高性能CFRP增强纤维表面状态分析及性能研究

为研究高性能炭纤维的表面特征及炭纤维与环氧树脂基体之间的界面结合,获得高性能的结构型炭纤维/环氧树脂复合材料(CFRP).采用红外光谱、扫描电镜、X射线光电子能谱仪、单向板、NOL环、Φ150 mm压力容器等方法,对炭纤维/环氧树脂复合材料(CFRP)3种高性能炭纤维表面状态及复合材料性能进行了系统研究.结果表明,3种炭纤维表面涂层均能参与环氧基团固化反应在界面上形成化学键;UT500系列炭纤维表面轴向沟槽可与树脂基体通过物理"机械啮合"作用形成更强的界面结合;UT500-12K炭纤维/E-51单向板剪切强度为91.46 MPa,NOL环剪切强度为77.16 MPa,分别比T700-12K/E-51体系高约40%.CFRP复合材料中炭纤维的微观结构、表面活性是决定复合材料界面结合的重要因素,直接影响复合材料制品的含胶量,进而影响其综合力学性能.     

苯酚电聚合膜修饰炭纤维表面对环氧基复合材料性能的影响

将连续炭纤维束用自制的空气梳分散成单丝状长带后, 通过采用循环伏安法的电化学方法将单体苯酚在炭纤维表面聚合成膜, 对炭纤维进行表面修饰, 以提高复合材料中炭纤维与树脂基体的界面粘结性能。红外光谱分析表明, 苯酚电聚合膜能够增加炭纤维表面的羟基、 醚键等活性官能团, 从而提高炭纤维与环氧树脂基体的界面粘结强度。与未进行表面修饰的炭纤维增强环氧树脂复合材料相比, 以聚苯酚膜修饰的炭纤维单丝带增强的环氧树脂基复合材料横向拉伸强度最大提高了90%, 纵向拉伸强度最大提高了45%, 层间剪切强度最大提高了110%。实验也表明, 将炭纤维束分散成炭纤维单丝带后能够更有效地增强复合材料的各项力学性能。      

不同原料合成COPNA树脂及其黏结性

以四种不同的油浆为原料，在酸性催化剂存在下，与对苯二甲醇反应，得到四种COPNA树脂。以COPNA树脂、酚醛、环氧树脂为基体，与炭纤维复合，通过模压成型，得到四种不同基体的复合材料。考察并比较了COPNA树脂的软化点、残炭、B树脂含量等黏结性参数以及树脂／炭纤维复合材料的抗冲击强度和层间剪切强度。从大庆油浆得到的COPNA树脂为基体的炭纤维复合材料，表现出的力学性能优于酚醛、环氧树脂，间接证明了COPNA树脂与炭纤维有较强的亲和性，这为COPNA树脂的应用提供了一个很好的方向。     

超临界正丙醇回收炭纤维增强环氧树脂复合材料（英文）

研究了降解温度、反应时间和添加剂对超临界正丙醇中炭纤维增强环氧树脂基复合材料回收的影响。利用扫描电镜、热重、X射线光电子能谱、接触角和单丝拉伸对回收炭纤维进行表征。结果表明,随温度的升高,复合材料降解速率加快,但回收炭纤维力学性能略微降低。随反应时间的延长,复合材料降解速率降低,回收炭纤维力学性能降低。1%质量含量的KOH能明显提高复合材料的回收效率。伴随KOH含量增加,复合材料降解速率没有明显提高,而使回收炭纤维力学性能变差。合适的反应条件对回收具有清洁表面、良好热稳定性和力学性能完好保留的炭纤维至关重要。回收炭纤维表面化学的微弱变化使回收炭纤维同环氧树脂的接触角略增加。超临界正丙醇是一种回收炭纤维复合材料的有效方法。     

炭纤维表面性质及上浆剂对炭纤维聚碳酸酯复合材料界面性能的影响

通过对比未处理炭纤维、氧化炭纤维、商业化环氧树脂用炭纤维和实验室用聚氨酯及环氧树脂自上浆炭纤维的表面性质和其增强聚碳酸酯层间剪切强度,研究炭纤维表面性质与上浆剂对界面结构与性能的影响。结果表明,未处理炭纤维表面官能团与树脂的浸润性最小,层剪值最低为38.1 MPa。氧化纤维表面官能团增加,浸润性提高,层剪值提高到50.6 MPa。商业化环氧树脂用炭纤维表面官能团与树脂浸润性相比氧化纤维明显提高,层剪值相当,为50.8 MPa。说明浸润性是强界面产生前提,但不是充分条件。自上环氧浆炭纤维复合材料的层剪值相比商业炭纤维更低,约为31.7～39.5 MPa,而聚氨酯上浆炭纤维表面官能团与浸润性跟商业化环氧树脂用炭纤维相当,但层剪值提升18.9%,为60.4 MPa。说明界面结合强度提高的原因更依赖于氨酯键与炭纤维表面及聚碳酸酯树脂基体均能产生强的化学作用。     

