孔隙率对碳纤维/环氧树脂复合材料层合板湿热性能的影响

针对某飞机上应用的典型铺层[(±45)4/(0,90)/(±45)2]S和[(±45)/(0,90)2/(±45)]S,研究了孔隙对碳纤维增强环氧树脂基复合材料层合板的吸湿行为和层间剪切强度的影响。采用不同的热压罐固化压力制备了不同孔隙率的试样。采用显微图像分析技术对孔隙率和孔隙的微观结构特征进行了详细的分析。研究结果表明:孔隙主要分布于层间,且随着孔隙率的增大,孔隙的尺寸增大;2种层合板的吸湿率和最大吸湿量随着孔隙率的增加而增加;湿热老化和未经湿热老化的层间剪切强度都随着孔隙率的增加而下降。铺层[(±45)4/(0,90)/(±45)2]S未经湿热和湿热后的层间剪切强度随着孔隙率增加分别下降6%(孔隙率:0.6%~6.3%)和9%(孔隙率:0.4%~7.0%);铺层[(±45)/(0,90)2/(±45)]S未经湿热和湿热后的层间剪切强度随着孔隙率增加分别下降14%(孔隙率:0.4%~6.9%)和7%(孔隙率:0.2%~8.9%)。     

A strategy for improving mechanical properties of a fiber reinforced epoxy composite using functionalized carbon nanotubes

Carbon fiber reinforced epoxy composite laminates are studied for improvements in quasi static strength and stiffness and tension-tension fatigue cycling at stress-ratio (R-ratio) = +0.1 through strategically incorporating amine functionalized single wall carbon nanotubes (a-SWCNTs) at the fiber/fabric-matrix interfaces over the laminate cross-section. In a comparison to composite laminate material without carbon nanotube reinforcements there are modest improvements in the mechanical properties of strength and stiffness; but, a potentially significant increase is demonstrated for the long-term fatigue life of these functionalized nanotube reinforced composite materials. These results are compared with previous research on the cyclic life of this carbon fiber epoxy composite laminate system reinforced similarly with side wall fluorine functionalized industrial grade carbon nanotubes. Optical and scanning electron microscopy and Raman spectrometry are used to confirm the effectiveness of this strategy for the improvements in strength, stiffness and fatigue life of composite laminate materials using functionalized carbon nanotubes.     

碳/环氧复合材料层压板孔隙的形态研究

为深刻了解铺层为[(±45)4/(0,90)/(±45)2]S和[(±45)/04/(0,90)/02]S层压板内孔隙的尺寸、形状及分布情况,通过改变固化压力产生不同孔隙率,采用显微图像分析方法对复合材料层压板厚度方向内孔隙的形态进行了观察,并利用图像分析软件对孔隙的形状和尺寸进行了统计分析.研究表明,对于铺层为[(±45)4/(0,90)/(±45)2]S层压板,孔隙大多出现在层间树脂富集的地方,且孔隙均会沿层间发展;对于铺层为[(±45)/04/(0,90)/02]S层压板,孔隙率较小时孔隙主要出现在层间,而当孔隙率较大时孔隙开始在层内出现,且纵横比较小.对于这两种铺层,孔隙的长度、面积和纵横比均随着孔隙率的增加而增加.     

单向碳纤维增强树脂基复合材料的超低温力学性能

采用真空袋-热压罐工艺制备单向碳纤维增强树脂基复合材料(CFs/EP)层合板,并将高低温试验箱与万能试验机相结合,通过合理使用低温胶和低温引伸计,并在降温过程中实施应力-应变实时调零等关键技术,在室温和液氧超低温度(-183℃)下对单向CFs/EP层合板进行拉伸和弯曲试验,研究了其超低温力学性能,并根据室温和超低温试验后试样的微观和宏观特征,揭示了超低温环境下复合材料力学性能变化机制。结果表明,与室温力学性能相比,单向CFs/EP层合板超低温拉伸强度下降约为9.5%,而拉伸模量上升约为6.2%,主要是由于超低温环境下,树脂的收缩使绝大部分碳纤维与树脂间形成了强界面,拉伸后试样呈"劈裂式"破坏形式,无法使每根纤维都充分发挥其强度,拉伸强度下降,同时超低温也限制了树脂大分子链的运动,所以导致单向CFs/EP层合板拉伸模量上升;单向CFs/EP层合板超低温弯曲强度和弯曲模量分别提高约54.75%和11.64%,这是由于单向CFs/EP层合板的常温和超低温的弯曲破坏形式均为分层剪切破坏,超低温下复合材料的界面增强,提高了单向CFs/EP层合板抵抗剪切分层的能力,进而使CFs/EP的弯曲性能得到提高。     

