Dynamic tensile properties of carbon fiber composite based on thermoplastic epoxy resin loaded in matrix-dominant directions

The dynamic tensile properties of carbon fiber (CF) composite loaded in the matrix-dominant direction are experimentally determined. In this study, thermoplastic epoxy resin is used as a matrix of the CF composite. A dynamic tensile test is performed using a tension-type split Hopkinson bar technique. The experimental results show that there are not linear relationships between tensile strength and strain rate in case of the 10°, 30° and 45° specimens, although the tensile strength of CF composite, whose matrix is typical thermosetting epoxy resin, linearly increases with the strain rate for all fiber orientation angles. From the fracture surface observation, it is found that the ductile fracture of the matrix can be observed only when 10° off-axis specimen is tested under dynamic loading condition. It is inferred that the softening of the thermoplastic epoxy resin in the vicinity of interface area takes place with increasing strain rate.     

碳纤维/聚苯硫醚热塑性复合材料电阻焊接工艺

本文针对航空器结构用碳纤维/聚苯硫醚(CF/PPS)复合材料为研究对象，开展电阻焊接工艺研究；利用CF/PPS复合材料混编织物作为电阻元件，成功制备了CF/PPS复合材料层板电阻焊接接头；重点利用Taguchi方法和方差分析获取CF/PPS复合材料层板电阻焊接最佳工艺参数(电流为12 A，压力为1.5 MPa，时间为30 min)及各参数对焊接接头剪切强度的贡献(电流为83.37%，压力为9.55%，时间为6.02%)。最佳焊接工艺参数焊接的接头单搭接剪切强度约为17.88 MPa；同时，对最佳参数焊接试样(H-LSS)和较低剪切强度试样(L-LSS)的焊接接头截面和剪切失效断口形貌进行了观察和分析。结果表明:H-LSS试样的焊缝区域树脂填充和浸润良好，且主要剪切失效形式为层间剪切失效，即为纤维与树脂基体脱黏及CF/PPS织物复合材料断裂混合失效；L-LSS试样的焊缝区域树脂填充和浸润较差，存在较多空隙，且剪切失效形式为焊缝界面脱黏失效。      

Enhanced mechanical properties of multiscale carbon fiber/epoxy composites by fiber surface treatment with graphene oxide/polyhedral oligomeric silsesquioxane

Graphene oxide (GO) and polyhedral oligomeric silsesquioxane (POSS) grafted carbon fiber (CF) was demonstrated to reinforce the mechanical properties of fiber composites. Such a fiber composite was prepared by grafting POSS onto the CF surface using GO as the linkage. The presence of GO linkage and POSS could significantly enhance both the area and wettability of fiber surface, leading to an increase in the interfacial strength between fibers and resin. Compared with the desized CF composites, the grafted CF composites fabricated by compression molding method exhibited 53.05% enhancement in the interlaminar shear strength. The changed surface morphology, surface composition and surface energy were supposed to be related with the interfacial performance of unidirectional composites, as revealed by scanning electron microscopy, atomic force microscope, dynamic contact angle test and X-ray photoelectron microscopy charaterizations.     

三维编织超高分子量聚乙烯纤维/碳纤维/环氧树脂混杂复合材料力学行为及混杂效应

采用复合处理工艺对三维混杂超高分子量聚乙烯纤维/碳纤维编织体进行表面处理, 通过RTM工艺制备了环氧树脂基混杂复合材料（UHMWPE/CF/ER）, 并研究了其力学性能及混杂效应。结果表明, 在纤维总体积分数一定的情况下, 随着超高分子量聚乙烯纤维/碳纤维混杂比的减小, 复合材料的弯曲强度、 弯曲模量及压缩强度增大, 而其纵向剪切强度及冲击韧性降低。三维编织混杂复合材料的断裂机制由混杂纤维的混杂比及其性质决定, 通过调节混杂比可实现对复合材料力学性能的有效调控。      

三维编织超高分子量聚乙烯纤维-碳纤维混杂增强环氧树脂复合材料摩擦磨损性能

以超高分子量聚乙烯纤维(UHMWPE)-碳纤维(CF)三维混杂编织体为增强体,环氧树脂(ER)为基体,通过树脂传递模塑(RTM)工艺制备了三维编织混杂复合材料,研究了其摩擦磨损性能了,并采用混合正压力模型对摩擦系数进行了预测。结果表明,在纤维总体积含量一定的情况下,随着CF体积含量的增加,复合材料的摩擦系数增大,而其比磨损率降低。UH_3D/ER复合材料的磨损机制以粘着磨损为主,CF_3D/ER复合材料则以磨粒磨损为主,混杂复合材料的磨损机制主要取决于CF与UHMWPE纤维的相对含量 ,通过调节UHMWPE纤维和CF的体积比例可实现对复合材料摩擦磨损性能的有效调控。采用的计算模型可较好地预测UH_3D/ER的摩擦系数。     

