Quasi-static penetration and ballistic properties of kenaf–aramid hybrid composites

In this research, quasi-static penetration and ballistic properties of non-woven kenaf fibres/Kevlar epoxy hybrid laminates with thicknesses ranging from 3.1 mm to 10.8 mm by hard projectile at normal incidence have been experimentally investigated. Hybrid composites were fabricated by hand lay-up technique in a mould and cured at room temperature for 24 h by static load. Hybrid composites consist of Kevlar layers and non-woven kenaf layers at three different configurations, i.e. kenaf at the innermost layers, outermost layers and at the alternating layers. Kevlar/epoxy and kenaf/epoxy composites were also fabricated for comparison purpose. Quasi-static experiments were conducted using a tensile testing machine at the speed of 1.27 mm/min and 2.54 mm/min. Ballistic tests were conducted using 9 mm full metal jacket bullet using a powder gun at speeds varying from 172 to 339 m/s, with the initial and a residual velocity of the projectiles is measured. The tested sample was carefully examined with respect to failure modes. Results showed the effect of hybridization in term of force–displacement curves, energy dissipation and damage mechanisms for quasi-static test. Maximum force to initiate penetration is higher in hybrid composites compared to kenaf/epoxy and Kevlar/epoxy composites. Hybridization of kenaf–Kevlar resulted in a positive effect in terms of energy absorbed (penetration) and maximum load. In the case of ballistic tests, hybrid composites recorded lower ballistic limit (V₅₀) and energy absorption than the Kevlar/epoxy composite. The V₅₀ of hybrid composites with kenaf at the outermost layers is superior to other hybrid composites. These finding inspired further exploration of hybrid composite for ballistic armour spall-liner application.     

弹道防护用先进复合材料弹道响应的研究进展

本文对弹道防护用先进复合材料的弹道响应研究及其在工程领域的应用现状进行了综述。首先,基于工程应用研究的试验结果,对超高分子量聚乙烯(UHMWPE)纤维、对位芳香族聚酰胺(PPTA)纤维、芳Ⅲ纤维、聚对苯撑苯并双噁唑(PBO)纤维和聚酰亚胺(PI)纤维等高性能纤维的防弹性能及其复合材料在弹道防护工程领域的应用现状进行了概述,近年来先进复合材料的防弹性能随着纤维力学性能的突破而逐渐提高;其次,讨论了先进复合材料弹道响应的影响因素及其作用机制,发现先进复合材料的塑性拉伸变形是其抵挡弹丸侵彻的主要防弹机制;最后,对弹道防护用先进复合材料的研究方向进行了展望。      

The effect of hybridization on the ballistic impact behavior of hybrid composite armors

In the present study, effect of hybridization on the hybrid composite armors under ballistic impact is investigated using hydrocode simulations. The hybrid composite armor is constructed using various combinations and stacking sequences of fiber reinforced composites having woven form of fibers specifically high specific-modulus/high specific-strength Kevlar fiber (KF), tough, high strain-to-failure fiber Glass fiber (GF) and high strength/high stiffness Carbon fiber (CF). Different combinations of composite armors studied are KF layer in GF laminate, GF layer in KF laminate, KF layer in CF laminate and CF layer in KF laminate at various positions of hybridized layers for a fixed thickness of the target. In this article the results obtained from the finite element model are validated for the case of KF layer in a GF laminate with experimental predictions reported in the literature in terms of energy absorption and residual velocity and good agreement is observed. Further, the effect of stacking sequence, projectile geometry and target thickness on the ballistic limit velocity, energy absorbed by the target and the residual velocity are presented for different combinations of hybrid composite armors. The simulations show that, at a fixed thickness of the hybrid composite armor, stacking sequence of hybridized layer shows significant effect on the ballistic performance. The results also indicate energy absorption and ballistic limit velocity are sensitive to projectile geometry. Specifically, it is found that arranging the KF layer at the rear side, GF layer in the exterior and CF layer on the front side offers good ballistic impact resistance. The hybrid composite armor consisting of a CF layer in KF laminate acquires maximum impact resistance and is the best choice for the design compared to that of other combinations studied.     

