2D Carbon Fiber Reinforced High Density Polyethylene Multi-Layered Laminated Composite Panels: Structural,Mechanical, Thermal,and Morphological Profile

Carbon fiber reinforced high density polyethylene multi-layered laminated composite panels(HDPE/CF MLCP) with excellent in-plane properties along transverse direction have been formulated. Composite architectures with carbon fiber(CF) designed in 2D layout in conventional composites can alleviate their properties in thickness direction, but all attempts so far developed have achieved restrained success. Here,we have exposed an approach to the high strength composite challenge, without altering the 2D stack design on the basis of concept of fiber reinforced laminated composites that would provide enhanced mechanical and thermal properties along transverse direction. CF sheets allowed the buckling of adjoining plies in 2D MLCP. We fabricated 2D MLCP by stacking the alternative CF and HDPE layers under different loading conditions, which resulted in high strength composites. These plies of CF and HDPE served as unit cells for MLCP, with CF offering much-needed fracture toughness and hardness to these materials.For 2D HDPE/CF MLCP, we demonstrated noteworthy improvement in physical and chemical interaction between CF and HDPE, in-plane fracture strain, flexural strength(30.684 MPa), bending modulus(7436.254 MPa), thermal stability(40.94%), and surface morphology, upon increasing the CF layers up to twenty, enabling these composites truly for high temperature and high strength applications.     

Toughness properties of a three-dimensional carbon-epoxy composite

The three-dimensional (3D) orthogonal interlocked fabric contains through-the-thickness rein-forcement in order to enhance the interlaminar fracture toughness of the composite. The interlaminar fracture toughness of a carbon-epoxy orthogonal interlocked fabric composite was experimentally determined by use of the recently developed tabbed double cantilever beam specimen. The data reduction methods applicable to these tests and materials and the interpretation of the results were discussed. The results of critical strain energy release rate,G _Ic, were compared to those of a two-dimensional (2D) laminate having the same in-plane structure. The energy-dissipating crack propagation processes were described. The in-plane fracture toughness of the 3D fabric was experimentally measured and compared to that of the 2D laminate. The through-the-thickness fibres were found to create a ten-fold increase in interlaminar toughness, and a 25% improvement in the in-plane fracture toughness.     

A comparative study of tensile properties of non-crimp 3D orthogonal weave and multi-layer plain weave E-glass composites. Part 2: Comprehensive experimental results

This Part 2 paper presents results of comparative experimental study of progressive damage in 2D and 3D woven glass/epoxy composites under in-plane tensile loading. As Part 1, this Part 2 work is focused on the comparison of in-plane tensile properties of two non-crimp single-ply 3D orthogonal weave E-glass fibre composites on one side and a laminate reinforced with four plies of E-glass plain weave on the other. The damage investigation methodology combines mechanical testing with acoustic emission registration (that provides damage initiation thresholds), progressive cracks observation on transparent samples, full-field surface strain mapping and cracks observation on micrographs, altogether enabling for a thorough characterisation of the local micro- and meso-damage modes of the studied composites. The obtained results demonstrate that the non-crimp 3D orthogonal woven composites have significantly higher in-plane strengths, failure strains and damage initiation thresholds than their 2D woven laminated counterpart. The growth of transverse cracks in the yarns of 3D composites is delayed, and they are less prone to a yarn–matrix interfacial crack formation and propagation. Delaminations developing between the plies of plain weave fabric in the laminate at certain load level never appear in the 3D woven single-ply composites.     

Characterization of interlaminar fracture behaviour of woven fabric reinforced polymeric composites

An experimental study was conducted to characterize the interlaminar fracture behaviour of 2-D woven fabric reinforced epoxy composites under mode I loading using double cantilever beam tests. A large displacement, small strain non-linear beam model was used to calculate the interlaminar fracture toughness. The fabrics used included fibreglass and Kevlar woven structures with different weave patterns. An attempt was made to enhance the composite interlaminar toughness by adding different types of microfibres into the matrix. Toughening mechanisms of the composites were analysed using scanning electron microscopy. It was found that the weave patterns of fabrics exhibited a strong influence on the interlaminar fracture behaviour, and that the addition of the microfibres to the epoxy matrix could improve the interlaminar fracture toughness significantly.     

