随着复合材料在主承力结构上的应用,复合材料修理技术已经成为复合材料服役周期内的重要一环,其中利用金属的铆接修补方法在快速修补技术中具有重要应用.采用中心挖跑道形孔法模拟碳纤维复合材料损伤,分别使用不锈钢板与钛合金板对复合材料损伤件进行铆钉修补,对损伤件和两种修补件进行轴向拉伸试验,并采用应变计监测复合材料孔边及金属板中心应变.试验结果表明:采用不锈钢和钛合金与复合材料损伤件以铆接方式得到的修补件可承受的最大载荷相同,与未修补的相比提升了 65.2％,说明对复合材料损伤板使用金属材料铆接修补具有一定补强效果,并且与使用不锈钢和钛合金材料进行修补的效果相当;在修补件拉伸过程中,碳纤维复合材料先于修补用金属材料失效;2种金属铆接修补件的破坏应变比无修补的损伤件的破坏应变略有增加但影响不大.

基于标准试验方法ASTM D7078/D7078M-12和ASTM D5379/D5379M-12对2.5D机织碳纤维增强树脂基复合材料V形缺口试样进行剪切试验,重点研究在两种V形缺口剪切试验方法和两种不同规格电阻应变计测试条件下的经、纬向剪切性能,对比试样不同面粘贴的应变计测量的剪切模量的差异,并对试样剪切后的表面损伤进行观察.结果表明:2.5D机织复合材料的V形缺口剪切应力-应变曲线总体呈现非线性特征,±45°方向的正应变曲线对称性良好;采用ASTM D7078/D7078M-12方法更适合2.5D机织复合材料剪切试验;大尺寸应变计测出的剪切模量高于小尺寸应变计;剪切破坏模式主要是表面树脂沿纬纱方向产生裂纹,随后出现纱线屈曲和界面脱粘.

对于纤维增强树脂基复合材料而言,在服役过程中湿度、温度等因素会严重影响复合材料的力学性能和使用寿命.从湿热老化机理、力学性能变化规律、老化寿命预测三个方面,阐述了近年来国内外纤维增强树脂基复合材料湿热老化行为的研究现状.指出了纤维增强树脂基复合材料湿热老化行为研究存在的问题:如机理研究不深入、研究系统性不足,对航空常用复合材料体系的寿命预测研究较少,据此提出了复合材料湿热老化行为研究的主要方向.

Based on the three-point bending test, the bending performances of S6C10-800/AC318 composite unidirectional plates with different span-thickness ratios (hereinafter referred to as unidirectional plates) were tested, and the effect of span-thickness ratio on the bending strength and bending modulus of unidirectional plate was studied. The influence and fracture mode of the specimens with different span-thickness ratios were analyzed to obtain the bending failure mechanism, and the critical span-thickness ratio of three-point bending test of unidirectional plate was determined. The results show that the bending strength of the unidirectional plate increases with the increase of the span-thickness ratio, and the bending modulus first increases and then decreases with the increase of the span-thickness ratio. The fracture mode of the unidirectional plate changes when the span-thickness ratio α＝20, and the degree of delamination damage of unidirectional plate gradually decreases with the increase of span-thickness ratio, but the degree of splitting increases. When α≤20, the stress-strain curve conforms to the linear relationship with the increase of the span-thickness ratio, but when α＞20, the stress-strain curve does not conform to the linear relationship. Therefore, the predicting formula of bending strength of unidirectional plate under arbitrary span-thickness ratio and a failure criterion for three-point bending test of unidirectional plate are obtained. It is recommended that the critical span-thickness ratio of the three-point bending performance test of unidirectional plate is 20. This is of great significance for optimizing the three-point bending test method of glass fiber composite materials to more accurately test the bending performance of composite materials.

