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.     

织物形式对苎麻纤维渗透率及其复合材料力学性能的影响

采用树脂传递模塑工艺(RTM)研究了三种典型苎麻纤维织物结构(平纹、 斜纹和缎纹)对树脂流动性的影响, 并研究了三种苎麻纤维织物结构对其增强酚醛树脂复合材料的拉伸性能和层间剪切性能的影响。结果表明, 苎麻纤维织物树脂渗透率主要受纤维屈曲和流道面积的影响。斜纹和缎纹苎麻织物的纤维屈曲较小且流道面积较大, 其织物的树脂渗透率较大, 同时, 较小的纤维屈曲使其增强的复合材料拉伸性能也较优。然而, 不同织物形式对苎麻纤维织物/树脂复合材料的层间性能影响不大。     

Characterization of a novel natural cellulose fabric from Manicaria saccifera palm as possible reinforcement of composite materials

Identifying novel natural fibers/fabrics with proper properties as reinforcement material is a new challenge in the field of bio-composites. Hence, the aim of this paper is to study the possibility of using a natural fabric extracted from Manicaria saccifera palm as a novel reinforcement in composites. This fabric was extensively characterized by chemical composition analysis, infrared spectroscopy (FTIR) analysis, morphological studies (SEM), thermo-gravimetric analysis (TGA) and physical /mechanical properties studies. From SEM analysis it was identified globular protrusions spread uniformly over the fiber which could help the mechanical interlock with the resin. As well, Manicaria fabric showed good thermal stability, low density, low moisture content and good tensile properties. Further, their properties are comparable to most natural cellulose fabrics and some synthetic fabrics, such as fiber glass fabrics. Manciaria saccifera fabric showed to be a suitable candidate as natural reinforcement material for the development of bio- composite.     

Reinforcement of cementitious matrices by warp knitted fabrics

The efficiency of knitted fabrics for reinforcing cementitious composites was studied. Weft insertion warp kiitting fabrics of controlled structure were especially produced for this work consisting of high modulus (Kevlar and Polyethylene) and low modulus (Polypropylene) polymers. The performance of the fabrics was studied by evaluating the flexural properties of the composites and the bond to the matrix. The performance of the knitted fabrics was compared to that of the straight yarns from which the knitted fabrics were made, as well as comparison with woven fabric reinforcement. It was concluded that: (i) in the knitted fabric reinforcement greater efficiency was achieved in fabrics consisting of high modulus polymer yarns, which are made of bundles consising of a smaller number of filaments, (ii) the reinforcing effect of the knitted fabric is smaller than that of the individual straight yarns, (iii) the reinforcing efficiency of woven fabric reinforcement is better than that of the knitted fabric, due to the crimped structure of the yarns in the woven fabric. In view of these conclusions, it might be stated that the use of weft insertion warp knitting fabric for cement reinforcement is advantageous in the sense that the fabric can provide the means by which a composite can be produced with continuous and aligned yarns. However, with this kind of fabric some of the reinforcing efficiency of the individual yarns is lost. In contrast, the use of woven fabric can provide all of the above, with the added advantage of enhanced reinforcing efficiency over the straight yarns, induced by their crimping in the woven fabric.     

The mechanical properties of non-crimped fabric-based composites

The mechanical properties of composites prepared from two types of non-crimped fabric (NCF), namely biaxial, ±45° and quadriaxial with a 0°, ±45°, 90°, −45° ply sequence, are examined as a function of fabric weight and compared with those of alternative composite forms. In general, the properties of NCF laminates decrease slightly as the areal weight of the fabric increases. Laminates produced from biaxial fabrics exhibit superior properties for a given volume fraction of reinforcement than do laminates produced using woven rovings or continuous fibre prepregs, while quadriaxial NCF laminates have equivalent properties to woven roving laminates at certain orientations but, unlike woven roving laminates, retain their properties when rotated through 45°. Biaxial NCFS loaded at 45° to the fibre and quadriaxial fabrics produce composites with superior properties to those predicted using finite element and laminate analysis for idealized laminates based on the same materials.     

