Mesoscopic scale analyses of textile composite reinforcement compaction

Transverse compaction of textile composite reinforcements is an important deformation mode arising during composite forming and manufacture. The mesoscopic simulations of the transverse compression of textile preforms presented in this paper are based on 3D FE models of each yarn in contact with friction with its neighbours. A hypoelastic model based on the fibre rotation depicts the mechanical behaviour of the yarn. The compression responses of several layer stacks with parallel or different orientations are computed. The numerical simulations show good agreement when compared to compaction experiments. The mesoscopic simulations can be used as virtual compression tests. In addition they determine the internal geometry of the reinforcement after compaction. The internal geometry can be used to compute the permeability of the deformed reinforcement and to calculate the homogenised mechanical properties of the final composite part.     

Hyperelastic modelling for mesoscopic analyses of composite reinforcements

A hyperelastic constitutive law is proposed to describe the mechanical behaviour of fibre bundles of woven composite reinforcements. The objective of this model is to compute the 3D geometry of the deformed woven unit cell. This geometry is important for permeability calculations and for the mechanical behaviour of the composite into service. The finite element models of a woven unit cell can also be used as virtual mechanical tests. The highlight of four deformation modes of the fibre bundle leads to definition of a strain energy potential from four specific invariants. The parameters of the hyperelastic constitutive law are identified in the case of a glass plain weave reinforcement thanks to uniaxial and equibiaxial tensile tests on the fibre bundle and on the whole reinforcement. This constitutive law is then validated in comparison to biaxial tension and in-plane shear tests.     

Consistent Finite Element mesh generation for meso-scale modeling of textile composites with preformed and compacted reinforcements

A new automated method to generate smooth Finite Element meshes for the meso-scale representation of textile composites unit cells with preformed and compacted reinforcements is presented. The reinforcement geometry is obtained from textile geometry preprocessors or by modeling of the preforming step. It is then transformed into a geometric model of the entire composite unit cell, taking into account the real yarn shape after preforming and compaction, the contact interactions between the yarns, as well as the resulting local variations of fiber volume fraction. A consistent mesh of the complete cell, conformal between the parts, is ensured, without the need for inserting artificial matrix layers between the yarns. The methodology is illustrated by mechanical modeling of the representative unit cell of a multi-layer composite with a compacted and nested woven reinforcement.     

Rate constitutive equations for computational analyses of textile composite reinforcement mechanical behaviour during forming

Textile composite reinforcements are made up of fibres. Consequently, their mechanical behaviour is a result of the possible sliding and the interactions between the fibres. When they are formed on double curved shapes, these fabrics are submitted to large strains, in particular large in-plane shear. Among the mechanical behaviour models for these textile reinforcements, continuous models are most commonly used for forming simulations because they can be used with standard finite elements. The objective of the present paper is to propose a continuous approach for textile reinforcement deformation analysis based on a rate constitutive equation specific to materials made of fibres. The objective derivative of this constitutive model is defined by the fibre rotation. This constitutive model is implemented in ABAQUS and can be used in most commercial F.E. software. The approach is extended to materials with two-fibre directions in order to perform simulations of woven fabric forming processes. A set of simulations of large deformations of textile composite reinforcements at the mesoscopic scale (deformation of a woven unit cell) and at the macroscopic scale (deep drawing) is presented to show the efficiency of the proposed approach.     

Computation of permeability of a non-crimp carbon textile reinforcement based on X-ray computed tomography images

The paper demonstrates the possibility of a correct (within the experimental scatter) calculation of a textile reinforcement permeability based on X-ray micro-computed tomography registration of the textile internal architecture, introduces the image segmentation procedures to achieve the necessary precision of reconstruction of the geometry and studies variability of the geometry and local permeability. The homogenized permeability of a non-crimp textile reinforcement is computed using computational fluid dynamics with voxel geometrical models. The models are constructed from X-ray computed tomography images using a statistical image segmentation method based on a Gaussian mixture model. The computed permeability shows a significant variability across different unit cells, in the range of (0.5…3.5) × 10⁻⁴ mm², which is strongly correlated with the solid volume fraction in the unit cell.     

