Properties of yarn pull-out in para-aramid fabric structure and analysis by statistical model

The aim of this study is to analyze and determine the pull-out properties of para-aramid woven fabrics. Para-aramid Kevlar29® and Kevlar129® woven fabrics were used to conduct the pull-out tests. They have high and low fabric densities. A yarn pull-out fixture was developed to test various fabric sample dimensions. Data generated from single and multiple yarn pull-out tests in various dimensions of Kevlar29® and Kevlar129® woven fabrics included fabric pull-out forces, yarn crimp extensions in the fabrics and fabric displacements. The regression model showed that yarn pull-out forces depend on fabric density, fabric sample dimensions and the number of pulled ends in the fabric. Yarn crimp extensions depend on the crimp ratios of the fabric and fabric density. Fabric displacements depend on fabric sample dimensions and the number of pulled yarns.     

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 inter‐yarn friction in woven fabric armour

The effects of inter‐yarn friction on the ballistic performance of woven fabric armour are investigated in this paper. Frictional sliding between yarns is implemented in a computational model of the fabric that takes the form of a network. Yarn crimp and its viscoelastic properties are taken into account. Ballistic experiments are performed to verify the predictions of the model. Parametric studies show that the ballistic response of woven fabric is very sensitive to yarn friction when the friction coefficient is low but insensitive beyond a certain level. The results also show that very high inter‐yarn friction can lead to premature yarn rupture, thus reducing the ability of the fabric to absorb impact energy. Copyright © 2005 John Wiley & Sons, Ltd.     

Influences of weaving architectures on the impact resistance of multi-layer fabrics

Fabrics constructed from different weaving architectures such as plain, basket, twill and satin provide varying flexibility and durability when applied on surfaces of complex structures for protective applications. They also affect the manufacturing processes and mechanical properties of both fabrics and composite structures in various applications such as soft armours, helmets, aircraft engine cowlings or automobile monocoques. In this work, the influences of weaving architectures on the ballistic resistance and energy absorption of both single and multi-layer Twaron® fabrics are investigated. A mesoscale yarn model is constructed, validated experimentally, and analytical. Finite element fabric models of different fabric structures are then developed and their firmness is quantified using interlacing factors. Numerical models for plain weave are validated against experimental results from single-ply ballistic tests. The evolutions of kinetic, strain, and friction energy components, normalised with areal mass, are presented to demonstrate the better ballistic protection of the plain weave compared with other weaving architectures. Further investigations on multi-ply systems illustrate the energy absorption capacities for different types of woven fabrics and the associated ballistic resistances. The research results indicate that weaving architectures and fabric firmness are less influential on the overall ballistic protection of multi-ply systems compared to the single-ply cases.     

Experimental and numerical investigation of fabric impact behavior

This paper presents experimental and numerical research regarding blunt trauma resistance of ten fabrics made of high strength fibers. Fabrics of various architecture were examined, including plain woven fabrics, unidirectional laminates and multiaxial fabrics. The fabrics were compared with respect to the depth of the depression formed and the amount of energy transferred to the backing during projectile impact. Absolute values of mentioned parameters were compared, as well as their values after normalization with respect to thickness and areal density of the fabrics. A numerical method for estimating the amount of energy transferred to the backing was proposed.Normalized results, obtained experimentally and numerically, proved that most of the analyzed fabrics provide a similar level of protection, but the best blunt trauma resistance is given by multiaxial fabrics and the least by plain woven fabrics. This study has also shown that the depth of the depression in the backing material is an insufficient parameter in describing protective properties of fabric against blunt trauma. It is possible that impacts into ballistic packages composed of different fabrics with the same depth of depression may cause completely dissimilar injuries because of the amount of energy transferred to the backing material.     

