Experimental and numerical study of oblique impact on woven composite sandwich structure: Influence of the firing axis orientation

During flight, aircrafts can be submitted to complex loadings. The reliability of their structure is an essential aspect in ensuring passenger safety. In the specific case of helicopters, blades are subjected to impact loading. The following work will focus on the experimental and numerical study of an oblique impact on the skin of the blade. It is equivalent in a first approach to an impact on a sandwich panel comprising a foam core and a thin woven composite skin. This study aims to identify the mechanisms of damage to the skin for different orientations of the firing axis, and to develop a representative model of the damage kinetics adapted to the modeling of the complete structure. Thus, an F.E. semi-continuous explicit model has been developed. It relies on the development of a specific damageable element at the woven mesh scale. Numerical results obtained are accurate, allowing the identification of the damage mechanism of the woven skin for different firing orientations.     

平面编织复合材料层合板低速冲击后的拉伸性能

对两种不同铺层形式的平面编织复合材料层合板低速冲击后拉伸性能进行了实验研究,在此基础上建立了有限元损伤扩展仿真模拟。在所建立的有限元模型中,将低速冲击损伤等效为形状规则的软化夹杂,并针对两种铺层形式采用不同的损伤判据和模量衰减准则。研究结果表明:该有限元模拟结果与实验结果符合,说明该模型能够准确地预测低速冲击后平面编织复合材料层合板的损伤扩展规律和剩余拉伸强度;不同铺层形式的平面编织复合材料层合板在低速冲击后拉伸的损伤扩展规律不同;它们的冲击后拉伸强度降均>50%,在复合材料结构设计中应该受到重视。      

Modeling strategies of 3D woven composites: A review

Due to advancements made in 3D weaving process, 3D woven composites have evolved as an attractive structural material for multi-directional load bearing and impact applications, due to their unique transverse properties such as stiffness, strength, fracture toughness and damage resistance. Substantial progress has been made in recent years for the development of new modeling techniques in design and analysis to understand the unique mechanical behavior of 3D woven composites. This paper systematically reviews the modeling techniques along with their capabilities and limitations for characterization of the micro-geometry, mechanical/thermo-mechanical behavior and impact behavior of 3D woven composites. Advantages, disadvantages and applications of 3D woven composites have also been delineated. In addition, this reference list provides a good database for future research on 3D woven composites.     

基于ANSYS环境的平面编织层合板拉伸破坏数值仿真

以ANSYS为平台编制了具有可移植性的APDL程序, 建立了损伤累积模型, 对平面编织层合板的损伤破坏行为进行了数值仿真。该模型对适合于单向铺层的Hanshin判据和Reddy刚度衰减方法进行了相应的修正。为验证模型的有效性, 对G803/5224平面编织光滑板、 孔板进行了相应的试验研究。结果表明, 该模型仿真结果与试验结果吻合, 并且比较简单直观, 为平面编织层合板的损伤扩展与破坏的研究提供了便于工程应用的数字化手段。      

A Modeling Approach Across Length Scales for Progressive Failure Analysis of Woven Composites

This paper presents a multiscale modeling approach for the progressive failure analysis of carbon-fiber-reinforced woven composite materials. Hierarchical models of woven composites at three different length scales (micro, meso, and macro) were developed according to their unique geometrical and material characteristics. A novel strategy of two-way information transfer is developed for the multiscale analysis of woven composites. In this strategy, the macroscopic effective material properties are obtained from property homogenizations at micro and meso scales and the stresses at three length scales are computed with stress amplification method from macroscale to microscale. By means of the two-way information transfer, the micro, meso and macro structural characterizations of composites are carried out so that the micromechanisms of damage and their interactions are successfully investigated in a single macro model. In addition, both the nucleation and growth of damages are tracked during the progressive failure analysis. A continuum damage mechanics (CDM) method is used for post-failure modeling. The material stiffness, tensile strength and damage patterns of an open-hole woven composite laminate are predicted with the proposed multiscale method. The predictions are in good agreement with the experimental results.     

Damage modes in 3D glass fiber epoxy woven composites under high rate of impact loading

A qualitative analysis of experimental results from small caliber ballistic impact and dynamic indentation on a 3D glass fiber reinforced composite are presented. Microscopic analysis of the damaged specimens revealed that the current 3D weaving scheme creates inherently two weak planes which act as potential sites for delamination in the above experiments. It is concluded that while the z-yarns may be effective in limiting the delamination damage at low loads and at low rates of impact, at high loads and high loading rates delamination continues to be the dominant failure mode in 3D woven composites. It is shown that dynamic indentation can be used to capture the progression of damage during impact of 3D woven composites.     

Influence of Fibre Architecture on Impact Damage Tolerance in 3D Woven Composites

3D woven composites, due to the presence of through-thickness fibre-bridging, have the potential to improve damage tolerance and at the same time to reduce the manufacturing costs. However, ability to withstand damage depends on weave topology as well as geometry of individual tows. There is an extensive literature on damage tolerance of 2D prepreg laminates but limited work is reported on the damage tolerance of 3D weaves. In view of the recent interest in 3D woven composites from aerospace as well as non-aerospace sectors, this paper aims to provide an understanding of the impact damage resistance as well as damage tolerance of 3D woven composites. Four different 3D woven architectures, orthogonal, angle interlocked, layer-to-layer and modified layer-to-layer structures, have been produced under identical weaving conditions. Two additional structures, Unidirectional (UD) cross-ply and 2D plain weave, have been developed for comparison with 3D weaves. All the four 3D woven laminates have similar order of magnitude of damage area and damage width, but significantly lower than UD and 2D woven laminates. Damage Resistance, calculated as impact energy per unit damage area, has been shown to be significantly higher for 3D woven laminates. Rate of change of CAI strength with impact energy appears to be similar for all four 3D woven laminates as well as UD laminate; 2D woven laminate has higher rate of degradation with respect to impact energy. Undamaged compression strength has been shown to be a function of average tow waviness angle. Additionally, 3D weaves exhibit a critical damage size; below this size there is no appreciable reduction in compression strength. 3D woven laminates have also exhibited a degree of plasticity during compression whereas UD laminates fail instantly. The experimental work reported in this paper forms a foundation for systematic development of computational models for 3D woven architectures for damage tolerance.     

