Analysis of the multilayer woven fabric behaviour during the forming process: focus on the loss of cohesion within the woven fibre network

The first step in the composite manufacturing process consists of forming a flat textile reinforcing structure into a 3D shape. The quality of the final composite part is affected by the presence of defects induced during the forming process. Loss of cohesion in the woven fibre network (intra-ply yarn sliding) is a frequent defect in the forming process. It is expected when the cohesion between the yarns is weak or when the blank holder pressure is high. However, the mechanism of formation of this defect is not fully understood. In the present study, forming experiments with friction-based holder have been conducted for a monolayer twill woven carbon fabric in two orientations and for two plies of this fabric with different relative orientations. The occurrence of the intra-ply yarns sliding has been observed as a function of the blank holder pressure. A correlation between the occurrence of this defect and the fabric orientation has been noticed. Furthermore, the effect of the fabric orientation, number of plies, relative plies orientation and blank holder pressure on the recorded forming force and on the fabric in-plane shear is also reported and analysed

Analysis of the multilayer woven fabric behaviour during the forming process. Focus on the loss of cohesion within the woven fibre network

International audienceThe composite manufacturing process occupies a more prominent place in the aerospace and automotive industries due to the lightweight and high performance of the fibre reinforced polymers. The first step in this manufacturing process consists in forming a flat textile reinforcing structure into a designed (tailored) form. The woven textile preform is widely used in the composite manufacturing for its good draping and flexibility properties. The quality of the final woven composite part depends on the fibre distribution and orientation. It also depends on the absence or presence of forming defects. The reasons of occurrence of defects are related to tool geometry, process parameters, textile characteristics, relative plies orientation, inter-ply friction and fabric-tools interaction. Loss of cohesion in the woven fibre network (intra-ply yarn sliding) is a frequent defect in the forming process and it is expected when the cohesion between the yarns is weak or when the blank holder pressure is high. However, the mechanism of formation of this defect is not fully understood. In the present study, forming experiments with friction-based holder have been conducted for one layer of 2x2 twill woven carbon fabric (HexForce 48600 U 1250) in two fabric orientations and also for two plies of this fabric with different relative plies orientation. The occurrence of the intra-ply yarns sliding has been observed in the different configurations and as a function of the blank holder pressure. A correlation between the occurrence of this defect and the fabric orientation has been observed. Otherwise, the effect of the fabric orientation, number of plies, relative plies orientation and blank holder pressure on the recorded forming force and on the fabric in-plane shear is also reported and analysed. That permits to better understand the multilayer woven fabric behaviour during forming and this leads to a better understanding of the loss of cohesion defect (intra-ply yarn sliding) within the woven fibre network

Influence du nombre de couches sur les propriétés mécaniques de tissus 3D interlock chaine en lin

International audience3D warp interlock weaving allows to realize thicker preform for composites materials. Nevertheless, this technology is not widely used with natural fibres. This study demonstrates the feasibility of 3D warp interlock weaving with natural fibres, and the influence of the number of layers on structural and mechanical properties of this fabric. Thanks to the characterization results, structural parameters as the weft density, the thickness or the areal density have been found correlated to the number of layers. Mechanical parameters are also studied and explained thanks to structural parameters.Le tissage 3D interlock chaine permet de réaliser des préformes épaisses pour matériaux composites. Or, cette technologie est très peu employée pour des renforts à base de fibres naturelles. Cette étude démontre à la fois la faisabilité du tissage 3D interlock chaine pour les fibres naturelles et s'intéresse à l'influence du nombre de couches sur les propriétés structurelles et mécaniques. À partir de rovings de lin 1000 Tex, cinq tissus 3D interlock chaine, dérivée de la toile, ont été tissés. Suite à la chaine de caractérisation mise en place, de nombreux paramètres structuraux tels que la densité trame, l'épaisseur ou la masse surfacique sont proportionnels au nombre de couches de la structure tissée 3D interlock chaine. Le comportement en traction uni-axiale de ces structures sèches est également étudié via les paramètres structuraux