Pristine and amino functionalized carbon nanotubes reinforced glass fiber epoxy composites

Multi-phase composites have been studied by incorporating carbon nanotubes (CNTs) as a secondary reinforcement in an epoxy matrix which was then reinforced with glass fiber mat. Different types of CNTs e.g. amino functionalized carbon nanotubes (ACNT) and pristine carbon nanotubes (PCNT) were homogeneously dispersed in the epoxy matrix and two-ply laminates were fabricated using vacuum-assisted resin infusion molding technique. The issues related to CNT dispersion and interfacial bonding and its affect on the mechanical properties have been studied. An important finding of this study is that PCNT scores over ACNT in composites prepared under certain conditions. This is a very significant finding since PCNT is available at a much lower cost than ACNT.     

碳纳米管/碳纤维/环氧树脂复合材料研究

制备了碳纳米管(CNTs)/碳纤维(CF)/环氧树脂(EP)三元复合材料。研究了CNTs含量对复合材料层间剪切强度、弯曲强度和弯曲模量的影响,并采用场发射扫描电镜分析了CNTs在基体树脂中的分散情况。结果表明:复合材料性能的变化源自于CNTs在基体树脂中的分散状态。当CNTs含量为0.2%(wt,下同)时,复合材料剪切强度和弯曲强度达到最大值,分别为99.2MPa和1811.4MPa,但其弯曲模量下降了8.7GPa。当CNTs添加量达到1%时,其弯曲模量达到135.9GPa,较未加入CNTs时提高了11.1%,层间剪切强度和弯曲强度分别降低了5.5MPa和359.5MPa。     

紫外老化对碳纤维增强环氧树脂复合材料性能的影响

采用拉挤成型工艺制备碳纤维增强环氧树脂基复合材料,并对其进行人工加速紫外老化实验,对不同老化时间的试样进行弯曲强度测试、冲击强度测试、动态热机械分析(DMA)。结果表明,紫外老化仅影响到受紫外辐射的碳纤维环氧复合材料最外层,使对外层性能敏感的力学性能下降;紫外老化使复合材料玻璃化转变温度(Tg)提高,老化前期提高幅度相对较大,后期变化不明显;随着老化时间的增加,受到紫外辐射的最外层碳纤维/环氧树脂界面受到一定程度削弱。     

Adhesive bonding of carbon fiber reinforced composite using UV-curing epoxy resin

Carbon fiber reinforced materials are widely used in a variety of products due to their stiffness, high strength and light weight. However, the strength of fiber reinforced composites will dramatically decrease when they have suffered damage from impact. Therefore, repair is necessary to maintain integrity. In many cases, speed of this repair is paramount. In this work, UV resins adhered to a damaged panel to form a hard patch are considered for fast repair. The challenge in using UV curing resins on carbon fiber reinforced materials is the non-UV transparency of the composite. In this work, a cationic UV epoxy resin is used due to its characteristic of dark polymerization after UV exposure. ASTM lap shear testing showed the shear stress was above 1000 psi. However, the large scale testing failed due to partial curing of adhesive before repair indicating that control in dosing and resin delivery is critical, yet problematic.     

