Elastic moduli and damage evolution of three-axis woven fabric composites

Three-axis orthogonal woven fabric composites composed of carbon fibres and epoxy resin have been fabricated. Examined from micrographs, the fabric weaving yarns were found to be very slender with aspect ratios ranging from 11–13.6. Based upon the observed geometry, the composite has been modelled by a unit cell comprising wavy yarns. Both elliptical and lenticular cross-sections were adopted to simulate the slender weaving yarns. Taking into account one-dimensional stress concentration and yarn undulation, an iso-phase approach has been developed to analyse the composite elastic moduli. A higher weaving yarn aspect ratio was found to result in a lower modulus. Modulus reduction due to yarn undulation was more significant in weaving directions. Material characterization has been conducted based upon monotonic tensile and three-point flexural tests, and detailed damage mechanisms for both loadings have been examined. The onset of damage under tensile loading was found to be z-axis yarn debonding, followed by debonding and splitting in y-axis yarns. When subjected to flexural loading, yarn debonding, transverse cracking, and interyarn matrix cracking were the dominant damage mechanisms which appeared on specimen tensile sides. Stress transfer among yarns and how it relates to the composite damage have been discussed in detail. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fibre damage in the manufacture of advanced three-dimensional woven composites

Fibre damage caused by the weaving of three-dimensional (3D) fabric preforms for advanced composite materials is investigated. A Jacquard loom was used to weave continuous fibreglass yarns into a 3D orthogonal woven fabric. Samples of warp and through-thickness yarns that form the 3D fabric were taken from the loom at different stages in the weaving process to examine for fibre damage and determine their residual tensile properties. It was discovered that the fibres are abraded against each other and the loom machinery during weaving, and the resulting abrasion damage and removal of sizing agent causes a reduction in yarn strength of between 30 and 50% depending on the type of yarn. Some fibres are also broken during weaving, and this causes a small reduction to the yarn stiffness and contributes to the large loss in yarn strength. The implication of these findings for the design of advanced 3D woven composites in structural applications is discussed.     

Three-scale modeling and numerical simulations of fabric materials

Based on the underlying structure of fabric materials, a three-scale model is developed to describe the mechanical behavior of fabric materials. The current model assumes that fabric materials take on an overall behavior of anisotropic membranes, thus the membrane-scale is taken as the macroscopic scale of the model. Since fabric materials exist only as thin structures and there is no corresponding bulk material having a similar constitutive property, the direct approach of the mechanics of surfaces is employed. Following the membrane-scale, a yarn-scale is introduced, in which yarns and their weaving structure are accounted for explicitly. Yarns are modeled as an extensible elasticae. A unit cell consisting of two overlapping yarns is used to formulate the weaving patterns and the interaction between the yarns, which governs the nonlinear constitutive behavior of fabric materials. The third scale, named fibril-scale, accounts for the fibrils constituting a yarn and incorporates their mechanical properties. Via a coupling (handshake) process between these three scales a couple model is introduced. The overall behavior and performance of various fabric products becomes predictable by the knowledge of the material properties of a single fibril and the weaving structure of the fabrics. In addition, potential damage during deformation is also captured in the current model through breakage of fibrils in the fibril-scale.     

双轴向衬纱纬编玄武岩纤维复合材料弯曲性能

经纬纱和针织纱分别选用不同线密度的高模高强玄武岩纤维, 以不同衬纱方式编织出机织针织复合(CWK)织物和多层双轴向纬编(MBWK)织物, 并以其作为增强体, 采用真空辅助树脂传递模塑工艺制备了玄武岩纤维/乙烯复合材料。对两种复合材料0°、 90°和45°方向的弯曲性能进行测试, 分析比较了弯曲应力-应变特征曲线及纱线强度。结果表明: 两种复合材料具有较好的弯曲性能, 0°和90°方向的弯曲性能均优于各自45°方向的, 弯曲应力-应变曲线均表现出一定的塑性破坏特征; MBWK织物增强复合材料0°和90°方向的弯曲性能又分别高于CWK织物增强复合材料0°和90°方向的弯曲性能; 复合材料中经纱和纬纱的屈曲程度不同, 致使MBWK织物增强复合材料的比模量和纱线强度均高于CWK织物增强复合材料, 两种复合材料的弯曲性能受不同衬纱方式的影响, 而两种复合材料试样的弯曲破坏形态相近。研究结果为双轴向衬纱纬编玄武岩纤维复合材料的应用提供了参考。     

