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.     

Analysis on failure mechanisms of an interlock woven fabric under ballistic impact

In this paper, damage mechanisms of a 3D interlock woven fabric subjected to ballistic impact were analyzed using a numerical model. Two impact configurations were carried out in order to validate the numerical model with experimental observations: perforation (900 m/s) and no-perforation (90 m/s). Global deformation of the fabric during impact is determined continuously to detail fabric impact behavior. Also, in this study, the effects of boundary conditions on failure mechanisms have been investigated. Boundary conditions are divided into two cases: (1) only warp yarns fixed and (2) only weft yarns fixed. Basing on continuous evolutions of global deformation, projectile velocity, different energies and reaction force onto projectile, the influence of both these fixation conditions is investigated.     

A homogenization procedure for the numerical analysis of woven fabric composites

The paper presents a procedure for the numerical evaluation of the mechanical properties of woven fabric laminates. Woven fabrics usually present orthogonal interlaced yarns (warp and weft) and distribution of the fibers in the yarns and of the yarns in the composite may be considered regular. This allows us to apply the homogenization theory for periodic media both to the yarn and to the fabric. Three-dimensional finite element models are used in two steps to predict both the stiffness and the strength of woven fabric laminates. The model includes all the important parameters that influence the mechanical behavior: the lamina thickness, the yarn orientation, the fiber volume fraction and the mechanical characteristics of the components. The capabilities of the numerical model were verified studying the elastic behavior of a woven fabric laminate available in the literature and the ultimate strength of a glass fabric laminate experimentally investigated. The procedure, that can be implemented into commercial finite element codes, appears to be an efficient tool for the design of textile composites.     

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.     

Ballistic impact modeling of woven fabrics considering yarn strength,friction, projectile impact location,and fabric boundary condition effects

The combined effects of yarn tensile strength, inter-yarn friction, projectile impact location, and fabric clamping conditions on the probabilistic impact response of flexible woven Kevlar KM2 fabrics are studied using a 0.22 caliber spherical projectile. The statistical nature of yarn tensile strength is accounted for by mapping Weibull strength distributions onto the individual yarns of the fabric model. Variability in projectile impact location relative to the yarns at the impact site is accounted for by randomly selecting one of 25 predetermined impact locations around a warp-fill yarn cross-over location at the center of the fabric. Five different inter-yarn friction levels are deterministically implemented, ranging from 0.0 to 0.4. Two boundary conditions are considered, 4-sided clamped and 2-sided clamped. Forty impact simulations are used to generate a probabilistic impact response (PVR) curve for each test case, describing the probability of fabric penetration as a function of projectile impact velocity. The fabric V₅₀ velocity and impact performance variability were observed to decrease with increasing inter-yarn friction levels for the 4-sided clamped cases, while they increased for the 2-sided clamped cases.     

Internal geometry evaluation of non-crimp 3D orthogonal woven carbon fabric composite

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here “non-crimp” has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4–8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3–4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.     

A numerical investigation of the influence of friction on energy absorption by a high-strength fabric subjected to ballistic impact

A finite element analysis was conducted to study the influence of friction during ballistic impact of a rigid sphere onto a square fabric panel that was firmly clamped along its four edges. Projectile-fabric friction and yarn–yarn friction were investigated. Modeling indicates that friction dramatically affects the local fabric structure at the impact region by hindering the lateral mobility of principal yarns. Reduction of lateral yarn mobility allows the projectile to load and break more yarns so that fabric possessing a high level of friction absorbs more energy than fabric with no friction. The projectile-fabric friction delays yarn breakage by distributing the maximum stress along the periphery of the projectile-fabric contact zone. The delay of yarn breakage substantially increases the fabric energy absorption during the later stages of the impact. The yarn–yarn friction hinders the relative motion between yarns and thus resists de-crimping of fabric weave tightness. It induces the fabric to fail earlier during the impact process. The overall influence of projectile-fabric friction and yarn–yarn friction cannot be calculated by simply adding their individual effects.     