镀镍碳纤维-碳纤维-玻璃纤维/乙烯基酯树脂导电复合材料的设计制备及其电磁性能

本研究旨在设计制备兼具电和磁功能的新型导电复合材料。采用具有良好导电性的短切碳纤维（CF）与兼具磁性和导电性的短切镀镍碳纤维（Ni-CF）作为功能体,以短切玻璃纤维（GF）作为填料,以乙烯基酯树脂（VER）作为基体,设计制备电磁性能可调控的导电复合材料。分别研究了CF含量对CF-GF/VER导电复合材料体积电阻率的影响、Ni-CF长度对（Ni-CF）-CF-GF/VER导电复合材料体积电阻率的影响,重点研究了Ni-CF含量对（Ni-CF）-CF-GF/VER导电复合材料体积电阻率和磁导率的影响,并初步探索了导电复合材料的电磁屏蔽性能。结果表明：（Ni-CF）-CF-GF/VER导电复合材料体积电阻率在0.35~36.48 Ω·cm范围内可调,磁导率在0.2~0.7内可调。CF和Ni-CF的含量和长度都会对（Ni-CF）-CF-GF/VER导电复合材料电磁性能产生较大影响。制备的（Ni-CF）-CF-GF/VER导电复合材料有望应用于电磁屏蔽领域。     

Effects of carbon nanotubes and carbon fiber reinforcements on thermal conductivity and ablation properties of carbon/phenolic composites

The ablation properties and thermal conductivity of carbon nanotube (CNT) and carbon fiber (CF)/phenolic composites were evaluated for different filler types and structures. It was found that the mechanical and thermal properties of phenolic-polymer matrix composites were improved significantly by the addition of carbon materials as reinforcement. The concentrations of CF and CNT reinforcing materials used in this study were 30 vol% and 0.5 wt%, respectively. The thermal conductivity and thermal diffusion of the different composites were observed during ablation testing, using an oxygen–kerosene (1:1) flame torch. The thermal conductivity of CF mat/phenolic composites was higher than that of random CF/phenolic composites. Both CF mat and CNT/phenolic composites exhibited much better thermal conductivity and ablation properties than did neat phenolic resin. The more conductive carbon materials significantly enhanced the heat conduction and dissipation from the flame location, thereby minimizing local thermal damage.     

Hierarchical composites of carbon nanotubes on carbon fiber: Influence of growth condition on fiber tensile properties

Growing carbon nanotubes (CNT) on the surface of high performance carbon fibers (CF) provides a means to tailor the thermal, electrical and mechanical properties of the fiber–resin interface of a composite. However, many CNT growth processes require pretreatment of the fiber, deposition of an intermediate layer, or harsh growth conditions which can degrade tensile properties and limit the conduction between the fiber and the nanotubes. In this study, high density multi-wall carbon nanotubes were grown directly on two different polyacrylonitrile (PAN)-based carbon fibers (T650 and IM-7) using thermal Chemical Vapor Deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of the resultant hybrid fibers were shown to depend on the carbon fiber used, the presence of a sizing (coating), the CNT growth temperature, growth time, and atmospheric conditions within the CVD chamber. The CNT density and alignment morphology was varied with growth temperature and precursor flow rate. Overall, it was concluded that a hybrid fiber with a well-adhered array of dense MWCNTs could be grown on the unsized T650 fiber with no significant degradation in tensile properties.     

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.     

Development of a carbonization-in-nitrogen method for measuring the fiber content of carbon fiber reinforced thermoset composites

Carbon fiber reinforced thermoset composites such as carbon fiber epoxy composites are widely used in aircraft and aerospace, and are being increasingly used in automotive applications because of their lightweight characteristics, high specific strength, and stiffness. The carbon fiber content in the composite plays a critical role in enhancing structural performance. The carbon fibers contribute to the strength and stiffness; therefore, the mechanical properties of the composite are greatly influenced by the carbon fiber content. Measurement of carbon fiber content is essential for product quality control and process optimization. In this work, a novel carbonization-in-nitrogen (CIN) method is developed to characterize the fiber content in carbon fiber thermoset composites. A carbon fiber composite sample is carbonized in a nitrogen environment at elevated temperatures, alongside a neat resin sample. The carbon fibers are protected from oxidization while the resin (the neat resin and the resin matrix in the composite sample) is carbonized under nitrogen environment. The neat resin sample is used to calibrate the resin carbonization rate and calculate the amount of the resin matrix in the composite sample. The new method has been validated on several thermoset resin systems, and found to yield accurate estimation of fiber content in carbon fiber thermoset composites.     

