Experimental studies and analysis of the draping of woven fabrics

This study investigates and compares the draping and forming of four types of woven fabrics, namely a loose plain weave (basket weave), a tight plain weave, a satin and a twill weave. The fabrics were draped over a hat mould consisting of a hemispherical dome surrounded by a flat base. The draping of each fabric was examined in terms of wrinkle formation, boundary profile of the draped fabric, distribution of fibre orientation and local shear angles. A theoretical analysis of the experimental results involved the calculation of the distributions of the fibre volume fraction and mechanical properties, in terms of components of the reduced stiffness matrix, from the experimental data of local shear angles.     

Drapability of dry textile fabrics for stampable thermoplastic preforms

Sandwiches based on stampable foam core and face sheets offer potential for cost-effective applications. Since the formability of such sandwich structures mainly depends on the drapability of the face sheets, the deformation behaviour of several types of textile preforms was evaluated. Glass fibre fabric preforms in the form of plain weave, twill, crowfoot and eight-harness satin as well as warp and weft-knitted architectures were studied. The tensile properties of the dry fabrics at various orientations and the locking angle of woven fabrics in the bias direction were determined. An analytical model is proposed to relate the fabric parameters to the locking angle. Drapability tests were performed on several woven and knitted fabrics in order to relate the forming energy to the preform architecture. Due to their high drapability and low forming energy, warp-knitted structures were selected as textile reinforcement for the sandwich face sheets.     

Woven fabric permeability: From textile deformation to fluid flow mesoscale simulations

A two-step methodology is proposed in order to estimate from numerical simulations the permeability of deformed woven fabrics. Firstly, the shear deformation of a glass plain weave until the shear locking is studied from a mesoscale analysis achieved with a representative volume element (RVE) of the periodic plain weave. Simulations have been carried out within the scope of large transformations, accounting for yarn–yarn contacts, and assuming that yarns behave as hypoelastic materials with transverse isotropy. From the simulated deformed solid RVE, a complementary periodic fluid RVE is then built and the slow flow of an incompressible Newtonian fluid within it is investigated. This allows to compute, in a second step, the permeability of the deformed plain weave. The role of the shear deformation on the permeability of multi-layers or single layer preforms is discussed.     

The shear properties of woven carbon fabric

This paper presents experimental and theoretical studies of the shearing properties of carbon plain weave fabrics and prepregs. The shearing characteristics of these materials are determined by the use of a picture frame shear rig which is loaded by a mechanical test machine. The shear force/angle curves are presented for the experiments conducted with the various test materials. A proposed shear model based on previous research which idealizes the fabric yarns as beam elements is presented. Using fabric geometric and material parameters, the model predicts the initial slip region of the fabric, as well as the more dominant elastic deformation range. Comparisons of the experimental and theoretical results were conducted to validate the model. A discussion of the findings from the analysis is also given, with particular focus relating to the accuracy, limitations and advantages offered by such a model. Results indicated that the slip model gives modestly accurate predictions, whilst the elastic modulus model showed very good correlation with experimental data.     

Numerical prediction of in-plane permeability for multilayer woven fabrics with manufacture-induced deformation

A unit cell based Computational Fluid Dynamics model is presented for predicting permeability of multilayer fabric structures. In Liquid Composites Moulding processes, fabric lay-ups undergo significant manufacture-induced deformation, combining compression, shear, and inter-layer nesting. Starting from the configuration of un-deformed fabric, the deformation is simulated geometrically by accounting for self-imposed kinematic constraints of interweaving yarns. The geometrical modelling approach is implemented in the open-source software TexGen. The permeability tensor is retrieved from flow analysis in ANSYS/CFX, based on TexGen voxel models. Using only measured geometrical data for un-deformed fabrics, deformed plain weave fabric and twill weave fabric lay-ups were modelled and their permeability tensors predicted. Comparison with experimental data demonstrates the generally good accuracy of predictions derived from the proposed numerical method.     

Research on the Shear Behaviour of Plain Weave Prepreg at Lateral Compaction Stage

Abstract:  An investigation of the shear behaviour of plain weave prepreg at lateral compaction stage was undertaken by the picture-frame test. A unit cell of weave prepreg was modelled and three moments were assumed in the unit cell: (i) the moment of shear force that picture frame applies on the unit cell; (ii) the friction moment at crossover of yarns; and (iii) the compaction moment between the yarns. Through moment balance, a relationship between the load and the shear rate was deduced. A plain sheet shearing film resin model was established to obtain the friction moment at crossover. To get the compaction moment, a constitutive equation of a single prepreged yarn was deduced and a transverse viscosity coefficient equation was given. Moreover, through an equivalent cross-sectional area model, the lateral contact thickness between the yarns was obtained. The comparison between the experimental and theoretical results shows that the presented model can describe the shear behaviour of weave prepreg at lateral compaction stage well.     