Amélioration de la tissabilité des préformes pour applications composites par l'utilisation de rovings guipés chanvre/PA12

International audienceHemp fibers are more and more used to reinforce biobased composite materials, thanks to their low density, their low production cost and their good properties. Composite reinforcements with hemp fibers currently available on the market are nonwovens or unidirectional preforms. The few woven preforms available are made of yarns, which leads to poor impregnation and poor mechanical properties of the composite. In order to increase composite properties, rovings (with higher fiber number in cross section and lower twist level than yarns) can be used, but their properties are not sufficient for manufacturing processes of preforms. In textile industry, properties are traditionally improved by chemical treatment, which increase environmental impact of reinforcement. The study presented in this paper proposes an improvement of roving properties by wrapping a multifilament of thermoplastic polymer (polyamide 12) around a roving made of hemp fibers. Contributions of this technology are studied, both at the roving and the preform scales, to highlight advantages and disadvantages compared to the more traditional chemical treatment method.Les fibres de chanvre sont de plus en plus utilisées pour le renfort de matériaux composites biosourcés, du fait de leur faible densité, de leur faible coût de production et de leurs bonnes propriétés. Les renforts en fibres de chanvre actuellement disponibles sur le marché sont sous forme de nontissés ou d'unidirectionnels. Les quelques préformes tissées disponibles sont produites à partir de fils, ce qui entraine une faible imprégnation du renfort et ainsi de faibles propriétés mécaniques. Afin d'optimiser les performances des matériaux composites, des rovings (comportant un meilleur taux de fibres en section et une plus faible torsion que les fils) peuvent être utilisés, mais leurs propriétés ne sont pas adaptées aux technologies textiles d'élaboration des préformes. L'industrie textile a traditionnellement recours au traitement chimique pour remédier à cet inconvénient, ce qui augmente l'impact environnemental du renfort. L'étude présentée ici propose une amélioration des propriétés du roving en ayant recours au guipage par un multifilament de polymère thermoplastique (polyamide 12) autour du roving. Les apports de cette technologie sont étudiés, tant à l'échelle du roving qu'à l'échelle de la préforme, pour mettre en évidence ses avantages et ses inconvénients par rapport à la méthode plus classique du traitement chimique

Intra-ply yarn sliding defect in hemisphere preforming of a woven preform

Preforming is the first step to manufacture a complex composite part via Liquid Composite Moulding processes. The defects that may be encountered during this phase within the preform architecture may decrease the expected mechanical performances of the final part. The intra-ply yarn sliding is a defect frequently observed during preforming of a woven preform but its mechanism is far from being fully understood. The aim of this study is to analyse the mechanism of this defect arising when preforming of a carbon woven fabric into hemispheric shape. An experimental study followed by analytical analysis was performed to evaluate the effect of the process parameters, material properties and ply configuration conditions on the yarn tension and contact stresses. A significant effect of the yarn tension and the contact shear stresses on the defect occurrence was demonstrated. Based on this analysis, solutions were tested with success to prevent this defect

Analysis of the multilayer woven fabric behaviour during the forming process. Focus on the loss of cohesion within the woven fibre network

The composite manufacturing process occupies a more prominent place in the aerospace and automotive industries due to the lightweight and high performance of the fibre reinforced polymers. The first step in this manufacturing process consists in forming a flat textile reinforcing structure into a designed (tailored) form. The woven textile preform is widely used in the composite manufacturing for its good draping and flexibility properties. The quality of the final woven composite part depends on the fibre distribution and orientation. It also depends on the absence or presence of forming defects. The reasons of occurrence of defects are related to tool geometry, process parameters, textile characteristics, relative plies orientation, inter-ply friction and fabric-tools interaction. Loss of cohesion in the woven fibre network (intra-ply yarn sliding) is a frequent defect in the forming process and it is expected when the cohesion between the yarns is weak or when the blank holder pressure is high. However, the mechanism of formation of this defect is not fully understood. In the present study, forming experiments with friction-based holder have been conducted for one layer of 2x2 twill woven carbon fabric (HexForce 48600 U 1250) in two fabric orientations and also for two plies of this fabric with different relative plies orientation. The occurrence of the intra-ply yarns sliding has been observed in the different configurations and as a function of the blank holder pressure. A correlation between the occurrence of this defect and the fabric orientation has been observed. Otherwise, the effect of the fabric orientation, number of plies, relative plies orientation and blank holder pressure on the recorded forming force and on the fabric in-plane shear is also reported and analysed. That permits to better understand the multilayer woven fabric behaviour during forming and this leads to a better understanding of the loss of cohesion defect (intra-ply yarn sliding) within the woven fibre network

