Shear deformation and micromechanics of woven fabrics

This paper includes an experimental study and a mathematical analysis of the shear deformation of woven fabrics by using picture-frame type shear testing. Four types of weaves were tested and compared: a loose plain weave, a tight plain weave, a twill and a satin weave. The locking shear angle was determined both in picture-frame tests and manual shear tests. The experimental data presented for each fabric include curves of shear load–shear stress as a function of either the shear angle or the shear rate, and measured locking shear angles. The shear deformation data were analysed by following elasticity principles and taking into account the effects of fibre inextensibility. A microstructural analysis was carried out in all four fabrics to investigate the shear locking on the basis of a geometrical approach and the maximum packing fibre fraction.     

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.     

Compression modeling of plain weave textile fabric using finite elements

Textile composite are used extensively in aerospace as they offer a 3D reinforcement in a single layer providing better mechanical properties in both in‐plane and transverse directions. This paper reports on the mechanical behavior of a plain weave textile fabric under the compressive loading. Unit cell geometry of the plain weave fabric structure is identified and its model is created using TexGen geometric modeling scheme developed by the University of Nottingham (U.K.). Later on its mechanical behavior is predicted using finite element modeling (FEM) based simulation software ABAQUS^® incorporating a transversely isotropic material law. Strain energy of the developed model has been compared with that of the published results and shows very good agreement. The analysis indicated that transverse‐longitudinal shear (TLS) modulus plays an important role in characterizing the behavior of the woven fabric under compression, while the friction between the yarns and longitudinal stiffness has less significant influence on compaction behavior. In order to ascertain the effectiveness of the developed model, exhaustive parametric studies have also been conducted to investigate the effect of transverse‐longitudinal shear modulus on some of the important parameters such as artificial strain energy, external work, frictional dissipation, internal energy, kinetic energy, strain energy and total energy of the model. The developed model has the capacity to predict and simulate the behavior of variety of fabric architectures based on their constituent yarn properties under various regimes of service loads.     

碳纤维复合材料超声振动辅助RTM工艺的浸润特性

研究了织物类型、纤维体积分数和超声振动对树脂在碳纤维织物中流动特性的影响规律,设计了超声振动辅助RTM工艺过程中单向渗透率测量装置,开展了16组渗透率测试实验,并结合COMSOL软件仿真分析了织物中的树脂流动特性。研究表明,在相同纤维体积分数水平下,斜纹编织物的纤维束间隙通道比平纹织物的更宽,2/2斜纹编织织物渗透率比平纹织物提高了约21.5%。纤维体积分数与织物渗透率呈负相关,其函数关系与半经验公式Kozeny-Carman(KC)方程吻合较好。树脂流动过程中加入超声振动,其超声空化效应、加速度效应和微射流效应作用于纤维丝束表面,提高了织物渗透率约58.2%。有限元仿真模拟了椭圆形和近矩形纤维束截面设计的织物模型的流动过程,结果发现近矩形纤维束截面高流速区域范围更广,流体向纤维布夹层浸渍的速度分量更大。超声作用于织物纤维可能带动纤维丝束蠕动,使纤维束截面趋于近矩形状,从而提高了树脂对纤维织物的浸润性。上述研究结果对优化碳纤维复合材料成型工艺和成型性能具有一定的指导意义。      

In-plane permeability characterization of a unidirectional flax/paper reinforcement for liquid composite molding processes

Principal in-plane permeabilities of a unidirectional flax/paper reinforcement are characterized in terms of reinforcement material and manufacturing parameters at a constant fiber volume fraction (V_f). ANOVA result shows that surface density of the unidirectional flax layer is the most important parameter on the mean and variance of the K₁ permeability. On the other hand all four studied parameters are concluded to affect the K₂ permeability. The K₁ permeability is found close to that of a twill weave flax fiber fabric reported in the literature and only one order of magnitude lower than a plain weave glass fiber fabric. Impregnation of the reinforcement with epoxy resin shows that a large area of the molded plaques was dominated by capillary forces during resin injection. This means capillary number and subsequently the resin injection velocity should be optimized for reducing void content in the final composite.     

Weft Yarn Interlacement Modelling for 3D Profiled Structures

Applied Composite Materials - Currently, generation of 3D woven T-joint models with complex weave geometries, using TexGen software, is a manual process. One of the main challenges to automatic...     