二氧化硅纳米颗粒增强炭纤维/环氧树脂界面性能

纤维与基体间的界面性能是决定纤维增强树脂基复合材料力学性能的关键因素。采用单纤维断裂实验方法研究二氧化硅纳米颗粒对炭纤维/环氧树脂复合材料界面的增强作用。实验结果表明,涂覆在炭纤维表面和均匀分散在环氧树脂基体中的二氧化硅纳米颗粒含量分别为4.9g/m2和25%(质量分数)时,复合材料界面性能均得到改善,界面抗剪强度相比纯树脂体系分别提高了10.0%和15.0%。通过对纤维断点处双折射光斑和样品断面形貌等信息分析,可知纳米颗粒均匀分散并镶嵌到炭纤维表面沟槽中形成的锁扣结构是界面性能提高的重要原因。     

工业用环氧树脂及其复合材料的闭环回收再制造

环氧树脂基碳纤维增强复合材料因其优异的力学、热学性能已广泛应用于航天航空等领域。环氧树脂由三维共价交联网络组成，难以被降解。工业中通常需高温(300～800℃)、高压(3～27 MPa)等严苛环境或有毒催化剂来破坏树脂基体，以回收复合材料废弃物中昂贵的碳纤维，这一过程往往会造成纤维性能的严重损失。本文利用环氧树脂与醇溶剂之间的动态键交换反应，将工业中常用的高性能环氧树脂降解为低聚物，降解条件温和(200℃、0 MPa)，且无需额外催化剂。通过树脂降解，回收得到结构完整的碳纤维织物，其强度保持在94%以上，可继续用于制备复合材料。将低聚物作为反应物制备新的环氧树脂，称为再制造环氧树脂。当再制造环氧树脂中低聚物的含量为20wt%时，其强度与原环氧树脂相当，而断裂伸长率提高了20%。用再制造环氧树脂制备碳纤维复合材料，其强度与原环氧基复合材料相当，同时断裂伸长率提高了50%。本文实现了工业用环氧树脂及其复合材料从制造到回收到再制造过程，即闭环回收再制造。同时，本文新提出了一种绿色、简单、有效的环氧树脂增韧方法。     

酚醛树脂表面处理剂对炭纤维增强环氧树脂复合材料界面强度的影响

采用酚醛树脂作为炭纤维表面处理剂, 可以显著提高多种炭纤维和环氧树脂界面强度。通过XPS、AFM、SEM和层间剪切强度等方法, 研究了不同浓度的酚醛树脂表面处理剂对炭纤维增强环氧树脂复合材料层间剪切强度、炭纤维表面元素和化学键组成的影响, 以及炭纤维增强环氧树脂复合材料断面微观形貌的变化。XPS和AFM分析结果表明酚醛树脂和炭纤维表面发生了化学反应, 而且酚醛树脂处理剂浓度越高, 和炭纤维表面发生反应的基团也越多, 表面越光滑平整, SEM和层间剪切强度研究表明酚醛树脂处理后的复合材料界面粘结性能得到很大的改善, 而且界面粘结性能强烈依靠处理剂浓度。      

湿纺和干湿纺炭纤维的表面结构分析

采用SEM、AFM及XPS等测试技术对湿法和干湿法制备的炭纤维的表面形貌、组织结构及化学组成进行了表征,分析材料的微观组织对复合材料界面的影响.研究结果发现,湿法炭纤维表面粗糙度大,沿纤维轴向沟槽深浅不均匀,且走向杂乱,有利于与复合材料中的基体树脂产生物理机械锁合作用,促进界面粘结;湿法炭纤维的表面含氧量和含氮量高于干湿法炭纤维,且表面活性同样高于干湿法炭纤维,有利于与基体树脂发生化学反应,形成较强的界面作用,从而使湿法炭纤维复合材料的层间剪切强度比干湿法炭纤维提高了13.92％.     

炭纤维表面化学结构对其增强环氧树脂基复合材料性能的影响

采用阳极氧化法对炭纤维的表面进行处理,通过改变氧化程度制备具有不同表面化学结构的炭纤维,并将其作为增强体再制备成复合材料。研究了炭纤维表面化学结构对其增强环氧树脂基复合材料性能的影响。结果表明,阳极氧化处理后炭纤维表面活性大幅提高,O,N元素含量分别由处理前的3.10%,1.12%提高到处理后的13.07%,5.96%;当电流密度低于15A/m2时,O/C,N/C值越高越有利于炭纤维表面与环氧树脂基体之间的界面黏合;在含氧官能团中,-COOH是决定炭纤维/环氧树脂基体间化学键合强度高低的关键因素。     

Pull-through performance of carbon fibre epoxy composites

An investigation of the through-thickness properties of carbon fibre prepreg laminates, Non-Crimp Fabric laminates and non-crimp 3D orthogonal woven composites by pull-through testing was performed. Influence of matrix system and curing temperature on the performance of the 3D woven composites was investigated.     

