Composite T-stiffened skins, widely used in aeronautical structures nowadays, are fabricated by co-curing and co-bonding processes in this work. An experimental study was focused on the interface fracture progression of T-stiffened skins under tensile loading, including the macroscopic failure process and the microscopic failure mode at several bonding interfaces. The experimental results showed that a similar damage evolution process is found in co-curing and co-bonding processes. Damage is found to initiate in the triangle filling area or the stiffener/filler bonding interface, and it gradually extends to the web part, and finally rapidly extends to the stiffener/skin bonding interface with a complete separation failure. The final failure position occurs in the skin layers closest to the adhesive layer under the stiffener in the co-bonding process with a failure load of 39% higher than the initial damage load, while the final failure position occurs at the flange/skin bonding interface in the co-curing process. The mixed crack growth of mode I and mode II is the main failure mode at the bonding interfaces of composite T-stiffened skins.

为提高热压罐成型过程模具温度分布的均匀性和固化结束后制件的成形质量,采用与复合材料构件热膨胀系数差值较小的短切CF/PC复合材料为模具材料,3D打印大尺寸框架式模具.通过数值模拟、方差分析和实验研究了模具结构及工艺参数对3D打印模具型面温度分布的均匀性的影响规律.结果表明,3D打印模具型面厚度越小和热压罐入口风速越大,越有利于提高模具型面温度均匀性.模具型面温度模拟值和实验值的相对误差最大值为6.7％,验证了利用有限元方法模拟热压罐成型过程模具型面温度场分布的高可靠性.升温结束时,3D打印成型模具型面温度呈阶梯状分布,在支撑晶格与模具型面接触处易出现低温区.

开发了一套预浸纱制备系统,可快速、无损制备干法缠绕预浸纱.通过预浸纱树脂性能测试,明确预浸纱固化工艺为:90℃/2h→120℃/2h.通过对预浸纱复合材料进行测试,验证预浸纱干法缠绕成型工艺可行性.最后,采用6.8L铝内胆干法缠绕制备复合材料气瓶,气瓶水压爆破压力达到118.9MPa.经计算,干法缠绕复合材料气瓶纤维强度发挥率0.91,高于湿法缠绕纤维强度发挥率.

A comprehensive consideration of delamination location, delamination size and delamination quantity was focused to determine a quantitative evaluation of the influence of delamination on the tensile strength of T-stiffened panels under the out-of-plane tensile load. Moreover, the failure behavior of T-stiffened panels without delamination and those with delamination under tensile loading was also examined. A characteristic parameter about delamination in the stiffener/panel interface was proposed by means of the ratio (S-r) of the delamination size in the filler/panel interface to the filling area in the filler/panel interface. It is found that the delamination located closely to the stiffener/panel interface, especially closely to the filler/panel interface has the most significant influence on the tensile strength. Another interesting observation is that delamination in the stiffener/panel interface and the stiffener corner also changes the failure mode which cracks along the interior of panels near the adhesive layer.

分层是复合材料层合板最主要的缺陷/损伤形式,当前研究多集中于复合材料使用过程中的分层损伤,对制造过程中的分层缺陷研究较少.复合材料层合板的分层缺陷在整体成型过程中因不均匀温度场、非对称结构等原因易发生扩展,采用预埋隔离纸模拟分层缺陷,研究分层缺陷在整体成型过程中的扩展行为,对分层扩展的驱动力进行了计算分析,并通过分析热循环对T300/QY8911复合材料层合板界面性能的影响以及计算裂纹尖端能量释放率,从实验研究和有限元计算两方面证明了分层扩展是一个动态过程.研究结果表明,热残余应力是T300/QY8911复合材料层合板整体成型过程中发生分层缺陷扩展的主要驱动力;增加热循环次数和提高热循环温度会显著降低T300/QY8911复合材料层合板的层间剪切强度,当能量释放率降低到低于层间断裂韧性值时,分层动态扩展过程则停止.

采用动态差示扫描量热法研究了环氧树脂E-51/双氰胺/有机脲类促进剂体系的固化过程,研究了固化剂和促进剂用量的最佳配比,确定了固化工艺.结果表明:双氰胺和有机脲类促进剂的最佳用量分别为7和1phr,固化工艺为90℃/3h+110℃/1h+130℃/1h,其固化产物固化度可达97.4％,玻璃化转变温度为131.17℃.