The high-temperature compressive properties are indispensable mechanical performance parameters for the structural design of composites, but it is difficult to be measured effectively by traditional techniques. In this study, the high temperature compressive experiment of carbon fiber reinforced plastics (CFRP) laminates was conducted in high-temperature experimental system based on digital image correlation (DIC) method. And the compressive properties, stress-strain curves and the evolution of axial full-field strain of CCF300/5228A with 0° and 90° ply-ups at 130℃ were obtained. Moreover, they were compared with those obtained at room temperature. Furthermore, the fracture analysis of the compressed specimens was carried out through scanning electron microscopy (SEM), meanwhile the effects of high temperature and lay-up on the compressive properties were discussed combining with the experimental results. Finally, an experimental verification was carried out and the results obtained demonstrated the feasibility and reliability of the experimental system and relevant experimental methods. The results show that the retention rate of 0° and 90° compressive strength at 130℃ are 70.5% and 62.6%, respectively, while the retention rate of compressive modulus are 88.0% and 75.4%, respectively, indicating that the strength and modulus of the laminates which are controlled by the matrix are more sensitive to high temperature.

平面断裂韧性对于结构强度设计具有重要意义.针对含有预制裂纹的聚甲基丙烯酰亚胺(PMI)泡沫紧凑拉伸(CT)试样,开展了平面断裂韧性实验,获得了相应载荷-位移曲线.随后通过光学方法获得了CT试样断口的显微图和三维形貌,标定了裂纹前缘,并精确测量了裂纹长度.最终通过计算获得PMI泡沫的平面断裂韧性KIC为0.103 MPa·m1/2,离散系数为2.66％,证明了实验的可行性和可靠性.

The high-temperature compressive properties are indispensable mechanical performance parameters for the structural design of composites, but it is difficult to be measured effectively by traditional techniques. In this study, the high temperature compressive experiment of carbon fiber reinforced plastics (CFRP) laminates was conducted in high-temperature experimental system based on digital image correlation (DIC) method. And the compressive properties, stress-strain curves and the evolution of axial full-field strain of CCF300/5228A with 0 degrees and 90 degrees ply-ups at 130 degrees C were obtained. Moreover, they were compared with those obtained at room temperature. Furthermore, the fracture analysis of the compressed specimens was carried out through scanning electron microscopy (SEM), meanwhile the effects of high temperature and lay-up on the compressive properties were discussed combining with the experimental results. Finally, an experimental verification was carried out and the results obtained demonstrated the feasibility and reliability of the experimental system and relevant experimental methods. The results show that the retention rate of 0 degrees and 90 degrees compressive strength at 130 degrees C are 70.5% and 62.6%, respectively, while the retention rate of compressive modulus are 88.0% and 75.4%, respectively, indicating that the strength and modulus of the laminates which are controlled by the matrix are more sensitive to high temperature.

综述了近年来国内外关于氧化处理法、表面涂层法、等离子体处理法对CF本体性能、CFRP力学性能的影响研究进展,分析了不同处理法改性CF对CFRP力学性能的作用机制、改性效果和优缺点.指出了近年来国内外研究存在的问题和今后的发展趋势,推动高性能CFRP在航空航天领域进一步应用,为今后研究者进一步研发和生产新型复合材料、改进CFRP综合性能提供完整的数据信息和理论依据.

拉伸性能是复合材料层合板的基本力学性能,研究湿热环境对玻璃纤维复合材料拉伸性能的影响可以为复合材料工程应用提供重要参考.开展了不同湿热环境下的AC318/S6C10-800复合材料拉伸性能研究,分析了环境对AC318/S6C10-800复合材料弹性模量及拉伸强度的影响.研究结果表明,低温干态环境下强度性能数据相对室温环境略高,70℃湿态环境下强度性能最低,随着试验温度的升高,0.拉伸强度、90.拉伸强度基本呈线性下降趋势.研究结果为AC318/S6C10-800复合材料工程应用提供参考.

