短切炭纤维的表面处理对沥青基C／C复合材料性能的影响

采用模压半炭化成型工艺，在大气环境下制备了短切炭纤维增强的沥青基C／C炭复合材料。借助材料万能试验机和扫描电镜研究了短切炭纤维的表面处理对C／C复合材料体积密度和抗压强度的影响。结果表明：随着短切炭纤维表面处理强度的增大，C／C复合材料的抗压强度明显提高。用联合处理方法改性的短切炭纤维制备的C／C复合材料的抗压强度，比未处理的短切炭纤维增强的C／C复合材料的抗压强度，约提高了138．5％。     

短切炭纤维的表面处理对沥青基C/C复合材科性能的影响

采用模压半炭化成型工艺,在大气环境下制备了短切炭纤维增强的沥青基C/C炭复合材料.借助材料万能试验机和扫描电镜研究了短切炭纤维的表面处理对C/C复合材料体积密度和抗压强度的影响.结果表明:随着短切炭纤维表面处理强度的增大,C/C复合材料的抗压强度明显提高.用联合处理方法改性的短切炭纤维制备的C/C复合材料的抗压强度,比未处理的短切炭纤维增强的C/C复合材料的抗压强度,约提高了138.5%.     

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料（简称SCFRC）。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察，分析了短切炭纤维对SCFRC材料的增强机制。结果表明，当短切炭纤维的体积分数由0％增大到11．8％时，SCFRC材料的力学性能随之呈线性增加；短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。     

沥青基C／C复合材料的致密效率研究

以高温煤沥青为浸渍剂，国产PAN基炭纤维编织的轴棒法预制体为增强材料，采用浸渍炭化致密工艺制备了沥青基炭／炭（C／C）复合材料，考察不同制备步骤下预制体致密效率的变化情况，并用扫描电子显微镜观察了C／C复合材料及基体炭的微观形貌。研究表明，随循环次数的增多，材料密度逐渐增大，密度增量逐渐减小；中间石墨化处理略微降低材料...     

C/C复合材料不同基体炭的微观结构

借助偏光显微镜、扫描电镜、透射电镜和X射线衍射仪对C/C复合材料不同基体炭的微观结构进行了研究。结果表明:不同基体炭在偏光显微镜下呈现出不同的光学活性度,其平均光学活性度依次由普通沥青炭、热解炭的光滑层、热解炭的粗糙层、中间相沥青炭逐渐增强;在SEM下,普通沥青以"葡萄状"结构为主,热解炭分为块状和"皱褶状"片层状结构,中间相沥青炭为形状各异的片层条带状结构;在HRTEM下,中间相沥青炭的晶格条纹排列规整,是一种长程有序的晶体结构,晶化程度很高。XRD分析表明,材料B(中间相沥青基C/C复合材料)的石墨化度最高,层间距最小,材料D(热解炭基C/C复合材料)次之。     

添加石墨对热压法制备C/C复合材料摩擦磨损性能的影响

以表面酚醛树脂包覆处理过的石墨颗粒,硝酸氧化处理的炭纤维和沥青为原料,经热压烧结制备短切炭纤维增强沥青基C/C复合材料,利用环一块磨损试验机对材料进行了摩擦磨损实验,借助SEM观察样品的磨痕和磨屑,研究了不同石墨含量对样品摩擦磨损性能的影响.结果表明,随着石墨含量的增多,样品的密度和弯曲强度逐渐提高,同时在摩擦磨损表面形成具有自润滑作用的摩擦膜,有利于降低磨损量,并保持摩擦系数的稳定.添加适量的石墨可获得摩擦磨损性能优良的C/C复合材料.     

