碳纤维拉伸性能影响因素分析

以QZ6026和QZ5526级国产聚丙烯腈(PAN)基高强型碳纤维为研究对象，采用万能材料试验机作为表征手段，考察了加强片、加强树脂种类、夹具类型和加强树脂固化温度对碳纤维拉伸性能和离散性的影响。结果表明：加强片、加强树脂种类、夹具类型和加强树脂固化温度均对高强型碳纤维的拉伸性能有显著影响。采用砂纸作为加强片测得的碳纤维拉伸强度较高，采用504树脂作为加强树脂的样条拉伸强度高于E44树脂，且纤维强度愈高，稳定性越好；采用气动夹具夹持，测得的碳纤维拉伸强度高，拉伸强度离散系数小；固化温度过高或过低均会导致碳纤维拉伸强度下降。     

基于根数的短切碳纤维爆炸分散度表征方法

为了表征短切碳纤维在大气环境中的爆炸分散效果,提出基于根数的短切碳纤维分散度表征方法,在无风条件下进行短切碳纤维爆炸分散试验,测试短切碳纤维分散单元的尺寸、形貌和分布规律,绘制频率分布和累积分布曲线。结果表明:短切碳纤维爆炸分散以径向纤维间分离为主,同时伴有轴向断裂现象;径向纤维间分离的最小离散单元是单根碳纤维丝,较大的离散单元是由多根碳纤维单丝构成的平面聚集体;50%的短切碳纤维分散为由1~3根碳纤维单丝构成的离散单元,其中27%的短切碳纤维分散为由1~2根碳纤维单丝构成的离散单元和轴向断裂形成的碎段。     

短碳纤维的分散性对CFRC力学性能的影响

碳纤维增强水泥基复合材料(CFRC)是一种新型建筑智能材料,碳纤维在水泥基体中的分散性直接影响着它的力学性能.借助超声波和甲基纤维素(MC)分散剂,实现了短碳纤维在水泥基体中的均匀分散,对所制备的CFRC复合材料的断口形貌作了SEM观察;测试了试件的抗压强度、抗拉强度和抗折强度.结果发现,碳纤维均匀分散时,复合材料的抗压强度提高19%,抗拉强度比不加碳纤维时提高2.2倍,弹性模量提高1.4倍.此外,复合材料的抗弯强度、抗折强度均高于未均匀分散时的强度.     

碳纤维增强尼龙1010的力学性能及其对摩擦磨损的影响

用碳纤维填充尼龙1010制备了碳纤维增强尼龙复合材料,并对碳纤维增强尼龙复合材料的力学性能和摩擦学性能进行了实验研究。力学实验结果表明:碳纤维增强使尼龙复合材料的拉伸强度、表面硬度增大,碳纤维增强尼龙材料的拉伸强度在20%碳纤维含量时达到最大值;碳纤维表面处理对尼龙复合材料的拉伸强度有很大影响,碳纤维表面氧化处理提高了碳纤维增强尼龙复合材料的拉伸强度。摩擦磨损实验表明:碳纤维增强尼龙复合材料的摩擦系数和磨损率与其拉伸强度和硬度有密切关系。随着拉伸强度和硬度的提高,尼龙复合材料摩擦系数和磨损率降低;摩擦系数和磨损率与拉伸强度具有反比关系,与材料硬度具有二次方程关系,与碳纤维填充量之间存在负指数变化规律。      

Al2O3涂层碳纤维/环氧基复合材料的性能研究

采用溶胶-凝胶法在碳纤维的表面涂覆了一层Al2O3涂层,透射电镜分析表明涂层中粒子的大小约为10nm,接触角分析表明涂层后碳纤维的表面张力有大幅提高.通过比较涂层前后碳纤维/环氧复合材料的力学性能发现,Al2O3涂层后复合材料的层间剪切强度,拉伸强度和弯曲强度分别提高了17.7%,4.8%和3.1%.扫描电镜分析表明,Al2O3涂层后的碳纤维与环氧树脂基体的结合更加紧密.且在碳纤维表面形成的Al2O3涂层在350℃～700℃能有效地减缓碳纤维环氧基复合材料的氧化失重速率.     

硅烷偶联剂对电子束固化碳纤维复合材料界面的增效研究

根据碳纤维表面的特点及其复合材料中树脂基体进行电子束固化的机理,对碳纤维表面进行预氧化以提高碳纤维表面含氧宫能团的含量,利用偶联剂的化学架桥作用对电子束固化复合材料界面进行了增效研究.采用X射线光电子能谱(XPS)对处理后碳纤维表面化学成分进行了分析,并采用层间剪切强度对电子束固化复合材料界面粘合性能进行了评价.结果表明,碳纤维表面的含氮官能团使电子束固化复合材料中碳纤维与环氧树脂基体之间的粘合强度减弱,偶联剂与预氧化碳纤维表面进行了强相互作用,使电子束固化复合材料层间剪切强度得到提高.     