主要开展了AC318/S6C10-800复合材料的面内剪切和吸湿状态处理后面内剪切性能试验.试验环境为低温干态、室温干态、高温80℃干态和70℃、85％RH条件下平衡吸湿后55℃高温和70℃高温.采用ASTM D3518《聚合物基复合材料面内剪切性能标准试验方法》对AC318/S6C10-800复合材料进行面内剪切试验,测量面内剪切强度和模量等力学常数.研究结果为AC318/S6C10-800复合材料结构设计及工程应用提供参考.

制备了一批AC318/S6 C10-800玻璃纤维复合材料压缩试样,并根据ASTM D6641《聚合物基复合材料压缩性能标准试验方法》对AC318/S6 C10-800复合材料进行压缩试验,测量了压缩强度和压缩模量等力学常数.采用DOT/FAA/AR-03/19《聚合物基复合材料体系的材料认证(取证)和等价性:已更新程序》对AC318/S6 C10-800玻璃纤维复合材料压缩试样进行吸湿状态处理,分析了湿热环境对AC318/S6 C10-800玻璃纤维复合材料压缩力学性能影响.研究结果表明,低温干态环境下强度性能数据相对室温环境略高,70℃湿态环境下强度性能最低,为AC318/S6 C10-800玻璃纤维复合材料结构设计及工程应用提供重要参考.

开展5224/CF3052平纹织物复合材料层压板低速冲击后的拉伸疲劳试验,冲击能量为1J/mm和3.4J/mm.绘制冲击能量为1J/mm时90％ 存活率的低周疲劳S-N曲线,分析冲击能量为3.4J/mm时最大应力变化对刚度降的影响.结果表明:层压板在低能量(3.4J/mm)冲击后具有优异的抗拉伸疲劳性能,冲击后层压板疲劳损伤不扩展(以106计)的应力水平超过有损静强度的90％;104循环—106循环刚度降随着拉伸疲劳最大应力的增大而增大.

石英纤维增强树脂复合材料常用于多物理场耦合环境下,为保证足够的层间性能,常采用2.5 D机织的结构形式.本文对一种浅交弯联2.5 D机织石英纤维增强双马树脂复合材料的三维力学性能进行全面测试,对比分析了材料在不同方向的拉伸性能和压缩性能,以及面内、面外剪切性能.测试结果表明,该复合材料的纬向拉伸、压缩模量略高于经向,而拉伸、压缩强度远高于经向,导致经向和纬向拉、压破坏模式差异显著,拉伸时弯曲的经向纤维被拉断,平直的纬向纤维劈裂,压缩时平直的纬向纤维压断,弯曲的经向纤维屈曲.同时,该种材料具有较高的面内、面外剪切变形能力.此外,本文基于混合定律,提出了一个2.5 D机织复合材料经、纬向模量估算公式.基于材料微观结构特征,以包含经纱和纬纱的一个单胞作为代表性体积单元,建立有限元模型,预测该2.5 D机织复合材料经向模量,预测结果与试验结果吻合很好.本文的研究对2.5 D机织石英纤维/双马树脂复合材料的研发具有一定的指导意义.

为了评价将可剥布从层压板表面剥离时的难易程度,针对47批次由不同可剥布和预浸料制备的复合材料层压板试样,根据胶粘剂浮辊剥离阻抗试验方法(ASTM D3167)开展浮辊剥离试验.通过回归分析发现,剥离强度均值和剥离强度峰值的均值、剥离强度谷值的均值、平均剥离振幅之间线性相关,相关系数R2分别为0.991、0.994和0.782.提出采用剥离强度均值、剥离强度峰值的均值或剥离强度谷值的均值为主要指标,平均剥离振幅为次要指标来评价可剥布剥离工艺性.根据剥离强度和剥离振幅不同,将可剥布剥离工艺性划分为5个等级,为可剥布选材提供依据.