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.     

平面编织复合材料层板弹性性能的预测

本文在平面编织纤维增强树脂复合材料的单方向直波纹模型的基础上,分别采用经典层合板理论和有限元应变能等效方法,预测了平面编织复合材料层合板迭层对其弹性性能的影响。根据经典层合板理论,由对平面织物复合材料的单向直纹模型的上、下表面施加不同的约束条件,得出层板弹性常数变化范围。用有限元能量法,则预测出不同铺层数的编织复合材料层板的弹性性能。与实验结果比较,表明纵向模量的预测是可靠的。     

Experimental determination of the permeability of engineering textiles: Benchmark II

In this second international permeability benchmark, the in-plane permeability values of a carbon fabric were studied by twelve research groups worldwide. One participant also investigated the deformation of the tested carbon fabric. The aim of this work was to obtain comparable results in order to make a step toward standardization of permeability measurements. Unidirectional injections were thus conducted to determine the unsaturated in-plane permeability tensor of the fabric. Procedures used by participants were specified in the guidelines defined for this benchmark. Participants were asked to use the same values for parameters such as fiber volume fraction, injection pressure and fluid viscosity to minimize sources of scatter. The comparison of the results from each participant was encouraging. The scatter between data obtained while respecting the guidelines was below 25%. However, a higher dispersion was observed when some parameters differed from the recommendations of this exercise.     

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.     

Three-dimensional viscoelastic simulation of woven composite substrates for multilayer circuit boards

Viscoelastic properties of woven composite substrates are essential to design dimensionally stable multilayer printed circuit boards. Unlike most existing numerical work which rely on simplified constitutive (elastic) and geometrical models, this study involves a fully three-dimensional viscoelastic model of a plain weave composite with accurate characterization of the woven geometry. Comparisons between numerical predictions and experimental data clearly indicate that the creep compliance of the composite depends not only on the relaxation of the matrix, but also on the time-dependent flexural deformations of the woven fabric bundles. Predictions of the inhomogeneous deformation fields over the repeating cell agree with experimental observations.     

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.     

Sublaminate-based lamination theory and symmetry properties of textile composite laminates

Textile composites have distinct mechanical characteristics different from those of unidirectional composites. Several common weave patterns, 5-harness or 8-harness satin weaves, for example, lack certain symmetry properties common to composites composed of unidirectional layers. The lack of symmetry of woven fabric composites can be drastically reduced, but not totally eliminated, if a laminate consists of one or more flipped pairs, each with one normal layer placed symmetrically about the laminate mid-plane to the flipped layer. To explore more possible combinations in a more general way, a systematic approach is presented by considering a single fabric layer as a sublaminate characterized by a set of stiffness parameters. Mechanical properties of laminates constructed from such sublaminates are obtained by combining the sublaminate stiffness matrices and force and moment resultants. The effects of operations like 90° rotation, flipping, mirroring and their combinations on a sublaminate are discussed. The symmetry properties of weave patterns are classified based on the type of operation necessary for the patterns to be equivalent before and after the operation. The classification of fabric patterns and their coupling coefficients of plate stiffness matrices are found to be dependent on the distribution of crimped regions, or more specifically, the skewness of that distribution. Techniques for achieving symmetry and balance by constructing laminates from flipped and/or rotated pairs are then discussed and found to be, to a certain extent, dependent on the type of equivalence of the weave pattern. It is shown in this study that perfect symmetry cannot be achieved for weave patterns, such as 8-harness satin weaves, with only rotation-flip equivalence. Perfect symmetry and balance can be achieved using as few as four layers, within cell alignment errors, for weave patterns with only mirror-rotation equivalence, like 5-harness satin weaves.     

Effect of fabric compaction and yarn waviness on 3D woven composite compressive properties

3D-woven fabrics incorporate through-thickness reinforcement and can exhibit remarkable inter-laminar properties that aid damage suppression and delay crack propagation. However, distortions in the internal architecture such as yarn waviness can reduce in-plane properties, especially in compression. The degree of yarn waviness present in a 3D woven fabric can be affected by a range of factors including weave parameters and manufacturing-induced distortions such as fabric compaction. This paper presents a thorough analysis of the effect of fabric compaction and yarn waviness on the mechanical properties and failure mechanisms of an angel-interlock fabric in compression. Tests were conducted on coupons moulded to different volume fractions and data compared to previous measurements of local yarn angle. Major findings show the importance of yarn straightness on compressive strength and how this can be affected by optimising moulding thickness. Failure initiation was also found to be heavily influenced by weave style and yarn interlacing.     

