The influence of fibre pretreatmert on the mechanical properties of epoxy-asbestos composites

This study is devoted to the mechanical properties of asbestos-epoxy composites. Chrysotile fibres were first pretreated by means of an interfacial polymerization technique effecting eventually a poly (hexamethylene adipamide) coating on the asbestos surface. The interface characteristics were significantly altered and due to the well-known compatibility between epoxy and polyamide phase considerable deviation from the behaviour encountered when using untreated fibres was confirmed. Accordingly, while varying pretreated fibre content and also concentration of the polyamide coating, the tensile properties of the resulted composites were examined.     

Polyamide coating on carbon fibres and potential application in carbon/kevlar/epoxy hybrid composites

Hybrid unidirectional composite materials, consisting of alternately laminated layers of Kevlar-49 fibres and carbon fibres in an epoxy resin, have been studied. Before embedding, the carbon fibres were coated with a Nylon 6,6 film by an interfacial in-situ polymerization technique. Emphasis is given to the mechanical properties of the hybrid composites based on coated carbon, with those based on uncoated carbon, for various values of partial volume fraction of the carbon fibres, V_cf, polyamide content deposited on the carbon fibres, C_N, and total fibre (Kevlar + carbon) volume fraction, V_f.     

Strain-sensitive Raman spectroscopy and electrical resistance of carbon nanotube-coated glass fibre sensors

This paper presents the development of glass fibres coated with nanocomposites consisting of carbon nanotubes (CNTs) and epoxy. Single glass fibres with different CNT content coating are embedded in a polymer matrix as a strain sensor for composite structures. Raman spectroscopy and electrical response of glass fibres under mechanical load are coupled for in situ sensing of deformation in composites. The results show that the fibres with nanocomposite coating exhibit efficient stress transfer across the fibre/matrix interface, and these with a higher CNT content are more prone to fibre fragmentation at the same matrix strain. A relationship between the fibre stress and the change in electrical resistance against the fibre strain is established. The major finding of this study has a practical implication in that the fibres with nanocomposite coating can serve as a sensor to monitor the deformation and damage process in composites.     

Electrochemical coating for prevention of carbon fibre release from polymer composites: Thermogravimetric analysis of organophosphorus coatings on carbon fibres

Fire retardant coatings of phosphorus compounds were formed on graphite fibres by a new electrochemical technique. Thus, tetrakis (hydroxymethyl)-phosphonium sulphate, ammonium polyphosphate, titanium di(dioctylpyrophosphate) oxyacetate, di(dioctylphosphato)ethylene titanate, and propargyltriphenyl-phosphonium bromide, were electrodeposited or electropolymerized on commercial graphite fibres used for polymer reinforcement. The effect of these coatings on the thermal oxidative behaviour of the coated carbon fibres, epoxy resin, and composites prepared from them was studied by thermogravimetric analysis, and compared with that of polyimide coatings. Generally, the coated fibres showed higher decomposition temperature than the untreated carbon fibres. The fire retardant phosphorus compounds promoted the formation of char from the matrix resin, and accelerated the decomposition of char. Organophosphorus titanate coatings left an incombustible, white residual layer of titanium dioxide. The polyphosphate coating caused the decomposition of the fibres in the epoxy composite to occur at a reduced temperature compared to that in the absence of the matrix resin. A synergistic interaction between the polyphosphate and the amine-cured, epoxy resin to catalyse the decomposition of carbon fibres is inferred from this. Polyimide precursor coatings lowered the oxidation temperature of the carbon fibres, both as neat coatings and in the presence of epoxy matrix resin, thus reducing the temperature of survival of the fibres under combustion conditions. The results confirm the potential of this novel approach of forming precursor coatings on carbon fibres to minimize the release of conductive fibre fragments from carbon fibre-reinforced polymer composites exposed to fire.     

The effect of thermoplastic coating on the mechanical properties of woven fabric carbon/epoxy composites

The effect of a polyetherimide (PEI) coating on the mechanical properties of woven fabric carbon/epoxy composites was investigated by thermal mechanical analysis, fractographical analysis and mechanical properties measurements. PEI coating enhanced the mechanical properties of carbon/epoxy composites mainly through the improvement of matrix properties. This was because most of the PEI coated on the carbon fiber diffused into the bulk of epoxy matrix due to its good miscibility with epoxy resin. As for mechanical properties of woven fabric carbon/epoxy composites, the extent of improvement by PEI coating highly depended on the applied stress state. Among the mechanical properties, mode II delamination resistance of carbon/epoxy composites showed the highest increment because matrix shear property played an important role in delamination resistance of woven fabric carbon/epoxy composite. Because of the woven geometry of carbon fiber, the improvement in impact property of carbon/epoxy composite was trivial except the large amount of PEI coated case.     