A numerical investigation into the influence of fabric construction on ballistic performance

The use of high-performance fibres has made it possible to produce lightweight and strong personal body armour. Parallel to the creation and use of new fibres, fabric construction also plays an essential role for performance improvement. In this research, finite element (FE) models were built up and used to predict the response of woven fabrics with different structural parameters, including fabric structure, thread density of the fabric and yarn linear density. The research confirmed that the plain woven fabric exhibits superior energy absorption over other structures in a ballistic event by absorbing 34% more impact energy than the fabric made from 7-end satin weave. This could be explained that the maximum interlacing points in this fabric which help transmit stress to a larger fabric area, enabling more secondary yarns to be involved for energy dissipation. It was found that fabric energy absorption decreases as fabric is made denser, and this phenomenon becomes more pronounced in a multi-ply ballistic system than in a single-ply system. The research results also indicated that the level of yarn crimp in a woven fabric is an effective parameter in influencing the ballistic performance of the fabrics. A low level of yarn crimp would lead to the increase of the fabric tensile modulus and consequently influencing the propagation of the transverse wave. In addition, it was found that for fabrics with the same level of yarn crimp, low yarn linear density and high fabric tightness were desirable for ballistic performance improvement.     

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.     

Effect of statistical yarn tensile strength on the probabilistic impact response of woven fabrics

The probabilistic impact response of flexible woven fabrics can be described through the V₀–V₁₀₀ or probabilistic velocity response (PVR) curve which describes the probability of fabric penetration as a function of projectile impact velocity. One source of variability that affects the probabilistic nature of fabric impact performance is the statistical distribution of yarn tensile strengths. In this paper the effects of the statistical yarn strength distribution characteristics on the probabilistic fabric impact response are computationally studied using five different strength distributions with differing mean strengths and distribution widths. Corresponding fabric PVR curves are generated for each strength distribution using a probabilistic computational framework that involves randomly mapping yarn strengths onto the individual woven yarns of a fabric finite element model and then running a series of impact simulations for the case of a four-sided clamped fabric impacted at the center by a spherical projectile.     

General definition of 3D warp interlock fabric architecture

3D warp interlock fabric can be used as a fibrous reinforcement for composite material. Despite of the numerous research papers dealing with this specific woven structure, few researches were conducted to clearly define this multi-layer fabric. Moreover, in many research papers, unskilled scientists of weaving technology have some difficulty to describe the different components of the 3D warp interlock fabric and sometimes make some confusion between the different architecture. Then, with a lack of a clear definition of these 3D multi-layer fabrics, most of the research papers are conducted on a very limited number of structures such as orthogonal, angle and layer to layer interlock.Thus, based on different definitions proposed by skilled scientists, a new general definition of a 3D warp interlock fabric has been proposed to better describe the position of the several yarns located inside the 3D woven structure. Thanks to this improved definition, we hope that the scientific community will use it in order to better design new architectures and conduct finer research based on these product parameters.     

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.     

Modeling the effects of yarn material properties and friction on the ballistic impact of a plain-weave fabric

Impact of a rigid sphere onto a high-strength plain-weave Kevlar KM2^® fabric was modeled using LS–DYNA^® focusing on the influence of friction and material properties on ballistic performance. Quasi-static friction was experimentally determined and incorporated into the model. Two clamped edges and two free edges were used as boundary conditions to correlate the model to an experimental test providing yarn–yarn movement. Yarns were modeled as continua with modulus and strength dominating along the length. Parametric studies incorporating different yarn material properties and initial projectile velocities were then performed with the above set of boundary conditions. Results indicate that ballistic performance depends upon friction, elastic modulus and strength of the yarns. While friction improves ballistic performance by maintaining the integrity of the weave pattern, material properties of the yarns have a significant influence on the effect of friction. It is shown that fabrics comprised of yarns characterized by higher stiffness and strength relative to the baseline Kevlar KM2^®, exhibited a stronger influence on ballistic performance. Therefore all three parameters viz., friction, elastic modulus and strength along with other variables (fabric architecture, boundary conditions, and projectile parameters) are needed to examine ballistic performance of high-strength fabric structures.     

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.     

Composite structures under ballistic impact

In the present study, investigations on the ballistic impact behaviour of two-dimensional woven fabric composites has been presented. Ballistic impact behaviour of plain weave E-glass/epoxy and twill weave T300 carbon/epoxy composites has been compared. The analytical method presented is based on our earlier work. Different damage and energy absorbing mechanisms during ballistic impact have been identified. These are: cone formation on the back face of the target, tensile failure of 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.     