针对复合材料构件热压罐成型过程中常见的分层缺陷,考察了整体成型工艺温度对分层扩展、QY8911双马树脂基体韧性及T300/QY8911层合板Ⅰ型层间断裂韧性的影响,并通过分层扩展断面形貌深入分析了复合材料整体成型工艺中分层扩展的路径和断面破坏模式,给出了复合材料整体成型工艺和结构设计的优化建议措施.结果表明,随着整体成型最高温度的升高,分层扩展程度增大,QY8911双马树脂基体的拉伸强度和拉伸模量逐渐降低,T300/QY8911层合板Ⅰ型层间断裂韧性逐渐增大;对分层扩展断面进行SEM扫描电镜分析发现分层扩展沿着层间开裂,断面内存在基体断裂和基体/纤维界面脱粘两种破坏模式,Ⅰ型层间断裂是复合材料整体成型工艺中分层扩展的典型微观特征.

针对密闭碳纤维新能源汽车电池箱难以散热问题,研究锂电池模组放电工作中的集中发热功率和温度变化.电池模组底部增加水冷板装置,构建密闭碳纤维电池箱冷却系统.采用有限元软件对碳纤维电池箱进行温度场分析,通过箱体内增设分布式风扇,形成密闭箱体热空气内循环辅助散热模式.仿真结果表明,通过不同位置风扇优化布局,密闭碳纤维电池箱体温度分布更加均匀,有助于箱体内部散热,箱体内最高温度降低3.84℃,电池模组温差降低3.1℃.同时发现风扇风速对降低箱体内部温度有积极作用,本论文工作有助于密闭碳纤维新能源电池箱设计.

For composite T-stiffened skins widely used in the aircraft industry nowadays, the triangle filling area of this structure is the weakest part of compaction quality and mechanical properties. In this paper, T-stiffened skins were prepared by the integral molding process of co-bonding, with a focus on the influence of the tool assembly schemes and different curvature radii on the fiber compaction and tensile strength of the triangle filling area. Three quantitative characteristic parameters of the fiber compaction in the triangle filling area were proposed: stiffener thickness non-uniformity (H-d), fiber volume fraction (V-f) and deformation index (a). The results show that an uneven fiber distribution is found in the inner of the triangle filling area, and the maximum difference of V-f is almost 10%. The deformation index of the triangle filling area is the closest to the theoretical value when rigid tool with triangle flexible tool assembly scheme is adopted. An increase of curvature radius (especially greater than 5 mm) causes a decrease of the stiffener thickness non-uniformity, a decrease of the deformation index of the triangle filling area which is close to the theoretical value of 0.5 for the curvature radius of 7 mm and 9 mm, and an increase of the tensile strength (initial damage load and failure load) of T-stiffened skins under the out of plane tensile load with the highest tensile strength for the curvature radius of 7 mm.

分层缺陷是复合材料构件热压罐成型过程中常见的一种缺陷形式,其种类繁多、成因复杂,严重影响了复合材料构件使用的可靠性.本文在归纳分层缺陷种类及成因分析的基础上,系统开展了分层缺陷实验模拟方法研究,并按照复合材料构件整体成型工艺温度制度考核了四种预埋分层缺陷的扩展情况.研究结果表明,埋入防粘纸产生的分层与实际的制造分层最为类似;埋入聚四氟乙烯薄膜与真空袋与上下两层的铺层结合成为一体形成夹杂缺陷,而不是分层;由于聚四氟乙烯布上有孔,也不宜用来模拟分层;同时,防粘纸最易引起分层扩展,对整体成型工艺质量的影响最大.

Composite T-stiffened skins widely used in aircraft industry nowadays were fabricated by using the co-curing, co-bonding and secondary bonding processes. The stiffener thickness and the tensile property of T-stiffened skins under tensile loading were performed as evaluation indexes to evaluate the manufacturing quality and mechanical property of T-stiffened skins, respectively. The results show that the better manufacturing quality and higher tensile property of T-stiffened skins are found in the co-bonding process, and the tensile property increases with the increase of the adhesive film thickness in the co-bonding process. The co-curing process provides a similar tensile property of the co-bonding process with 0.15 mm thickness adhesive film, but different failure modes in the stiffener/skin interface are found in co-curing and co-bonding processes. Moreover, the filler content and the filler type in the triangle filling area of T-stiffened skins also have significant influence on the tensile property of T-stiffened skins, and rolling adhesive films as fillers into the triangle filling area exhibits the highest tensile property in five kinds of fillers during the co-bonding process.