碳纳米管／环氧树脂复合材料的研究

研究了碳纳米管（CNTs）／环氧树脂复合材料的分散性能及电性能。探讨了碳纳米管的含量、管径和稀释剂的用量对环氧树脂电学性能的影响，并用透射电子显微镜（TEM）和扫描电子显微镜（SEM）对其进行表征。结果表明，碳纳米管的分散和含量对环氧树脂的电性能影响很大，而加入碳纳米管能够使环氧树脂由绝缘体变为导体（电阻率〈^10mΩ·cm）。     

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。     

快速固化环氧树脂及其碳纤维/环氧复合材料性能

采用双酚A型环氧树脂（DGEBA）、改性咪唑（MIM）及改性脂肪胺（MAA）研制快速固化树脂体系。分别利用DSC和流变仪测试了树脂体系的固化特性与流变行为,优选了树脂配方。采用真空辅助树脂灌注工艺（VARIM）制备了快速成型的碳纤维/环氧复合材料层板,考察了层板的成型质量和力学性能,并与常规固化的层板性能进行了对比。结果表明：采用优选的树脂配方,120 ℃下树脂在5 min内固化度达95%,碳纤维/环氧复合材料层板成型固化时间可控制在13 min以内,固化度达95%以上,并且没有明显缺陷;与常规固化相比（固化时间大于2 h）,快速固化碳纤维/环氧复合材料层板的弯曲性能和耐热性能降低幅度较小。     

Torsion fatigue behavior of unidirectional carbon/epoxy and glass/epoxy composites

This paper presents results of the feasibility of carbon/epoxy composites (CFRP) as a future helicopter flexbeam material. Torsional behaviors of unidirectional CFRP and glass/epoxy composites (GFRP) with the same resin matrix were investigated. The initial torsional rigidity of CFRP was almost identical to that of GFRP. The torsional rigidities calculated using finite element analyses (FEA) agreed with the experimental results: the torsional rigidities are governed mainly by the material’s shear stiffness. Torsion fatigue tests were also conducted by controlling the angle of twist of the sinusoidal wave under a constant tensile axial load. No catastrophic failure occurred with either GFRP or CFRP, although decreased amplitudes of torque and torsional rigidities were observed according to the number of cycles. Results of X-ray CT inspections and numerical calculation by FEA revealed that degradation of a torsional rigidity is caused mainly by splitting crack propagation along the fiber direction. The torsion fatigue life of CFRP was superior to that of GFRP. Consequently, results confirmed that CFRP exhibits excellent properties as a torsional element of a helicopter flexbeam in terms of torsional rigidity and tension–torsion fatigue behaviors.     

Time dependency of carbon/epoxy interface strength

This paper describes time-dependent fiber/matrix interfacial strength of carbon fiber reinforced polymeric composite. The time-dependent interfacial strength is extracted from the results of transverse tensile tests with various loading rates and their fractography in the unidirectional composite. The results show that the material failure is dominated by interface failure under relatively high-loading rate whereas matrix failure is dominant under relatively low-loading rate. In light of the results, it is concluded that the time dependency of the interfacial strength might be neglected or at least could be less significant than that of matrix strength.     

Thermally mendable epoxy resin strengthened with carbon nanofibres

This paper investigates the strengthening and toughening effects of carbon nanofibres (CNFs) on a self-healing thermoset/thermoplastic blend, i.e. an epoxy/poly (ε-caprolactone) (PCL) blend. The self-healing material system was prepared by polymer blending that produced a co-continuous phase-separated structure. The addition of CNFs altered the phase structures, leading to smaller domain sizes or even completely altering the phase separation mechanism, e.g. conversion from a co-continuous phase-separated structure to a particulate phase structure when the CNF content reached a certain level (0.3 wt% in this work). As the content of CNFs increased, the resulting nanocomposite became stronger and tougher, but the self-healing efficiency diminished; the optimal CNF content was found to be 0.2 wt%, which produced the highest strength, toughness and hardness, while achieving around 70% of healing efficiency.     

Impact of carbon fibre/epoxy corrugated cores

The dynamic compressive response of corrugated carbon-fibre reinforced epoxy sandwich cores has been investigated using a Kolsky-bar set-up. Compression at quasi-static rates up to v₀ = 200 ms⁻¹ have been tested on three different slenderness ratios of strut. High speed photography was used to capture the failure mechanisms and relate these to the measured axial compressive stress. Experiments show significant strength enhancement as the loading rate increases. Although material rate sensitivity accounts for some of this, it has been shown that the majority of the strength enhancement is due to inertial stabilisation of the core members. Inertial strength enhancement rises non-linearly with impact velocity. The largest gains are associated with a shift to buckle modes composed of 2–3 half sine waves. The loading rates tested within this study are similar to those that are expected when a sandwich core is compressed due to a blast event.     

Failure characteristics in carbon/epoxy composite tows

In this paper the failure mechanisms of unidirectional aligned carbon fibre/epoxy composites are investigated. Experimental results are presented for the strength of carbon/epoxy composite tows, as well as for single carbon fibres supplied in the sized and unsized condition. Laser Raman spectroscopy was used in this study to assess the effect of fibre breaks on the stress distribution within a composite. Fibre stress mapping of composite tows using laser Raman spectroscopy showed redistribution due to fibre failure and a value of the stress concentration factor, K_r, was obtained. The results were analysed using a Weibull distribution for the strength of the reinforcing fibres and composite.