An experimental study on the effect of tow variations on compressive characteristics of plain weave carbon/epoxy composites under compressions

The effect of tow deformation on the static and fatigue characteristics of fabric composites under compression was investigated by experimental approach. Sheared specimens made of plain weave carbon/epoxy prepregs were prepared using a picture frame rig and the shear angles were 0°, 16°, 26°, 34°, 46°. To verify the effect of the tow variations of the fabric composites on compressive characteristics, the unidirectional composite specimens composed of the same fibre and matrix system with the same stacking sequences as the fabric composites were prepared for comparison. The static compressive test results showed that the static compressive strength of sheared fabric specimens was lower than that of the unidirectional specimens with the same stacking angle. On the other hand, the fatigue test results showed that fatigue life of sheared fabric specimens was higher than that of the unidirectional specimens for mild shear deformation cases. It was proved that these results were fully affected by the tow deformation caused by the shear deformation of the fabric specimens. The compression–compression fatigue behaviours of sheared fabric specimens were verified by appropriate unit-cell models.     

Shear Plugging and Frictional Behaviour of Composites and Fabrics Under Quasi‐static Loading

Experimental studies are presented on the shear plugging and frictional behaviour of composites and fabrics under quasi‐static loading. The primary focus is on the effect of specimen thickness on quasi‐static shear plugging behaviour. In the present study, quasi‐static shear plugging and through‐the‐thickness frictional tests are carried out on three types of materials. The materials investigated are 2D plain weave E‐glass/epoxy, 2D plain weave T300 carbon/epoxy and 2D plain weave E‐glass fabric. Typical results on shear plugging strength and frictional behaviour are presented. Effect of specimen thickness on quasi‐static shear plugging behaviour is also investigated.     

预定型机织物剪切变形实验研究

在改进像框实验的基础上,对斜纹和缎纹预定型碳纤维织物的剪切性能进行了实验观察。研究发现,预定型机织物的剪切机制与织物剪切相似。根据实验结果,从定型剂的浓度和织物结构分析了预定型织物的剪切性能。随着定型剂浓度提高,织物的折皱角越大,织物剪切性能越差;与预定型斜纹织物相比,预定型缎纹织物相对较容易成型,剪切载荷较小。利用立式显微镜观察剪切过程中纱线宽度的变化,拟合得到了宽度变化方程,建立预定型机织物的折皱角模型,预测结果与实验结果误差在2°内,证明了该模型的有效性。     

Prediction of the elastic behaviour of hybrid and non-hybrid woven composites

A micromechanical model called MESOTEX is presented for prediction of the elastic behaviour of composites reinforced with non-hybrid weave (plain weave, satin weave and twill weave) and hybrid weave (hybrid plain weave and hybrid twill weave) fabrics. By using the classical thin laminate theory applied to each woven structure, this analytical model takes into account the strand undulations in the two directions and also integrates the geometrical and mechanical parameters of each constituent (resin, fill and warp strands). A representative volume is chosen for each woven composite and the fibre architecture is described by several functions. To determine the effectiveness of this analysis, the elastic properties predicted for each woven composite are compared with experimental results and results extracted from the literature. This correlation shows excellent agreement between measured and predicted values, with a very low calculation cost (CPU time of less than 0·01 s).     

Deformation of PBO/epoxy plain weave fabric laminae followed using Raman spectroscopy

Understanding of microscopic deformation behaviour of plain weave fabric lamina is essential in the analysis of the macroscopic mechanical properties of woven fabric composites. Many analytical models have been proposed to predict elastic properties of woven fabric laminae. The present paper is an attempt is made to fit experimental data obtained from the analysis of fibre deformation using Raman spectroscopy to the slice array model (SAM) to predict the local fibre strain distribution in the loading direction along the defined cell of a plain-weave lamina. Another model is proposed that combines the slice array and the off-axis (crimp) model and the experimental data are shown to fit this model rather better.     

Deformation and energy absorption of composite egg-box panels

Static compressive tests of composite egg-box panels, whose stacking sequences and number of plies were controlled, were carried out to investigate their deformation behaviour and energy absorption capacity. Silicon rubber moulds were first moulded from an aluminium egg-box panel template. These moulds were in turn used to fabricate composite specimens. Two fabric prepregs, carbon/epoxy plain weave fabric and glass/epoxy 4-harness satin weave were draped over the rubber mould with various stacking angles. The specimens were cured in an autoclave using vacuum bag degassing moulding and an appropriate cure cycle. The nominal stress–strain relations of the specimens were compared and multiply-interrupted compressive tests were used to identify fracture initiation and development. The energy absorption per unit mass of composite egg-box panels were compared with that of an aluminium egg-box panel. From the test results it was concluded that the compressive behaviour of the composite structure is affected by the local stacking sequence of the fabrics and by shear deformation during initial lay-up and draping. By considering the stress–stain behaviour, energy absorption and material cost, the optimal material and draping condition were proposed for a composite egg-box panel.     

