纤维/聚合物基体界面性能的原位表征

建立了复合材料界面强度原位测试系统,研制出界面剪切强度有限元分析软件并探讨了影响界面剪应力分析的因素,提出了改进的微观力学模型;利用该系统,研究了表面经不同改性处理的CF增强PMR-15聚酰亚胺复合材料界面的微观力学性能,结果表明:有效的表面处理可使CF/PMR-15界面剪切强度明显提高,并与其宏观性能具有较好的对应趋势。本文还初步探讨了界面破坏的过程。     

用SEM研究表面处理对炭纤维增强复合材料剪切断裂的影响

利用扫描电子显微镜（ＳＥＭ）,对炭纤维表面处理前后,炭纤维增强复合材料（ＣＦＲＰ）的剪切断面的观察,并分析了不同表面处理方法对ＣＦＲＰ的界面性质的影响。结果表明,经气液双效法处理后,ＣＦＲＰ得到高的层间剪切强度（ＩＬＳＳ）,同时表现出二剪和三剪的断裂模式。     

碳纤维γ射线辐照处理对其复合材料界面性能的影响

采用γ射线辐照方法对碳纤维（ＣＦ）进行改性,研究了辐照对ＣＦ增强复合材料层间剪切强度（ＩＬＳＳ）、ＣＦ复丝拉伸强度的影响,并使用Ｘ射线光电子能谱（ＸＰＳ）、扭辫分析、微脱粘测试等分析方法,对ＣＦ的表面化学组成和复合材料界面粘合强度进行了表征。结果表明,辐照使ＣＦ表面与环氧涂层发生了化学反应,复合材料界面粘合强度提高,ＩＬＳＳ增大,ＣＦ本体拉伸强度未发生变化。     

碳纤维表面处理对C/PLA复合材料界面粘结强度的影响(Ⅱ)

对硝酸表面处理前后碳纤维增强聚乳酸（Ｃ／ＰＬＡ）复合材料的界面状态进行了研究。重点研究了碳纤维的硝酸表面处理对Ｃ／ＰＬＡ复合材料界面粘结强度的影响以及粘结机理。研究表明,硝酸表面处理可使复合材料的界面粘结强度大幅度增加,复合材料的冲击强度、弯曲强度、弯曲模量和剪切强度亦有不同程度的提高。ＸＰＳ研究发现,央纤维与ＰＬＡ基体间有化学反应发生。界面化学反应程度的增加是复合材料界面粘结强度提高的主要原因;此外,碳纤维表面粗糙度的增加也对界面粘结强度的提高有一定的贡献。     

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。      

接枝改性对F-12纤维及其环氧复合材料力学性能影响的研究

采用稀氢氧化钾溶液对Ｆ－ １２ 纤维表面进行处理,将—ＣＯＯＫ 基团引入到Ｆ－ １２纤维表面,作为环氧氯丙烷接枝的引发剂．并分析了温度和时间对Ｆ－ １２ 纤维拉伸强度及其环氧复合材料层间剪切强度的影响．表明：在温和条件下将—ＣＯＯＫ 基团引入到Ｆ－ １２纤维表面,进而引发环氧氯丙烷的接枝,可以提高Ｆ－ １２环氧复合材料的层间剪切强度,而纤维的拉伸强度只有较小的损伤．     

碳纤维／PF尼龙复合材料性能及界面研究

制备了碳纤维／ＰＦ尼龙复合材料，采用Ｘ光电子能谱仪及化学滴定法定量分析了碳纤维表面的含氧状况，利用扫描电镜研究了碳纤维的表面形态及碳纤维／ＰＦ尼龙复合材料的界面形态，探讨了碳纤维表面形态和含氧量对复合材料力学性能和界面粘结状况的影响。结果表明，规整ＣＦ表面的羧基与ＰＦ尼龙分子中的胺基发生化学键合是复合材料具有良好力学性能及界面具有良好粘结的主要因素。     

树脂基复合材料界面及界面表征

在树脂基体和成型工艺一定的条件下，碳纤维表面及表面涂层的性质在很大程度上决定了复合材料界面的性质，通过对ＣＦ表面进行性改及改变ＣＦ表面涂层的性质，可优化界面，最大限度发挥界面的特性，有用了界面微脱粘仪及透射电镜照片伪彩色处理对界面进行直观表征。     

多向细编碳／碳复合材料界面力学性能测试与表征

本文用自制装置研究了多向细编Ｃ／Ｃ复合材料纤维束性能，分析了工艺过程的影响。同时用界面微脱粘实验技术研究了Ｃ／Ｃ复合材料界面性能，给出了相应的理论模型和界面应力分布，提出了由界面脱粘力，纤维、基体和复合材料性能表征界面剪切强度的方法，为Ｃ／Ｃ复合材料优化设计提供了定量参数。结果表明：织物结构、织物编织工艺以及织物／基体复合对纤维的强度影响很大，降为原始纤维的２０％左右，对模量影响小。不同界面层次，纤维／基体的界面结合情况和界面剪切强度不同，Ｚ向纤维束中纤维／基体结合好，具有最高的结合强度，ＳＥＭ观察证实有大量基体碳在纤维上枝联。     