HF30F-24K碳纤维经编织物性能分析

对国产HF30F-24K碳纤维的力学性能、表截面形貌、单向和0°/90°经编织物性能及其复合材料性能进行了测试分析，结果表明：HF30F-24K碳纤维拉伸强度达到5000MPa以上，拉伸模量超过250GPa,且拉伸强度、拉伸模量和断裂伸长率的离散系数即C_v值全部低于5%,该产品具有较好的力学性能和稳定性，并具有典型的湿法纺丝工艺特点；HF30F-24K碳纤维单向织物经向断裂强力达到了3800N/25mm以上，0°/90°经编织物经向断裂强力超过了2800N/25mm,纬向断裂强力大于2600N/25mm; HF30F-24K碳纤维单向和0°/90°经编织物复合材料层间剪切强度分别为125.8MPa和77.2MPa,体现了湿法纺丝工艺碳纤维的界面结合优势，HF30F-24K碳纤维的单向和0°/90°经编织物预浸料复合材料也因此表现出较好的拉伸、压缩、弯曲性能。     

空心结构短切碳纤维散射特性研究

在相同质量分数下空心碳纤维相对实心碳纤维数量更多,可以形成更致密的网络结构,因而有更好的应用特性.为了研究空心结构短切碳纤维的散射特性,基于有限元方法,推导了支配方程,对单根纤维建立仿真模型,并进行区域离散和设定边界条件,建立方程组并求解出碳纤维表面电场的分布情况.计算结果表明,相同外直径下,空心碳纤维表面电场强度比实心碳纤维小;空心碳纤维表面电场强度随着直径、壁厚和电导的增大而增大.     

碳纤维/环氧复合材料界面改性的不均匀性EI北大核心CSCD

研究了等离子体表面改性和等离子体接枝改性碳纤维/环氧树脂基复合材料界面的不均匀性。层间剪切强度(ILSS)测量及其偏差评估的结果表明,在相同等离子体条件下,等离子体表面改性对ILSS的提升率只有8.6%,而等离子体接枝改性的提升率高达37%;但是,接枝改性ILSS的离散程度比较高。扫描电镜、金相显微镜和红外光谱分析的结果进一步表明,接枝改性可通过取代反应将较多的活性基团键接在碳纤维表面从而更容易实现界面提升,但是接枝层的不均匀及其产生的纤维粘连使ILSS的离散程度提高。     

微滴包埋拉出法测定复合材料界面剪切强度的影响因素分析

采用微滴包埋拉出测试的方法,分别测定两种不同表面性质中间相沥青基碳纤维与环氧树脂的界面剪切强度(σIFSS)。从负载-位移曲线读取树脂小球从碳纤维上脱落时的脱粘力值,并利用扫描电子显微镜观察了脱粘树脂小球和碳纤维的状态,然后定量地计算出σIFSS的平均值以及其标准方差、离散系数,并讨论了σIFSS同树脂小球的长度与直径、纤维直径的关系,研究发现:所测量的界面剪切强度值与环氧树脂小球的长径比正比,与纤维直径成反比,与环氧树脂小球的长度和纤维直径的比值反比,与环氧树脂小球的直径和纤维直径的比值成反比。     

Effect of epoxy coatings on carbon fibers during manufacture of carbon fiber reinforced resin matrix composites

The changes in oxygen and nitrogen during manufacture of the carbon fiber reinforced resin matrix composites were measured using the X-ray photoelectron spectroscopy method. The effects of the change in oxygen and nitrogen on the strength of the carbon fibers were investigated and the results revealed that the change of the tensile strength with increasing heat curing temperature was attributed to the change in the surface flaws of the carbon fibers because the carbon fibers are sensitive to the surface flaws. The effect of the surface energy that was calculated using Kaelble’s method on the strength of the carbon fibers was investigated. Furthermore, the surface roughness of the carbon fibers was measured using atom force microscopy. The change trend of roughness was reverse to that of the strength, which was because of the brittle fracture of the carbon fibers.     

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6?GPa), and ultrahigh modulus pitch-based (more than 900?GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25?mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5?mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

碳纤维的性能缺陷及改进方法

碳纤维的实际强度远小于其理论计算值 ,导致碳纤维材料强度下降的最主要的因素是缺陷。本文介绍了碳纤维理论强度的计算和缺陷的分类、表征及来源 ,以及减少缺陷 ,提高碳纤维力学性能的方法。     

单丝断裂能量法研究温度对碳纤维/环氧界面性能的影响

针对两种不同上浆剂碳纤维/高温固化环氧树脂体系, 采用基于WND(Wagner-Nairn-Detassis)能量模型的单丝断裂法, 测试分析了从室温到130 ℃范围内单丝复合体系界面断裂能的变化规律, 研究了碳纤维上浆剂对界面耐热性能的影响, 并结合复合材料层板的短梁剪切性能, 分析了微观和宏观界面性能的关联性。结果表明: 在测试温度范围内, 碳纤维/环氧体系的界面断裂能随温度升高呈先下降而后基本不变的趋势, 去除上浆剂后界面断裂能及其随温度的变化程度与未去除上浆剂的情况存在差异, 说明上浆剂对界面耐热性有重要作用。碳纤维/环氧树脂层板层间剪切强度随温度升高线性下降, 与界面断裂能的变化规律不一致, 这与两种测试方法的原理及界面破坏位置的不同有关。      