Defect information obtained by non-destructive identification for more than four thousand composite components fabricated by convex mould in autoclave molding was statistically analyzed in this paper. The correlated rules between curvature radius of composite component and manufacturing defect were revealed. By self-designed solid pressure distribution testing method, the pressure distribution in the interface between flexible mould and rigid convex mould was also measured. Furthermore, combined with stress analysis in corner section and defect micrograph, the forming mechanism of the defect was primarily analyzed. The process control measures to avoid manufacturing defect were given. The results indicate that the defect ratio and the size of delamination in corner section of composite component both decrease with the increase of the curvature radius of component. The thickness distribution tends to be thick in the corner and thin on both sides of flat part, which is related to the coupling action between percolation mechanism and shear flow mechanism and the uniformity of pressure distribution.

Atomistic molecular dynamics simulations are performed to study the thermal stability of bulk superlattices consisting of alkylthiol-coated gold nanocrystals. Using nanocrystals passivated by dodecanethiol chains, we show that the gold superlattice possesses a remarkable high-temperature stability, in agreement with experiment. When heated from room temperature, the superlattice expands slightly at lower temperature (<500 K) and then exhibits a considerable lattice contraction above 500 K, while maintaining the intact crystal structure up to 710 K. Once the temperature increases above 720 K, the gold superlattice becomes structurally unstable due to the local sintering of adjacent nanocrystals. Continuous heating to 750 K drives a large number of gold nanocrystals to coalesce and finally results in a tremendous destruction of the superstructure. The structural change and instability of superlattice are mainly attributed to the ligand desorption from nanocrystal surface induced by the variation in temperature. Furthermore, longer ligand length can effectively improve the thermal stability of gold superlattices. These findings are expected to provide a deep microscopic understanding of the thermal stability of superlattice materials.

In order to study the hygrothermal properties of domestic carbon fiber composites, both domestic T700 and Toray T700S carbon fibers were used as reinforcements to match with domestic QY9611 to prepare bismaleimide composites by autoclave moulding. Surface physical/chemical states of the carbon fibers, as well as moisture absorption characteristics, glass transition temperature after moisture absorption and hygrothermal mechanical properties of the two composites were studied. Experiment results show that the saturated moisture absorption rate of domestic T700/BMI and T700S/BMI is 0.77％(35 days), and 0.80％(19 days), respectively. After 168 h water immersion at 71℃, the glass transition temperature Tg of domestic T700/BMI and T700S/BMI decreases 10.3％ ( from 252.1℃ to 226.2℃) and 8.7％ ( from 256.6℃ to 234.3℃) , respectively. In 150℃hygrothermal temperature, domestic T700/BMI composite has an identical 90° tensile strength, 17.9％higher 0° compression strength and 9. 3％ higher interlaminar shear strength, compared with T700S/BMI, demonstrating that domestic T700S/BMI composite has a better hygrothermal and mechanical properties.

聚丙烯腈基碳纤维及其复合材料是航空应用选材的理想材料,用量和应用部位是衡量飞机结构先进性的重要标志之一.综述了国产聚丙烯腈基碳纤维发展现状,指出了国产聚丙烯腈基碳纤维在产业布局、质量稳定性、配套装备、产业链等8个方面存在的主要问题;然后,分析与探讨了航空评价与应用的3个关键问题;最后给出了国产聚丙烯腈基碳纤维的发展建议,以期牵引和推动国产聚丙烯腈基碳纤维的健康可持续发展.