沥青过渡层对C/C复合材料力学性能的影响

在2D碳／碳（C／C）复合材料的碳纤维与基体热解碳间引入中间相沥青做过渡层，研究了中间相沥青的引入对C／C复合材料力学性能的影响．结果表明，与没有过渡层，普通沥青做过渡层、中间相沥青做过渡层的三类C／C复合材料比较．采用沥青做过渡层可以提高复合材料的力学性能，采用中间相沥青做过渡层制备的C／C复合材料的弯曲强度比采用普通沥青做过渡层提高44％，剪切强度提高15％．中间相沥青的引入可以使碳纤维束间和束内的结合强度不同，从而使基体断裂产生的裂纹扩散时发生偏转，复合材料的强度和韧性同时得到提高．     

石墨化度及纤维含量对C/C复合材料性能的影响

以短切高模炭纤维为增强体.制备C/C复合材料,并采用XRD、SEM等方法研究了纤维体积含量和石墨化度对复合材料性能的影响.结果表明:当短切高模炭纤维体积含量小于7%时,随着炭纤维体积含量增加,C/C复合材料的力学性能逐渐升高,高于7%时力学性能降低;随着石墨化度提高,C/C复合材料的力学性能显著降低,短切高模炭纤维增强作用下降;C/C复合材料的石墨化度对电阻率影响大,纤维体积含量对电阻率几乎没有影响;C/C复合材料的石墨化度对材料的抗氧化性影响显著.     

沥青基C/C复合材料的致密效率研究

以高温煤沥青为浸渍剂,国产PAN基炭纤维编织的轴棒法预制体为增强材料,采用浸渍炭化致密工艺制备了沥青基炭/炭(C/C)复合材料,考察不同制备步骤下预制体致密效率的变化情况,并用扫描电子显微镜观察了C/C复合材料及基体炭的微观形貌。研究表明,随循环次数的增多,材料密度逐渐增大,密度增量逐渐减小;中间石墨化处理略微降低材料的密度,但材料的最终密度可大于1.90g/cm3。通过显微镜发现沥青基C/C复合材料内部在微观上仍存在少量裂纹和孔隙,基体炭的形态主要有区域型、流线型和镶嵌型。     

氧化处理对MCMB为基体的C/C复合材料性能的影响

以自烧结性中间相沥青炭微球(MCMB)为基体,以沥青基磨碎炭纤维为增强体,采用简单的氧化处理、混合、热压成型、炭化等工艺一步制备C/C复合材料。研究了MCMB氧化处理深度对C/C复合材料的密度、失重、体积收缩率、弯曲强度及断面形态的影响。结果表明:C/C复合材料的密度和体积收缩率均较无炭纤维添加的炭块有所下降,当添加的炭纤维氧化程度足够深时,炭材料的抗弯强度得到明显提高;随着MCMB氧化时间的延长,C/C复合材料的断面逐渐变得平整;经250℃氧化60 min的MCMB与硝酸90℃氧化10h的炭纤维混合,热压成型后1000℃炭化1h得到的C/C复合材料的密度可达1.64 g/cm3,抗弯强度可达72.0 MPa。与现行的制备C/C复合材料的方法相比,本技术具有工艺简单、制备成本低廉等特点,是一种具有很大发展潜力的制备高性能C/C复合材料的新方法。     

碳纤维无纺布对CFRP层板层间的增韧作用及机制

为了揭示短纤维无纺布对碳纤维增强树脂基复合材料(CFRP)层板层间韧性的影响规律,测试了不同面密度(1.95、3.90、7.80和15.60 mg/cm2)和不同纤维平均长度(0.8 mm和4.3 mm)的碳纤维无纺布增韧的CFRP层板I型层间断裂韧性。实验结果表明:对于不同短纤维增韧的CFRP层板,平均长度为0.8mm的短纤维增韧效果优于平均长度为4.3mm的短纤维,并且面密度为7.8mg/cm2、厚度约为150μm、平均长度为0.8mm的碳纤维无纺布显著提高了CFRP层板的层间断裂韧性,与未改性的CFRP层板相比,其能量释放率最大可提高99%。光学显微镜观察结果表明环氧基体中长度为0.8mm的短纤维具有三维交织结构,该结构可以有效地阻止裂纹的扩展;SEM观察结果表明短纤维从环氧基体中的脱粘和拔出以及短纤维周围环氧基体的塑性变形是CFRP层板的主要增韧机制。研究结论为层板短纤维增韧技术的应用奠定了基础。     