Electrical properties of hybrid carbon black/carbon fiber polypropylene composites

The electrical conductivity and morphology of injection molded polypropylene based composites containing two conductive fillers, carbon black (CB) and carbon fibers (CF) were studied. Injection moldings containing both, CB and CF, where the content of each filler was above its own percolation threshold, resulted in similar or lower values of overall composite volume resistivity compared with the resistivity of systems filled only with CB at the corresponding content. However, the resistivity of two-filler systems is always higher than the resistivity of systems filled only with CF at the corresponding content. The morphology and fiber length analysis of the injection molded composites are quite intriguing. Fiber orientation in the injection molded two-filler systems was found to be almost perpendicular to the melt flow direction, with no significant skin-core fiber orientation patterns, contrary to the typically observed fiber orientation in injection molded fiber filled composites. Moreover, the CF breakage in the presence of the CB was found more intense than when just CF is used, resulting in shorter fibers with narrower length distributions. This unexpected fiber behavior is responsible for the unexpected electrical behavior. However, the coexistence of CB and CF electrically conductive networks, supporting each other, was confirmed, in spite of the mechanical disturbances caused by the presence of fibrilar and particulate fillers.     

湿热环境对碳纤维增强聚苯硫醚层合板感应焊接接头性能的影响

以碳纤维增强聚苯硫醚(Carbon fiber reinforced polyphenylene sulfide, CF/PPS)复合材料层合板为研究对象,采用感应焊接方法对CF/PPS层板进行了焊接,重点研究了湿热环境对CF/PPS层板焊接接头性能的影响,实验结果表明:吸湿前后PPS树脂未发生化学变化;室温环境下,随着吸湿时间的增加,焊接接头剪切强度逐渐下降,与干态焊接接头相比分别降低了15%、18%、23%、32%和38%,不锈钢网-树脂基体-碳纤维界面处的湿应力不断增大,削弱了焊接接头界面的结合性能,影响了焊接接头的失效形式;120℃环境下,不同吸湿时间焊接接头剪切强度的下降率分别为12%、15%、22%、37%和44%,高温高湿使不锈钢网-树脂基体-碳纤维界面处热应力和湿应力增大,加剧了界面结合的损伤,界面脱粘成为焊接接头主要的失效形式。      

Interfacial evaluation of carbon fiber/epoxy composites using electrical resistance measurements at room and a cryogenic temperature

Interfacial properties between fiber and matrix were evaluated using an electrical resistance (ER) fragmentation method. The single carbon fiber (CF) tensile test was performed in conjunction with electrical resistance measurements. The relationship between tensile properties of single carbon fiber specimens and the electrical resistance ratio (ERR) was investigated. The data showed a linear relationship between these properties. Fragmentation specimens were tested under tensile loading, and it was observed that, due to stress transfer from the matrix to the reinforcing fiber, the single carbon fiber broke first. The stress distribution along the carbon fiber was monitored via electrical resistance changes. ER fragmentation measurements were performed to predict CF fractured strength embedded in epoxy by an empirical formula of CF tensile results. These interfacial properties of CF epoxy composites were measured at room and a cryogenic temperature. Work of adhesion between the carbon fiber and the matrix was measured to verify the results of the ER fragmentation method, and the two procedures yielded consistent results and conclusions.     

斜纹编织碳纤维/环氧树脂复合材料II型分层性能及损伤演化表征

为研究编织复合材料在静载及疲劳载荷下的分层特性及损伤演化模式,对斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料II型静开裂及疲劳开裂性能进行了测试。结果表明:斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料裂纹扩展行为受纬向纤维影响存在周期性局部受阻现象,分层破坏模式除层间开裂外还存在纬向纤维脱粘;斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料裂纹扩展速率符合Paris公式,不同加载控制模式下编织复合材料疲劳驱动力增长规律存在本质区别:恒幅疲劳载荷下斜纹编织复合材料疲劳驱动力呈抛物线型单调增长;而恒幅疲劳位移下复合材料疲劳驱动力随分层长度呈波峰型分布;采用基于载荷控制模式和位移控制模式下的疲劳驱动力模型,可对斜纹编织CF3052/3238A碳纤维/环氧树脂复合材料进行损伤演化表征,其表征效果良好,具有工程参考价值。      

Comparison of drying methods for the preparation of carbon fiber felt/carbon nanotubes modified epoxy composites

Carbon fiber felt with carbon nanotubes (CNTs) were prepared by immersing three-dimensional (3D) felt into CNT aqueous solution (with dispersant) followed by removing water with different drying methods. Epoxy resin was then introduced into the felt to obtain 3D fiber felt/CNTs modified epoxy composites. This paper highlights the effect of drying method on macro-morphologies of the felt, morphological dispersion of CNTs and some relevant properties of the composites, including electrical conductivity and flexural performance. The results demonstrate that compared to the commonly used heat drying method, freeze drying technique possesses obvious advantages for the fabrication of fiber felt/CNT modified epoxy composites.     