Fabrication and characterization of carbon fiber reinforced clay/epoxy composite

In this study, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 1, 2, 3, and 4 wt% clay filled SC-15 epoxy to identify the effect of clay weight fraction on thermal and mechanical properties of the epoxy matrix. The flexural results indicate that 2.0 wt% clay filled epoxy showed the highest improvement in flexural strength. DMA studies also revealed that 2.0 wt% system exhibit the highest storage modulus and T _g as compared to neat and other weight fraction. However, TGA results show that thermal stability of composite is insensitive to the clay content. Based on these results, the nanophased epoxy with 2 wt% clay was then utilized in a vacuum assisted resin transfer molding set up with carbon fabric to fabricate laminated composites. The effectiveness of clay addition on thermal and mechanical properties of composites has been evaluated by TGA, DMA, tensile, flexural, and fatigue test. 5 °C increase in glass transition temperature was found in nanocomposite, and the tensile and flexural strengths improved by 5.7 and 13.5 %, respectively as compared to the neat composite. The fatigue strength was also improved significantly. Based on the experimental result, a linear damage model combined with the Weibull distribution function has been established to describe static failure processing of neat and nanophased carbon/epoxy. The simulated stress–strain curves from the model are in good agreement with the test data. Simulated results show that damage processing of neat and nanophased carbon/epoxy described by bimodal Weibull distribution function.     

Effect of fiber surface texture on the mechanical properties of glass fiber reinforced epoxy composite

The effect of fiber sizing and surface texture on the strength and energy absorbing capacity of fiber reinforced composites has been evaluated at two length scales using the macromechanical quasi-static punch shear test and the micromechanical microdroplet test methods. E-Glass/SC-79 epoxy composite laminates with four different fiber sizing formulations with various degrees of chemical bonding and surface texture have been investigated. The failure modes during perforation and different energy dissipating damage mechanisms were identified and quantified. The punch shear strength and the total energy absorption per unit volume of composite with hybrid sizing have increased by 48% and 100% over the incompatible sizing. These results showed linear correlations with the interphase properties reported earlier by the authors (Gao et al., 2011) and provided a methodology for developing new sizing by tailoring chemical bonding and the fiber surface texture at the fiber–matrix interphase for improving both strength and energy absorption of composites.     

碳纤维增强镁基复合材料的界面研究进展

综合评述了碳纤维增强镁基复合材料的界面研究进展.介绍了碳纤维增强体的优点和两种不同的去胶方法,比较了不同的碳纤维涂层和基体成分对复合材料界面状态的影响,并对今后碳纤维增强镁基复合材料的研究方向进行了展望.     

The effect of multiwall carbon nanotubes on the in-plane shear behavior of epoxy glass fiber reinforced composites

In this study, we investigate how multi-wall carbon nanotubes (MWCNTs) affect the in-plane shear mechanical behavior of glass fiber/epoxy composite. These multi-scale composites are fabricated using vacuum infusion: pristine MWCNT and amino-functionalized MWCNT are incorporated into epoxy resins at concentrations of both 0.1 and 0.3 wt.% and are subsequently evaluated. The MWCNT are mixed into the resins by mechanical stirring and sonication prior to resin infusion, and the MWCNT distribution in the cured laminate is then evaluated by performing a heat conduction assessment. Monotonic and cyclic quasi-static room temperature in-plane shear tests are performed following the ASTM D 4255 standard. The initial shear modulus, the deterioration of the shear modulus during plastic deformation and material hardening are evaluated. Incorporating MWCNT into the resins did not affect the parameters investigated under the imposed conditions.     

环氧树脂基体中碳纤维单丝及其界面的温敏效应

为探索树脂基碳纤维复合材料(CFRP)温敏效应的机理,针对环氧树脂基体中碳纤维单丝及正交搭接的碳纤维界面进行了温敏效应实验。实验结果表明碳纤维单丝具有NTC效应,其温敏曲线线性稳定,碳纤维单丝被树脂浸润后,由于树脂膨胀带动纤维在其轴向的伸长,使得树脂基中碳纤维单丝的NTC效应有所减弱;树脂基中碳纤维界面表现出非线性变化的PTC效应,温度越高,其界面电阻随温度变化的趋势越显著,树脂基碳纤维复合材料的温敏特性是树脂基体中碳纤维单丝及其界面的温敏效应协同作用的结果,相对于碳纤维本身而言,碳纤维界面对温度变化更敏感,在CFRP温敏效应中占主导地位。     

