钩针工艺之于活性碳纤维/环氧树脂电路屏吸波复合材料的设计

通过钩针工艺将活性碳纤维(ACF)和玻璃纤维(GF)混编,提高了频率选择性表面(FSS)的可设计性和复杂性,制备了ACF钩针结构单元电路屏碳纤维/环氧树脂(ACF/EP)复合材料。研究了不同编织结构和ACF质量分数对复合材料吸波性能的影响。结果表明:ACF质量分数为100%的4针枣形FSS的ACF/EP复合材料和质量分数为50%的16针枣形FSS复合材料的最大反射损耗(RL)可以达到-50dB以上,有效吸收带宽(RL-10dB)达10GHz以上。复杂的钩针设计使ACF/EP复合材料的多孔结构增多,有效吸收带宽变宽,4针枣形结构具有较多不规整孔径使吸波效果显著。适量的ACF质量分数结合编织结构有利于获得理想的CF/EP吸波复合材料。     

Fabrication of radar absorbing structure (RAS) using GFR-nano composite and spring-back compensation of hybrid composite RAS shells

The fiber-reinforced composite materials have been advanced to provide excellent mechanical and electromagnetic properties. The radar absorbing structure (RAS) is such an example that satisfies both radar absorbing property and structural characteristics. The absorbing efficiency of RAS can be obtained from selected materials having special absorptive properties and structural characteristics such as multi-layer and stacking sequence.

In this research, to develop a RAS, three-phase composites consisted of {glass fiber}/{epoxy}/{nano size carbon materials} were fabricated, and their radar absorbing efficiency was measured on the X-band frequency range (8–12 GHz). Although some of GFR (Glass Fiber–Reinforced)-nano composites showed outstanding absorbing efficiency, during their manufacturing process, undesired thermal deformation (so called spring-back) was produced. The main cause of spring-back is thought to be temperature drop from the cure temperature to the room temperature. In order to reduce spring-back, two types of hybrid composite shells were fabricated with {carbon/epoxy} and {glass/epoxy} composites. Their spring-back was measured by experiment and predicted by finite element analysis (ANSYS). To fabricate desired final geometry, a spring-back compensated mold was designed and manufactured. Using the mold, hybrid composite shells with good dimensional tolerance were fabricated.     

镀Al空心玻璃微球FeCo合金/环氧树脂复合材料的吸波性能

利用磁控溅射法对空心玻璃微球表面镀Al。研究了由镀Al空心玻璃微球FeCo合金/环氧树脂制成的复合材料在2~18GHz频段范围内的电磁特性, 利用模型计算了所制备样品的微波反射率。结果表明, 在镀Al空心玻璃微球和FeCo合金粉末总体积分数一定的条件下, 随着镀Al空心玻璃微球与FeCo 合金体积比的增加, 复合材料介电常数实部ε′减小, 虚部ε″ 变化不明显; 磁导率的实部μ′ 和虚部μ″ 均减小; 反射率峰值向高频方向移动。 当 镀Al空心玻璃微球与FeCo合金体积比2∶1时, 涂层厚度为2mm, 吸收峰值达到-29.69dB, 其面密度仅为3.71kg/m2, 吸收率小于-10dB的带宽达到2.4GHz。由此可见, 通过改变镀Al空心玻璃微球与FeCo合金的体积比, 可以调节电磁参数, 提高材料的吸波性能。      

微量碳纤维/树脂复合吸波材料的研究

分别研究了平行和正交排布碳纤维复合材料的微波吸收特性，并对碳纤维的吸波机理和吸波性能的影响因素（纤维间距、支数）作了初步探讨。结果表明：碳纤维平行排布吸波材料只在入射电场方向与纤维排布方向平行时具有吸波性能；随纤维间距的减小，其反射衰减曲线的最大吸收峰向高频方向移动；纤维支数增大，吸波性能增强。正交排布碳纤维的吸波性能与纤维的间距密切相关。本实验条件下当纤维间距为8mm时，可获得有效带宽4．7GHz、最大吸收峰值-21．6dB的反射衰减。     

Fabrication process of carbon nanotube/light metal matrix composites by squeeze casting

Multi-walled carbon nanotubes (MWCNTs) should be attractive for the reinforcement of metal-matrix composites, because of their high strength, high modulus and high thermal conductivity. However, the fiber diameter of MWCNTs is hundreds of times smaller than that of carbon fiber. This causes difficulty in infiltration into the MWCNT preform. Moreover, the threshold pressure which was applied to the preform will cause preform deformation. Therefore, knowledge of preform compressive properties which are the buckling strength and elastic modulus are necessary to fabricate the composites. In this study, at first, wettability of the basal plane of graphite by molten aluminum or magnesium was measured using the sessile drop method. Moreover, trial fabrication of MWCNT-reinforced aluminum or magnesium alloy composites was carried out by squeeze casting. As a result, these composites were fully infiltrated. An order-of-magnitude agreement was found between the estimated threshold pressure and the applied infiltration pressure to the MWCNT preform.     