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.     

A continuum shell finite element model for impact simulation of woven fabrics

A new computational approach is developed to predict the impact behaviour of fabric panels based on the detailed response of the smallest repeating unit (unit cell) in the fabric. The unit cell is constructed and calibrated using measured geometrical (weave architecture, crimp, voids, etc.) and mechanical properties of the fabric. A pre-processor is developed to create a 3D finite element mesh of the unit cell using the measured fabric cross-sectional micro-images. To render an efficient method for simulation of multi-layer packs, these unit cells are replaced with orthotropic shell elements that have similar macroscopic (smeared) mechanical properties as the unit cell. The aim is to capture the essence of the response of a unit cell in a single representative shell element, which would replace the more complicated and numerically costly 3D solid model of the yarns in a crossover. The 3D finite element analysis of the unit cell is used to provide a baseline mechanical response for calibrating the constitutive model in the equivalent shell representation. This shell element takes advantage of a simple physics-based analytical relationship to predict the behaviour of the fabric's warp and weft yarns under general applied displacements in these directions. The analytical model is implemented in the commercial explicit finite element code, LS-DYNA, as a user material routine (UMAT) for shell elements. Layers of fabric constructed from these specialized elements are stacked together to create fabric targets that are then analysed under projectile impact. This approach provides an efficient numerical model for the dynamic analysis of multi-layer fabric structures while taking into account several geometrical and material attributes of the yarns and the fabric.     

Hybrid composites made of carbon and glass woven fabrics under quasi-static loading

Experimental studies are presented on in-plane mechanical properties for two types of hybrid composites made using 8H satin weave T300 carbon fabrics and plain weave E-glass fabrics with epoxy resin. Results are also presented for 8H satin weave T300 carbon/epoxy and plain weave E-glass/epoxy. Studies are carried out under both tensile and compressive in-plane quasi-static loading. It is observed that for hybrid composites, placing glass fabric layers in the exterior and carbon fabric layers in the interior gives higher tensile strength and ultimate tensile strain than placing carbon fabric layers in the exterior and glass fabric layers in the interior. Quantitative data is given for different mechanical properties.     

Characterization of thermoplastic natural fibre composites made from woven hybrid yarn prepregs with different weave pattern

This paper focuses on the effect of weave structure on mechanical behaviour and moisture absorption of the PLA/hemp woven fabric composites made by compression moulding. The unidirectional woven fabric prepregs were made from PLA (warp) and PLA/hemp wrapped-spun hybrid yarn (weft) with two different weave patterns; 8-harness satin and basket. Unidirectional composites with 30 mass% hemp content were fabricated from these prepregs, and compared to winded PLA/hemp hybrid yarn laminates with same composition. The composite from the satin fabric had significantly lowest porosities and best mechanical properties compared to the composite made from the winded hybrid yarn and basket fabric. The tensile, flexural, and impact strength were 88 MPa, 113.64 MPa, and 24.24 kJ/m², respectively. The effect of weave pattern on water absorption is significant. Although the composite from hybrid yarn laminate has larger water absorption than that of the pure PLA, it exhibits lower moisture absorption than both weaves.     

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。     

Compression of thermosetting fabric materials

Thermoset fabric prepregs are available commercially in a number of weaves and are occasionally stitched. A study has been made of the deformation of these materials subjected to compressive forces normal to the plane of the fabric. The effects of change of scale, stitching, temperature, viscosity and weave have been investigated. From the experiments two significant features that may influence the processing and manufacture of parts formed from these materials were observed. The first was the percolation of the low viscosity resin through the fibres and the second was the substantial elastic recovery on removal of the load. In some cases this recovery was as much as fifty percent of the initial compression. In many manufacturing processes, the material undergoes various degrees of compression and the large elastic modulus observed in some of these mats is a potential source of distortion and of residual stresses after curing.