纳米SiO2改性炭纤维乳液上浆剂的性能评价

采用纳米SiO₂改性环氧树脂乳液上浆剂和未改性乳液上浆剂对聚丙烯腈(PAN)基炭纤维进行表面上浆。通过静置沉淀法和光学显微镜评价了两种乳液的稳定性。利用扫描电子显微镜(SEM)、 X射线能谱仪(EDS)、 原子力显微镜(AFM)和动态接触角测试仪(DCAA)研究了未上浆、 未改性和改性上浆炭纤维的表面性能, 并用单纤维碎裂法探讨了上浆剂对炭纤维与环氧树脂界面黏结的影响。结果表明: 未改性和经纳米SiO₂改性的两种乳液粒径较小, 稳定性较好, 而前者优于后者。上浆后, 炭纤维表面的粗糙度和表面能都增大, 而且最大值出现在改性乳液上浆炭纤维的表面。改性乳液上浆单纤维复合材料拥有最大的界面剪切强度(IFSS), 比未改性上浆的高出27.2%; 改性上浆炭纤维与基体的调和平均黏结功(W(h)_a )和几何平均黏结功(W(g)_a )也分别高出未改性上浆的12.7%和11.7%。      

炭黑/碳纤维/ABS电磁屏蔽复合材料的制备及其性能研究

采用硅烷偶联剂KH550改性炭黑(CB),浓硝酸氧化碳纤维(CF),将表面处理前后的炭黑和碳纤维与丙烯腈-丁二烯-苯乙烯(ABS)树脂通过混炼挤出制备了电磁屏蔽复合材料,考察了炭黑、碳纤维含量及表面处理对复合材料体积电阻率和屏蔽效能的影响。实验结果表明,采用KH550改性炭黑可以达到改性目的,浓硝酸氧化碳纤维后,其表面接上了羰基和羧基。随着炭黑含量增加,复合材料的体积电阻率逐渐下降,且变化规律符合"渗滤效应",在100～1800MHz频率范围内,屏蔽效能逐渐增加,采用1%KH550改性炭黑后,导电性能和屏蔽效能均得到提高。加入碳纤维后,复合材料的导电性能和屏蔽效能均有较大提高,且含量为2%时,分别达到最大值,采用浓硝酸氧化碳纤维后,导电性能得到进一步提高,屏蔽效能提高了1dB左右。     

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.     

碳纤维单丝偏轴拉伸力阻效应实验与理论分析

碳纤维在复合材料基体中的分布较大程度地影响了碳纤维智能材料的感知特性,故需在微米尺度下研究多角度偏轴拉伸下的碳纤维单丝的力电功能响应。测试了不同角度拉伸环境下碳纤维单丝的电阻变化,并对其电阻的变化情况进行了分析。结果表明碳纤维单丝在外载荷偏轴拉伸作用下电阻变化与拉伸角度间存在非线性关系。外载荷在纤维方向产生的应变对电阻变化率的作用强于垂直纤维方向应变对电阻变化率的作用,62°拉伸角为正负力阻效应的临界角度。     

Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating sliding in ambient air

For many technical applications friction and wear are critical issues. Reinforced polymer-matrix composites are widely used under vibrating contact condition in various automotive and aerospace applications as well as in structural engineering. In this paper, the friction and wear of bulk epoxy and unidirectional carbon fiber reinforced epoxy composite have been investigated under reciprocating sliding against either alumina or stainless steel balls in ambient air. The effect of sliding direction with respect to the long and unidirectional carbon fibers has been studied. We demonstrate that the carbon fiber reinforcement greatly improves the tribological properties of the thermoset epoxy: it reduces the coefficient of friction and the debris formation. It was found that on sliding in the anti-parallel direction a more significant degradation takes place than in the parallel direction. The coefficient of friction measured on bulk epoxy sliding against either stainless steel or alumina is around 0.65, whereas the coefficient of friction measured on epoxy reinforced with carbon fibers is significantly lower, namely down to 0.11. It was found that sliding with a stainless steel ball in a direction parallel to the fiber orientation results in a lower coefficient of friction than sliding in anti-parallel direction. The reduced coefficient of friction is largely influenced by the carbon fiber reinforcement due to the auto-protecting film formed as a paste in the contact area and along the wear track edges. The relationship between friction and degradation of the composite material including surface wear and debris formation are discussed based on an in-depth analysis of the worn surfaces by optical and scanning electron microscopy, micro-Raman spectroscopy, and white light interferometry.