Novel optimization method of single square FSS impinged and cascaded radar absorbing composites

It is well known that radar absorbing potentiality of existing magneto-dielectric composites can be significantly enhanced by the application of frequency selective surface (FSS) and cascaded electromagnetic (EM) structures. But the optimization of such complex EM structures and validation of the adopted optimization strategy is still a very challenging task for the researchers. Therefore, in this study, an effective effort has been made for the optimization and the corresponding validation for Single Square FSS (SS-FSS) impinged and cascaded radar wave absorbers using advanced computational EM software’s like FEldberechnung fur Korper mit beliebiger Oberflache – a German acronym (FEKO) and high frequency structure simulator (HFSS). In addition, a critical analysis of dielectric constant (ε′) has been carried out to select the best combination of composites for the development of efficient radar wave absorbers. A comparison between optimized and simulated results have been carried out to examine the effect of advanced EM approaches over reflection loss (RL) characteristics of composite radar absorbing materials (CRAMs). A rapid change in radar absorption properties of composites has been observed after the application of SSFSS and cascading. A SS-FSS impinged composite has been found to provide a wide absorption bandwidth of 3.6 GHz at X-band. A cascaded absorber having layer thickness 1.8 mm provides a peak RL of ?42.6 dB at 10.6 GHz with an absorption bandwidth of 2.5 GHz. The strong agreement between mathematical model, HFSS and FEKO results clearly reflects the efficiency of adopted approach for distinct practical EM applications.     

Computational method for radar absorbing composite lattice grids

Composite lattice grids reinforced by glass fibers (GFRC) and carbon fibers (CFRC) filled with spongy materials can be designed as lightweight radar absorbing structures (RAS). In the present paper, a computational approach based on periodic moment method (PMM) has been developed to calculate reflection coefficients of radar absorbing composite lattice grids. Total reflection backing (TRB) is considered directly in our PMM program by treating it as a dielectric material with large imaginary part of permittivity. Two different mechanisms of reflection reduction for radar absorbing lattice grids are revealed. At low frequency, reflection coefficients increase with the volume fraction of the grid cell wall. At high frequency, several grating lobes propagate away from the doubly periodic plane, and reflection coefficients depend on both the cell wall volume fraction and interelement distance.     

Preparation and properties of polyarylene ether nitrites/multi-walled carbon nanotubes composites

Polyarylene ether nitriles (PEN)/multi-walled carbon nanotube (MWNT) composites have been successfully fabricated via PEN solution mixing MWNT and then solution-casting. The cast nanocomposite films were characterized by SEM, thermal properties and mechanical properties. The Young's modulus of PEN/MWNT composites was greatly increased with the increase of MWNT concentration. The crystalline behaviors of nanocomposites increased with the increase of MWNT concentration. Thermogravimetric analysis (TGA) measurement showed that MWNT could stabilize PEN when its weight content was greater than 2.0%, and a high char yield in N₂ could be obtained for PEN/MWNT composite at 600 °C.     

多壁碳纳米管复合材料在8 mm波段的吸波性能

将相同厚度不同碳纳米管含量, 以及不同厚度相同碳纳米管含量的多壁碳纳米管加入玻璃纤维增强复合材料中, 并研究了其在26. 5～40. 0 GHz 频段的吸波性能。结果发现, 多壁碳纳米管具有吸波性能, 而且吸波性能随着多壁碳纳米管含量的增加而提高。多壁碳纳米管/ 玻璃纤维/ 环氧树脂复合材料层板在26. 5～40. 0 GHz频段表现出较好的吸收效果, 其吸波性在于碳纳米管本身具有吸波性能, 此外还与吸波材料的谐振吸波原理有关。通过对该复合材料的电磁参数的测定并计算, 证明实验结果与吸波原理相符合。      