Textile composites: modelling strategies

Textile materials are characterised by the distinct hierarchy of structure, which should be represented by a model of textile geometry and mechanical behaviour. In spite of a profound investigation of textile materials and a number of theoretical models existing in the textile literature for different structures, a model covering all structures typical for composite reinforcements is not available. Hence the challenge addressed in the present work is to take full advantage of the hierarchical principle of textile modelling, creating a truly integrated modelling and design tool for textile composites. It allows handling of complex textile structure computations in computer time counted by minutes instead of hours of the same non-linear, non-conservative behaviour of yarns in compression and bending. The architecture of the code implementing the model corresponds to the hierarchical structure of textile materials. The model of the textile geometry serves as a base for meso-mechanical and permeability models for composites, which provide therefore simulation tools for analysis of composite processing and properties.     

Quantifying variability within glass fibre reinforcements using an automated optical method

This paper presents a novel optical technique to quantify in-plane geometric variations within dry glass fibre reinforcement materials. Samples of up to 290 × 450 mm can be examined. Three different reinforcement structures have been studied; a random mat, a plain weave and a stitched bi-axial fabric. Using an empirically derived function, reinforcement areal weight has been predicted locally from a single reinforcement photograph. It was found that areal weight predictions were typically within 5% of experimentally obtained values for 25.4 mm square samples. For periodically structured (woven or stitched) reinforcements, local information describing the tow orientation and geometry has been collected automatically. Manual verification of the reinforcement geometry showed good agreement with the automated technique. 3D textile models have been created within a textile modelling software that include the measured variability.     

A semi‐discrete shell finite element for textile composite reinforcement forming simulation

A triangular shell element for the simulation of textile composite reinforcements forming is proposed. This element is made up of unit woven cells. The internal virtual works are added on all woven cells of the element. They depend on tensions, in‐plane shear and bending moments that are directly those given by the experimental tests that are specific to textile composite reinforcement. The element has only displacement degrees of freedom; the bending curvatures are obtained from the displacement of the neighbouring elements. A set of example shows the efficiency of the approach and the relative roles of the tensile, in‐plane shear and bending rigidities. Especially their influence on the appearance and the development of wrinkles in draping and forming tests is analysed. Copyright © 2009 John Wiley & Sons, Ltd.     

Micro-CT analysis of the internal deformed geometry of a non-crimp 3D orthogonal weave E-glass composite reinforcement

An investigation at the unit cell level of the sheared geometry of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.) is performed by X-ray micro-computed tomography (micro-CT) observations. The aim is to observe, understand and quantify the effect of in-plane shear deformation on the composite reinforcement geometry, at meso-scale (i.e. unit cell level). It was observed that, increasing the shear deformation, Z-yarns maintain unchanged the distance between the yarns and as consequence the yarn cross-section has a reduced variation of width, mainly in the weft direction.Furthermore, the effect of the shear angle on the textile thickness during compression is measured, this being an important parameter after the forming and molding phases of a composite component production. Compression tests and micro-CT measurements of the thickness show similar values and are in agreement with the prediction obtained assuming the theoretical invariance of the volume in the considered range of shear deformations.     

3D digital image correlation measurements during shaping of a non-crimp 3D orthogonal woven E-glass reinforcement

This paper illustrates a methodology for the characterization of textile composite reinforcements during experimental simulation of forming processes. In particular, being the shear deformation considered as the primary deformation mechanism during shaping, the evolution of shear angle distribution on the reinforcement surface is measured by means of 3D digital image correlation analyses. Two different image correlation software programs, i.e. VIC-3D and MatchID3D, are used to study the forming process of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.). The comparison of the displacement and shear angle distributions of the reinforcement, shaped on tetrahedral and double-dome moulds, pointed out a good agreement between the results obtained with both software packages.     