Electrophoretic deposition of aramid nanofibers on carbon fibers for highly enhanced interfacial adhesion at low content

Here, an anodic electrophoretic deposition was adopted to facilitate the large-scale uniform coating of nano-fillers onto carbon fibers to enhance the interfacial properties between carbon fibers and epoxy matrix. As interface–reinforcing materials, aramid nanofibers were introduced because of their superior mechanical properties and epoxy matrix-friendly functional groups. Furthermore, aramid nanofibers can be readily coated on carbon fibers via electrophoretic deposition because they are negatively-charged in solution with high electrical mobility. Finally, aramid nanofiber-coated carbon fibers showed significantly improved interfacial properties such as higher surface free energy and interfacial shear strengths (39.7% and 34.9% increases, respectively) than those of a pristine carbon fiber despite a very small amount of embedding (0.025 wt% of aramid nanofibers in a carbon fiber), and the short beam strength of the laminated composite prepared with the aramid nanofiber-coated carbon fibers was also improved by 17.0% compared to a non-modified composite.     

Structure-property relations for silicon nitride matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon fibers

Si₃N₄ matrix composites reinforced with pyrolytic carbon pre-coated Hi-Nicalon (SiC) fibers, were studied using tensile testing and transmission electron microscopy. Three types of samples were evaluated all with a nominal coating thickness of 200 nm. The composites were densified by hot pressing at 1550 °C (type I and II) and at 1600 °C (type III). The fibers were coated with pyrolytic carbon via CVD with identical (sample I) and opposite (samples II and III) directions of the gas flow and of the fiber movement through the reactor. Tensile testing indicated for the three sample types respectively: brittle behaviour with huge pull out of the fibers, pseudo-plastic behaviour and brittle behaviour with little pull out. TEM indicated for the three sample types debonding typically at the fiber/coating interface, at the coating/matrix interface and in the coating, respectively. The relation between processing, structure, particularly of the coating and its interfaces with the matrix and the fibers and mechanical properties is addressed.     

Microstructure characterization of CVI-densified carbon/carbon composites with various fiber distributions

Mechanical behavior of multi-phase composites is crucially influenced by volume fractions, orientation distributions and geometries of microconstituents. In the case of carbon–carbon composites manufactured by chemical vapor infiltration, the microconstituents are carbon fibers, pyrolytic carbon matrix, and pores. The local variable thickness of the pyrolytic carbon coating, distribution of the fibers and porosity are the main factors influencing the properties of these materials. Two types of fiber arrangements are considered in this paper: 2D laminated preform and random felt. The materials are characterized by determining their densities and their fiber distribution functions, by establishing types of pyrolytic carbon matrix present in the composites, and by studying the porosity. A technique utilizing X-ray computed tomography for estimation of the orientation distribution of the fibers and pores with arbitrary shapes is developed. A methodology based on the processing of microstructure images with subsequent numerical simulation of the coating growth around the fibers is proposed for estimation of the local thickness of the coating. The obtained information is appropriate for micromechanical modeling and prediction of the overall thermo-mechanical properties of the studied composites.     

Carbon and glass hierarchical fibers: Influence of carbon nanotubes on tensile,flexural and impact properties of short fiber reinforced composites

Dense carbon nanotubes (CNTs) were grown uniformly on the surface of carbon fibers and glass fibers to create hierarchical fibers by use of floating catalyst chemical vapor deposition. Morphologies of the CNTs were investigated using scanning electronic microscope (SEM) and transmission electron microscope (TEM). Larger diameter dimension and distinct growing mechanism of nanotubes on glass fiber were revealed. Short carbon and glass fiber reinforced polypropylene composites were fabricated using the hierarchical fibers and compared with composites made using neat fibers. Tensile, flexural and impact properties of the composites were measured, which showed evident enhancement in all mechanical properties compared to neat short fiber composites. SEM micrographs of composite fracture surface demonstrated improved adhesion between CNT-coated fiber and the matrix. The enhanced mechanical properties of short fiber composites was attributed to the synergistic effects of CNTs in improving fiber–matrix interfacial properties as well as the CNTs acting as supplemental reinforcement in short fiber-composites.     

