Impactor diameter effect on low velocity impact response of woven glass epoxy composite plates

In this study, the effect of impactor diameter on the impact response of woven glass–epoxy laminates has been investigated. Impact tests were performed by using Fractovis Plus test machine with four different impactor nose diameters as 12.7, 20.0, 25.4 and 31.8 mm. Specimens were impacted at various impact energies ranging from 5 J to perforation thresholds of the composite at room temperature. Variation of the impact characteristics such as the maximum contact load, maximum deflection, maximum contact time and absorbed energy versus impact energy are investigated. Results indicated that the projectile diameter highly affects the impact and Compression After Impact (CAI) response of composite materials.     

Flexural and impact response of woven glass fiber fabric/polypropylene composites

Impact tests with a falling dart and flexural measurements were carried out on polypropylene based laminates reinforced with glass fibers fabrics. Research has shown that the strong fiber/matrix interface obtained through the use of a compatibilizer increased the mechanical performance of such composite systems. The improved adhesion between fibers and matrix weakly affects the flexural modulus but strongly influences the ultimate properties of the investigated woven fabric composites. In fact, bending tests have shown a clear improvement in the flexural strength for the compatibilized systems, in particular when a high viscosity/high crystallinity polypropylene was used. On the contrary, the low velocity impact tests indicated an opposite dependence on the interface strength, and higher energy absorption in not compatibilized composites was detected. This result has been explained in terms of failure mechanisms at the fiber/matrix interface, which are able to dissipate large amounts of energy through friction phenomena. Pull-out of fibers from the polypropylene matrices have been evidenced by the morphological analysis of fracture surfaces after failure and takes place before the fibers breakage, as confirmed by the evaluation of the ductility index.     

On the effect of stacked fabric layers on the stiffness of a woven composite

Most micromechanical models for stiffness prediction of woven composites assume independence of the Q-matrix on the number of fabric layers in the composite. For example, the moduli of single and 10 layer composites are assumed to be equal in the case when all layers have the same in-plane orientation. Although this statement is likely to be true for isotropic materials or even for unidirectional laminated composites, it may not be valid in some cases of woven composites.

This paper contains experimental and theoretical investigations of plain weave carbon fiber/polyester composites. Specimens with one single and eight layers of fabrics are tested and observable differences of mechanical properties are obtained.

The theoretical part of this article consists of derivation and application of several micromechanical models on these particular composites. The use of those simplified models finally allows us to find the main mechanisms which cause the observed effects.     

A comparative study on low-velocity impact response of fabric composite laminates

Impact behaviors at low velocity of composite laminates reinforced with fabrics of different architectures are investigated. Unidirectional prepreg, 2D woven and 3D orthogonal fabrics, all formed of Ultrahigh Molecular Weight Polyethylene (UHMWPE) filaments, were selected as reinforcements to form composite laminates using hot pressing technology. Low velocity impact tests were conducted using a drop-weight impact equipment at the energy level of 35 J. A three-coordinate measuring device was employed to determine the volume of plastic deformation and surface dent diameter. The results show that the composite laminates of single-ply 3D orthogonal woven fabric exhibit better energy absorbed capacity and impact damage resistance as compared to those of unidirectional and 2D plain-woven fabric.     

织物纤维增强橡胶复合板抗射流侵彻的防护效能

基于DOP实验方法开展了玻璃纤维、 碳纤维、 Kevlar-49及PBO等四种织物增强橡胶复合靶板抗射流侵彻性能实验研究。在68°倾角下, 获取了射流侵彻四种不同结构的复合板在鉴证靶上的剩余穿深。分析了面板变形形态及四种纤维的破坏模式, 计算得到了空间防护系数及差分防护系数。结果表明: 面板的变形是干扰射流的一个重要因素, 面板孔壁与射流作用区域越长, 对射流干扰越明显。四种纤维铺层的破坏模式有着较大的差异, Kevlar-49及PBO织物增强橡胶复合板的防护能力远大于玻璃纤维和碳纤维橡胶复合板。     

Finite element analysis of damaged woven fabric composite materials

Since fiber reinforced composite materials have been used in main parts of structures, an accurate evaluation of their mechanical characteristics becomes very important. Due to their anisotropic nature and complicated architecture, it is very difficult to reveal the damage mechanisms of these materials from the results of mechanical tests. Therefore, there is a need to conduct reliable simulations and analytical evaluations. In this paper, the damage behavior of FRP is simulated by finite element analysis using an anisotropic damage model based on damage mechanics. The proposed procedure is applied to an example; the finite element analysis of microscopic damage propagation in woven fabric composites. Experimental tests have been conducted to evaluate the validity of the proposed method. It is recognized that there is a good agreement between the computational and experimental results, and that the proposed simulation method is very useful for the evaluation of damage mechanisms.     

