Interlaminar Fracture Toughness of Carbon Fiber/Epoxy Composites using Short Kevlar Fiber and/or Nylon-6 Powder Reinforcement

Mode I (G_IC) and Mode II (G_IIC) interlaminar fracture toughness of carbon-fiber/epoxy composites have been investigated as a function of the amount of short Kevlar-29 fiber (SKF) and/or Nylon-6 powder (N6P) between continuous fiber layers. G_IIC increased with increasing crack length as a consequence of the presence of SKFs bridging in the wake of propagating crack. G_IIC of SKF alone could reach the maximum at an intermediate amount of SKF. G_IIC of SKF and N6P was lower than that of SKF alone because N6P prevented the orientation of SKF to out-of-plane. The extent of SKF's bridging phenomenon may be influenced by the amount and orientation of SKF. G_IC showed no significant effect with SKF and uniform irrespective of crack length. Scanning electron microscopy after G_IIC test showed that new surfaces were created by extensive fiber bridging, pull-out and fracture of SKF in random direction without any fixed pattern. © 1997 John Wiley & Sons, Ltd.     

Kevlar纤维叠层织物防弹机理和性能研究

选取多种形状的冲击体对Kevlar纤维叠层织物进行了弹道冲击实验.研究了Kevlar纤维受冲击时的表观破坏形态和微观损伤机理.结果表明:纤维的变形破坏随冲击物的形状和速度变化呈现出多形态、多阶段模式;纤维的微观变形形态为:除拉伸破坏外,断口处产生大量的侧向劈裂,并且呈现明显的塑性流动.同时研究了试样面密度、冲击速度等因素对材料防弹性能的影响规律.构建了材料防弹性能的一般方程.     

铺装层对钢箱梁结构抗爆性能影响试验研究

为了研究混凝土铺装层对钢箱梁结构抗爆性能的影响,在一定的药量和爆炸距离下,对配置钢丝网的钢箱梁混凝土铺装层进行了爆炸试验。实验表明,配置钢丝网的混凝土铺装层可以减少钢箱梁顶板在爆炸荷载作用下塑性破坏的程度(最大可降低50%以上);增设Kevlar布的钢丝网混凝土铺装层抗爆能力比单纯的钢丝网混凝土铺装层效果更好(最大可降低63%以上);钢丝网层数设置越多,混凝土铺装层破坏核心区直径越小;增设Kevlar布,在一定厚度下,可以减小混凝土铺装层破坏核心区直径;随着Kevlar布厚度增加,混凝土铺装层反而破坏严重,需要对Kevlar布的厚度和施工方法进行优化设计。     

Enzymatic surface modification of Kevlar fibers

Horseradish peroxidase catalyzed grafting of acrylamide (AM) onto Kevlar fibers has been studied. The modified fiber has been characterized with scanning electron microscopy (SEM), elemental analysis and the grafting yield. From the SEM micrographs, the surface of the grafted Kevlar fiber is rougher than that of the untreated fiber, and the elemental analysis indicated that the nitrogen content of the treated fibers is higher than that of the untreated fiber. All the results suggested that AM must have been grafted onto the Kevlar surface through HRP-mediated radical initiated grafting reaction. The probably mechanism of HRP catalyzed grafting of AM onto Kevlar surface is proposed.     

Kevlar纤维增强复合材料动态压缩力学性能实验研究

通过实验较系统地研究了Kevlar纤维增强复合材料的动态压缩力学性能,实验结果表明,在冲击压缩载荷作用下Kevlar纤维增强复合材料有明显的损伤软化现象和应变率效应,针对Kevlar纤维增强复合材料动态应力应变实验曲线,提出了含损伤的率相关动态本构方程,由于所引入的损伤最反映了Kevlar纤维增强复合材料内部基体开裂、脱层、纤维断裂等多种破坏模式的总体效果,因此所提出的本构方程形式相对说来比较简便并易于嵌入目前有关冲击力学的有限元或有限差分程序,有一定的工程应用价值。     

3种高性能纤维的热学性能

对比研究Kevlar 129、PBO和Kennel等3种高性能纤维热学性能.通过在氮气中的热重分析(TGA),发现PBO有较高的降解温度,初始降解温度为556.5℃,比Kevlar129和Kennel高出了约100℃.根据它们的降解特征温度,选择100,200,300,400℃热处理1.5h,3种高性能纤维的强度和断裂伸长率都发生了下降,模量随温度变化是先增加后降低.PBO总体上显示了较好的力学保持性能.从它们断裂拉伸形貌可以看到各自的皮芯分布,但Kennel没有出现如PBO和Kevlar那样的带状原纤.     

High strain rate compression testing of intra-ply and inter-ply hybrid thermoplastic composites reinforced with Kevlar/basalt fibers

In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage.     

The effect of oxygen-plasma treatment on Kevlar fibers and the properties of Kevlar fibers/bismaleimide composites

The effect of oxygen-plasma treatment for Kevlar fibers on the interfacial adhesion and typical macro-properties of Kevlar fiber/bismaleimide composites was intensively studied. It is found that oxygen-plasma treatment significantly affects the interfacial adhesion by changing the chemistry and morphology of the surfaces of the fibers, and thus leading to improved interlaminar shear strength, water resistance and dielectric properties of the composites. However, the improvement is closely related to the treatment power and time. The best condition for treating Kevlar fiber is 70 W for 5 min. Oxygen-plasma treatment provides an effective technique for overcoming the poor interfacial adhesion of Kevlar fiber based composites, and thus showing great potential in fabricating high performance copper clad laminates.     

PVA覆膜对Kevlar纤维表面化学镀Cu层性能的影响

通过聚乙烯醇 (PVA) 覆膜处理的方法提高了Kevlar纤维表面金属镀层稳定性和完整性,从而提升了镀层的抗剥落能力.采用弯折剥离实验考察了镀层的抗剥落破坏情况、采用电阻仪和电子万能试验机测试了试样的导电性和力学性能,利用扫描电子显微镜(SEM)和X射线光电子能谱(XPS)研究了试样的表面形貌和表面化学价态. 结果表明:PVA覆膜能够有效提升金属镀层的抗剥落破坏能力;随着PVA水解浓度的增加,PVA覆膜Cu/Kevlar纤维的表面电阻增加而柔韧性降低;当PVA溶液的水解质量浓度为5 g/L时,PVA覆膜Cu/Kevlar纤维的柔韧性、导电性和抗剥落能力能够维持在最佳状态;在此浓度下,PVA覆膜Cu/Kevlar纤维的表面电阻为0.41 Ω/cm,单丝拉伸强度为2.396 GPa,Weibull分布拟合度为0.988 1.