Modeling friction effects on the ballistic impact behavior of a single-ply high-strength fabric

It has been shown through experiments that interfacial friction affects the energy absorption of fabrics subjected to ballistic impact. However, how the friction plays a role is not well understood. In this paper, a commercially available finite element analysis code, LS-DYNA, is used to model the ballistic impact of a square patch of single-ply plain-woven fabric. Three types of boundary conditions are applied on the fabric: four edges clamped, two edges clamped, and four edges free. The friction between yarns at their crossovers and the friction between projectile and fabric are taken into account. Effects of the friction during the phase prior to yarn failure are parametrically studied. Simulation results show that at a given time, the fabric with high friction absorbs more energy than the fabric with no friction. For the boundary condition with four edges free, friction contributes to increasing the fabric energy absorption mainly through the mechanism of frictional sliding dissipated energy. For the boundary conditions with two or four edges clamped, the energy dissipated through frictional sliding only accounts for a very small portion of the total absorbed energy; however, both the yarn strain energy and the yarn kinetic energy are increased when there is friction. Friction has an indirect effect on the fabric energy absorption by influencing the number of yarns that become involved. Simulation results also indicate that the boundary conditions significantly affect the fabric deformation, stress distribution, and time history of energy absorption.     

Effect of Frictions on the Ballistic Performance of a 3D Warp Interlock Fabric: Numerical Analysis

3D interlock woven fabrics are promising materials to replace the 2D structures in the field of ballistic protection. The structural complexity of this material caused many difficulties in numerical modeling. This paper presents a new tool that permits to generate a geometry model of any woven fabric, then, mesh this model in shell or solid elements, and apply the mechanical properties of yarns to them. The tool shows many advantages over existing software. It is very handy in use with an organization of the functions in menu and using a graphic interface. It can describe correctly the geometry of all textile woven fabrics. With this tool, the orientation of the local axes of finite elements following the yarn direction facilitates defining the yarn mechanical properties in a numerical model. This tool can be largely applied because it is compatible with popular finite element codes such as Abaqus, Ansys, Radioss etc. Thanks to this tool, a finite element model was carried out to describe a ballistic impact on a 3D warp interlock Kevlar KM2? fabric. This work focuses on studying the effect of friction onto the ballistic impact behavior of this textile interlock structure. Results showed that the friction among yarns affects considerably on the impact behavior of this fabric. The effect of the friction between projectile and yarn is less important. The friction plays an important role in keeping the fabric structural stability during the impact event. This phenomenon explained why the projectile is easier to penetrate this 3D warp interlock fabric in the no-friction case. This result also indicates that the ballistic performance of the interlock woven fabrics can be improved by using fibers with great friction coefficients.     

三维正交机织物结构的几何模型

以经、纬纱为直线, 捆绑纱为正弦和直线组合的曲线, 建立了三维正交机织物的几何结构模型。根据捆绑纱所限定纱线的截面积, 建立了以织物结构参数为未知量的非线性方程组, 使用数值计算方法求出了非线性方程组的近似解, 确定了捆绑纱曲线模型中的待定量。制织了纬纱捆绑和经纱捆绑两种玻璃纤维三维正交机织布, 并与不饱和聚酯树脂复合, 然后观察复合材料中捆绑纱的形态, 发现捆绑纱的测试曲线与模型曲线具有很好的一致性。进一步比较捆绑纱织缩率的测试值与计算值、纤维体积含量的测试值与计算值, 表明建立的织物结构几何模型, 能够较为真实地反映三维正交机织物的实际结构。      

Determination of Materials for Hybrid Design of 3D Soft Body Armour Panels

In order to optimise the construction of soft body armour panels by hybridization, this study aims to identify materials determination for hybrid panel. Different ballistic characteristics of aramid woven fabrics and Ultra High Molecular Weight Polyethylene uni-directional laminates were investigated through ballistic test and fractorgaphic analysis. With an increasing of total layer numbers in a panel, specific energy absorption of Twaron woven panel shows a decrease trend, and Dyneema UD panel exhibits an increasing trend. Such reverse trend of ballistic performance is due to different failure modes of two materials. According to fractorgraphic analysis, Twaron fabric has large transverse deformation for back layers in a perforated panel. This results in higher energy absorption in back layers. For Dyneema UD, thermal damage is the dominant failure mode, which can result in performance degradation especially for front layers on the strike face. In addition, Dyneema UD exhibits significant advantage of minimize Backface Signature (BFS) and a little higher perforation ratio than that of Twaron woven panels. Based on these findings, an optimized hybrid panel is designed by combing Twaron woven fabric before Dyneema UD. In comparison with other panels with different layer sequences, this hybridization manner exhibited better ballistic performance, including improvement of energy absorption, minimized BFS of the non-perforated panel and reduction of perforation ratio. These findings indicated that material determination for hybrid design should be based on ballistic characteristics of different materials and requirements of different regions in a panel.     