活性碳毡电路屏(直立碳纤维)/树脂复合吸波材料

研究了含活性碳毡电路屏和直立碳纤维吸波复合材料的微波吸收特性。结果表明: 含碳毡电路屏吸波材料的吸波性能与电路屏的种类(感性、容性) 和尺寸密切相关。含感性屏的吸波材料, 当毡条间距、宽度分别为7 mm、5 mm 时, 材料在整个雷达波段(8～18 GHz) 有- 10 dB 以下的反射衰减。含容性屏的吸波材料, 随电路屏中碳毡块间距和边长的减小, 吸波性能提高。含直立碳纤维材料的吸波性能与纤维间距有关, 间距为4 mm 时可获得有效带宽7. 6 GHz 的吸波材料。用分块设计的思想设计吸波材料, 可提高其吸波性能。分块中心对称的感性电路屏(毡条宽5 mm , 间距10 mm) 和直立碳纤维(间距8 mm) 混杂吸波体在11. 8～18 GHz 频带内有低于- 20 dB 的反射衰减, 最大吸收峰值- 30 dB。     

Mechanical and sliding wear properties of multi-layered laminates from glass fabric/graphite/epoxy composites

Multi-layered laminates of bi-directionally woven E-glass fabric/epoxy with different loading of graphite particles were made by hand layup followed by compression molding. Tensile and flexural behaviors, impact strength, hardness and density of these laminates were determined. Wear behaviors of these composites were investigated by a pin-on-disc wear test apparatus. Specific wear rates of these composites strongly depend on their filler content and applied normal loads. The hybrid composite containing 3 wt% of graphite exhibits the optimum mechanical and wear performances. A further increase in the graphite content increases the specific wear rate and deteriorates the mechanical behavior. The lowest (σ e)⁻¹ factor (the reciprocal of the product of tensile strength and elongation at break) signifies the lowest specific wear rate. The results of the morphology study of the wear test specimens support the results of the wear test.     

碳纳米管加载量对复合材料吸波性能的影响

将不同质量分数的碳纳米管和环氧树脂充分混合，制成复合吸波涂料并涂覆在铝板上制成吸波涂层。采用TEM对碳纳米管的形貌进行观察。使用反射率扫频测量系统HP8757E标量网络分析仪检测复合材料的吸波性能。结果表明，复合材料在2GHz～18GHz均有良好的吸波性能。碳纳米管加载质量分数为8％和10％时，复合材料吸波性能最佳。8％碳纳米管加载量，峰值最大，达到～22．55dB，波峰出现在12．32GHz，带宽分别为2．56GHz（R〈-8dB）和4．00GHz（R〈-5dB）。10％碳纳米管添加量，带宽最大，分别达到2．80GHz（R〈-8dB）和7．00GHz（R〈-5dB），波峰出现在13．67GHz，峰值为-14．59dB。     

活性碳纤维/树脂复合吸波材料的设计

研究了长度为1—2mm的活性碳纤维的介电特性。发现随频率的增大,介电常数的实部减小,虚部增大,具有频响效应。介电常数的实部和虚部均随复合材料中纤维质量百分含量的升高而增大。依据纤维的介电常数,通过阻抗匹配设计方法,优化设计两层和四层活性碳纤维吸波复合材料。根据优化结果制备了含有四个结构层的吸波复合材料,材料-10dB以下的频带宽度为8GHz,最大反射衰减-39．3dB。     

聚苯胺/碳纳米管复合物的制备及其工艺研究

以低温原位静置法制备了聚苯胺包覆碳纳米管复合物,考察了碳纳米管含量和掺杂酸种类2个工艺参数对复合物的形貌、热稳定性、吸波性能的影响。研究表明:碳纳米管含量为10%时,两者完全包覆出现类似玉米棒形貌,有机酸掺杂制备出针形的聚苯胺且随单体浓度降低直径变小针状更明显;酸种类参数对热稳定性的影响更大,10%碳纳米管含量对氨基苯磺酸掺杂的样品热稳定性最好;有机酸掺杂样的损耗正切远小于盐酸掺杂样的,以盐酸掺杂的碳管含量为10%的样品在低频处有很好的吸收。     