Flexural behavior of three-axis woven carbon/carbon composites

This work examines the processing characteristics and flexural behavior of 3D woven carbon/carbon composites. Two types of the composites have been made, both having 3-axis orthogonal structures. The first combines solid rods along the axial direction. The rod, 1 mm in diameter, is composed of unidirectional carbon fibers and a phenolic resin. The second is a conventional type composed of carbon yarns in all axes. Both preforms were then impregnated by the phenolic resin. Matched molds were used to enhance fiber packing and to cure the resin under a hot press. The green composites were then heat-treated at various temperatures ranging from 200° through 1000° C. The second set of specimens was made by applying multi-cycle impregnation and carbonization. Flexural tests were carried out for these two sets of specimens. Their responses to the load and the induced damage behavior have been examined. The use of rods enhances fiber packing and reduces fiber crimp, leading to higher material performance. Decomposition of the resin due to the heat-treatment results in weak interfacial bonding and compressive failure in axial yarns. The efficiency of densification has been examined. The induced damage configurations vary significantly in these specimens, as a result of the processing. Some unique modes associated with the 3D structure are discussed.     

Ballistic impact behaviour of woven fabric composites: Formulation

Resistance to high velocity impact is an important requirement for high performance structural materials. Even though, polymer matrix composites are characterized by high specific stiffness and high specific strength, they are susceptible to impact loading. For the effective use of such materials in structural applications, their behaviour under high velocity impact should be clearly understood. In the present study, investigations on the ballistic impact behaviour of two-dimensional woven fabric composites have been presented. Ballistic impact is generally a low-mass high velocity impact caused by a propelling source. The analytical method presented is based on wave theory. Different damage and energy absorbing mechanisms during ballistic impact have been identified. These are: cone formation on the back face of the target, tension in primary yarns, deformation of secondary yarns, delamination, matrix cracking, shear plugging and friction during penetration. Analytical formulation has been presented for each energy absorbing mechanism. Energy absorbed during each time interval and the corresponding reduction in velocity of the projectile has been determined. The solution is based on the target material properties at high strain rate and the geometry and the projectile parameters. Using the analytical formulation, ballistic limit, contact duration at ballistic limit, surface radius of the cone formed and the radius of the damaged zone have been predicted for typical woven fabric composites. The analytical predictions have been compared with the experimental results. A good correlation has been observed.     

Characterisation of polylactic acid biocomposites made from prepregs composed of woven polylactic acid/hemp–Lyocell hybrid yarn fabrics

This paper describes the mechanical properties and water absorption characteristics for biocomposites made from woven PLA/hemp/Lyocell prepregs. The aim was to improve the properties with the addition of Lyocell fibre into a hybrid yarn. Well-aligned hybrid yarns composed of hemp/PLA, hemp–Lyocell/PLA, respective, Lyocell/PLA were made by wrap spinning. Unidirectional satin fabrics were made by weaving with PLA (warp) and the hybrid yarns (weft). Uniaxial composites were fabricated with 30 fibre mass% using compression moulding. The composites were investigated for tensile, flexural and impact properties. Combining hemp with Lyocell in a PLA matrix improves the mechanical properties, compared to hemp/PLA composites. The composite made from the satin Lyocell/PLA fabric gave the best mechanical properties. The type of fibre reinforcement compositions did not significantly affect the water absorption of the biocomposites. Scanning electron microscopy showed that fibre pull-outs appear more often in hemp/PLA composites than in composites also including Lyocell fibre.     

Effect of weaving processes on compressive behavior of 3D woven composites

This work is an attempt to examine the effect of weaving process on the compressive failure behavior of 3D carbon/epoxy composites. Three weaving processes were designed and studied: unidirectional, bi-directional, and symmetric weaving. They result in 3D fabrics with the same three-axis, orthogonal yarn structure in the interior but with different interlacing patterns on surface. To manifest the influence of the transverse yarns, a unidirectional composite with the same axial fiber content and a monolithic epoxy material are also tested. Resin transfer molding was employed to impregnate and consolidate the fabrics. Since the specimens are relatively thick, an end-supported, end-loaded fixture was used to apply the compressive load. The strength was measured and the induced damage was examined. The symmetric weaving results in composites with the least fiber undulation in axial yarns. Two prevailing failure modes of different dimensional scales were observed in the materials. One is the microscopic fracture band, consisting of fiber kink-bands in axial yarns and matrix cracks in the transverse yarns. The other is the miniscopic fracture band, consisting of the fracture of yarns in all three directions. The microscopic bands are intensive but less detrimental, while the miniscopic fracture band is more crucial and is responsible for the major drop in load. The onset and growth of these modes are discussed, and how these modes relate to the interlacing loops on surface is also examined.     