Effects of Woven Fabric Geometry on the Bonding Performance of Cementitious Composites: Mechanical Performance

The effect of the geometry of woven fabrics on the bond between monofilament polyethylene yarns and cement matrix was studied in the present work. The fabrics were all plain weave, with varied fills density: 5, 7, or 10 fills per cm; the warps’ density was kept constant at 22 warps per cm. The interfacial bond was evaluated by pullout tests. To characterize the influence of the fabric’s geometry on bond performance, the influence of different parameters of the fabric’s geometry that may affect bond were separated: (1) pullout of a single crimped yarn untied from the fabric to characterize the influence of the shape of the individual crimped yarn; (2) pullout of a single yarn from free fabric (not embedded in the cement matrix); and (3) pullout of a yarn from a fabric embedded in the cement matrix. Straight yarns were also tested for comparison. It was found that the woven fabric provided a considerably better bond to the cementitious matrix than the bond of a single straight yarn. The crimped geometry of the yarn in the fabric was found to have a significant influence on increasing the bond between the woven fabric and the cementitious matrix.     

Effect of hybrid woven fabrics structure on their electrical properties

The aim of this study is to investigate the influence of hybrid textile woven fabric structure on the electrical resistivity. Weave structure was varied by varying the weave pattern and the conductive yarn density in the woven fabrics. Electrical surface and volume resistivity were measured and compared to the fabric structural properties. Results showed that not only the conductive yarns percentage has an important effect on the electrical resistivity but also the weave structure. The most influencing structural parameter on surface resistivity was the woven fabric surface profile as it controls the contact quality between the conductive yarns and the measuring electrodes. A high surface resistivity was noticed when the contact quality was poor. When this contact quality was good, a linear correlation was found between surface electrical resistivity and the cover firmness factor, the apparent conductive fiber surface area as well as the conductive yarn floating length of the woven structures.     

Woven fabric reinforcement of cement matrix

The performance of woven fabric reinforced cement was studied to resolve the influence of the structure of the fabric on its reinforcing efficiency. Special fabrics were produced for this study in which the longitudinal (warp) yarn density was kept constant and the perpendicular (fill) yarn density was varied, in the range of 0 to 22 yarns per centimeter. Specimens for flexural and pull out testing were produced from the fabrics and crimped yarns untied from the fabric. Scanning electron microscope tests were carried out to resolve the microstructure of the composite, in particular at the yarn-matrix interface. The results point to three main conclusions: (1) Woven fabric structure improved the bonding capacity as compared to polyethylene monofilament fibers and cement matrix. (2) The crimped structure of the yarns in the fabric plays an important role in this improvement of the bond, providing mechanical anchoring between the woven fabric and the cement matrix. (3) There is an optimal density of fill yarn in the fabric, which causes the higher flexural strength within the tested densities and matrix formulations. This optimum is achieved in the fabric with five fill yarns per centimeter, and it may be accounted for by the fact that at higher density the matrix does not penetrate efficiently into the spaces in the fabric.     

Computational simulation of fabric armour subjected to ballistic impacts

In computational simulations of ballistic impacts on woven polymeric fabric armour, specialized fabric models are normally used. Attempts have also been made to use commercial finite element packages for such purposes. However, such attempts normally result in either overly simplified models or prohibitively detailed finite element discretization of the fabric to capture the unique properties of woven fabric. This paper presents an FE model of woven fabric that reflects the orthotropic properties of the fabric, the viscoelastic nature of the yarns, the crimping of the yarns, the sliding contact between yarns and yarn breakage using an assembly of viscoelastic bar elements. Excellent agreement between simulation and ballistic test data is obtained in terms of the deformation of the fabric during impact, residual velocity of the projectile and the energy absorbed by the fabric. This is achieved despite the modest number of degrees of freedom employed by the model.     

