Three-Dimentional Textile Preform Using Advanced Textile Technologies for Composite Manufacturing

Textile reinforcement structure plays an important role in the reinforcement/composite performances during the composite manufacturing and in-service life of the composite material. Structures with a three-dimensional (3D) fiber topology are desired due to their superior multiaxial performance and efforts have been made to modify 2D textile technologies to produce complex 3D shapes. Most of these 3D solutions are based on the principle of adding out-of-plane reinforcements to a planar 2D fabric. Well-established 3D textile methods such as braiding and knitting have also been demonstrated to directly produce near net-shape structures. To understand these potentialities, the first section of this chapter will present the several textile technologies with strengths and weaknesses of these processes to manufacture technical reinforcements for composite applications. In the following sections, several applications with specific textile architectures will be given, in particular, the applications of the through-the-thickness reinforcement and 3D textile ply during the composite manufacturing

From fibre extraction to the composite manufacturing processes: Which path to adopt to maximise the mechanical properties of natural fibre based composites?

This work proposes to analyse the different aspects that should be taken into account from the fibre extraction from plants to the forming process to achieve correct part forming. The study will focus in a first extent on the impact of the textile operations leading to the yarn manufacturing. The properties of the flax fabric will then be associated to its behaviour during experimental forming and related to the possible appearence of defects such as tow buckling and solutions to prevent its appearance is widely discussed

Contribution for analysing the intra-ply yarn sliding mechanism in preforming of the woven fabric

International audienceManufacturing complex composite part via Liquid Composite Molding (LCM) processes involves preforming dry textile perform before injecting the liquid resin. The defect that may be encountered within the textile structure during preforming step decreases the expected mechanical properties of the composite 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. In this paper, a contribution for analyzing the mechanism of this defect and the influencing process parameters is presented. This analysis is based on an experimental study performed for one ply carbon fabric using a hemispheric punch. The effect of the ply orientation and blank holder force on the fabric behavior during preforming is evaluated regarding the required preforming force and yarn slippage. For the performed tests, it was obvious the impact of these two factors on the fabric behavior. The slippage phenomenon occurred in zones with low shear angles, for specific ply orientation. The fabric behavior has been analyzed by considering the evolution of the yarn tension which is related to the contact shear stress induced by sliding the fabric across the die and blank holder during preforming. Using an analytical model for the yarn tension in friction sliding, the influencing ply geometry and process parameters have been identified. Based on this analysis a solution relative the ply geometry to reduce the yarn tension is examined

Analysis of the deformability of flax-fibre nonwoven fabrics during manufacturing.

The use of natural fibres for technical advanced products such as composites is widely increasing with the view to reduce the impact of the material throughout its life cycle on the environment. Some work has been performed on natural fibre based reinforcement textiles for composite materials. The mechanical and the formability behaviours of woven fabrics has particularly been characterised. However, few research work concerns the forming aptitude of nonwoven fabrics despite promising preliminary studies. In the present work, the mechanical characterizations of flax-fibre nonwoven reinforcements are carried out firstly. Then the forming tests of the nonwoven fabrics are performed to quantify their formability behaviour. The tensile and forming tests showed very different mechanical behaviours in comparison to the ones observed on woven fabrics due to the non-uniformity of nonwoven fabric. The high deformation potential of the nonwoven fabrics is established. The specific behaviour of the nonwoven fabrics is studied by analysing the local and global deformation mechanisms of the reinforcement during forming. Moreover, the manufacturing defects experienced in nonwoven fabric forming are demonstrated. The slippage/damage of network is a typical problem in the nonwoven fabric forming, which depends strongly on the fibre density (area density) of fabric and blank-holder pressure

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

Analysis of the blank holder force effect on the preforming process using a simple discrete approach

Simulation of the dry reinforcement preforming, first step of the Resin Transfer Moulding process, become necessary to determine the feasibility of the forming process, compute the fiber directions in the final composite component, and optimize process parameters during this step. Contrary to geometrical approaches, based on fishnet algorithms [1, 2], finite element methods can take into account the actual physical parameters, the real boundary conditions and the mechanical behaviour of the textile reinforcement [3, 4]. The fabric can be modelled either as continuum media with specific material behaviour [5, 6], or using discrete structural elements to describe the textile structure at the mesoscopic scale [7, 8]. A semi-discrete approach, which is a compromise between the above continuous and discrete approaches [9, 10], is also used for simulation. A discrete approach for the simulation of the preforming of dry woven reinforcement has been proposed and presented in a previous paper [11]. This model is based on a “unit cell” formulated with elastic isotropic shells coupled to axial connectors. The connectors, which replace bars or beams largely studied in other discrete approaches [12], reinforce the structure in the yarn directions and naturally capture the specific anisotropic behaviour of fabric. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomena with the punch and die. The linear characteristic of the connectors [11], has been extended to a non linear behaviour in the present paper to better account for fabric undulation. Using this numerical model, we propose, in this work to study the effect of process parameters on the woven fabric deformation during the performing step. The emphasis will be placed on the analysis of the influence of the blank holder pressure on the shear angle distribution.This work has been undertaken within the framework of the Défi composite project. The authors would like to thank Oséo for its financial support, the project leader Airbus-France and other partners (EADS IW and LoireTech) for provided facilities

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

Measurement of the appearance and growth of tow buckling defect in the frame of complex shape manufacturing process by using fringe projection technique

During the manufacturing of composite complex shape parts, defects such as tow buckles characterised by out of plane elevation may appear. The parameters controlling the appearance and growth of the defect are not completely understood and need to be investigated. A device capable of reproducing tow buckles has been used to study the tow buckling phenomenon. Several techniques able to measure out of plane elevations are discussed to detect the appearance and evaluate continuously the growth of the tow buckle in relation to its size and shape. The fringe projection technique was chosen as it gives the best compromise between the size of the defect to measure and its resolution. If the in-plane bending angle is the main criterion at the origin of the tow buckle appearance and growth, it is not the only one. This work shows that the fabric architecture such as the space between the tows perpendicular to the one showing the buckle is also crucial to control the buckle’s appearance and growth. It also shows that the differential bi-axial loading of the fabric as well as the stiffness of the tows in the three main directions greatly in fluences the appearance of the defect

Influence of the non-linearity of fabric tensile behavior for preforming modeling of a woven flax fabric

he preforming step, which is the first stage of the RESIN Transfer Molding process, has been analyzed by many experimental or numerical approaches in the literature for reinforcements made of synthetic fibers. The complex mechanical behavior of a flax-based plain weave fabric was studied with the view to investigate its formability. Non-linearities in the fabric tensile behavior were observed. A preforming numerical finite element tool was used and validated by performing comparisons between experimental and numerical results. Different tensile behavior models (linear and strongly non-linear) were implemented to investigate their effect on the final shape characteristics. The tool was also used to investigate the effect of the process parameters on the computed preform shape (shear angles and draw-in) for both implemented tensile behaviors. Results show that better correlations take place when using the non-linear tensile behavior. This therefore demonstrates the importance of taking into account non-linearities in the tensile reinforcement behavior while simulating the forming of woven textile reinforcements