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。     

A three-constituent multicontinuum theory for woven fabric composite materials

Multicontinuum theory (MCT) refers to the use of phase averaged constituent stress/strain fields for predicting failure in composite structural analysis. Given the composite material mechanical properties as well as those of the constituents, well known closed form algebraic expressions exist to decompose the composite stress/strain fields down to the constituent level. Recent research indicates constituent based failure algorithms show a great deal of promise in predicting material failure when coupled to nonlinear finite element codes. A limitation of MCT is that the traditional constituent decomposition is only valid for materials composed of two constituents. In this paper, the MCT decomposition is generalized to handle composite materials composed of three constituents. The application of interest is a woven fabric composite material. The three constituents consist of the warp bundles, fill bundles, and pure matrix pockets. Numerical results are presented for the proposed three-constituent decomposition and are shown to be in good agreement with phase averaged stresses obtained from direct volume averaging of finite element micromechanics models.     

Mass criterion for wave controlled impact response of composite plates

Impact duration strongly influences the impact response of plates. Long impacts cause a quasi-static response influenced by the plate size and boundary conditions. Short impacts cause a response governed by wave propagation unaffected of plate size and boundary conditions. This paper shows that the response type is governed by the impactor–plate mass ratio and not by impact velocity and derives a criterion for small-mass (wave controlled) impact response of orthotropic plates. Published criteria for large-mass (quasi-static) impact are discussed. Small-mass impacts on composite laminates are shown to be more critical than large-mass impacts of the same energy. Use of mass criteria for selecting analytical response models and considerations for sandwich plates are also discussed.     

Ballistic impact behaviour of woven fabric composites: Formulation

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

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.     

Numerical multi-scale modeling for textile woven fabric against ballistic impact

In this study, a FEM analysis has been carried out to find out pertinent multi-scale model for an investigation of a ballistic impact on 2D KM2® plain-woven fabrics. Multi-scale models are a combination between macroscopic and mesoscopic models. This study aims at testing a multi-scale model in order to minimize the computing time. Three configurations were analyzed by varying the ratio of macroscopic and mesoscopic areas: 75.3–24.7%, 65.5–34.5%, 56.3–43.7% with two impact velocities 60 m/s and 245 m/s. In these multi-scale models, the continuity in macroscopic–mesoscopic interfaces is ensured by checking the evolution of global displacements of the fabric during impact. The effect of the macroscopic area of multi-scale models on the ballistic performance of the fabric is also investigated. The optimal multi-scale model was validated by comparison with results obtained from a mesoscopic model in terms of the evolutions of the projectile velocity, energy forms, the overall behavior of the fabric during impact and the force applied on the projectile. The failure criterion Forming Limited Diagram (FLD) is suggested for bundle failure. The observed damage mechanisms of the fabric during penetration time of the projectile are discussed and compared among numerical models.     

Progressive failure modeling of woven fabric composite materials using multicontinuum theory

Failure of composite materials often results from damage accumulation in the individual constituents (fiber and matrix) of the composite. At times, damage may even be limited to a single constituent. The ability to accurately predict not only ultimate strength values but also intermediate constituent level failures is crucial to the success of introducing composite materials into demanding structural applications.In this paper, we develop two progressive failure models for the analysis of a plain weave composite material. The formulations are based on treating the weave as consisting of separate but linked continua representing the warp fiber bundles, fill fiber bundles, and pure matrix pockets. Retaining constituent identities allows one to access constituent (phase averaged) stress fields that are used in conjunction with both a stress based and damage based failure criterion to construct a nonlinear progressive failure algorithm for the woven fabric composite material. The MCT decomposition and the nonlinear progressive failure algorithm are incorporated within the framework of a traditional finite element analysis.The constituent based progressive failure algorithm combined with both the stress based and damage based failure criteria are compared against experimental data for a plain weave, woven fabric composite under various loading conditions. The analytical results from the damage based approach show a marked improvement over the stress based predictions and are in excellent agreement with the experimental data.     

Interlaminar fracture properties of weft-knitted/woven fabric interply hybrid composite materials

An experimental study has been undertaken to characterize the delamination behavior and tensile properties of interply hybrid laminated composites reinforced by interlock weft-knitted and woven glass fiber preform fabrics. The hybrid composites, comprising the alternate layers of interlock and uniweave fabrics, were compared to interlock knitted (only) and uniweave (only) composites with respect to delamination and tensile performances. Mode-I double cantilever beam and mode-II end-notched flexure tests were carried out to assess the interlaminar fracture toughness using aluminum-strip stiffened specimens. The mode-I and mode-II interlaminar fracture toughness values, G _IC and G _IIC, for the hybrid composite were about three and two times higher than that for the uniweave composite, respectively. The tensile strength and modulus of the hybrid composite were 315 MPa and 12.8 GPa in the wale direction, respectively, demonstrating that the strength and modulus were found to be slightly lower than those of the uniweave composite, and significantly improved in comparison with the interlock knitted composites.     