Effect of Mesoscale and Multiscale Modeling on the Performance of Kevlar Woven Fabric Subjected to Ballistic Impact: A Numerical Study

In this study, an optimal finite element model of Kevlar woven fabric that is more computational efficient compared with existing models was developed to simulate ballistic impact onto fabric. Kevlar woven fabric was modeled to yarn level architecture by using the hybrid elements analysis (HEA), which uses solid elements in modeling the yarns at the impact region and uses shell elements in modeling the yarns away from the impact region. Three HEA configurations were constructed, in which the solid element region was set as about one, two, and three times that of the projectile’s diameter with impact velocities of 30 m/s (non-perforation case) and 200 m/s (perforation case) to determine the optimal ratio between the solid element region and the shell element region. To further reduce computational time and to maintain the necessary accuracy, three multiscale models were presented also. These multiscale models combine the local region with the yarn level architecture by using the HEA approach and the global region with homogenous level architecture. The effect of the varying ratios of the local and global area on the ballistic performance of fabric was discussed. The deformation and damage mechanisms of fabric were analyzed and compared among numerical models. Simulation results indicate that the multiscale model based on HEA accurately reproduces the baseline results and obviously decreases computational time.     

Experimental Investigation About Stamping Behaviour of 3D Warp Interlock Composite Preforms

Forming of continuous fibre reinforcements and thermoplastic resin commingled prepregs can be performed at room temperature due to its similar textile structure. The “cool” forming stage is better controlled and more economical. The increase of temperature and the resin consolidation phases after the forming can be carried out under the isothermal condition thanks to a closed system. It can avoid the manufacturing defects easily experienced in the non-isothermal thermoforming, in particular the wrinkling [1]. Glass/Polypropylene commingled yarns have been woven inside different three-dimensional (3D) warp interlock fabrics and then formed using a double-curved shape stamping tool. The present study investigates the in-plane and through-thickness behaviour of the 3D warp interlock fibrous reinforcements during forming with a hemispherical punch. Experimental data allow analysing the forming behaviour in the warp and weft directions and on the influence of warp interlock architectures. The results point out that the layer to layer warp interlock preform has a better stamping behaviour, in particular no forming defects and good homogeneity in thickness.     

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.     

Computational modeling of the probabilistic impact response of flexible fabrics

The impact response of flexible woven fabrics is probabilistic in nature and described through a probabilistic velocity response curve or V₀–V₁₀₀ curve. Computational impact analyses based on deterministic methods are incapable of predicting the experimentally observed probabilistic fabric impact response. To overcome this limitation we have developed a probabilistic computational framework within a finite element analysis to predict the V₀–V₁₀₀ response. The finite element model is a yarn-based representation of the fabric architecture, with a principal stress based failure criterion implemented uniformly within each yarn, but varying for each yarn within the fabric. For each impact simulation, individual yarn strengths are mapped from experimentally obtained yarn strength distributions, resulting in fabric models with spatially non-uniform failure conditions. Impact simulations are run for the case of a spherical projectile of diameter 5.556 mm impacting a single layer of 50.8 × 50.8 mm, edge-clamped, unbacked, aramid fabric. Three different yarn strength models are implemented, representing spool yarns, and yarns extracted from greige and scoured woven fabrics. Decreases in yarn strength are found to correlate to decreases in the V₁, V₅₀, and V₉₉ velocities predicted by the simulations. The relationships between yarn strength distribution and probabilistic fabric impact response are discussed.     

Local strain measurements of yarns inside of 3D warp interlock fabric during forming process

The final geometry of 3D warp interlock fabric needs to be check during the 3D forming step to ensure the right locations of warp and weft yarns inside the final structure. Thus, a new monitoring approach has been proposed based on sensor yarns located in the fabric thickness. To ensure the accuracy of measurements, the observation of the surface deformation of the 3D warp interlock fabric has been joined to the sensor yarns measurements. At the end, it has been revealed a good correlation between strain measurement done globally by camera and locally performed by sensor yarns. Additionally, sensor yarns located in the two directions of the 3D warp interlock fabric have revealed a different forming behaviour depending on the architecture and the different slope values of the punch.