PAN基高模碳纤维阳极氧化的表面处理

采用阳极氧化法对PAN基高模碳纤维进行连续表面处理,重点研究了氧化电流密度对碳纤维宏观力学性能、表面形貌、表面酸性官能团以及碳纤维增强树脂基复合材料(CFRP)层间剪切强度(ILSS)的影响。结果表明,电流密度对纤维力学性能、表面形貌影响不大;氧化后纤维表面总的酸性官能团显著提高,最大增幅达13倍左右;适当的处理条件可使CFRP的ILSS从28.4 MPa提高到80 MPa以上。     

用SEM研究CFRP的界面效应

用气相氧化法对碳纤维进行表面处理,可使层间剪切强度(ILSS)提高40～76％。这归因于增加了碳纤维的表面积和表面化学官能团的浓度。同时,碳纤维增强塑料(CFRP)的剪切断裂形态也由未处理的多剪断裂变为处理后的抗剪断裂。用扫描电子显微镜(SEM)观察剪切断面已证实了这个问题。     

CFRP复合材料层间剪切强度的单模态Weibull分布

本文使用经典的Weibull分布理论研究了表面处理对碳纤维增强环氧树脂复合材料(CFRP)层间剪切强度的影响,并用极大似然法对函数进行参数估计。分布函数在双对数坐标系中为直线,理论分析与实践结果发生偏离,这在某种程度上反映了最弱连接理论的局限性。碳纤维(CF)经表面处理后,CFRP的层间剪切强度提高约50％,Weibull模数增加一倍多,变异系数有所下降。     

碳纤维表面电化学氧化的研究

主要采用电化学氧化法对聚丙烯腈(PAN)基碳纤维进行连续氧化处理,利用扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和动态力学热分析(DMTA)对碳纤维表面处理效果进行了研究。SEM表面形貌研究结果表明,碳纤维经电化学氧化处理后,其表面的粗糙度和比表面积增大。XPS表面化学分析表明,经电化学氧化处理后的碳纤维表面羟基含量提高55％,活性碳原子数增加18％。DMTA谱图表明经电化学氧化处理的碳纤维增强树脂基复合材料(CFRP)其玻璃化温度(Tg)提高5℃、损耗角正切(tanδ)较未处理的降低30％。定量计算出的界面黏结参数A和α与CHRP的层间剪切强度(ILSS)所反映的碳纤维与树脂间界面黏结效果是一致的。研究结果表明,采用适当的处理条件可使CFRP的ILSS提高20％以上。     

碳纤维表面阳极氧化处理及对CFRP性能的影响

以NH_4HCO_3为电解质对碳纤维表面进行了连续阳极氧化处理。用正交试验方法确定了最佳处理工艺参数,研究了阳极氧化处理前后CFRP的层间剪切强度、抗拉强度、冲击强度的变化。并利用XPS、SEM对纤维表面组成及CFRP断口形貌进行了分析和观察。提出了阳极氧化作用机理和处理前后CFRP断裂模式的变化。     

CFRP表面的激光处理及其结构与性能研究

采用光纤激光器对碳纤维复合材料(CFRP)表面进行处理,通过研究激光的光斑直径(D_g)和Z轴距离(L_Z)的关系,研究了L_Z对CFRP表面形貌、结构,以及对CFRP与铝合金单搭接接头胶接拉伸剪切强度(τ)的影响。结果表明:L_Z为5～25 mm时,随着L_Z的增加,D_g增大;L_Z为20 mm时,激光处理后的CFRP表面的环氧树脂基本去除,碳纤维几乎没有被破坏,排列仍然规整,环氧树脂去除的效果较好,且其表面烧蚀率最大为7.6 g/s,CFRP与铝合金单搭接接头的τ最大为15.46 MPa。     

碳纤维增强树脂复合材料界面效应的研究

在一立方厘米的碳纤维增强树脂复合材料(CFRP)中,碳纤维(CF)与树脂的接触界面高达4000平方厘米左右。两相界面间的粘结程度是决定层问剪切强度(ILSS)的主要因素。CF经表面处理后,可改善两相间的粘接,从而使ILSS得到显著提高。用扫描电镜研究剪切断面已证实了这点。     

碳纤维的改性及其界面性能

采用化学接枝的方法对篮球鞋用碳纤维进行了表面改性处理,将柠檬酸接枝到碳纤维表面制备了碳纤维/环氧树脂复合材料,对比分析了改性前后碳纤维的表面形貌、界面剪切强度和层间剪切强度,并对断口形貌进行了观察。结果表明:经过柠檬酸改性后的碳纤维表面粗糙度明显增加,与树脂基体的结合力最强;碳纤维、氧化后的碳纤维、对苯二胺接枝的碳纤维、聚柠檬酸接枝的碳纤维和二次接枝对苯二胺的碳纤维的界面剪切强度分别为46.8,53.4,68.2,62.4,82.2 MPa,改性碳纤维的界面剪切强度都高于原始碳纤维,二次接枝对苯二胺的碳纤维的界面剪切强度最大;经过表面改性处理的碳纤维的层间剪切强度都有不同程度提高,且二次接枝对苯二胺的碳纤维的层间剪切强度最大。     