Numerical and experimental investigations into ballistic performance of hybrid fabric panels

Strong, low density fibres have been favoured materials for ballistic protection, but the choice of fibres is limited for making body armour that is both protective and lightweight. In addition to developments of improved fibres, alternative approaches are required for creating more protective and lighter body armour. This paper reports on a study on hybrid fabric panels for ballistic protection. The Finite Element (FE) method was used to predict the response of different layers of fabric in a twelve-layer fabric model upon impact. It was found that the front layers of fabric are more likely to be broken in shear, and the rear layers of fabric tend to fail in tension. This suggested that using shear resistant materials for the front layer and tensile resistant materials for the rear layer may improve the ballistic performance of fabric panels. Two types of structure, ultra-high-molecular-weight polyethylene (UHMWPE) woven and unidirectional (UD) materials, were analyzed for their failure mode and response upon ballistic impact by using both FE and experimental methods. It was found that woven structures exhibit better shear resistance and UD structures gives better tensile resistance and wider transverse deflection upon ballistic impact. Two types of hybrid ballistic panels were designed from the fabrics. The experimental results showed that placing woven fabrics close to the impact face and UD material as the rear layers led to better ballistic performance than the panel constructed in the reverse sequence. It has also been found that the optimum ratio of woven to UD materials in the hybrid ballistic panel was 1:3. The improvement in ballistic protection of the hybrid fabric panels allows less material to be used, leading to lighter weight body armour.     

Modelling and simulation of earthquake resistant 3D woven textile structural concrete composites

Concrete is a composite material composed of water, sand, coarse granular material called aggregate and cement that fills the space among the aggregate particles and glues them together. Conventional building structures are made up of steel skeleton with concrete impregnation. These are very heavy weight structures with steel vulnerable to corrosion. The conventional concrete structures tend to undergo large deformations in the event of a strong earthquake. Mechanical simulation of various textile structural concretes is carried out successfully for their ductility behaviour. 3D woven reinforced concretes display superior ductile character showing ray of hope to develop seismic resistant building. Simulation of three 3D woven fabrics and their composites was carried to predict ductility and strengths of fabric reinforced concrete structures. Maximum deformation was observed for beam reinforced with orthogonal interlock fabric under the same load and minimum deformation was observed for plain concrete. Maximum equivalent stress was observed to be highest for plain concrete followed by beam reinforced with angle interlock fabric followed by orthogonal fabric and warp interlock fabric under similar loading conditions. From the results it was clear that 3D fabric reinforced structures are more ductile than the traditional steel reinforced structures. Hence 3D fabric reinforced concrete structures are much better in strength and ductility as compared to conventional construction materials. Among the three 3D fabric, orthogonal fabric reinforced composites are most ductile and are also less stiff. They can deform more than the other two fabric composites. Hence, orthogonal fabric reinforced composites can undergo higher deformations without collapsing. These composites can be more elastic under earthquake shaking.     

管道修复用涤纶-苎麻复合机织物性能试验

针对传统管道内衬修复材料施工中易出现内壁塌陷等问题,结合目前快速发展的绿色纤维复合材料,提出在涤纶机织物内衬材料中加入苎麻纱线,制作涤纶-苎麻复合机织物材料来提高树脂对管道修复用内衬机织物的浸透性能,增强内衬材料和管壁的粘结性能。以纤维外观、抽拔实验后纤维断面形貌的电镜观察,并通过树脂与织物接触角的测试、粘结实验,综合分析了涤-麻复合机织物的树脂浸透性,同时对涤纶-苎麻复合机织物力学性能进行测试来保障内衬复合材料满足强度的要求。实验结果表明,采用上述涤-麻复合织造的方法,可以显著提高树脂的浸透性能,有利于携带更多的树脂粘结剂提高树脂与管壁的粘结性,减少塌陷发生的可能性。同时加入麻复合的机织物,拉伸顶破性能都满足高压燃气管道的修复要求。     

In-plane permeability of sheared fabrics

Shear is the main mode of deformation in the draping of fabrics over complex mould geometries in composites manufacturing. Hence, the measurement and prediction of the in-plane permeability of sheared fabrics is a crucial task for the design of resin transfer moulding and other composites processing techniques of complex shaped articles. A mathematical model has been developed and applied to predict the in-plane permeability in the two principal directions and the angle of the flow ellipse for sheared assemblies of bi-directional woven fabrics that are in-plane isotropic to flow when unsheared. Modelling was accompanied by in-plane permeability measurements for unsheared and sheared woven fabric assemblies, and a comparison of this experimental permeability data with the proposed model proved encouraging. A study into the change of the areal density of different woven fabrics with shear angle has also been included.     