碳纳米管纤维/环氧树脂复合材料的界面剪切强度及微观结构

研究了碳纳米管纤维的微观结构和拉伸性能,并进一步分析了其与环氧树脂形成界面剪切强度及微观结构。采用单丝断裂试验测试了碳纳米管纤维/环氧树脂复合材料体系的界面剪切强度,结合单丝断裂过程中的偏光显微镜照片、复合材料的拉曼谱图和断口扫描电镜照片,研究了碳纳米管纤维/环氧树脂复合材料界面的微观结构。结果表明: 碳纳米管纤维/环氧树脂复合材料的界面剪切强度约为14 MPa;在碳纳米管纤维和环氧树脂形成界面的过程中,环氧树脂可以浸渍纤维,形成具有一定厚度的复合相,这种浸渍过程和界面相的形成都有利于碳纳米管纤维与基体之间的连接。     

Ag纳米晶颗粒/碳纳米管复合材料的制备与结构研究

利用热蒸发方法在多壁碳纳米管表面沉积Ag纳米颗粒,XRD结果显示,Ag纳米颗粒以晶体形态存在,同时透射电镜分析结果表明,Ag纳米晶颗粒引起碳纳米管横截面形变,从而形成Ag纳米晶颗粒/碳纳米管异质复合材料,这些纳米异质复合材料相互连接,形成网络化分布的结构.     

空心粉煤灰对铁氧体-炭黑/水泥基复合材料吸波性能的影响

通过改变空心粉煤灰微珠、铁氧体、炭黑的配比,分析了影响混凝土电磁吸收效能的主要因素,并探讨了空心粉煤灰微珠、铁氧体和炭黑的加入对水泥基复合材料电磁吸收性能的影响机制。结果表明:8~18GHz频率范围内,空心粉煤灰微珠是影响水泥基复合材料吸波性能的最主要因素,最佳水平组合为20wt%铁氧体、20wt%粉煤灰、10vol%炭黑,-10dB吸收带宽可达10GHz且明显优于无粉煤灰样品,其机制在于空心粉煤灰微珠的掺入同时改善了材料表面透射性能和介电损耗。     

吸波材料吸波性能的计算及其优化设计

吸波材料是现代武器系统隐身技术的关键材料,随着近年来隐身技术的迅猛发展,吸波材料的研究已经受到世界各国的高度重视。本文较详细地阐述了目前常用的涂覆型吸波材料和结构型吸波材料吸波性能的基本计算方法,并且对吸波材料的优化设计进行了简要的介绍。     

玻璃纤维增强环氧复合材料上超疏水表面层的制备

先采用真空袋压法制备含CaCO3/环氧树脂表面功能层的玻璃纤维增强环氧树脂复合材料,再通过化学刻蚀与表面修饰,在玻璃纤维增强环氧树脂复合材料上制备出超疏水表面。采用扫描电镜和动/静态接触角分析仪,表征表面的形貌和疏水性,结果表明,在复合材料表面构建了具有微-纳米尺度二元粗糙结构;采用1%(质量分数)的硬脂酸修饰后,其表面与水的接触角最高达160.03°;制备的超疏水表面结构在室温环境下具有长期的稳定性。     

The manufacture and investigation of multi-walled carbon nanotube/polypyrrole/EVA nano-polymeric composites for electromagnetic interference shielding

In this study, the multi-walled carbon nanotube (MWNT)-polypyrrole (PPy) was synthesized by chemical oxidative polymerization using cetyltrimethylammonium bromide (CTAB) as the cationic surfactant. The high electric conductivity of the MWNT-PPy(Cl⁻) was affirmed by the measurement of 4-point-probe method. Then, the MWNT-PPy(Cl⁻) was used as conductive fillers and was compounded with ethylene-vinyl acetate (EVA) by blending to form polymeric composite (MWNT-PPy(Cl⁻)/EVA) that possesses excellent electromagnetic interference shielding (EMI SE). Because of the high conductivity of the MWNT-PPy(Cl⁻) (29/71 wt.%), the MWNT-PPy(Cl⁻) would interdict the conductive network in the composites. This polymeric composite material could shield the electromagnetic wave. As the cationic surfactant CTAB was added in the MWNT-PPy(Cl⁻) chemical oxidative polymerization process, the effect of the surfactant was dispersed, absorbed and attenuated on the MWNT in the chemical oxidative polymerization. For this reason, the EMI SE of the MWNT-PPy(Cl⁻)/EVA composites had an obvious improvement from 10-15 dB to 45-55 dB. In this investigation, the optimum conductive filler was 75.0 phr PPy(Cl⁻) coated on 18.0 phr MWNT. The morphology of the composite also presented a uniform conducting network when a lot of MWNT-PPy(Cl⁻) was added.