Electrical and impact properties of the hybrid knitted inlaid fabric reinforced polypropylene composites

A range of conductive knitted fabric reinforced polypropylene composites have been developed and their electromagnetic shielding effectiveness (EMSE), electrostatic discharge (ESD) and impact properties have been investigated. Carbon and aramid fibers are used as the reinforcement phase in the composites, while copper and stainless steel wires are incorporated as conductive fillers to provide the ESD and EMSE properties of the composite materials. The hollow spindle spinning system has been used to make SS/PP, Cu/PP, SS/C/PP, Cu/C/PP and Cu/K/PP uncommingled yarns. The double plain knitted fabric and its inlaid fabrics were fabricated from the yarns using a 5G traverse knitted machine. Changing the yarn composition, fabric knit structure, and stitch density varies the amount of copper and stainless steel conductive fillers in the composites. 4 layer cross-ply laminates were laid-up by hand, then formed into 3-mm thick conductive thermoplastic composites using a compression molding. It was observed that the EMSE and ESD of the composites increase with increasing the incident frequency, especially at higher frequency range. The effects of inlaid ends, materials and yarn constitutions on the EMSE of the conductive thermoplastic composites were investigated. The results indicate that the composites can be used for the purpose of electromagnetic shielding and ESD attenuation, as well as for some microwave applications.     

Evaluation of electromagnetic shielding effectiveness of multi-axial fabrics and their reinforced PES composites

The usage of electrical and electronic equipments has been increasing in daily life, which has a potential hazardous impact on humans and other living organisms. In this paper, multi-axial fabrics containing steel yarns and carbon filaments, and their polyester (PES) resin-reinforced composites have been prepared for electromagnetic shielding applications. The electromagnetic shielding effectiveness (EMSE) of these structures was determined by using coaxial transmission line measurement technique. There were eight different multi-axial fabrics constructed. It was observed that the amount and the orientation of carbon and stainless steel yarns influenced the EMSE performances of multi-axial fabrics and their reinforced PES composites. The structures containing both carbon filaments and stainless steel yarns exhibited better EMSE than the ones including only one type of conductive yarns or filaments. Also, the EMSE performance of multi-axial fabrics was found better than their reinforced composites. The best EMSE results were obtained for the fabric, including two layers of yarns (steel and carbon) on top of each other in the centre with the angle of 45 and ?45°.     

Multiscale modeling of the impact of textile fabrics based on hybrid element analysis

In this work, a multi scale modeling approach has been developed to simulate the impact of woven fabrics using a finite element (FE) analysis. A yarn level of resolution is used in the model. This approach, referred to as the hybrid element analysis (HEA) is based on decreasing the complexity of the finite element model with distance away from the impact zone based on the multiscale nature of the fabric architecture and the physics of the impact event. Solid elements are used to discretize the yarns around the impact region, which transition to shell elements in the surrounding region. A new method for modeling the shell yarns is incorporated that more accurately represents the contours of the yarn cross section. Impedances have been matched across the solid–shell interface to prevent interfacial reflections of the longitudinal strain wave. The HEA method is validated by first applying it to the FE model of a single yarn for which an analytical solution is known. The HEA method is then applied to a woven fabric model and validated by comparing it against a baseline model consisting of yarns discretized using only solid elements.     

Impact response of woven composites with small weaving angles

This paper presents experimental investigations on impact response of woven composites with various weaving angles between interlacing yarns. A method for preparing novel woven composites with small weaving angles is presented. The effects of the weaving angle on the impact characteristics such as peak force, contact duration, maximum deflection and absorbed energy are also examined. An energy profiling method seems to be useful for identifying the penetration and perforation thresholds of the woven composites. The damage process of individual woven composites can be reconstructed from comparing the corresponding load–deflection curves, energy profile and images of damaged specimens. The study concludes that the energy absorption capability and perforation threshold of woven composites can be significantly improved by using a small weaving angle between interlacing yarns. For example, the perforation threshold of [0/20]₄ woven composite, which has a weaving angle of 20° between interlacing yarns, is about 40% higher than that of [0/90]₄ woven composite, which has a weaving angle of 90° between interlacing yarns. The higher energy absorption capability of [0/20]₄ over [0/90]₄ is attributed to a lower stiffness caused by a more polarized fiber orientation and a smaller fiber crimp, resulting in a larger maximum deflection, a more extended damage zone and a larger amount of fiber pullout.     

Effect of weaving damage on the tensile properties of three-dimensional woven composites

This research paper examines the damage mechanisms and reductions to the tensile properties of E-glass yarns during weaving of three-dimensional (3D) fabrics for polymer-based composites. The paper also assesses the influence of weaving damage to load-bearing glass yarns on the tensile properties of 3D orthogonal woven composites. It is found that damage occurs to yarns at most stages of the 3D weaving process due to abrasion and breakage caused when sliding against the loom machinery. The abrasion damage causes a large reduction (30%) to the tensile strength of the dry woven yarns, although the tensile stiffness remains unaffected. The damage and reduction to the tensile properties of the dry yarns at different weaving stages are described. Tensile studies performed on single yarn/resin composites and larger coupons of 3D orthogonal woven composites reveal that weaving damage is responsible for a significant reduction to the tensile strength.     

