d’activités civiques aux jeunes dans le milieu scolaire

Limited heat tolerance in an Arctic passerine: Thermoregulatory implications for cold-specialized birds in a rapidly warming world

Arctic animals inhabit some of the coldest environments on the planet and have evolved physiological mechanisms for minimizing heat loss under extreme cold. However, the Arctic is warming faster than the global average and how well Arctic animals tolerate even moderately high air temperatures (Ta) is unknown. Using flow-through respirometry, we investigated the heat tolerance and evaporative cooling capacity of snow buntings (Plectrophenax nivalis; ≈31 g, N = 42), a cold specialist, Arctic songbird. We exposed buntings to increasing Ta and measured body temperature (Tb), resting metabolic rate (RMR), rates of evaporative water loss (EWL), and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production). Buntings had an average (±SD) Tb of 41.3 ± 0.2°C at thermoneutral Ta and increased Tb to a maximum of 43.5 ± 0.3°C. Buntings started panting at Ta of 33.2 ± 1.7°C, with rapid increases in EWL starting at Ta = 34.6°C, meaning they experienced heat stress when air temperatures were well below their body temperature. Maximum rates of EWL were only 2.9× baseline rates at thermoneutral Ta, a markedly lower increase than seen in more heat-tolerant arid-zone species (e.g., ≥4.7× baseline rates). Heat-stressed buntings also had low evaporative cooling efficiencies, with 95% of individuals unable to evaporatively dissipate an amount of heat equivalent to their own metabolic heat production. Our results suggest that buntings’ well-developed cold tolerance may come at the cost of reduced heat tolerance. As the Arctic warms, and this and other species experience increased periods of heat stress, a limited capacity for evaporative cooling may force birds to increasingly rely on behavioral thermoregulation, such as minimizing activity, at the expense of diminished performance or reproductive investment

Village néolithique de Klimonas (Ayios Tychonas) - 2017

Données scientifiques produites : Nouvelles données sur les débuts du Néolithique à ChypreAgios Tychonas - Klimonas: French Archaeological Mission par le Département des Antiquités de ChypreMission archéologique française de Klimonas par l’Institut française de ChypreProgrammes « Ayios Tychonas – Klimonas, le plus ancien village chypriote » par l’AIBLBlog sur Klimonas Rappels des résultats antérieurs Le site de Klimonas, localisé sur la commune d’Ayios Thychonas près de Limassol, a été découv..