莫来石纤维增强SiO_2气凝胶复合材料的力学性能试验

为了探究莫来石纤维增强SiO_2气凝胶复合材料的拉伸和层间剪切性能,开展了相关试验。首先,进行了复合材料在室温下的面内拉伸试验,获得了复合材料的室温面内拉伸模量;然后,采用引伸计方法和数字图像相关法分别对拉伸变形进行测量,并对2种方法进行了对比分析;最后,开展了不同温度下的层间剪切试验,研究了复合材料在不同温度下的层间剪切性能,并对其微观结构进行了分析。结果表明:复合材料的拉伸模量约为285.17 MPa;由引伸计方法测得的拉伸变形计算出的拉伸模量比数字图像相关法获得的拉伸模量高2.4%;在室温和高温下,试样呈现明显的层间剪切破坏;对复合材料的微观分析发现,SiO_2气凝胶基体主要分布在层间区域,增强纤维主要分布在铺层内。所得结论表明莫来石纤维增强SiO_2气凝胶复合材料拉伸和层间性能较差,当承受层间载荷时,SiO_2气凝胶基体起主要作用,且温度对复合材料的性能影响较大。     

Mode I and mode II fracture toughness of E-glass non-crimp fabric/carbon nanotube (CNT) modified polymer based composites

In this study, mode I and mode II interlaminar fracture toughness, and interlaminar shear strength of E-glass non-crimp fabric/carbon nanotube modified polymer matrix composites were investigated. The matrix resin containing 0.1 wt.% of amino functionalized multi walled carbon nanotubes were prepared, utilizing the 3-roll milling technique. Composite laminates were manufactured via vacuum assisted resin transfer molding process. Carbon nanotube modified laminates were found to exhibit 8% and 11% higher mode II interlaminar fracture toughness and interlaminar shear strength values, respectively, as compared to the base laminates. However, no significant improvement was observed for mode I interlaminar fracture toughness values. Furthermore, Optical microscopy and scanning electron microscopy were utilized to monitor the distribution of carbon nanotubes within the composite microstructure and to examine the fracture surfaces of the failed specimens, respectively.     

Review of z-pinned composite laminates

This paper reviews published research into polymer composite laminates reinforced in the through-thickness direction with z-pins. Research into the manufacture, microstructure, delamination resistance, damage tolerance, joint strength and mechanical properties of z-pinned composites is described. Benefits of reinforcing composites with z-pins are assessed, including improvements to the delamination toughness, impact damage resistance, post-impact damage tolerance and through-thickness properties. Improvements to the failure strength of bonded and bearing joints due to z-pinning are also examined. The paper also reviews research into the adverse effects of z-pins on the in-plane mechanical properties, which includes reduced elastic modulus, strength and fatigue performance. Mechanisms responsible for the reduction to the in-plane properties are discussed, and techniques to minimise the adverse effect of z-pins are described. The benefits and drawbacks of z-pinning on the interlaminar toughness, damage tolerance and in-plane mechanical properties are compared against other common types of through-thickness reinforcement for composites, such as 3D weaving and stitching. Gaps in our understanding and unresolved research problems with z-pinned composites are identified to provide a road map for future research into these materials.     

复合材料微细杆增强复合材料研究进展

纤维增强树脂基复合材料具有轻质高强的特点,但复合材料层合板层间韧性和抗冲击性能差,复合材料微细杆(Z-pin)增强技术极大地改善了这一不足,被广泛应用于各工业制造领域.近年来,Z-pin增强复合材料的制备工艺不断发展,目前主要有热压罐法和超声植入法(UAZ).Z-pin增强复合材料的层间增韧和抗冲击性能提高效果显著,但...     

玻璃纤维立体织物增强环氧树脂泡沫夹层复合材料的制备及力学性能

为了进一步提高泡沫夹层复合材料的承载能力和综合性能,实现其在轨道交通及汽车等工业领域的应用,开展了玻璃纤维立体织物增强环氧树脂泡沫(GF-Fabric/EP)复合材料的制备及其力学性能的研究。制备GF-Fabric/EP复合材料及其夹层结构,探索了GF-Fabric/EP复合材料及其夹层结构的失效行为,以揭示立体织物的增强机制。结果表明：立体织物的引入可显著改善GF-Fabric/EP复合材料的强度、刚度及破坏应变;但在不同承载条件下,各纱线发挥承载作用和效果不同。面板、芯材各自的性能、尺寸及面/芯界面性能均是影响GF-Fabric/EP夹层复合材料力学性能及失效特征的重要因素。以三点加载下的弯曲性能为例,针对不同的GF-Fabric/EP夹层复合材料,需调整跨厚比和试样尺寸并获得理想的失效特征,方可对其弯曲性能或层间剪切性能进行有效、合理的评价。     