芳纶复合材料的界面粘结

为改善芳纶纤维增强树脂基复合材料中界面粘结强度,本研究用Mctowo.Takayanagi——化学处理法,对芳纶1414纤维进行表面处理.并依据红外光谱分析(IR),元素分析(E.A.),XPS能谱分析等近似估价芳纶1414纤维表面导入约88mol%接技率的E-51环氧化合物.用单纤维拉拔实验法直接测定芳纶1414纤维/环氧树脂基体体系的界面剪切强度.实验结果表明,芳纶1414纤维经表面环氧接技化处理后,可较明显地提高界面剪切强度而对纤维拉伸强度的降低较小.树脂基体性能对界面剪切强度的影响较显著.通过电子显微镜(SEM)观察被拔出纤维及树脂孔穴的破坏形貌,解析界面破坏机理.     

碳纳米管纤维/环氧树脂复合材料的界面剪切强度及微观结构

研究了碳纳米管纤维的微观结构和拉伸性能,并进一步分析了其与环氧树脂形成界面剪切强度及微观结构。采用单丝断裂试验测试了碳纳米管纤维/环氧树脂复合材料体系的界面剪切强度,结合单丝断裂过程中的偏光显微镜照片、复合材料的拉曼谱图和断口扫描电镜照片,研究了碳纳米管纤维/环氧树脂复合材料界面的微观结构。结果表明: 碳纳米管纤维/环氧树脂复合材料的界面剪切强度约为14 MPa;在碳纳米管纤维和环氧树脂形成界面的过程中,环氧树脂可以浸渍纤维,形成具有一定厚度的复合相,这种浸渍过程和界面相的形成都有利于碳纳米管纤维与基体之间的连接。     

Ceramic composites: roles of fiber and interface

Results are presented that elucidate: (a) the effects of fiber coating on retained fiber strength and mechanical properties of Nicalon-fiber-reinforced SiC matrix composites; and (b) the role of residual stresses in the interfacial bond strength of SiC-fiber-reinforced reaction-bonded Si₃N₄ matrix composites. For Nicalon-fiber-reinforced SiC matrix composites that were fractured in a flexural mode, retained in-situ fiber strength, ultimate strength and work-of-fracture (WOF) of the composites increased with increasing thickness of the fiber coating and reached maximum values at a coating thickness of ≈0.3 μm. A direct correlation between the variation of in-situ fiber strength and the variation of ultimate strength and WOF of the composites clearly indicates the critical role of the retained in-situ strength of reinforcing fibers in composites. Fiber pushout tests performed on SiC-fiber-reinforced reaction-bonded Si₃N₄ matrix composites indicate that both debonding and frictional shear stresses decreased with increasing fiber content. These variations are consistent with the variation of residual radial stress on fibers, as measured by neutron diffraction, i.e. residual stresses decreased with increasing fiber content. Because fracture behavior is strongly controlled by interfacial bond strength, which is proportional to the residual radial stress, appropriate control of residual stresses is critical in the design of composites with desired fracture properties.     

Determination of interfacial mechanical properties of ceramic composites by the compression of micro-pillar test specimens

A novel method to determine the fiber-matrix interfacial properties of ceramic matrix composites is proposed and evaluated; where micro-pillar samples containing inclined fiber/matrix interfaces were prepared from a SiC fiber-reinforced SiC matrix composites and then compression-tested using the nano-indentation technique. This new test method employs a simple geometry and mitigates the uncertainties associated with complex stress state in the conventional single-filament push-out method or tensile unloading–reloading hysteresis loop analysis method for the determination of interfacial properties. Based on the test results using samples with different interface orientations, the interfacial debond shear strength and the internal friction coefficient are explicitly determined and compared with values obtained by other test methods. SEM observation showed that micro compression caused an adhesive type of debonding between the fiber and the pyrolytic carbon interface. The results suggest that the debonding/failure behavior of the micro-pillars followed the Coulomb fracture criterion. The determined interfacial debond shear strength is ~100 MPa, which appears to be smaller than that determined from fiber push-out test for similar composite systems. The difference can be explained by the effect of normal stress (clamping stress) on the apparent interfacial debond shear strength.     

Measurement and analytical validation of interfacial bond strength of PAN-fiber-reinforced carbon matrix composites

Carbon/carbon composites are well suited to high-friction applications due to their excellent mechanical and thermal properties. Since interfacial shear strength is critical to composite performance, characterization of fiber/matrix interface is a crucial step in tailored design of composites. This article presents a hybrid experimental/analytical study to evaluate the interfacial shear strength (IFSS) of PAN-fiber-reinforced carbon matrix composites. Microstructure was studied by light and high-resolution transmission electron microscopy (HRTEM). A series of push-out tests were conducted to examine the fiber/matrix debonding process. The residual fiber displacement was confirmed by scanning electron microcopy (SEM). The validity of the calculated IFSS value was demonstrated by a simplified analytical approach, where the components contributing to the measured displacement were analyzed considering the mechanics of the indentation. The method described in this article has been successfully used for determining the IFSS of PAN-fiber-reinforced carbon matrix composites.     