Modelling of moisture diffusion in multilayer woven fabric composites

Advanced woven fibre reinforced composites have wide applications in industries. However, the mechanical performance of this kind of composites is significantly affected by the moisture absorption of the polymer matrix. This paper presents a numerical investigation on the moisture diffusion taking place in multilayer woven fabric composites. The transient diffusion process of moisture is examined based on the repeating Representative Unit Cell (RUC) of woven fabrics. Using finite element analysis methods, the microscopic heterogeneity of RUC is described in terms of the tow size, tow cross-section shape and tow weaving configuration of fabrics. The model is then applied to simulate the moisture diffusion within the composites of varied number of plies. Finally, by using a data fitting function for the modelling results, a simple predicting model for moisture saturation time with the increase of the number of plies is proposed for the purpose of practical applications.     

Basalt woven fiber reinforced vinylester composites: Flexural and electrical properties

A preliminary comparative study of basalt and E-glass woven fabric reinforced composites was performed. The fabrics were characterized by the same weave pattern and the laminates tested by the same fiber volume fraction. Results of the flexural and interlaminar characterization are reported. Basalt fiber composites showed higher flexural modulus and apparent interlaminar shear strength (ILSS) in comparison with E-glass ones but also a lower flexural strength and similar electrical properties. With this fiber volume fraction, scanning electron microscopy (SEM) analysis of the fractured surfaces enabled a better understanding both of the failure modes involved and of points of concern. Nevertheless, the results of this study seem promising in view of a full exploitation of basalt fibers as reinforcement in polymer matrix composites (PMCs).     

Elastic and damage behavior of three-dimensional woven composites incorporating solid rods

This articles examines the relationship between processing and performance of three-dimensional (3D) woven composites. Four types of fabrics were made with the solid rods incorporated in the axial direction. The first is a 3-axis orthogonal type having yarns in two weaving directions; the second is similar except that no beat-up is applied to the weaving yarns. The third type combines the rods in two directions. The last is a 5-axis type that adds two off-axis yarns to the first type. Both Kevlar and carbon tows were used in the rods and weaving yarns. No pressing force was applied during curing of the vinyl-ester resin to preserve the as-formed fabric configuration. Microstructures of the materials have been observed, and unit cells have been defined to model the composites. The fabric geometry model is adopted for predicting the elastic moduli. Material characterization has been carried out based on flexure and Izod impact tests. The dominant damage modes under the flexural and impact loads have been identified for each type of materials. The concept of weaker-plane that dictates material failure has been introduced for the multi-directionally reinforced composites. Weaving loops on fabric surfaces have been found to play a crucial role in the formation of cracks. Failure and the associated energy-absorbing mechanisms of the present materials have been discussed in detail.     

A Comparison of the Vibration Characteristics of Carbon Fiber Reinforced Plastic Plates with those of Magnesium Plates

An experimental and numerical investigation is conducted to evaluate vibration characteristics of an advanced composite material system, namely carbon fiber reinforced plastic (CFRP), relative to a magnesium alloy currently used in the vibration testing industry. Experimental test specimens for both materials, with varying thicknesses, are tested with two boundary conditions — the free condition, to evaluate the natural frequencies and damping of the two materials and, secondly, a general constrained condition, typical of vibration testing. Experimental modal analysis techniques are used to measure the vibration characteristics including natural frequencies, damping and mode shapes. The results from these tests show that the natural frequency and mode shape for relatively thin CFRP plates were comparable with those of magnesium plate. Although the mode shapes also compare well for thick CFRP and magnesium specimens, the natural frequencies were found to have significant differences between the two material systems. The largest difference between the two material systems, present for all thicknesses, is found to be the damping values for the respective vibration modes. This unique characteristic of the CFRP material presents an opportunity for a performance increase in the vibration testing system’s community.     

Research on the Planar Electrical Anisotropy of Conductive Woven Fabrics

The main aim of the research is to determine electrical anisotropy of woven fabrics to describe the multidirectional dependence of the electrical resistance of woven fabrics. The van der Pauw electrodes configuration is used to determine the electrical resistance. Scanning electron microscope–energy-dispersion X-ray spectroscopy (SEM–EDS) analysis is carried out to identify the real amount of conductive elements on a fabric surface as a result of yarns or fabric metallization and to explain the electrical conductivity of the textile materials. The planar electrical anisotropy of electroconductive woven fabrics is observed. The maximum and minimum values of resistances of woven fabric are connected with the weft/warp of which direction coincides with the direction of the longitudinal and transversal axes in the sample plane. SEM–EDS analysis confirms that the electrical conductivity of fabrics depends on the samples elemental composition and the amount of metals deposited on yarns or woven fabrics. It is observed that the sample metallization with thick coating gives a better solution than weaving textiles from coated yarns from the point of view of electrical properties.     