Analytical study of strength and failure behaviour of plain weave fabric composites made of twisted yarns

A two-dimensional analytical method is presented for the failure behaviour of plain weave fabric composites made of twisted yarns. The studies have been carried out on laminates with different configurations under on-axis uni-axial tensile loading. The cross-sectional area of the yarn was taken to be elliptical and the yarn path was taken to be sinusoidal. Different stages of failure are considered in the analysis. It has been observed that there is no significant reduction in tensile strength properties of plain weave fabric composites as a result of twisting of yarns. For E-glass yarns, twisting of yarns up to 5°, can facilitate ease of fabrication without significantly compromising the strength properties of the woven fabric composites.     

不同针织结构经编碳纤维复合材料弯曲性能

通过对3种不同针织方式碳纤维经编织物结构的分析和弯曲性能测试, 研究了织物针织方式对NCFs复合材料力学性能的影响。采用链式缝编的 织物与经平缝编的 织物相比, 束缚效果更好, 经编线引起的纤维变形区的宽度较小, 因此 织物增强的复合材料中的富树脂区和空洞相对较少, 弯曲强度和模量均高于 复合材料。单向经编织物也采用经平缝编, 纤维取向与双轴向织物相比更准确, 由于缝编引起的纤维变形和损伤较少, 复合材料的弯曲性能高于两种双轴向经编材料。      

Engineering Design and Mechanical Property Characterisation of 3D Warp Interlock Woven Fabrics

3D warp interlock fabrics have been used both in composite materials as fibrous reinforcement as well as in protective solutions against impact mainly due to their improved capacity to absorb energy by higher intra-ply resistance to delamination. However, depending on the type of architecture used, the binding warp yarns may provide different types of mechanical behaviour. By the same, the choice of the yarn raw material coupled with the suited 3D warp interlock architecture is still a challenge to solve due to the lack of knowledge on the optimized fabric parameters to be chosen. Thus, to fill this gap, we have designed, produced on same dobby loom and tested different types of 3D warp interlock architectures (O-T 4 3–4 Basket 3–3 and A-T 4 5–4 Twill 6) with different types of raw material (E-glass EC9 900 Tex, para-aramid 336 Tex and flax Tex 500 yarns). Thanks to these tests, it has been highlighted different mechanical behaviours of 3D warp interlock fabrics with the same weave pattern but with different types of yarns (E-glass, flax and para-aramid) both in the warp and weft directions. It has been also revealed that the warp shrinkage of warp yarns inside the woven structure has a major influence on the whole fabric behaviour.     

Three dimensional (3D) fabrics as reinforcements for cement-based composites

This research studied the flexural behavior of cement-based elements reinforced with 3D fabrics. The effects of the through-thickness (Z direction) yarns were examined in terms of four parameters: (i) yarn properties, (ii) varying the composite content of (i.e., coverage by) high-performance aramid yarn, (iii) treatment of the fabric with epoxy, and (iv) 2D and 3D fabric composites were compared. Overall, the 3D fabric composites performed better than the 2D fabric composites, which tended to delaminate. Our results indicate that even though the Z yarns are not oriented in the direction of the applied loads, 3D fabrics still have potential applications as reinforcements for cement-based composites. Indeed, the Z yarns hold the entire fabric together, which leads to improved mechanical anchoring and mechanical properties particularly when the fabric has been treated with epoxy, i.e., to create a stiff reinforcing unit.     

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.     

Highly aligned flax/polypropylene nonwoven preforms for thermoplastic composites

A major challenge for natural fibre composites is to achieve high mechanical performance at a competitive price. Composites constructed from unidirectional yarns and woven fabrics are known to perform significantly better than composites made from random nonwoven mats, but unidirectional yarns and fabrics are much more expensive to manufacture than random nonwoven mats. Here, we report on highly aligned natural fibre nonwoven mats that can be used as a replacement for unidirectional woven fabrics. A drawing operation is added to the conventional nonwoven process to improve fibre alignment in the nonwoven preforms and the final composites. The modified nonwoven manufacturing process is much simpler and cheaper than the unidirectional woven fabric process because of the elimination of expensive spinning and weaving operations. The composites fabricated from the highly aligned nonwoven mats showed similar mechanical strength as the composites made from unidirectional woven fabrics.