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.     

Meshfree modeling and homogenization of 3D orthogonal woven composites

In this paper, evaluation of 3D orthogonal woven fabric composite elastic moduli is achieved by applying meshfree methods on the micromechanical model of the woven composites. A new, realistic and smooth fabric unit cell model of 3D orthogonal woven composite is presented. As an alternative to finite element method, meshfree methods show a notable advantage, which is the simplicity in meshing while modeling the matrix and different yarns. Radial basis function and moving kriging interpolation are used for the shape function constructions. The Galerkin method is employed in formulating the discretized system equations. The numerical results are compared with the finite element and the experimental results.     

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.     

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.     

Finite element analysis for the evaluation of the low-velocity impact response of a composite plate

The low-velocity impact responses of cross-ply CFRP composite plates are investigated experimentally and are simulated using the finite element code LS-DYNA. An experimental test was initially performed and two different modeling approaches were then employed to model the composite plates. In the first numerical modeling approach, solid elements are utilized for the composite layers, whereas in the second, shell elements are used. The numerical model using the shell elements shows a good correlation with the experimental results, while the impact damage in the form of delamination is predicted more precisely using solid elements.     

A unit cell approach of finite element calculation of ballistic impact damage of 3-D orthogonal woven composite

This paper presents ballistic impact damages of 3-D orthogonal woven composite in finite element analysis (FEA) and experimental. A unit-cell model of the 3-D woven composite was developed to define the material behavior and failure evolution. A user-defined subroutine VUAMT was compiled and connected with commercial available FEA code ABAQUS/Explicit to calculate the ballistic penetration. Ballistic impact tests were conducted to investigate impact damage of 3-D kevlar/glass hybrid woven composite. Residual velocities of conically-cylindrical steel projectiles (Type 56 in China Military Standard) and impact damage of the composite targets after ballistic perforation were compared both in theoretical and experimental. The reasonable agreements between FEA results and experimental results prove the validity of the unit-cell model in ballistic limit prediction of the 3-D woven composite. We believe such an effort could be extended to bulletproof armor design with the 3-D woven composite.     

Finite Element Analysis of 2.5D Woven Composites,Part II: Damage Behavior Simulation and Strength Prediction

In the first part of the work, a new 2.5D woven composites finite element model (2.5D WCFEM) which took into consideration the impact of face structures and can accurately predict the main elastic performances has been established. In this part, the stress–strain behavior and the damage characteristic of this material under uniaxial tension are simulated using nonlinear progressive damage analysis based on damage mechanics. Meanwhile, experimental investigation and fracture analysis are conducted to evaluate the validity of the proposed method. Finally, the influence of woven parameters on the mechanical behavior is discussed. Compared with the test results, a good agreement between the computational and experimental results has been obtained. The progressive damage characteristic and main failure modes are also revealed.     

Ballistic limit prediction using a numerical model with progressive damage capability

The ultimate objective of this study is to provide further understanding of the behaviour of laminated composites of varying lamina orientations and stacking sequences, when under high-velocity impact. Emphasis is placed on the determination of ballistic limits of these composites. To this end, an experimental program is carried out and a computational model, with progressive damage modeling capabilities, is developed using LS-DYNA. Experiments are performed whereby striking velocities are measured, via high-speed photography, to determine the ballistic limits of carbon fiber-reinforced polymer (CFRP) laminates of various stacking sequences. The results are reproduced closely by a numerical simulation, indicating that the numerical analysis conducted, including the choice of material model and contact definition, is an accurate means for modeling the high-speed impact characteristics of CFRP laminates. It is found that the use of static elastic and strength properties to describe the material is reasonable, since strain rate effects are found to be negligible. The kinetic energy of the projectile, plotted over the simulated impact duration, is used as the prime parameter to compare the experimental and numerical results. The numerical results accurately predict the experimental ballistic limit for six of the seven tested laminate stacking sequences. Failure due to delamination is found to play a vital role with respect to the energy absorbing ability and lamina stacking sequence of CFRP laminates.     

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.     

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.     

Sandwich structures with textile-reinforced composite foldcores under impact loads

The mechanical behaviour of composite sandwich structures with textile-reinforced composite foldcores, which are produced by folding prepreg sheets to three-dimensional zigzag structures, is evaluated under compression, shear and impact loads. While foldcores made of woven aramid fibres are characterised by a rather ductile behaviour, carbon foldcores with their brittle nature absorb energy by crushing, showing extremely high weight-specific stiffness and strength properties. The impact damage under low and high velocity impact loads tends to be very localised. In addition to regular single-core sandwich structures, a dual-core configuration with two foldcores is also investigated, showing the potential of a two-phase energy absorption behaviour. In addition to experimental testing, finite element models for impact simulations with LS-DYNA have been developed. Despite the high degree of complexity of the models due to the various skin and core failure modes that have to be covered, the results correlate well with test data, allowing for efficient parameter studies or detailed evaluations of damage patterns and energy absorption mechanisms.