Electrospun nanofibre toughened carbon/epoxy composites: Effects of polyetherketone cardo (PEK-C) nanofibre diameter and interlayer thickness

Polyetherketone cardo (PEK-C) nanofibres were produced by an electrospinning technique and directly deposited on carbon fabric to improve the interlaminar fracture toughness of carbon/epoxy composites. The influences of nanofibre diameter and interlayer thickness on the Mode I delamination fracture toughness, flexure property and thermal mechanical properties of the resultant composites were examined. Considerably enhanced interlaminar fracture toughness has been achieved by interleaving PEK-C nanofibres with the weight loading as low as 0.4% (based on weight of the composite). Finer nanofibres result in more stable crack propagation and better mechanical performance under flexure loading. Composites modified by finer nanofibres maintained the glass transition temperature (T_g) of the cured resin. Increasing nanofibre interlayer thickness improved the fracture toughness but compromised the flexure performance. The T_g of the cured resin deteriorated after the thickness increased to a certain extent.     

Enhanced crack detection sensitivity of carbon fiber composites by carbon nanotubes directly grown on carbon fibers

The ability of highly conductive hybrid carbon–fiber/carbon nanotube loaded epoxy composites to sense matrix cracking damage in situ is demonstrated. Multi-walled carbon-nanotubes (MWCNTs) are grown perpendicular to and on the surface of a woven carbon–fiber fabric using a chemical vapor deposition process. An increase in sensitivity of resistance change under interlaminar fracture is shown through a series of double cantilever beam (DCB) tests on samples prepared with MWCNTs grown on both sides of carbon–fiber fabric lamina placed at the top and bottom surfaces of an 8-layer test panel whereas samples with MWCNTs inside the samples did not show much increase in sensitivity of resistance change compared with the baseline samples without MWCNTs. The results suggest that the addition of surface positioned hierarchical carbon-nanotube lamina on composite structures has the potential for autonomic sensing of internal matrix damage.     

Synchronous effects of multiscale reinforced and toughened CFRP composites by MWNTs-EP/PSF hybrid nanofibers with preferred orientation

MWNTs-EP/PSF (polysulfone) hybrid nanofibers with preferred orientation were directly electrospun onto carbon fiber/epoxy prepregs and interlaminar synchronously reinforced and toughened CFRP composites were successfully fabricated. With MWNTs-EP loading increasing, the oriented nanofibers were obtained accompanying with enhanced alignment of inner MWNTs-EP. Flexural properties and interlaminar shear strength of composites were improved with increasing MWNTs-EP loadings, whereas fracture toughness attained maximum at 10 wt% MWNTs-EP loading and then decreased. Based on these results, multiscale schematic modeling and mechanism schematic of hybrid nanofibers reinforced and toughened composites were suggested. Due to the preferred orientation of nanofibers, MWNTs-EP was inclined to align vertically to carbon fiber direction along the in-plane of interface layer. The proposed network structures, containing four correlative phases of MWNTs-EP/PSF sphere/carbon fiber/epoxy matrix, contributed to simultaneous improvement of strength and toughness of composites, which was realized by crack pinning, crack deflection, crack bridging and effective load transfer.     

Compressive strength of unidirectional and crossply carbon fibre/PEEK composites

The commonly accepted production methods of composite systems generally result in departure of the plies properties from transverse isotropy due to stresses acting during fibre—matrix bond formation. This anisotropy coupled with the composite structure affects compressive loading; the ultimate stresses as well as the direction, in- or out-of-plane, of kink propagation. A unidirectional and a crossply carbon fibre/PEEK composites were compression tested at ambient and elevated temperature as well as exposed to various chemical environments. Significant disruptions in fibre—matrix interface in the crossply composite were indicated. The compression tests showed that failure occurred through in-plane and out-of-plane fibre bucking and kinking in the unidirectional and crossply composites, respectively. Failure of the longitudinal plies in the crossply laminate occurred at significantly higher compression stress than for the unidirectional composite. Compressive failure mechanisms in unidirectional and multi-directional laminates are considered.     