三维编织复合材料弹道侵彻准细观层次有限元计算

三维编织复合材料相比于层合复合材料有较高的层间剪切强度和断裂韧性,因而具有更高的冲击损伤容限。用钢芯弹对三维编织复合材料作弹道贯穿测试,得到弹体的入射速度和剩余速度,并考察侵彻破坏模式。目前对三维编织复合材料弹道侵彻性能计算主要建立在连续介质假设上,从真实细观结构计算三维编织复合材料弹道冲击性能尚有一定难度,用三维结构复合材料的纤维倾斜模型在准细观结构层次上分解三维编织复合材料,就其中的一块倾斜单向板作弹道侵彻有限元计算,由弹体动能损失得到贯穿整个复合材料靶体后弹体的剩余速度。有限元计算及与弹道测试结果的比较证明在准细观层次上计算三维编织复合材料弹道冲击性能的有效性。      

Energy transfer in ballistic perforation of fibre reinforced composites

High speed cine techniques have been used to examine the perforation of thin targets constructed of glass fibre reinforced plastic (GRP), Spectra (Allied Signal) and Kevlar (Du Pont) composites as well as nylon and Kevlar fabrics. From the film record the kinetic, strain and (for the composites only) delamination/surface energy terms were evaluated for the rear layer of material. Simple models for the deformation of the panels were used to compare these energies, summed for all layers, with the projectile energy loss. All the energy terms are shown to be significant. The Kevlar fabric does not fit the pattern of the other materials, in that for this material nearly all the projectile energy appeared as tensile strain energy in only the rear layer of the target. This result was a consequence of the high apparent strain observed in the fabric, and is not simply explained. Energy terms not evaluated, but which may be significant, are crushing and ejection of fibres for GRP composites and spalling of matrix phase with the Spectra composites. The work highlights many of the features which need to be accounted for in modelling ballistic perforation of fabric and fibre reinforced composite materials. © 1998 Chapman & Hall     

Preparation and characterization of three-dimensional braided carbon/Kevlar/epoxy hybrid composites

Though unidirectional, short, and laminated hybrid composites have been extensively investigated because of their wider range of properties than non-hybrid composites, literature on three-dimensional (3-D) braided hybrid composites is very limited. In this work, Kevlar fibers were hybridized to carbon fibers to prepare 3-D carbon/Kevlar/epoxy composites with various carbon to Kevlar fiber volume ratios in an attempt to find alternative materials for osteosynthesis devices. The flexural, shear, and impact properties of the 3-D braided hybrid composites were measured in order to investigate the effect of carbon to Kevlar ratio and evaluate hybrid effects. In addition, residual flexural strength was tested for the impacted samples and the damage tolerance was assessed. Our experimental results revealed the existence of positive hybrid effects on the shear and flexural strengths flexural strain for the 3-D braided composites. The absorbed energy and flexural strength retention of the 3-D braided hybrid composites were found to decrease with relative carbon fiber content. It was shown that hybridizing ductile 3-D braided Kevlar fabric with stiff carbon fabric could result in the hybrid composites with flexural strength comparable to the all-carbon composite and impact damage tolerance superior to the all-Kevlar composite.     

Asymmetric hybrid composite: A design concept to improve flexural properties of Kevlar Aramid composites

Asymmetric hybridization is proposed as a mechnanism for improvement of flexural properties of composites reinforced with Kevlar¹ aramid fiber, where the compressive strength of the fiber is a limiting factor. A calculation based on a bi-material beam model is presented, which determines the placement and arrangement of fibers in a composite such that the stress developed on the tensile side of the composite equals the ultimate tensile strength of Kevlar. An experimental investigation was conducted with asymmetric hybrid composites of J-polymer reinforced with Kevlar and carbon fibers. In the best cases, the observed ultimate flexural and shear strengths were improved by 40% and 25% by comparison with values typically seen for composites of J-polymer and Kevlar.     

Response of composite materials to hypervelocity impact

Investigation of composite materials response to hypervelocity impact by space debris has been carried out. In order to simulate hypervelocity impact, a unique laser driven flyer plate (LDFP) system was used, generating hypervelocity debris with velocities of up to 3 km/s. The materials studied in this research were Kevlar 29/epoxy and Spectra1000/epoxy thin film micro-composites (thickness of about 100 μm). Both Spectra and Kevlar fibers are used in long-duration spacecraft outer wall shielding to reduce the perforation threat. The micro-mechanical response of different composites was studied and correlated to the fiber, the matrix and the fiber/matrix interface properties. Visual and microscopic examinations of the damaged area identified fiber debonding as the prevailing failure mechanism. On the basis of a simple energy balance model it can be stated that for Spectra/epoxy composite the dominant mechanism is new surface creation, whereas for Spectra surface-treated fibers/epoxy the fiber pull out is the dominant mechanism. For Kevlar/epoxy fiber, pull out mechanism plays an important role.     