Effect of electrophoretically deposited carbon nanotubes on the interface of carbon fiber reinforced epoxy composite

The interface between reinforcing fiber and matrix is a crucial element in composite performance. Homogeneous and interconnected carbon nanotubes (CNTs) were deposited onto the surface of carbon fibers to produce multiscale reinforcement by electrophoretic deposition (EPD). Single fiber tensile tests showed that the tensile strength and Weibull modulus of the resulting multiscale materials were increased by 16 and 41%, respectively. Compared with as-received carbon fibers, CNTs-deposited carbon fibers provided the decreased surface energy by 20% and the increased adhesion work by 22% using modified Wilhelmy method. Results from single fiber pull-out testing showed that a significant improvement (up to 68.8%) of interfacial shear strength was obtained for the composites containing by CNTs/Carbon fiber multiscale reinforcement. All results strongly suggest that EPD process can provide a feasible platform for improving interface properties of advanced composites.     

Can carbon nanotubes grown on fibers fundamentally change stress distribution in a composite?

In carbon fiber reinforced polymer composites the onset of damage occurs at the fiber/matrix interface, where stress concentrations are the highest due to the property mismatch of the two materials. This article reports results of a modelling study indicating that carbon nanotubes (CNTs) grown on fibers are effective in suppressing stress concentrations at the fiber/matrix interface. In the case of high density CNT forests, they can even fundamentally change a profile of the interfacial stress. The study is performed using a novel two-scale finite element model of a nano-engineered composite based on the embedded regions technique.     

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。     

A one-step hot pressing molding method of polyacrylonitrile carbon fibers: influence on surface morphology,microstructure and mechanical property

Carbon fibers (CFs) have been the most popular material for decades and compound into various materials because of their excellent performance. Herein, a novel one-step hot pressing molding is proposed to prepare polyacrylonitrile (PAN) CFs, eliminating the time-consuming and energy-consuming thermal stabilization stage. The fibers are tiled and pressed tightly between the two plates. The unit is then carbonized in a tubular furnace. Hot pressing enforced the fiber structure to be cyclized and reduces the damage of fibers by mitigating the escape of heteroatoms gas. The thermoplasticity of PAN fibers is innovatively utilized in the preparation of carbon fibers by hot pressing, which is able to improve density and repair the cracks. The density and tensile strength of fibers at 900 °C have reached to 1.70 g cm^?3 and 1.1GPa. The CFs obtained by hot pressing molding have not only a smooth surface morphology, but also a high degree of microstructure cyclization. Hot pressing molding can not only realize the function of thermal stability stage, but also simplify the process, save energy and time, and reduce the cost.

     

粉末冶金法炭纤维/Mg复合材料的界面对其力学性能的影响

采用表面化学镀镍前后的短炭纤维(Cf)做为增强体,纯镁粉为基体金属,通过粉末冶金法和热挤压制备镁基复合材料.采用SEM-EDS、TEM、XRD和拉伸等测试手段表征短炭纤维增强镁基复合材料的微观形貌、元素组成、物相组成及其力学性能.结果表明:炭纤维在复合材料中分布均匀且沿挤压方向定向排列;采用经过表面化学镀镍处理的短炭纤维与金属镁复合后界面结合状态优良,Mg2Ni物相的存在表明润湿性的改善是通过金属镁与涂层发生反应而实现;对比屈服强度测试值和理论计算值的大小,表明涂层炭纤维增强镁基复合材料的增强机理主要是界面载荷传递效应.