碳纳米管有序排列对碳纤维增强环氧树脂基复合材料低温性能的影响

为了提高碳纤维增强环氧树脂(CF/EP)复合材料在低温(77K)循环条件下的抗微裂纹性能,采用共沉淀法制备了具有良好顺磁性的Fe_3O_4修饰氧化碳纳米管(Fe_3O_4-O—MWCNTs),并研究了Fe_3O_4-O—MWCNTs在环氧树脂(EP)基体中的有序排列对EP及CF/EP复合材料低温性能的影响。结果表明:Fe_3O_4-O—MWCNTs的有序排列可有效提高EP基体的低温力学性能及降低EP基体的热膨胀系数,相对于纯EP,Fe_3O_4-O—MWCNTs改性EP的热膨胀系数降低了41.6%;相对于CF/EP复合材料,Fe_3O_4-O—MWCNTs改性CF/EP复合材料在低温环境下的微裂纹密度降低了56.2%。     

Crashworthiness characteristics of a carbon fiber reinforced dual-phase epoxy–polyurea hybrid matrix composite

The crashworthiness characteristics of rectangular tubes made from a Carbon-fiber reinforced Hybrid-Polymeric Matrix (CHMC) composite were investigated using quasi-static and impact crush tests. The hybrid matrix formulation of the CHMC was created by combining an epoxy-based thermosetting polymer with a lightly crosslinked polyurea elastomer at various cure-time intervals and volumetric ratios. The load–displacement responses of both CHMC and carbon-fiber reinforced epoxy (CF/epoxy) specimens were obtained under various crushing speeds; and crashworthiness parameters, such as the average crushing force and specific energy absorption (SEA), were calculated using subsequent load–displacement relationships. The CHMC maintained a high level of structural integrity and post-crush performance, relative to traditional CF/epoxy. The influence of the curing time and volumetric ratios of the polyurea/epoxy dual-hybridized matrix system on the crashworthiness parameters was also investigated. The results reveal that the load carrying capacity and total energy absorption tend to increase with greater polyurea thickness and lower elapsed reaction curing time of the epoxy although this is typically a function of the loading rate. Finally, the mechanism by which the CHMC provides increased damage tolerance was also investigated using scanning electron microscopy (SEM).     

水性上浆剂对碳纤维表面及碳纤维/环氧树脂复合材料界面性能的影响

以4,4'-亚甲基双(异氰酸苯酯)(MDI)为扩链剂, 将Triton X-100(TX-100)引入到双酚A二缩水甘油醚(DGEBA) 中, 设计合成水性碳纤维上浆剂(DGEBA-MDI-TX-100), 并利用合成的水性上浆剂对碳纤维表面进行改性。在此基础上, 以环氧树脂为基体, 制备碳纤维/环氧树脂复合材料, 研究了水性上浆剂改性碳纤维对碳纤维表面性能及其复合材料界面性能的影响。结果表明:与未经处理的碳纤维相比, 经过上浆剂改性后的碳纤维润湿性能得到了较大的提高, 与环氧树脂的接触角下降了 9.1%;与环氧树脂复合后制备的复合材料的界面剪切强度提高了64.7%。      

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.     

An investigation into hybrid carbon/glass fiber reinforced epoxy composite automotive drive shaft

This paper examines the effect of fiber orientation angles and stacking sequence on the torsional stiffness, natural frequency, buckling strength, fatigue life and failure modes of composite tubes. Finite element analysis (FEA) has been used to predict the fatigue life of composite drive shaft (CDS) using linear dynamic analysis for different stacking sequence. Experimental program on scaled woven fabric composite models was carried out to investigate the torsional stiffness. FEA results showed that the natural frequency increases with decreasing fiber orientation angles. The CDS has a reduction equal to 54.3% of its frequency when the orientation angle of carbon fibers at one layer, among other three glass ones, transformed from 0° to 90°. On the other hand, the critical buckling torque has a peak value at 90° and lowest at a range of 20–40° when the angle of one or two layers in a hybrid or all layers in non-hybrid changed similarly. Experimentally, composite tubes of fiber orientation angles of ±45° experience higher load carrying capacity and higher torsional stiffness. Specimens of carbon/epoxy or glass/epoxy composites with fiber orientation angles of ±45° show catastrophic failure mode. In a hybrid of both materials, [±45°] configuration influenced the failure mode.