Characterising the shear–tension coupling and wrinkling behaviour of woven engineering fabrics

Modelling the forming process for engineering fabrics and textile composites using a mechanical approach, such as the finite element method, requires characterisation of the material’s behaviour under large shear deformation. For woven engineering fabrics, a coupling between in-plane tension and both shear compliance and the onset of wrinkling is to be expected. This paper focuses on a novel testing technique, the biaxial bias extension test, as a means to investigate this shear–tension coupling and fabric wrinkling. Novel methods of determining the wrinkling behaviour are demonstrated. The main difficulty with the technique lies in extracting the material contribution to the recorded signal. To do this, an experimental method is proposed and demonstrated using a plain weave glass fabric. Biaxial bias extension test results are compared against picture frame and uniaxial bias extension results.     

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.     

Impact and post impact behavior of layer fabric composites

In this study, the effect of impact and post impact behavior of E-glass/epoxy composite plates having different layer fabrics were investigated by considering energy profile diagram and the related load–deflection curves. Different impact energies (5 J–60 J)were subjected to the plates consisting of eight layers of plain weave (1D), double (2D) and triple (3D) layer fabrics. The impact tests were continued until complete perforation of layer fabrics. The damage modes and damage processes of layer fabrics under varied impact energies were also discussed. At the end of the impact tests, the damaged samples were mounted into a compression apparatus to determine the Compression After Impact (CAI) strength of layer fabric samples. The results of these impact and post impact tests showed that contact force occurring between the impactor and the composite specimen increased and the CAI strength reduced by increasing the impact energy. The objective of this study was to determine the perforation threshold of E-glass/epoxy composite plates having different layer fabrics as plain weave (1D), double (2D), and triple (3D) layer fabrics.     

2.5D fabrics for delamination resistant composite structures

With the introduction of laminates into primary loaded structures, it has become apparent that the delamination failure mode has the potential for being the major life-limiting failure mechanism. Delamination resistance has previously been increased using a number of techniques, including interleafing, rubber-toughened resin systems and stitching. However, all the methods proposed to date have attendant disadvantages, severely limiting their use in practical applications. This paper presents a novel solution—a 2.5-dimensional (2.5D) fabric—which has none of the aforementioned problems. The fabric is manufactured by cutting a simple three-dimensional weave, consisting of two two-dimensional (2D) fabrics connected by interwoven pile threads, to form a ‘hairy’ fabric. These 2.5D fabrics are impregnated with epoxy resin in the normal way, laminated and cured in an autoclave. Results are presented here for Mode I double cantilever beam and Mode II end load split tests performed on the plain 2D glass fabric and the 2.5D fabrics with glass piles. The fabrics were tested in different orientations (0°, i.e., parallel to the pile fibre weave direction, 90° and 45°), and a variety of pile lengths and pile densities were investigated. The presence of the short piles in the matrix-rich region between laminate plies is shown to increase the fracture toughness of the 2.5D composite over the conventional 2D fabric composite by virtue of the energy-absorbing effect produced by the piles in a similar manner to that produced during fibre bridging.     

Friction and wear behaviour of Kevlar fabrics

Experimental results of a number of tribological tests carried out on aramid woven fabrics are presented in this paper. Kevlar Ht, Kevlar 29 and Kevlar 49 aramid plain fabrics were employed in this work. The friction and wear phenomena of the fabrics were investigated, considering both fabric-fabric and metal-fabric interaction. From the experimental data, the evolution of parameters such as static and dynamic friction coefficients, dissipated energy, volume loss of the material, wear rate, specific wear and wear strength were studied. Moreover, values of the static force needed to pull out a single fibre from the woven fabric were measured. All these data are important for the numerical modelling of impact on such materials. In fact, experimental findings on yarn failure mechanisms show that apart from tensile rupture, failure modes such as cutting, shearing and fibre degradation take place in fabrics subjected to the ballistic impact of low-and medium-calibre ammunition.     

用均匀化方法预报平纹织物的渗透率

建立了平纹织物的细观结构模型,采用均匀化方法预报了其渗透率,与文献中的实验结果比较验证了本文中方法的合理性,同时还对平纹织物纤维预制体细观结构进行了参数研究。对3种平纹玻璃布预制体进行了渗透率测量,与理论预报进行了比较,表明本文中所建立的方法预报的渗透率与实验结果在同一数量级。     

Micro-CT analysis of internal structure of sheared textile composite reinforcement

Simple shear is a deformation mechanism typical for a woven fabric during draping. The mesoscopic internal structure of the fabric differs between the non-deformed state and a sheared state. This paper presents an analysis of the internal structure of woven fabrics in a sheared state based on micro-CT (X-ray micro computed tomography) imaging of the internal structure of woven fabrics in a sheared state. Two methods for the analysis of the fabric geometry are used: automatic mapping of the local fibre directions based of the micro-CT image analysis and manual measurements of the yarns cross section shape, size and middle line coordinate of yarns on the micro-CT images. Changes of the fibre orientations within the yarns and of the yarn geometrical parameters in a carbon fibre twill woven fabric before and after shear deformation are quantified.