Plasticizing and wettability-enhancing coatings on carbon,silicon carbide and boron fibers

This paper is concerned with two groups of coatings on high modulus and high strength fibers for reinforcing composite materials with metal and polymer matrices.The first group includes coatings for improving and stabilizing the strength of fibers through a plasticizing effect. For carbon fibers the best results were obtained by chemically applying a nickel coating 1 μm thick with subsequent annealing at 1000°C to form a solid solution of carbon in nickel. In the case of boron and silicon carbide fibers, strength stabilization is achieved by applying coatings, 0.5–2 μm thick, of aluminum and some aluminum alloys by pulling the fibers through a melt. Analysis of the physicochemical interaction of the fibers with the coatings indicates a selective dissolution of the atoms of the fiber material in the coating at stress concentrators, with the result that the stress concentrators are smoothed out. In addition, the plasticizing effect is promoted by the relaxation of stresses in the coating at the stage of microplastic strain of the fibers.The second group includes coatings that enhance the wettability of the fibers by metal melts. An essential role in the improvement of the impregmation of carbon fiber strands and fabrics is played by the highly dispersive surface structure of the coatings, which exhibit a capillary effect as the melt spreads. The best results are obtained in double-layer coatings in which the first layer, silicon carbide, is protective and the second, molybdenum, enhances wettability.     

Optimum dispersion conditions and interfacial modification of carbon fiber and CNT–phenolic composites by atmospheric pressure plasma treatment

Electric resistance measurements were used to determine the optimal dispersion conditions for carbon nanotubes (CNTs) in phenolic resins. Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fibers to matrices. Such treatment might also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength, change in tensile strength of the fiber was studied at different gage lengths before and after the plasma treatment. The wettability of carbon fibers was improved significantly after only 10 s of plasma treatment. Such plasma treatment resulted in a decrease in the advancing contact angle from 65° to 28°. Surface energies of carbon fiber and CNT–phenolic composites were measured using the Wilhelmy plate technique, indicating that the work of adhesion between plasma treated carbon fibers and CNT–phenolic composites was higher than it before plasma modification. The interfacial shear strength (IFSS) and apparent modulus were also increased by plasma treatment of the carbon fibers.     

沥青基碳纤维及其混杂纤维增强尼龙1010复合材料结构与性能的研究

本工作研究了通用型沥青基碳纤维、玻璃纤维及它们的混杂纤维增强尼龙1010复合材料的结构与性能,并与相应的聚丙烯腈基碳纤维及其混杂纤维复合材料的性能作了系统的比较.实验结果表明,随短纤维含量的增加,复合材料的模量和强度线性增加,当纤维含量达到一定临界值时,其强度有所下降.聚丙烯腈基碳纤维增强尼龙1010复合材料比相应的沥青基碳纤维复合材料具有较好的力学性能,但后者通过与高强度玻璃纤维混杂增强,可提高其力学性能.本工作还研究了这些复合材料的断裂特征和它们的混杂效应.      

碳纳米管增强PA6纤维的性能

将碳纳米管(CNT)在分散剂或分散剂和聚合物(PA6)载体中处理后制备出两种母粒,将其作为增强材料分别和PA6切片熔融共混纺丝,制备出碳纳米管的增强PA6纤维,研究其结构和力学性能.CNT含量低于0.5%(质量分数)时,使用两种母粒制备出的纤维强度和模量都提高,NT含量为0.03%时增强的效果最好.由碳纳米管和分散剂组成的母粒增强效果更好,NT的含量为0.03%时就能使PA6纤维的强度和模量分别提高23%和76%.这种增强纤维是一种微纤增强纤维,纳米CNT在纤维中均匀分散且沿着纤维轴的方向取向.这种结构能有效地转移载荷,具有增强作用,且取向性越好,增强效果越好.     

A comparison of the effect of hot stretching on microstructures and properties of polyacrylonitrile and rayon-based carbon fibers

The effect of a different stretching stress at different heat treatment temperatures (HTT) on the structure and the mechanical properties of polyacrylonitrile (PAN)- and rayon-based carbon fibers was studied. The tensile strength increases first and then decreases with increasing stretching stress, whereas the Young’s modulus of the fibers continuously increases. The behavior of PAN- and rayon-based carbon fibers is similar with increasing stretching stress, but the tensile strength of PAN fiber decreased while that of rayon fiber increased with increasing HTT, what is more, the latter have a considerable lower tensile strength and modulus for equivalent processing conditions. The structure of the fibers was investigated with X-ray diffraction. A continuous change toward a nanostructure with a higher order was observed, which explains the increase in the Young’s modulus. For more complex dependence of the tensile strength on the processing conditions, a quantitative model to describe the effect of stretching stress at different HTT on preferred orientation degree and shear modulus is proposed. From the critical stress fracture of carbon fiber analysis, we can understand the different changes of tensile strength of both type fibers with stretching stress at different HTT.