3D five-directional fabric reinforced C-f/Al composites were fabricated by a vacuum assisted pressure infiltration method. The microstructure and interfacial reaction of the composites prepared at different temperatures were investigated. The uniaxial tensile property of the composites was tested at room temperature and elevated temperature and the corresponding tensile fracture surface was analyzed. The results indicate that the relative density of the C-f/Al composites increases and the fiber segregation in partial region decreases with the fabrication temperature increasing. Meanwhile the content of Al4C3 compound at interface increases obviously. At room temperature, the ultimate tensile strength of the composites from 570 to 600 degrees C degenerates dramatically with aggravated interfacial reaction. However, the ultimate tensile strength at elevated temperature increases with the fabrication temperature increasing. The improvement of interfacial strength is beneficial to the high temperature mechanical properties. The matrix alloy softening and interface weakening due to elevated temperature can promote the fiber pulling-out and interface sliding during the fracture process.

The stress singularities of a dynamic crack tip in orthotropic composites were studied through caustics. The parametric equations of the caustic and its initial curve surrounding the dynamic crack tip were derived through the elastic dynamic crack solutions of orthotropic composites and the basic principle of reflective caustics. Theoretical caustics and initial curves for three kinds of orthotropic composites were simulated, and the effects of crack velocity on the caustics and initial curveswere analyzed. In comparison with numerical results, the dynamic caustic experiment was performed for dynamic cracks along the material axes in unidirectional, fiber-reinforced composites under drop-hammer, three-point-bend loading.

High performance carbon-reinforced composite materials have become important aeronautical materials. During the service time, the delamination fracture of composite structures is a common failure mode. In this study, in order to investigate the delamination behaviours of T800/epoxy composite materials under different mixture ratios, DCB, ENF and MMB tests were conducted on composite laminates with pre-set 0°/45° interface respectively. From the test, the initial delamination fracture toughness and delamination growth behaviour were obtained. The test results show that the fracture toughness and delamination behaviour are significantly affected by the mixture ratio. With the increase of mixture ratio, the fracture toughness increases, and steady delamination growth behaviour is more difficult to maintain. Based on the data fitting method, a prediction function for fracture toughness of the 0°/45° interface at arbitrary mixture ratio is established, which has some engineering values.

In this paper,the curved beam strength and strength-after-impact characteristics of carbon/epoxy laminated curved beams were studied experimentally using four-point bending test and low velocity impact.First,the post impact damage characterizations of the laminated curved beams with different radii were analyzed based on ultrasonic C-scan images.Second,the effect of impact damage on both the failure strength and the maximum interlaminar radial stresses of the laminated curved beams were investigated.Finally,the full field displacement distributions of the laminated curved beams were obtained using Digital Speckle Correlation Method (DSCM).Experimental results play a significant role for strength evaluating of laminated curved beams with and without impact damage.

层间剪切强度是评价复合材料层合板层间力学性能的一项重要指标.首先,按照ASTM D 2344开展了复合材料层合板短梁剪切试验,研究了CCF300/5228复合材料层合板层间剪切性能.其次,基于数字图像相关方法得到了不同载荷作用下层间全场位移和应变分布.最后,利用ABAQUS建立了复合材料层合板有限元模型,分析了复合材料层合板层间位移及应变分布,并与数字图像相关计算结果进行了对比.研究表明,数字图像相关方法试验结果与有限元分析结果具有较好的一致性.数字图像相关方法能够实时监测层合板层间应变分布,进而预测层间剪切破坏位置,为复合材料层间剪切性能研究提供有效的全场应变监测手段.

The fatigue crack propagation behavior of two different forms of PMMA was studied using two-stage zone model. First, the fatigue crack length and fatigue crack propagation velocities of different specimens were obtained experimentally. Then the effect of material forms and specimen types on the fatigue crack propagation velocities was analyzed. Finally, the data scatter of da/dN-ΔK curves in different forms and different types of specimens was analyzed. The results show that the expressions of fatigue crack propagation velocities of middle crack tension (MT) specimens and compact tension (CT) specimens in the same form PMMA are similar. And the scatter of MT specimens is larger than CT specimens in two forms of PMMA.