PROCESSING OF METAL AND CERAMIC MATRIX COMPOSITES WITH THREE-DIMENSIONAL BRAIDED REINFORCEMENT

This paper summarizes some of the pioneering work done in developing the processing techniques to consolidate metal and ceramic matrix composites with 3-D braided fiber architecture. The 3-D braided fiber architecture features a fully integrated structure with multidirectional reinforcement and allows for the braiding of complex shapes. For metal matrix composite, a 3-D braided AI₂O₃ fibers preform reinforced Al-Li matrix composite has been successfully fabricated by liquid vacuum infiltration methods. For ceramic matrix composites, chemical vapor infiltration technique has been used to densify a 3-D braided Nicalon fibers preform with SiC matrix composite. A significant improvement in composite performance can be achieved through the architecture of 3-D integrated reinforcement geometry. The future needs and directions for developing viable methods for fabricating strong, tough high temperature composites with 3-D reinforcements is also discussed.     

A Meso–Macro Three Node Finite Element for Draping of Textile Composite Preforms

The composite textile reinforcement draping simulations allows the conditions for a successful process to be determined and, most importantly, the positions of the fibres after forming to be known. This last point is essential for the structural computations of the composite part and for resin injection analyses in the case of LCM processes. Because the textile composite reinforcements are multiscale materials, continuous (macro) approaches and discrete (meso) approaches that model the yarns have been developed. The finite element that is proposed in this paper for textile fabric forming is composed of woven unit cells. The mechanical behaviour of these is analyzed by 3D computations at the mesoscale regarding biaxial tensions and in plane shear. The warp and weft directions of the woven fabric can be in arbitrary direction with respect to the direction of the element side. This is very important in the case of multi-ply deep drawing and when using remeshing. The element is efficient because it is close to the physic of the woven cell while avoiding the very large number of unknowns in the discrete approach. A set of validation tests and forming simulations on single ply and multi-ply are presented and show the efficiency of the approach. In particular the importance of the in-plane shear behaviour is emphasized in the case of a draping on a cube.     

Simulation of wrinkling during textile composite reinforcement forming. Influence of tensile, in-plane shear and bending stiffnesses

Wrinkling is one of the most common flaws that occur during textile composite reinforcement forming processes. These wrinkles are frequent because of the possible relative motion of fibres making up the reinforcement, leading to a very weak textile bending stiffness. It is necessary to simulate their onset but also their growth and their shape in order to verify that they do not extend to the useful part of the preform. In this paper the simulation of textile composite reinforcement forming and wrinkling is based on a simplified form of virtual internal work defined according to tensions, in-plane shear and bending moments on a unit woven cell. The role of the three rigidities (tensile, in-plane shear and bending) in wrinkling simulations is analysed. If in-plane shear stiffness plays a main role for onset of wrinkles in double-curved shape forming, there is no direct relation between shear angle and wrinkling. Wrinkling is a global phenomenon depending on all strains and stiffnesses and on boundary conditions. The bending stiffness mainly determines the shape of the wrinkles and it is not possible to perform a wrinkle simulation using a membrane approach.     

Beyond plain weave fabrics – I. Geometrical model

In response to the large variety of weaving styles offered by the textile industry, a new general approach for the geometrical modeling of 2D biaxial orthogonal woven fabric reinforcements for composite materials is proposed here. New geometrical parameters are introduced in order to describe general families of twill and satin woven patterns, and a new classification of woven fabrics is proposed based on these parameters. Generation of the 3D internal geometry of the woven fabric families is achieved based on new geometrical functions that consider the actual configuration of the composite material in all its complexity. The proposed geometrical model is intended as the foundation for further analytical or numerical modeling of the mechanical properties of the composite materials reinforced with these fabrics.     

Aspects of the stitch formation process on the quality of sewn multi-textile-preforms

Stitching technologies are considered to be one of the key technologies for automated manufacturing of complex textile preforms which are used for liquid composite moulding of fibre reinforced plastic parts [Proceedings of Sixth International Conference on Automated Composites (1999)]. The sewing or stitching process is applied for different purposes during the production of dry fibrous reinforcements as well as for structural aims in the composite component (through-the-thickness reinforcement), thus, the requirements on the stitch itself are wide spread [Complex Multi-textile Preforms – The Potential of Sewing. 90(4) (2000) 43; Stress Conc Compos Sci Technol, 59 (1999) 2125; Tech Textiles 43 (2000) 120; Compos Part A 31 (2000) 571; D 82 Dissertation RWTH Aaachen (1999)]. A detailed prediction of properties of the stitched reinforcements requires an understanding of the stitch formation process and the interaction between textile reinforcements, the stacking sequence thereof, the stitching process parameters and sewing thread properties.     