Progressive failure modelling of woven carbon composite under impact

The design of composite structures or components, subject to extreme loading conditions, such as crash, blast, etc. requires a fundamental understanding of the deterioration mechanism within the composite meso-structure. Existing predictive techniques for the analysis of composite structures and components near and beyond their ultimate strength are either based on simple scalar stress functions, or use very complex damage formulations with many material constants, some of which may be difficult to characterise. This paper presents a simple damage mechanics based progressive failure model for thin woven carbon composites under impact loading. The approach is based on an unconventional thermodynamic maximum energy dissipation approach, which entails controlling damage evolution and hence energy dissipation per second, rather than damage. The method has been implemented into the explicit dynamic finite element code DYNA3D. Numerical simulation results using the proposed model are compared with two experimental impact tests.The analysis methodology proposed in this paper reflects a very simple, but effective technique that can be used to model a wide range of problems from extreme events, such as crash or blast, to birdstrike, when tearing and perforation are major failure mechanisms. As damage is cumulative, the technique allows initial or/and post-impact static loads to be applied to the composite structure or component, thus allowing a cradle-to-grave design methodology.     

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.     

Effect of fabric compaction and yarn waviness on 3D woven composite compressive properties

3D-woven fabrics incorporate through-thickness reinforcement and can exhibit remarkable inter-laminar properties that aid damage suppression and delay crack propagation. However, distortions in the internal architecture such as yarn waviness can reduce in-plane properties, especially in compression. The degree of yarn waviness present in a 3D woven fabric can be affected by a range of factors including weave parameters and manufacturing-induced distortions such as fabric compaction. This paper presents a thorough analysis of the effect of fabric compaction and yarn waviness on the mechanical properties and failure mechanisms of an angel-interlock fabric in compression. Tests were conducted on coupons moulded to different volume fractions and data compared to previous measurements of local yarn angle. Major findings show the importance of yarn straightness on compressive strength and how this can be affected by optimising moulding thickness. Failure initiation was also found to be heavily influenced by weave style and yarn interlacing.     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

Transient response of composite sandwich plates

The transient response of orthotropic, layered composite sandwich plates is investigated by using two new C⁰ four and nine node finite element formulations of a refined form of Reddy's higher-order theory. This refined third order theory accounts for parabolic variation of the transverse shear stresses, and requires no shear correction factors. The assumed strain approach is employed to model both thin and thick plates without any major defects like shear locking and parasitic spurious zero energy modes. A consistent mass matrix formulation is adopted. The Newmark direct integration scheme is used to solve the governing equilibrium equations. The parametric effects of plate aspect ratio, length to thickness ratio, boundary conditions and lamination scheme on the transient response are investigated. The present results are in very close agreement with earlier published results in the literature and can serve as a benchmark for future investigators.     

Modelling deformation and damage characteristics of woven fabric under small projectile impact

Fabrics comprising highly oriented polymers possess high impact resistance and are often used in flexible armour applications. As these materials are viscoelastic, accurate modelling of their impact and perforation response requires formulation of constitutive equations representing such behaviour. This study incorporates viscoelasticity into the formulation of a model to analyse the impact of small spherical projectiles on plain-woven PPTA poly(p-phenylene-terephthalamide) fabric. The fabric is idealized as a network of viscoelastic fibre elements and a three-element viscoelastic constitutive model is used to represent polymer behaviour. Viscoelastic parameters are used to reflect intermolecular and intramolecular bond strengths as well as the static mechanical properties of fibres. Results of the theoretical analysis were compared with data from experimental tests on fabric specimens subjected to projectile impact ranging from 140 m/s to 420 m/s. Predictions of the threshold perforation velocity and energy absorbed by the fabric showed good agreement with experimental data. The proposed analysis is able to model deformation development and rupture of the fabric at the impact point. Fraying and unravelling of yarns are also accounted for. The study shows that a knowledge of static mechanical properties alone is insufficient and results in gross underestimation of impact resistance. An important parameter identified is the crimping of yarns. Yarns in woven fabric are not initially straightened out and hence part of the stretching in fabric is due to the straightening of yarns. The effect of crimping was found to be significant for high impact velocities.