Effect of nano-SiO2 modified emulsion sizing on the interfacial adhesion of carbon fibers reinforced composites

The influence of nano-SiO₂ modified epoxy emulsion sizing on the interfacial adhesion properties of carbon fibers reinforced composites was investigated. The interfacial interaction between carbon fibers and the matrix was characterized by X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM) and three-point short-beam shear testing. The results showed that the amount of hydroxyl groups was slightly increased on the carbon fibers surface after treatment with nano-SiO₂ modified sizing. Compared to the unsized composites, the interlaminar shear strength (ILSS) values for the composites with unmodified sizing and nano-SiO₂ modified sizing were increased by 9% and 14%, respectively. The holes and carbon fibers pullout were not observed in their fracture sections. Surprisingly, the fracture section of the composites with nano-SiO₂ modified sizing was more compact and the fiber debonding was more difficult.     

The role of interfacial debonding in increasing the strength and reliability of unidirectional fibrous composites

A Monte-Carlo simulation technique based on a finite-element method has been developed in order to clarify the effect of interfacial shear strength on the tensile strength and reliability of fibrous composites. In the simulation a boron/epoxy monolayer composite was modelled, and five hundred simulations were carried out for various interfacial shear strengths. The interfacial shear strength value which raised the average strength of the composite corresponded approximately to the value which reduced the coefficient of variation. This implies the existence of an optimum value of interfacial shear strength which can increase the strength and reliability. The simulated strength and reliability were closely related to the degree and type of damage around a fiber break. That is to say, large-scale debonding caused by a weak interfacial bond and matrix cracking caused by a strong bond reduced the number of fiber breaks accumulated up to the maximum stress, and decreased the strength and reliability. On the other hand, small-scale debonding promoted comparatively the cumulative effect of fiber breaks and played a key role in increasing the composite strength and reliability.     

电子束固化复合材料界面

电子束固化复合材料界面粘结性能较低是急待解决的问题。利用阳极氧化技术和偶联剂涂层对碳纤维表面进行处理。处理前后的碳纤维表面性能利用SEM、XPS和接触角测试方法进行分析,通过层间剪切强度表征电子束固化复合材料界面粘结性能,并且与热固化复合材料进行对比。结果表明: 当碳纤维在酸性电解液中进行阳极氧化时,有利于提高电子束固化复合材料界面粘合性能,在碱性电解液中进行阳极氧化时, 则导致较低界面粘接性能。阳极氧化与偶联剂双重增效作用能够提高电子束固化复合材料界面粘合性能。     

Role of a gradient interface layer in interfacial enhancement of carbon fiber/epoxy hierarchical composites

To improve the interfacial properties of carbon fibers/epoxy composites, we introduced a gradient interphase reinforced by graphene sheets between carbon fibers and matrix with a liquid phase deposition strategy. Interlaminar shear strength and flexural strength of the composites are both improved. The interfacial reinforcing mechanisms are explored by analyzing the structure of interfacial phase with linear scanning system of scanning electron microscope and atomic force microscope. Results indicate that carbon element shows a graded dispersion in the interface region and a gradient interface layer with the modulus decreasing from fibers and matrix is found to be built. To verify the effect of gradient interphase on the interfacial properties of composites, the mixture of carbon fiber/graphene/epoxy is sonicated before curing to disperse graphene sheets in matrix homogeneously. As a result, gradient interphase structures are disappeared and interfacial performance of composites is found to be weakened. The role of gradient interface layers in enhancing interfacial performances is further proved from a different angle.     

Adhesion and friction behavior between fluorinated carbon fibers and poly (vinylidene fluoride)

The potential use of fluorinated, polyacrylonirtile-based, high strength carbon fibers as reinforcement for a fluorocarbon polymer, namely poly (vinylidene fluoride) (PVDF), was investigated by means of the single fiber pull-out test. The apparent interfacial shear strength as a measure of practical adhesion was determined and the fracture and friction behavior of the model composites characterized.It was shown that the fracture behavior of the model composites is predominately brittle in nearly all cases. Fluorination of carbon fibers has a positive impact on the adhesive strength to PVDF. The apparent interfacial shear strength increases with increasing degree of fiber surface fluorination and becomes maximal at a degree of fiber fluorination (F/C-ratio) of around 0.8, determined by ESCA, which is close to that of PVDF. This result points to the fact that the increased practical adhesion is due to a physical compatibilization between the fluorinated fibers and the surrounding PVDF matrix. It was found that, even though the interfacial shear strength increases with increasing degree of fiber surface fluorination, the friction between fluorinated carbon fibers and the surrounding PVDF decreases.