Meso-scale strain mapping in UD woven composites

Unidirectional (UD) woven laminates have complex tow geometry due to unbalanced weave architecture. Warp tows are held together by fine weft. Unit cell models for textile composites found in the literature are based on balanced weaves with identical warp and weft specifications. In this paper, unit cell geometry of unbalanced UD weaves has been considered. Unbalanced laminates have complex tow geometry with in-plane tow waviness and a significant overlap between adjacent tows. Main objective of this work is to measure full-field strain distribution at meso-scale or unit cell level and compare the results with FE analysis. Raman spectroscopy is a powerful technique for in situ strain measurement. A UD woven composite laminate with Kevlar fibres is used in this study, as Kevlar fibres exhibit clear Raman band shifts under strain. Influence of in-plane tow waviness on local strain gradients has been demonstrated.     

复合材料三维编织结构的单元体模型

复合材料三维编织结构技术是国外八十年代发展起来的高新纺织技术。三维编织结构复合材料是一种新型结构形式的复合材料,它具有优良的抗冲击损伤性能、力学性能和耐烧蚀性能。本文讨论了三维编织结构的单元体模型,推导出有关参数之间的数学关系。     

Influence of the tufting yarns on formability of tufted 3-Dimensional composite reinforcement

In aerospace industry, thicker and more complex composite parts are needed. Multilayered reinforcement is largely used as the traditional method. Recently, three-dimensional (3D) fabrics are developed to replace the multilayered reinforcements in certain applications to increase the performance in thickness direction of part, e.g. interlock structure. Currently, the development of tufting technology can be employed to produce the 3D textile composite reinforcements. The tufting parameters, such as tufting density, tufting length and tufting yarn orientations, can be completely controlled by user. In order to improve the understanding of formability of the tufted 3D fabric during manufacturing, the present work analyzes the preforming behaviours of tufted 3D reinforcement in the hemispherical stamping process. Also the preforming behaviours are compared with the samples of the multilayered forming. The experimental data demonstrated the influence of tufting yarns on the material draw-in, interply sliding, and winkling phenomenon during forming. Furthermore, the orientations of tufting yarn affected the forming results, which leaded to misalignment defect in the zone of strong in-plane shear.     

Modeling forces generated within rigid liquid composite molding tools. Part B: Numerical analysis

Liquid composite molding (LCM) processes generate forces on tooling due to internal resin pressure fields and the resistance to compaction offered by fiber reinforcements. In Part A of this work the authors have presented a detailed study on the evolution of total clamping force during resin transfer molding (RTM) and injection/compression molding (I/CM) cycles. The influence of the complex compaction response of two different reinforcements was demonstrated, important effects including stress relaxation, an apparent lubrication by the injected fluid, and permanent deformation. In the current paper attempts are made to model clamping force evolution utilizing elastic reinforcement compaction models. The predictions are shown to have significant qualitative errors if a single elastic model is applied, particularly if forces due to reinforcement compaction dominate those due to fluid pressure. By using a combination of elastic models significant qualitative and quantitative improvements were made to the predictions. It is concluded that careful characterization of both reinforcement permeability and compaction response are required for an accurate LCM tooling force analysis.     

Potentiality of utilising natural textile materials for engineering composites applications

This paper gives an overview of utilising natural textile materials as reinforcements for engineering composites applications. The definition and types of textile materials are addressed to provide readers a thoughtful view on the role of these materials in a structural composite system. Available material properties of natural textile and their composites are critically reviewed here. In general, these materials are categorised into fibre, yarn and fabric forms. The load bearing capacity of natural textile fibre reinforced polymer composites is governed by the quantity, alignment and dispersion properties of fibres. It has been found that the natural fibre reinforced composites are limited to use in low to medium load bearing applications. However, a limited research work has been performed to date and there is a significant gap between the high performance textile fabric and their use as reinforcement in fibre reinforced composite materials.