Low velocity impact of combination Kevlar/carbon fiber sandwich composites

Impact, compression after impact, and tensile stiffness properties of carbon fiber and Kevlar combination sandwich composites were investigated in this study. The different samples consisted of impact-side facesheets having different combinations of carbon fiber/Kevlar and carbon fiber/hybrid. The bottom facesheets remained entirely carbon fiber to maintain the high overall flexural stiffness of the sandwich composite. The focus of this research was to determine if any improvement in impact properties existed as a result of replacing the impact-side facesheet layers of carbon fiber with Kevlar or hybrid. Impact tests were conducted on different sample types to obtain information about absorbed energy and maximum impact force. Also, compression after impact tests were conducted to determine the reduction in compressive strength when comparing impacted to non-impacted samples. The elastic moduli of carbon fiber, Kevlar, and hybrid were determined from tensile testing. This data was used to characterize the reduction in stiffness from replacing carbon fiber layers with the Kevlar or hybrid layers. The experimental data in its entirety helps define the benefits and disadvantages of replacing carbon fiber layers with Kevlar or hybrid.     

Ballistic Penetration of Dyneema Fiber Laminate

UHMWPE fiber (Dyneema) reinforced composites are an important class of materials for armors.These materials provide superior ballistic performance to the armor, such as the military armor systems requiring a reduction in back-armor effects or a substrate for hardened facings of steet or ceramic. The reported work characterized the ballistic impact and mechanical performance of Dyneema fiber in composite laminates. The capability of the laminate to absorb ballistic impact energy was influenced by the impact velocity and the laminate areal density. Two kinds of penetration were compared and a two-step model for the penetration was proposed.     

The ballistic impact characteristics of Kevlar® woven fabrics impregnated with a colloidal shear thickening fluid

This study reports the ballistic penetration performance of a composite material composed of woven Kevlar® fabric impregnated with a colloidal shear thickening fluid (silica particles (450 nm) dispersed in ethylene glycol). The impregnated Kevlar fabric yields a flexible, yet penetration resistant composite material. Fragment simulation projectile (FSP) ballistic penetration measurements at 244 m/s have been performed to demonstrate the efficacy of the novel composite material. The results demonstrate a significant enhancement in ballistic penetration resistance due to the addition of shear thickening fluid to the fabric, without any loss in material flexibility. Furthermore, under these ballistic test conditions, the impregnated fabric targets perform equivalently to neat fabric targets of equal areal density, while offering significantly less thickness and more material flexibility. The enhancement in ballistic performance is shown to be associated with the shear thickening response, and possible mechanisms of fabric-fluid interaction during ballistic impact are identified.     

LiCl处理对芳纶纤维表面结构与性能的影响

为提高芳纶纤维与复合材料基体间的界面强度,首先,使用LiCl乙醇溶液处理芳纶纤维一定时间;然后,对LiCl处理芳纶纤维表面的化学组成、微观形貌、单丝拉伸强度及芳纶纤维/环氧树脂复合材料的界面性能等进行了测试分析。结果表明:使用LiCl乙醇溶液处理芳纶纤维后,芳纶纤维表面的含氮官能团含量增加;处理后,芳纶纤维表面有刻蚀出的沟槽,表面粗糙度增大,进而改善了芳纶纤维与环氧树脂基体的界面粘接性能,使芳纶纤维/环氧树脂复合材料的层间剪切强度由处理前的21.75 MPa提升到37.98 MPa;最佳处理时间为3~4 h,而处理时间过长会导致芳纶纤维的单丝拉伸强度及复合材料的层间剪切强度下降。所得结论证实使用LiCl处理芳纶纤维是一种有效的表面改性方法。      

