Contreplaqué | EPFL Graph Search

thumb|Contreplaqué de bouleau. vignette|Principe de fabrication du contreplaqué. Le contreplaqué ou plus précisément panneau contreplaqué (en Belgique, multiplex ; en anglais, plywood) est un panneau à base de bois obtenu par collage de couches adjacentes à fils croisés, normalement des placages, habituellement à angles droits. Le contreplaqué est composé de plusieurs couches de placages, appelées plis, en nombre impair. L'épaisseur d'un panneau varie entre 1 mm et 50 mm. Conception La fabrication d'un panneau de contreplaqué nécessite six opérations principales : le déroulage, le tri, l'encollage, le pressage, le ponçage et le sciage. Les placages qui composent le panneau sont obtenus en déroulant une grume : il s'agit de faire tourner une bille de bois sur une lame, pour obtenir une feuille d'une épaisseur de 0,33 à . Ils sont ensuite séchés et massicotés à dimension. Il résulte de cette opération des bandes de placages plus petites que le panneau final, qui sont joi

Transverse cracking in the bulk and at the free edge of thin-ply composites: experiments and multiscale modelling

Robin Amacher, John Botsis, Joël Cugnoni, Sébastien Kohler

Thin-ply composites were shown to exhibit significantly delayed transverse cracking, but the linear onset of damage scaling with ply thickness reported by Amacher et al. (2014) did not correspond to the established LEFM based in situ strength model. This study further investigates this experimental behaviour by simultaneously comparing in situ free edge crack observation with acoustic emission measurements as well as performing ex-situ X-ray tomography observations of crack propagation. A multi-scale FE model was used to better understand the damage mechanisms at play, and showed a decreasing trend of the apparent toughness with decreasing ply thickness, which explains the deviation from the existing model. Transverse cracking at the free edges was observed to propagate quickly towards the center of the specimens for the thickest plies, while in the thinnest plies it is significantly delayed, up to a point where no cracks can reach the center of the sample before final failure.

2019

Towards aerospace grade thin-ply composites: Effect of ply thickness, fibre, matrix and interlayer toughening on strength and damage tolerance

Robin Amacher, John Botsis, Joël Cugnoni, Sébastien Kohler, Larissa Sorensen

Thin-ply composites represent a promising approach to further improve the performance of carbon fibre composite structures thanks to their ability to delay the onset of matrix cracking and delamination up to the point of fibre dominated failure. However, this increased strength comes with a more brittle failure response which raises concerns on damage tolerance. Thus a careful material optimization is needed to address this trade-off. In this work, eight different formulations of thin-ply composites ranging from low modulus to high modulus carbon fibres are evaluated to understand the effects of the fibre and matrix constituents on the onset of damage and strength in unnotched tensile (UNT) tests of quasi isotropic laminates for ply thicknesses between 300 and 30 microns. The obtained experimental data are combined in master curve diagrams for simplified material selection process. It is observed that certain thin-ply composites with a ply thickness t < 134 mu m can reach UNT strength corresponding to or approaching the ultimate strain of the fibres as well as UNT stress at onset of damage as high as 92% of the latter. Based on this knowledge, a novel aerospace grade toughened thin-ply composite system is developed which can reach a quasi-isotropic UNT strength above 1 GPa (> 95% of the fibre strain). The newly developed composite is further optimized to improve damage tolerance by toughening the resin and selected interfaces. The effect of those modifications on damage tolerance are evaluated through compression strength after impact (CAI) tests and open hole tensile tests (OHT). It is found that an optimized interlayer toughened thin-ply composite based on 68 microns plies of intermediate modulus fibre can reach both outstanding strength properties with comparable or better CAI and OHT strength compared to current aerospace grade composites.

ELSEVIER SCI LTD2018

Thin ply composites: Experimental characterization and modeling of size-effects

Robin Amacher, John Botsis, Joël Cugnoni, Larissa Sorensen

Thin-ply composites are rapidly gaining interest in the composite industry, not only because of the larger design possibilities that they offer, but also because of positive size effects that have been shown to improve performance in various loading conditions [1]. In this work, carbon fiber-epoxy composites of different ply thicknesses (30-300 g/m(2) fiber areal weight) were produced from the same batch of Toray M40JB fiber and NorthTPT TP80ep matrix to study the influence of ply thickness on the ultimate strength and on the onset of damage in lamina, laminates and components. Uniaxial tension, open-hole compression and open-hole tensile fatigue tests on quasi isotropic 45 degrees/90 degrees/-45 degrees/0 degrees laminates showed very significant improvements regarding the on-set of damage, and in some cases ultimate strength, when decreasing the ply thickness. These performance improvements are the result of major changes in the damage progression and failure modes of the laminates caused by a systematic delay or near suppression of transverse cracking and delamination growth in thin-ply composites. On the component level, thin-ply laminates enabled a marked improvement for bolted-joint bearing, especially in hot-wet conditions. Under impact, the 30 mu m thin ply laminate exhibited a quasi-brittle failure with extensive translaminar cracking while a ply thickness of 100 mu m was found as optimum to minimize the projected damage area. Ply thickness scaling of transverse and in-plane shear strength was identified based on classical laminate theory and unnotched tensile tests on quasi-isotropic specimens. The empirical scaling was found to follow a linear trend over a range of ply thicknesses from 30 to 250 mu m. Due to the near suppression of delamination, the strength of thin-ply composites could then be modeled more effectively than thick ply composites using classical laminate theory or standard multilayer shell modeling. (C) 2014 Elsevier Ltd. All rights reserved.

Elsevier2014