Solid-mechanics finite element simulations of the draping of fabrics: a sensitivity analysis

This paper covers numerical investigations of the draping of woven fabrics into a “hat” shape, combining a hemispherical cup with a wide flat rim. A mechanical approach is adopted using finite element analysis (FEA) methodology. In this, the fabric is considered as a solid sheet with mechanical properties and friction properties. In this study, a linear elastic anisotropic material model describes the deformation of fabrics. An explicit dynamic finite element analysis is applied and systematic parametric numerical studies are presented, which incorporate investigations of the effects of numerical parameters, material properties and processing conditions on the draping of fabrics. More specifically, the effects of the following variables and parameters are included: number of elements, number of time increments in the dynamic FEA analysis, punch speed, shear and tensile moduli of fabric, coefficient of friction for all interfaces and level of load on the fabric holder.     

Study on the Ballistic Performance of Multiply Wadded Through-the-thickness Angle-interlock Fabric Reinforced Composites

Applied Composite Materials - The paper presents a study on the ballistic performance of 3D woven wadded through-the-thickness angle-interlock fabrics (TTAI) fabric reinforced composites. Their...     

Effects of fabric parameters on the tensile behaviour of sustainable cementitious composites

The mechanical behaviour of fabric-reinforced composites can be affected by several parameters, such as the properties of fabrics and matrix, the fibre content, the bond interphase and the anchorage ability of fabrics. In this study, the effects of the fibre type, the fabric geometry, the physical and mechanical properties of fabrics and the volume fraction of fibres on the tensile stress–strain response and crack propagation of cementitious composites reinforced with natural fabrics were studied. To further examine the properties of the fibres, mineral fibres (glass) were also used to study the tensile behaviour of glass fabric-reinforced composites and contrast the results with those obtained for the natural fabric-reinforced composites. Composite samples were manufactured by the hand lay-up moulding technique using one, two and three layers of flax and sisal fabric strips and a natural hydraulic lime (NHL) grouting mix. Considering fabric geometry and physical properties such as the mass per unit area and the linear density, the flax fabric provided better anchorage development than the sisal and glass fabrics in the cement-based composites. The fabric geometry and the volume fraction of fibres were the parameters that had the greatest effects on the tensile behaviour of these composite systems.     

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.     

Mechanical and three-body abrasive wear behaviour of three-dimensional glass fabric reinforced vinyl ester composite

The mechanical and three-body abrasive wear behaviour of two- and three-dimensional E-glass woven fabric reinforced vinyl ester composites were studied in this article. The mechanical properties were evaluated using universal testing machine as per ASTM D-638. Three-body abrasive wear tests were conducted using rubber wheel abrasion tester (RWAT) under different abrading distances at two loads, wherein the wear volume loss were found to increase and that of specific wear rate decrease. The results indicate that the three-dimensional glass woven fabrics in vinyl ester (G_3D–V) have significant influence on wear under varied abrading distance/loads. Further, it was found that G_3D–V composite exhibited lower wear rate compared to two-dimensional glass woven fabric reinforced vinyl ester (G_2D–V) composite. The worn surface features, as examined through scanning electron microscope (SEM), show ruptured glass fiber in G_2D–V composite compared to G_3D–V composites.     

Modelling of Woven Fabrics with the Discrete Element Method

The mechanical behaviour of woven fabrics is dominated by the kinematics of the constituents on the microscopic scale. Their macroscopic response usually shows non-linearities which are due to the mobility of the interlaced yarns. The major deformation mechanisms of fabrics, i.e. the crimp interchange in case of biaxial tension and the trellising motion of the yarns in case of shear, reflect the dependency of the macroscopic material behaviour on the microstructural deformation mechanisms.
We present a novel modelling approach for woven fabrics which is capable to represent directly and locally the microstructure and its kinematics at yarn level. With only a small set of assumptions on the micro-scale the complex macroscopic material behaviour can be directly obtained. The proposed model uses the Discrete Element Method (DEM) for the representation of the fabric's microstructure. It is intrinsically dynamic since the equations of motion are solved numerically for every mass point through an application of an explicit finite difference technique. The model covers the full mobility of the fabric's microstructure while being efficiently enough to model macroscopic patches of the material.
With this model we can study the influence of the different material features of the micro-scale on the macroscopic material behaviour. With some further extensions accounting for coatings or embeddings, the range from pure fabrics to fabric reinforced membranes and composites can be covered. Problems related to large deformations and localization as well as damage can be addressed with the presented modelling approach.