磷酸处理芳纶纤维的缠绕环氧树脂基体

在用磷酸(PA)溶液处理芳纶纤维的基础上, 系统研究了适用于制备高性能芳纶纤维增强复合材料的缠绕环氧树脂基体, 测试了复合材料的力学性能和热机械性能, 讨论了树脂基体对芳纶纤维增强复合材料界面性能的影响。结果表明: 经过磷酸溶液处理的芳纶纤维表面存在一定量的极性官能团, 与缩水甘油酯类环氧树脂有良好的界面相容性; 经过优化的树脂体系其芳纶纤维增强复合材料的NOL环(Naval Ordnance Laboratory Ring)纤维强度转化率达到95％, 层间剪切强度(ILSS)达到79MPa, 界面剪切强度(IFSS)达到76MPa, 具有较好的界面性能。      

Characterization and comparative study of three-dimensional braided hybrid composites

Cartesian three-dimensional braiding as a method of preforming for hybrid composites has been investigated. The fundamental case of a two-sided hybrid 3-D braid was chosen. Hybrid preforms, along with a corresponding set of non-hybrid preforms for control, were fabricated using a Cartesian braiding method. The preforms were consolidated through a Resin Transfer Molding process and prepared for characterization and mechanical testing. Characterization of the braided hybrid composite specimens included yarn packing and deformation within an assumed unit cell, and measurement of constituent tow fiber volume fraction using digital image analysis. A comparison study of the elastic performance of Kevlar/epoxy and carbon/Kevlar hybrid composites was carried out. The tension test results show a near-linear stress-strain relationship for both specimen types within the range of the applied load. The tensile modulus for the carbon/epoxy and hybrid composite were found to be 41 GPa and 74 GPa, respectively. In addition, the Poisson ratio of near unity for both specimen types strongly suggests a fiber dominated material response. The difference in hybrid composite transverse strain due to the differing constituent fiberous materials is found to be appreciable. It is believed that this discrepancy in Poisson contraction, between the carbon and Kevlar sides of the specimens, causes the propagation of transverse cracks [primarily within the carbon tows] and ultimately leads to catastrophic composite failure. Composite ultimate strength and strain to failure were found to be 793 MPa and 1.9% for the Kevlar/epoxy sample and 896 MPa and 1.1% for the carbon/Kevlar hybrid.     

Punch shear based penetration model of ballistic impact of thick-section composites

Ballistic damage and penetration mechanics of thick-section composites are presented. In order to correlate the ballistic penetration damage mechanisms with quasi-static penetration, experiments are designed to maintain similar boundary conditions. It has been found that the ballistic damage mechanisms can be mimicked by conducting a series of quasi-static punch shear experiments at different support spans. A quasi-static punch shear test (QS-PST) methodology is developed to quantify and partition the penetration energy into elastic and absorbed energies as a function of penetration displacement and support span. Based on this QS-PST experimental methodology, a ‘Quasi-Static Penetration Model’ of ballistic penetration is developed to mimic different phases of ballistic penetration. QS-PST energy absorption due to material damage is shown to be 81% of the total energy absorption measured during ballistic experiments at the ballistic limit for the S-2 glass/SC15 composite studied.     

The effect of hybridization on the GFRP behavior under high velocity impact

In the present study, experimental and analytical investigations for the behavior of E-glass fiber reinforced composite hybridized with a layer of Kevlar 29 fiber, under high velocity impact, were performed. The experimental work includes the placement of the Kevlar layer at four different locations to verify the effects of the stacking sequence on the impact behavior. Three different projectile geometries, namely, flat-ended, hemispherical and conical were used. The experimental results reveal that hybridization improves the laminates performance under dynamic penetration. The results also indicate that the laminates response was found to be highly sensitive to the projectile geometry. In the case of analytical modeling, two energy models were conducted to calculate the projectile residual velocities. The results obtained from the two models were compared with those obtained experimentally and some conclusions were drawn.     