Toray T700S and domestic T700 carbon fibers were used as reinforcements to prepare bis-maleimide composites by autoclave moulding. Surface physical and chemical states of the carbon fibers, as well as interfacial of the composites and interlaminar shear strength were studied. The results show that the domestic T700 carbon fibers can form better physical adhesion with the resin matrix, which have more grooves on the surface and higher surface roughness than T700S carbon fibers. Although the two kinds of oxygen functional groups of carbon fiber are equivalent, the domestic T700 carbon fibers can form better chemical adhesion with the resin matrix, as they have more oxygenic functional groups than T700S carbon fibers. Hence, the interfacial shear strength of domestic T700 carbon fibers is higher than that of T700S carbon fibers by about 11%, and the interlaminar shear strength is higher by about 19%.

PAN-based carbon fiber and composite have series of excellent properties,such as low density,high specific strength,high specific modulus,fatigue-resistant,corrosion-resistant,outstanding properties in design,which have become the ideal material for aviation application.First,the development route of advanced PAN-based carbon fiber of Toray Corporation in Japan and Hexcel Corporation in America were summarized.Development trend and latest research of advanced PAN-based carbon fiber were introduced.Meanwhile,the development route of PAN-based carbon fiber of Toray Corporation and Hexcel Corporation were com-parison analyzed.Then,based on the development situation of domestic PAN-based carbon fiber,development suggestion of domes-tic carbon fiber was presented in order to promote sustainable development of domestic carbon fiber.

The morphologies,surface energies and surface chemical properties of the domestic T700 grade carbon fiber and the T700S carbon fiber were characterized by using scanning electronic microscopy (SEM),inverse gas chromatography(IGC) and X-ray photoelectron spectroscopy (XPS)respectively.The mechanical properties of the two carbon fibers/QY9611 composites were also discussed.The results indicate that the surface properties of carbon fibers have an important influence on the interfacial properties of composites.The interfacial properties of domestic T700 grade carbon fibers/QY9611 composite at room temperature/dry conditions are superior to T700S/QY9611 composite.The toughness of domestic T700 grade carbon fibers/QY9611composite is outstanding as well.The value of CAI has reached the level of foreign advanced composite IM7/5250-4.After hydrothermal treatment,the interfacial strength of domestic T700 grade carbon fibers/QY9611 composite is equal to that of T700S/QY9611 composite.It shows that domestic T700 grade carbon fibers/QY9611 composite has good hydrothermal-resistant properties.

Three types of T700 carbon fibers, A-3K, A-12K and T700SC-12K, were used as reinforcements of carbon fiber/bis-maleimide resin composites. The surface roughness and fuzziness of the three fibers, their damage in the preparation of the prepreg and the mechanical properties of the final composites were compared. Results indicate that the surface roughness and fuzziness of A-3K and A-12K produced using a wet-spinning method are larger than that of T700SC-12K from a dry-jet wet-spinning method. The tensile strength retention ratio in the direction parallel to the fiber axis from fibers to composites of T700SC-12K is higher than those of A-3K and A-12K, owing to the smooth surface, best wear resistance and the minimum damage produced during the preparation of the prepreg for the former. The decreasing order of tensile strength in the direction parallel to the fiber axis of the composites is T700SC-12K, A-3K and A-12K. The interfacial bonding for the composites from A-3K and A-12K is much better compared with T700SC-12K because the former two have stronger mechanical anchoring between fibers and resin matrix than the third.

This paper intends to analyze the surface characteristics of T800H carbon fiber and the interface matching performance between T800H and BA9918 resin. Scanning electronic microscopy ( SEM) , atomic force microscopy (AFM), X?ray photoelectron spectroscopy (XPS) and thermogravimetry analysis (TGA) were used to characterize the surface morphology/chemical properties of carbon fibers and the heat resistance of sizing agent. Then, the 0° compression strength, 90° tensile strength and interlaminar shear strength ( ILSS ) of T800H/BA9918 were tested before and after hygrothermal treatment. Last, the open hole compression and compression after impact performance of T800H/BA9918 were obtained. Tests found that there are obvious grooves in the surface of T800H, which benefits the interfacial mechanical engagement between fiber and resin. The compressive strength after a 29 J impact is 314 MPa. In 130℃ hygrothermal environment the retention ratio of 0° compression strength and ILSS are above 58% while open hole compression strength are above 60%. Test results demonstrates that T800H carbon fiber and BA9918 resin have good interface matching performance, and T800H/BA9918 composite material has good hygrothermal performance.