γ-射线辐照对碳纤维及其复合材料力学陛能的影响

以^60Co γ-射线为辐照源对碳纤维（CF）表面进行处理，利用扫描电子显微镜（SEM）观察经辐照处理后的碳纤维单丝表面及其与环氧树脂制备的复合材料试样的层间剪切断付；通过层间剪切强度比较了吸收剂量对其复合材料层间剪切强度（ILSS）的影响，并根据GB/T 3362—1982标准比较了辐照前后碳纤维复照拉伸强度的变化。结果表明：辐照处理后的碳纤维增强环氧树脂复合材料的界面明显得到改善，在一定的吸收剂量范围内能够有效地提高复合材料的ILSS，但是过大的辐照剂量和接枝率不利于复合材料的界面改性；当辐照剂量小于250kGy时，碳纤维的复丝拉伸强度有所提高。     

阳极氧化对碳纤维及其复合材料性能影响的研究

对聚丙烯腈基碳纤维表面进行电化学氧化处理,用SEM扫描电镜、力学分析研究了阳极氧化对碳纤维表面形貌及力学性能的变化过程.结果表明：随着阳极氧化电流的增大,碳纤维表面沟槽缺陷逐渐消失,碳纤维力学性能先上升后下降,80 A氧化电流使碳纤维层间剪切强度提高变化15.3％、拉伸强度提高l2.1％;阳极氧化有利于提高碳纤维在热塑性材料中的粒径尺寸.     

The effect of fibre surface treatment,resin type and fabrication process on the interlaminar shear strength of carbon fibre composites

Some data related to the preparation of carbon fibre composites is summarised. A limited investigation concerned with presenting markedly different fibre surfaces to the resin by coating with metals and stearic acid is also described. There are carbon fibre surface treatments which lead to improved shear strength, but it is not clear how they are affecting the fibre surface. It also seems likely that some facets of the processing technique can have a large effect on composite quality as indicated by shear strength measurements. The difficulties in interpreting results and identifying sources of variability points to the advisability of statistically planned experiments to assess the significance of changes when investigating possible materials and processing improvements.     

Fractographic study of static and fatigue failures in polymer composites

Abstract

A fractographic study of delamination failures in a range of carbon fibre and glass fibre reinforced plastics has been performed. Mode I (peel), mode II (shear), and mixed mode (I + II) interlaminar fracture surfaces, generated both statically and in fatigue, were examined. Intralaminar shear failures generated using a notched tension specimen were also studied. Fractographic features, including striations and matrix rollers, unique to fatigue failure, were identified on many of the mode II dominated specimens. As the mode I component of fracture was increased both the matrix rollers and striations were seen to diminish. While the features identified on the fatigue fracture surfaces enabled static fractures to be differentiated from fatigue failures, studies have shown that the use of these features for the determination of crack propagation directions and crack growth rates may be more limited. It appears that local variations in the stress state over the fracure surface tend to produce significant variations in their spacing and appearance.     

Anodic oxidation of high modulus carbon fibres in sulphuric acid

The continuous anodic oxidation of high modulus (HM) carbon fibres in sulphuric acid electrolyte, with varied concentrations as a possible surface treatment method, is presented. It can be shown that within the applied potential ranges and the resulting current densities no loss of mechanical fibre properties or increase in BET surfaces is observable. The formed surface oxides are detected by a thermal fibre decomposition treatment up to 1000° C and thus give an explanation for the increase in ILSS (interlaminar shear strength) caused by the different applied current densities. It is also shown that the specific electric charge (current density x pretreatment time) of a particular electrolyte concentration can be taken as a parameter to describe the surface activation by anodic oxidation and its consequent influence on the ILSS of composites fabricated from treated carbon fibres in epoxy polymer. However, this fibre activation is predominantly affected by the concentration of the electrolyte.     

碳纤维表面处理

本文主要综述了碳纤维表面性质及表面处理方法,通过表面处理能够达到提高碳纤维复合材料层间剪切强度的目的。     

PAN基碳纤维阳极电解氧化表面处理的研究

借助XPS、力学分析、SEM扫描电镜、傅立叶红外光谱 ,较系统地考察了碳纤维表面组成与结构的变化及阳极氧化表面处理对碳纤维复合材料层间剪切强度的作用与影响。结果表明 :采用碳酸氢铵为电解质对碳纤维进行阳极电解氧化表面处理后 ,其复合材料的层间剪切断裂转变为以张力断裂形式为主 ;通过适当地增加碳纤维表面的羟基含量 ,提高活性碳原子数与非活性碳原子数比 ,可有效地改善碳纤维复合材料的使用性能 ,使碳纤维层间剪切强度提高 49% ,层间剪切强度达 85 .5MPa。     