Friction core-spun yarns for electrical properties of woven fabrics

This paper reports a study to develop a spinning method of open-end friction core-spun yarn (OFCY) and its conductive fabric for shielding the electrostatic discharge and electromagnetic applications. To facilitate weaving of stainless steel (SW) and to reduce the material cost, initially OFCY yarn was made from SW core and polyester (PET) and stainless steel staple (SS) fibers, produced by a DREF III open-end friction spinning method. The core-spun yarns were woven into a variety of woven structures, which are made from semi-automatic loom, successfully. The conductive fabrics could be suitable for shielding home electronic and electrical appliances, cellular phones, and digital devices from electromagnetic fields. The variations of EMSE, and ESD of the woven fabric structure, and blend ratio of stainless steel yarns are also described. It has been shown that the EMSE and ESD attenuation of the woven fabric can be tailored in a number of ways including fabric structure, density, and the amount of conductive filler material.     

Tribological properties of woven para-aramid fabrics and their constituent yarns

The tribological behaviours of woven fabrics made from Kevlar® (DuPont's registered trademark) yarns of different linear densities were compared with the friction properties of their constituent yarns with different surface treatments. The latter were examined with a traditional friction meter, and the woven fabrics were studied with a pin-on-disc tribometer in alternate and continuous sliding mode. Scoured fabrics, a poly(tetrafluoroethylene)-coated fabric, and fabrics made of surface-treated yarns (polysiloxane oil, hydrophobic paraffin or ester oil lubricant) were compared. These treatments are not representative of commercial Kevlar® yarn finishes but are suitable models for simulating various tribological situations. Both the yarn texture and the surface treatment have an influence on friction coefficient values. Relative humidity affects the friction coefficient only in the case of hydrophilic surfaces, whereas hydrophobic surfaces exhibit fairly constant tribological characteristics. The largest impact on friction seems to be evidenced by the linear density factor. This comparative tribological analysis could lead the way to correlations between yarn friction, weaving performance and woven structure tribological characteristics.     

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.     

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 and constitutive modeling of aramid fibers at high strain rates

The quasi-static and rate-dependent mechanical properties of aramid yarns are presented together with a study on different methods of securing yarn specimens in tensile tests. While capstans were found to be suitable for quasi-static tests, they either were not strong enough or had too high inertia for dynamic tests in a Split Hopkinson Pressure Bar setup. Instead, specially designed clamps were used. A viscoelastic material model to describe the mechanical behavior of the yarns, including failure, is also presented. The material model was employed in the computational simulation of ballistic penetration of woven aramid fabrics. Comparison of the simulations and actual ballistic tests showed that predictions of the energy absorbed by the fabric were in good agreement with the experiments.     

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.     

Analysis of a two-way tension-shear coupling in woven fabrics under combined loading tests: Global to local transformation of non-orthogonal normalized forces and displacements

Dependence of shear rigidity of woven fabrics on yarn pre-tension has been reported in the recent literature, however some conflict regarding the trend of this effect is observed. Sources of this conflict are discussed and resolved in the present article using a new characterization framework and a custom-design combined loading fixture. It is shown that in order to correctly characterize the tension-shear coupling behavior in woven fabrics, instead of using global measured data, local normalized forces and displacements should be driven via a non-orthogonal transformation procedure, while considering kinematic force coupling in the setup. In addition, the effect of fabric shear on the tensile behavior of yarns has been investigated, suggesting that the coupling under question is in fact two-way. In particular, results revealed that applying yarn pre-tension increases the shear resistance of the fabric reinforcement, while the tensile behavior of the material becomes more compliant when undergoing shear deformation.