对位芳香族聚酰胺纤维/环氧树脂复合材料防弹性能及其破坏机制

为研究对位芳香族聚酰胺纤维/环氧树脂（Epoxy resin,EP）复合材料的防弹性能及其破坏机制,采用铅芯弹侵彻复合材料靶片。以对位芳香族聚酰胺纤维作增强纤维,EP作基体树脂,纳米SiO₂和聚乙烯醇缩丁醛（Polyvinyl butyral,PVB）作增韧剂,通过热压工艺制备单向（Unidirectional,UD）结构的对位芳香族聚酰胺纤维/EP复合材料靶片。研究单片纤维面密度、UD片材结构、射击角度和树脂改性对靶片防弹性能的影响;观察弹击实验后靶片的破坏形貌,分析靶片的破坏机制。研究结果表明:对位芳香族聚酰胺纤维/EP复合材料具有优异的防弹性能,随着单层纤维面密度的增大,靶片的防弹性能呈现整体上升、局部上下波动的变化趋势;铺层方式为0°/90°/0°/90°的四层单UD片材（4UD）结构的防弹性能优于铺层方式为0°/90°的两层单UD片材（2UD）结构;角度射击时,靶片的穿透比率更大,背衬凹陷深度（Back face signature,BFS）比率更小;PVB增韧改性EP提升了靶片的防弹性能;纤维拉伸变形破坏、片材分层和基体树脂碎裂是复合材料靶片主要的吸能方式。      

Microdamage analysis of fibrous composite monolayers under tensile stress

The quasi-static deformation and fracture modes of several types of fibrous composite materials are studied from a fundamental viewpoint using a new experimental approach. Microcomposite monolayers, consisting of single fibres accurately positioned into a thin poly-meric matrix, were manufactured using a specially developed technique, and tested for strength by means of a custom-made miniature tensile testing machine. The materials used were E-glass, and Kevlar 29, Kevlar 49 and Kevlar 149 para-aramid fibres, and a room-temperature curing epoxy resin. The tensile testing machine was fitted to the stage of a polarized light stereozoom microscope and the fracture process was recorded both via a standard 35 mm camera and a colour video camera. The fibre content of the first generation of micro-composite monolayers used in this work was low (<0.025) but definite effects on the modulus and strength were obtained as the experimental data followed the rule-of-mixtures quite accurately in most cases. The failure process was different in each type of composite and current statistical models for strength are unable to account for the modes of failure observed in some of the systems studied. The experimental approach proposed is potentially useful in the study of the effects of interface chemistry modifications, fibre-fibre interactions, matrix toughness modification, misalignment effects, and more, on the deformation and failure micromechanics of composites.Incumbent of the Jacob and Alphonse Laniado Career Development Chair.     

Dynamic penetration of graphite/epoxy laminates impacted by a blunt-ended projectile

The dynamic penetration of graphite/epoxy laminates as a result of impact by a blunt-ended projectile is investigated in the present study. The ballistic limit is determined by a series of high-velocity impact tests. A dynamic finite element analysis is performed to simulate the penetration process in composite laminates. A previously developed static penetration model is incorporated into the analysis to predict the ballistic limit. The ballistic characteristics are represented by the relationship between the striking and residual velocities of the projectile. Good agreement between experimental data and computational results implies that the ballistic limit of graphite/epoxy laminates can be predicted by the present analysis without performing dynamic impact tests.     

陶瓷/纤维层间混杂复合材料设计制作及抗弹体冲击性能测试

掩体作为战场中指挥、防御、观察、射击的综合性军事工事,其观察口为薄弱点,防护能力的大小关系着其内部人员是否安全。本文以防护轻武器为设计目标,设计、制作一种纤维/陶瓷层间混杂复合材料,并对其防弹能力进行测试。首先,基于显式有限元软件ABAQUS/Explicit,建立弹体冲击纤维/陶瓷层间混杂复合材料防护甲板的数值模型,研究混杂纤维与同种纤维、混杂纤维的不同比例及纤维的铺设角度对复合材料防护甲板抗冲击性能的影响。结果表明:两种纤维混杂且混杂比例为0.3~0.7、纤维铺设角度为:0°/30°/60°/90°/?60°/?30°/0°时防护效果最好。其次,根据模拟结果,利用缠绕成型和手糊工艺相结合的方式将高强玻璃纤维S-2/TDE-85环氧树脂复合材料层合板、SiC陶瓷及凯芙拉49纤维/TDE-85环氧树脂复合材料层合板依次堆叠,制作纤维/陶瓷层间混杂复合材料防护甲板试件。最后,利用改进的霍普金森压杆装置进行防护甲板的弹体冲击试验。结果表明:设计的防护甲板能够抵挡住平均速度为500 m/s子弹的贯穿,与理论计算的结果相符合。