Mode-I adhesive fracture energy of carbon fibre composite joints with nanoreinforced epoxy adhesives

The effect of the addition of carbon nanoreinforcements to an epoxy adhesive on the strength and toughness of carbon fibre/epoxy composite joints was studied. The laminate surfaces, treated with peel ply, were characterised by profilometry, image analysis and wettability. The mechanical properties of the joints were determined by lap shear testing and double cantilever beam testing. The fracture mechanisms were studied by scanning electron microscopy.The addition of carbon nanofibres and carbon nanotubes caused an increase in the mode-I adhesive fracture energy, G_IC, of the joints while their lap shear strengths remained approximately constant. This improvement in the fracture behaviour was attributed to the occurrence of toughening mechanisms when carbon nanoreinforcements were added to the epoxy adhesive. Additionally, the use of carbon nanotubes improved the interfacial strength between the adhesive and the substrate, changing the crack growth behaviour and the macroscopic failure mode.     

Interlaminar fracture toughness of selectively stitched thick carbon fibre reinforced polymer fabric composite laminates

Abstract

Carbon fibre reinforced polymer fabric specimens prepared from selectively stitched thick laminates have been tested under mode I (tension) and mode II (shear) loading, similar to already established tests used for thin unidirectional specimens. The respective interlaminar fracture toughness characteristics were derived for laminates of different stitching configurations. Results indicated significant interlaminar fracture toughness increase for all stitched samples compared with non-stitched samples, especially under mode I loading. It was concluded from parametric investigations that carbon thread stitching is more effective than its aramid counterpart in improving interlaminar fracture toughness. This is attributable to its higher stiffness and better bonding to the carbon fibre reinforced polymer system compared with the aramid thread.     

Evidence for the benefit of adding a carbon interphase in an all-carbon composite

T-800 polyacrylonitrile-based carbon fibres were coated with pyrolytic carbon and carbon/carbon/carbon (C/C/C) composites were prepared from them using coal tar pitch as the matrix precursor. Composites were characterised regarding pyrolysis behaviour, mechanical properties, microtexture, nanotexture, and fracture behaviour. All of the composite components, including interfacial areas, were characterised by high resolution transmission electron microscopy. It was checked that the presence of the carbon interphase did not affect the development of the matrix texture, nor deeply modified the fibre surface energetics. However, adding a pyrolytic carbon interphase resulted in improved mechanical properties for the C/C/C composites with respect to the similarly prepared but interphase-free composites (C/C), such as the increase in the flexural strength by a factor of five, and that of the flexural modulus a factor of two. It is shown that such a benefit brought by adding a carbon interphase is possible merely through the appropriate texture of the latter. Typically, the interphase has to exhibit features from both the matrix (anisotropic) and the fibres (isotropic) so that to reduce the discontinuity effect at the fibre/matrix contact, and should also exhibit features (elongated porosity) that promote multiple micro-cracking from the primary cracks, so that to somewhat absorb part of the fracture energy.     

Mechanical,morphological and thermal properties of short carbon and aramid fibres-filled bromo-isobutylene-isoprene rubber vulcanised with 4, 4’ bis(maleimido)diphenylmethane

ABSTRACT

This paper describes the use of a combination of 4, 4’ bis(maleimido)diphenylmethane and ZnO as a high-temperature processable vulcanising agent for the short aramid and carbon fibre-filled bromo-isobutylene-isoprene rubber. The fibre breakage analysis, cure characteristics, mechanical, thermal and morphological properties of the composites were evaluated with different fibre loading. The fibre breakage analyses revealed that the aramid fibres have good length retention property compared to carbon fibres. The morphological analysis of the extracted aramid fibres showed severe surface roughness primarily due to fibrillation after shear mixing. The fibrillated aramid fibres lead to aggregation and poor dispersion of the fibres in the rubber matrix. However, fibrillation imparted surface roughness and increased surface area on the aramid fibres which improved the fibre–matrix interaction via mechanical anchoring. On the other hand, the carbon fibre-filled composite showed poor fibre–matrix interaction and inferior strength and modulus.     

Treatment of an epoxy-resin by eximer laser radiation

The surface of carbon fibre reinforced plastics is usually cleaned prior to adhesive bonding. If epoxy resins are the matrix materials, grinding is the most often used procedure. Laser treatment seems to be a more reproducible alternative. In this paper the influence of eximer laser radiation (248 nm) on the surface properties of an epoxy resin is shown. At low laser energy densities the lap shear strength with the epoxy based adhesive Hysol® EA 9394 is on an appropriate level with an improved reproducibility, but at higher energy densities the lap shear strength decreases caused by the formation of a surface layer with a lower strength. This is caused by the decomposition of the resin surface, which is shown by XPS.