Sandwich composites impact and indentation behaviour study

In order to better exploit the natural cork available in Algeria, an experimental characterisation of a jute/epoxy–cork sandwich material to impact and indentation was undertaken. The aim of this work is to evaluate the impact energy and cork density influence over the sandwich plate damage behaviours by instrumented static and dynamic tests. The results show that the onset damage force, the maximum force and the damage size are influenced by the cork density and the impact energy. The sandwich material, with the heavy agglomerated cork having a density of 310 kg/m3 is characterised by a weaker energy dissipation capacity, by about 3.72% for impact test and 3.29% for indentation one, than the sandwich with lighter cork (160 kg/m3). This difference is an infusion process consequence. The infiltrated resin into the agglomerated cork pores changes the material local rigidity. Also, under impact loading the sandwich laminates dissipate 11% more energy than with the quasi-static indentation test

Influence of machining damage generated during trimming of CFRP composite on the compressive strength

Machining of composite materials is a challenging task due to the heterogeneity and anisotropy of composite structures. The induced defects reduce integrity of the machined surface as well as the loading capacity of the composite structure in service. Therefore, it is necessary to quantify the damage induced during trimming and correlate the quality of the machined surface to mechanical properties. The correlation of the surface roughness criteria, widely used in literature, to the mechanical behavior raise several contradictions. For this reason, new parameters for the characterization of the machined surface are proposed and correlated to the mechanical behavior under compressive loading. In this context, carbon fiber-reinforced plastic laminates are conventionally trimmed, and the machining damage is characterized using scanning electron microscope observations, X-ray tomography, and 3D optical topography. The results reveal that crater volume and maximum depth of damage quantify the machining damage more realistic compared to the classical surface roughness criteria

Caractérisation mécanique et étude numérique des tubes composites à enroulement filamentaires ±55° assemblés par collage sous chargement uniaxial

Le collage des tubes composites obtenus par le procédé d'enroulement filamentaires semble être technique d'assemblage la plus efficace pour ces structures tubulaires. Une telle technique représente de nombreux avantages par rapports aux autres techniques (boulonnage, rivetage). Cependant, la compréhension des mécanismes d'endommagement de ces structures assemblées est peu maitrisée, ce qui rend leur utilisation moins fréquente dans plusieurs domaines. Dans ce travail, une étude expérimentale a été menée afin de caractériser le comportement mécanique en traction des tubes composites à base de fibres de verre de type E et trois types de résines (Vinylester, Vinylester 470 et Polyester Isophtalique) assemblés par collage en utilisant la colle Araldite. Egalement le comportement mécanique de cette colle a été analysé à travers des essais de traction uniaxial. Une étude numérique a été menée afin de mieux prédire le comportement élastique des ces tubes

Microstructural investigation and hole quality evaluation in S2/FM94 glass-fibre composites under dry and cryogenic conditions

International audienceS2/FM94 glass fibre reinforced epoxy is an aerospace-grade composite currently bonded with aluminium alloys and installed in parts of the Airbus A380 fuselage. In addition to its abrasive and hard nature, S2/FM94 glass fibre is sensitive to thermal effects developed during the drilling process, and therefore using coolants becomes necessary. However, conventional oil and water-based coolants are not suitable for drilling of composites. Cryogenic coolants on the other hand are an attractive choice for machining composites and are environmentally friendly. In this study, a new environmentally friendly cryogenic cooling technique in a liquid nitrogen bath was used for the drilling of S2/FM94 glass fibre reinforced epoxy composite. The aim was to investigate the effect of drilling parameters and cryogenic cooling on cutting forces, surface roughness, hardness and delamination factor at hole entry and exit sides. The workpiece was drilled within a cryogenic bath. In this way, both cryogenic workpiece cooling and tool cooling were obtained. In addition, the drill geometry is fixed and only the cutting parameters (i.e. spindle speed and the feed rate) are varied under dry and cryogenic conditions. The results indicate that the spindle speed and cryogenic cooling had the most significant influence on the cutting forces and surface roughness parameters (R a and R z ), while the use of cryogenic cooling had the most significant influence on increasing the hardness and size of delamination at entry and exit sides of the holes

Surface integrity while trimming of composite structures: X-ray tomography analysis