Hybrid approach for woven fabric modelling based on discrete hypoelastic behaviour and experimental validation

A non-linear discrete hybrid approach based on the association of hypoelastic continuous elements (non-linear shear behaviour) with specific connectors (non-linear tension stiffness) is developed. It allows the simulation of a two-dimensional (2D) woven reinforcement forming via an accurate explicit finite element analysis. This approach allows the simulation of 2D unbalanced fabrics uncoupling tensile and shear behaviour. It only needs a few parameters to be identified, and shows a good agreement with the experiments. The identification of the model parameters is investigated, and their relevance is analysed in reference tests. To determine the continuous element behaviour, a VUMAT hypoelastic model is implemented in Abaqus/Explicit. This model allows the prediction of fibre stresses and the accurate determination of shear angle in large deformations. Identification and validation of the model are performed using standard characterisation fabric tests. The experimental characterisation provided the numerical data to produce a representational prediction of the deformed fabric geometry and shear angle distribution. Further, the behaviour of the carbon woven reinforcement is identified. A bias extension test is used to both calibrate and validate the model. The capability of the model is illustrated to simulate deep drawing, and to compare with the experimental results of hemispherical forming

Development of 3D multiaxis woven preforms for composite structures : technology, modelling and optimisation

La technologie de tissage 3D a été développée comme une réponse à la faible résistance au délaminage des structures de composite stratifiées en insérant des renforts fibreux dans l’épaisseur de la structure. Pourtant, cette technologie ne permet pas de positionner des fibres dans le plan autre que dans les directions à 0° et 90°. Cela implique de faibles résistances au cisaillement dans le plan. Pour cela une technologie de tissage 3D multiaxial a été développée permettant une insertion de fils dans d’autres orientations du plan. Dans cette thèse, une nouvelle technique dédié à produire des préformes 3D multiaxial tissées avec la possibilité de contrôler l’ordre des couches est présentée. Les paramètres des fils constitutifs et de la cellule unitaire des échantillons fabriqués sont mesurés avec l’investigation de la géométrie des fils (section et trajectoire) au sein de la structure. Associé à ces développements expérimentaux, un modèle géométrique, en tant qu’outil de conception permettant de décrire les préformes élaborées, a été développé. Cette modélisation géométrique permet de générer un VER, à l’échelle mésoscopique de la structure. Afin d’évaluer l’influence de ces préformes 3D sur les caractéristiques mécaniques, une chaîne numérique par éléments finis a été mise en place afin de calculer le comportement élastique équivalent. Les résultats sur les propriétés élastiques permettent de quantifier l’apport des fils dans le plan, comparativement aux structures 3D tissées. L’influence de l’ordre des couches dans l’épaisseur est également mis en évidence sur la minimisation des contraintes interlaminaires sur les dans le composite.3D weaving technology is developed in response to the poor delamination resistance of laminated composite structures by insertion through the thickness fiber reinforcements. However, this technology is limited relatively to a possibility to insert in-plane yarns oriented other than 0° and 90°. This results in reduction of the in-plane off axis tensile properties and the in-plane shear resistance. Therefore, 3D multiaxis weaving technology has been developed in order to enable this insertion. In the thesis, a novel technique able to produce 3D multiaxis woven preforms is presented with the possibility to control the sequencing of yarn layers. The constitutive yarns and unit cell parameters of the produced samples have been measured with investigation of yarns geometry (cross section shape and path) within the structure, by analyzing the captured micrographs for the samples cross section. Predictive geometrical model has been developed. This model is indispensable design tool providing approximate estimation of the geometrical properties of the dry preforms and composites. Moreover, a geometric modeling approach is improved helping to construct an RVE of this structure as accurate as possible based on the elaborated geometrical characterization. Based on the developed RVE, a mechanical modeling has been also improved and completed using the finite element method serving firstly, to evaluate the bias yarns effect on the elastic stiffness and in-plane off-axis properties in comparison with equivalent 3D orthogonal woven composite. Secondly, it helps to investigate the influence of the in-plane layers sequence on the induced interlaminare stresses at the composite free edges