PVDF对芳纶无纺布/环氧树脂共固化复合材料力学和阻尼性能的影响

为评价热塑性结晶聚合物聚偏二氟乙烯(PVDF)对共固化复合材料动态力学和阻尼性能的影响,首先,将PVDF负载到芳纶无纺布(ANF)上,采用共固化工艺制备了PVDF-ANF/环氧树脂(EP)结构阻尼复合材料。然后,利用动态机械分析仪测试了PVDF-ANF/EP复合材料的损耗因子、损耗模量和储能模量的温度谱;通过弯曲强度、弯曲模量和层间剪切强度的测试评价了复合材料的静态力学性能;通过单悬臂梁振动实验测试了复合材料的共振频率及自由振动衰减曲线,并计算了损耗因子;通过I型、II型层间断裂韧性实验及断面微观形貌的观察研究了复合材料的断裂韧性及增韧机制。最后,对复合材料的微观结构进行分析,探讨了其兼具力学性能和阻尼性能的结构内因。结果表明:通过在ANF表面负载PVDF,可在不引起复合材料力学性能明显下降的前提下,进一步提高PVDF-ANF/EP复合材料的阻尼性能和层间断裂韧性,复合材料的损耗因子提高了33.3%,I型和II型断裂韧性分别提高了168%和208%。     

Fracture Toughness (Mode-I) of Para-Aramid/Phenolic Nano Preform Composites

The mode-I interlaminar toughness properties of nanostitched para-aramid/phenolic multiwall carbon nanotube composites were studied. The toughness strength of the stitched and stitched/nano composites demonstrated 40 fold and 38 fold (beam theory) increases compared to the base composites, respectively. It was found that stitching yarn type, especially prepreg para-aramid stitching yarn, was effective. On the other hand, the initiation and propagation of the G_IC values for stitched and stitched/nano composites were considerably deviated due to strengthening mechanism of the para-aramid stitch yarn in the transverse direction of the composite. The fracture toughness resistance to arrest crack propagation in the stitched/nano composite was mainly due to through-the-thickness stitching fiber bridging and pull-out, and was also due to warp and weft directional fiber bridging and multiwall carbon nanotubes. The results demonstrated that mainly stitching and some extent the nanotubes arrested the crack growth. Therefore, the stitched/nano and especially stitched para-aramid/phenolic composites showed a better damage resistance performance.     

碳纳米管膜层间改性碳纤维/双马来酰亚胺复合材料的结构调控及性能

对比研究了热塑性层间增韧和碳纳米管(CNT)膜层间混杂碳纤维(CF)/双马来酰亚胺复合材料不同层间结构调控方法,分析了其复合材料的压缩、动态力学、导电和电磁屏蔽等性能的变化.结果表明,热密实可显著降低层间CNT膜的厚度,抑制其局部富树脂程度,CNT膜-CF混杂复合材料的压缩强度得以提升,其压缩断口形貌明显不同于初始的C...     

Delamination detection with carbon nanotube thread in self-sensing composite materials

Laminated composite materials can reach high mechanical properties at low weight. Composite materials, however, are susceptible to damage due to their low interlaminar mechanical properties and poor heat and charge transport in the transverse direction to the laminate. Moreover, methods to inspect and ensure the reliability of composites are expensive and labor intensive. Recently carbon nanotube forests were spun into thread that is tough and electrically conductive. The thread was integrated into composite materials and used for the first time as a sensor to monitor strains and detect damage including delamination in the material. These self-sensing composites were found to be very sensitive to damage and will help to revolutionize the maintenance of composite structures, which will now be based on their condition and not their amount of use.     

尼龙无纺布结构化增韧层增韧碳纤维/环氧树脂复合材料的湿热力学性能

采用尼龙无纺布(PNF)作为结构化增韧层,制备了PNF层间增韧改性的U3160碳纤维增强3266环氧树脂(U3160-PNF/3266)复合材料,研究了U3160-PNF/3266复合材料的面内力学性能及湿热老化后的力学性能变化,并分析了复合材料湿热老化前后的层间形貌。结果表明:PNF增韧层的引入并未导致复合材料面内力学性能的下降,与未增韧的U3160碳纤维增强3266环氧树脂(U3160/3266)复合材料相比,增韧复合材料U3160-PNF/3266的90°拉伸性能有所提高。而湿热老化处理对U3160-PNF/3266复合材料的基体和界面性能影响相对明显,尤其是尼龙纤维与树脂基体之间的界面结合性能,湿热老化处理后增韧复合材料的90°压缩和层间剪切性能保持率均明显低于未增韧复合材料的。