The aim of this paper is to study the influence of the process parameters (cutting speed and feed) of the conventional trimming on cutting forces, machining temperatures, tool wear and machining quality of Carbon Fibers Reinforced Plastics (CFRP) using PCD tool. The machining quality was characterized using three different techniques such as Scanning Electron Microscopy (SEM), 3D optical topography and X-ray tomography. The originality of this work is based mainly on the multi-scale characterization of the machined surfaces. In fact, a new parameter based on the measurement of the volume of craters is proposed and compared to the surface roughness criterion (Sa) and the X-ray tomography images. The obtained results show that, with the crater volume criterion as well as the X-ray tomography images, the effect of the machining parameters and the wear of the tool on the textured surfaces are well correlated to surface roughness criterion (Sa). In addition, it was observed that the feed speed and tool wear were the major factors affecting the cutting forces and the machining temperatures

New tool for reduction of harmful particulate dispersion and to improve machining quality when trimming carbon/epoxy composites

Conventional machining of carbon fiber reinforced plastic composites (CFRPs) generates minute chips that get suspended in air causing a hazard compromising operator safety. This study investigates the influence of cutting parameters (feed speed, cutting speed, radial depth of cut, tool geometry and tool wear) during trimming of CFRP on the form and quantity of harmful particles dispersed. Also, performance of two classical PCD tool geometries (two straight flutes, two helix flutes) have been compared with newly designed (in collaboration with ASAHI Company) four serrated straight flutes for the purpose of dust emission reduction. The quantification of the number of harmful particles was estimated using laser spectroscopic dust monitor. The results reveal that, trimming with a combination of higher feed speed and lower cutting speed can reduce the dispersion of harmful particles. Further, the four serrated straight flutes recorded the least number of harmful particles compared to the conventional tools

Délaminage lors du perçage d'un composite carbone-époxy

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Wear signature on hole defects as a function of cutting tool material for drilling 3D interlock composite

International audienceThe aim of this paper is to study the influence of machining parameters and tool geometry on the machining quality and the mechanisms of wear that develop when drilling a new 3D woven composite material. Various frictional contacts were analyzed using the cutting tools selected (a diamond-coated carbide twist drill and a core drill with electro deposited diamond grains). The signature of wear on the wall of the holes was investigated at both macro and micro levels using the cutting force measurements and SEM observations combined with 3D roughness measurements. The damage generated on the wall of the hole was uniformly distributed and was not affected by the fiber orientation when the core drill was used. However, with the twist drill, the damage observed was strongly influenced by the fiber orientation. In addition, wear tests indicated that the signature of the wear on the wall was different from one geometry to the other. When the core drill was used, the grain removal and grain smoothing of the diamond grains was observed. Moreover, when the twist drill was used, the tool wear mechanisms were driven by abrasion phenomena on the flank face accompanied with the delamination of the diamond layer. Finally, core drills were found to offer excellent wear resistance compared to twist drills during the drilling of 3D woven composites

Prédiction des efforts responsables du délaminage lors du perçage des structures composites fibres longues

International audienceIn this paper, we propose a numerical Finite Element analysis within a quasi static framework of the thrust forces responsible for the defect at exit of the hole during the drilling phase of long fibers composite structures. This numerical model-compared with the analytical models existing in the literature-takes into account the tool point geometry as well as the shear force effects in the laminate. The validation of the numerical model is carried out thanks to tests of punching at low speed on two types of semi products in carbon / epoxy long fiber manufactured by the Hexcel Composites company. The numerical results present a good correlation with the experimental values. Moreover, a comparison between the numerical thrust forces and those provided by the analytical models of the literature are discussed.Dans cet article, on propose une analyse numérique par E. F. dans un cadre quasi statique des efforts de poussée responsables du défaut en sortie du trou lors du perçage de plaques composites fibres longues. La particularité de ce modèle numérique, comparé aux modèles analytiques existants dans la littérature, est qu'il prend en considération la géométrie de la pointe de l'outil ainsi que les effets des efforts tranchants dans le stratifié. La validation de ce modèle numérique est réalisée grâce à des essais de poinçonnement à faible vitesse sur deux types de semi produits en carbone/époxy fibres longues fabriqués par Hexcel Composites. Les résultats numériques présentent une bonne corrélation avec les valeurs obtenues expérimentalement. De plus, une comparaison entre les efforts de poussée numériques et ceux fournis par les modèles analytiques de la littérature est discutée