Effect of the Fibre Orientation Distribution on the Mechanical and Preforming Behaviour of Nonwoven Preform Made of Recycled Carbon Fibres

Recycling carbon-fibre-reinforced plastic (CFRP) and recovering high-cost carbon fibre (CF) is a preoccupation of scientific and industrial committees due to the environmental and economic concerns. A commercialised nonwoven mat, made of recycled carbon fibre and manufactured using carding and needle-punching technology, can promote second-life opportunities for carbon fibre. This paper aims to evaluate the mechanical and preforming behaviour of this nonwoven material. We focus on the influence that the fibre orientation distribution in the nonwoven material has on its mechanical and preforming behaviour at the preform scale, as well as the tensile properties at composite scale. The anisotropy index induced by fibre orientation is evaluated by analysing SEM micrographs using the fast Fourier transform (FFT) method. Then, the anisotropy in the tensile, bending, and preforming behaviour of the preform is inspected, as well as in the tensile behaviour of the composite. Additionally, we evaluate the impact of the stacking order of multi-layers of the nonwoven material, associated with its preferred fibre orientation (nonwoven anisotropy), on its compaction behaviour. The nonwoven anisotropy, in terms of fibre orientation, induces a strong effect on the preform mechanical and preforming behaviour, as well as the tensile behaviour of the composite. The tensile behaviour of the nonwoven material is governed by the inter-fibre cohesion, which depends on the fibre orientation. The low inter-fibre cohesion, which characterises this nonwoven material, leads to poor resistance to tearing. This type of defect rapidly occurs during preforming, even at too-low membrane tension. Otherwise, the increase in nonwoven layer numbers leads to a decrease in the impact of the nonwoven anisotropy behaviour under compaction load

An investigation on the mechanical behavior of 3D warp interlock carbon fabrics

© 2019 by DEStech Publications, Inc. and American Society for Composites. All rights reserved.There is a challenge on the use of stiffer carbon yarns into fabric structures to be used as fibrous reinforcement of composite material and their capacity to be draped inside the mold. Thus, one of the solution to cope with this issue lies in the use of 3D warp interlock fabrics. However, it is a challenge to choose the right 3D warp interlock architecture that has optimal performance for the requested application. The aim of this research is filling this gap and explores the potential properties of the 3D warp interlock fabric as a function of its architecture and geometrical properties. The 3D warp interlock carbon fabrics were produced and their tensile properties were investigated in the research. All the fabrics were produced on the same dobby loom with same carbon yarn (6K - 400 Tex) and with similar warp and weft densities. They were differentiated by binding warp yarn parameters, weave diagram pattern and including or not stuffer warp yarns in the woven structure. The carbon yarn strength was controlled at the different fabrication scales from bobbin to fabric in order to track the effect of the weaving process on the yarn strength. No significant loss in the carbon strength is observed. 3D warp interlock fabrics are manufactured with different weave pattern and other weaving parameters. The tensile behavior of these fabrics are evaluated and analyzed in light of the measured shrinkage of the constituting yarns. High impact for the yarn shrinkage value is revealed resulting in a higher breaking strain for the fabric comparing to the breaking strain of the carbon yarn (less than 1 %)