Electrochemical deposition of polypyrrole on carbon fibres for improved adhesion to the epoxy resin matrix

A method of improving the interfacial bonding between carbon fibre and epoxy resin matrix is developed in the case of continuous electrochemical deposition (ECD) of polypyrrole on carbon fibres. The ECD-treated carbon fibres are characterized by electron spectroscopy for chemical analysis (ESCA), scanning electron microscope (SEM), porous structure analysis and wettability measurements. Furthermore, mechanical evaluation is used to assess the macro-interfacial bonding capability of carbon fibre/epoxy resin composites. It is shown that there is a good interfacial bonding between ECD-treated carbon fibres and the epoxy resin. On the other hand, we also postulate the structure of polypyrrole-coated fibre to explain the bonding mechanism of carbon fibre/epoxy resin composites.     

Surface,interphase and composite property relations in fibre-reinforced polymers

The aim of this study is to demonstrate the relations between surface, interphase and different composite properties in composites of carbon and glass fibres and thermosets (epoxy resin) or thermoplastics (polyamide, polypropylene). The surface characteristics of variously treated carbon and glass fibres have been determined by contact angle measurements, using a capillary penetration technique, and zeta potential measurements. Micromechanical tests (single-fibre pull-out) have been applied to model composites to establish the interphase properties. Bulk composites have been manufactured by impregnation with resins and curing by hot pressing or pressing of commingled yarn samples (continuous reinforcing fibres) or twin-screw extrusion and injection moulding (short reinforcing fibres). The composite properties have been tested by tensile and shear tests. Contact angle and electrokinetic measurements permit detection of differences in the surface treatment of glass and carbon fibres. Measurements of shear strength by pull-out, fibre fragmentation and yarn tensile shear tests show comparable results and correlate to the macromechanical properties.     

Role of fibre surface—matrix combination in carbon fibre reinforced epoxy composites

The effect of surface treatment of carbon fibres with concentrated as well as dilute nitric acid on the mechanical properties of carbon fibres has been reported. The role of the fibre—matrix interface in carbon fibre reinforced epoxy resin composites has been studied. Composites have been made both with untreated and surface treated carbon fibres and epoxy resin Araldite LY556 with different hardeners. Mechanical properties as well as fracture behaviour of these composites suggest that it is the physical interlocking between the fibres and the matrix, along with some chemical bonding between the two, and not the pure chemical bonding which yield better composites.     

The environmental fatigue behaviour of carbon fibre reinforced polyether ether ketone

The fatigue behaviour of carbon fibre/PEEK composite is compared with that of carbon/ epoxy material of similar construction, particularly in respect of the effect of hygrothermal conditioning treatments. Laminates of both materials were of 0/90 lay-up, and they were tested in repeated tension at 0° and at 45° to the major fibre axis. The superior toughness of the polyether ether ketone and its better adhesion to the carbon fibres results in composites of substantially greater toughness than that of the carbon/epoxy material, and this is reflected in the fatigue behaviour of the carbon fibre/PEEK. The tougher PEEK matrix inhibits the development of local fibre damage and fatigue crack growth, permitting a 0/90 composite with compliant XAS fibres to perform as well in fatigue as an epoxy laminate with stiffer HTS fibres. Hygrothermal treatments have no effect on the fatigue response of either material in the 0/90 orientation. The fatigue response of a cross-plied carbon/PEEK laminate in the ±45° orientation is much better than that of equivalent carbon/epoxy composites, again because the superior properties of the thermoplastic matrix.     

The thermal conductivity of glass-fibre and carbon-fibre/epoxy composites from 2 to 80 k

The thermal conductivity of one type of glass-fibre/epoxy and three types of carbon-fibre/epoxy composites has been measured from 2 to 80 K in directions parallel and perpendicular to the fibres for various volume concentrations of fibre. In the liquid helium region the conductivity of the carbon fibre composites is in general lower than that of epoxy alone. The conductivity of the fibres themselves has also been measured. The results on composites in the parallel direction are in good agreement with a volume average theory at all temperatures for glass, and above 10 K for carbon fibre, but below 10 K it would appear that account should be taken of the reduction in the phonon mean free path in the epoxy due to the presence of the fibres. In the perpendicular direction, allowance must be made for the acoustic mismatch between fibre and matrix and here the theory does not agree so well with the experimental results.     

The effect of surface treatment on the interfacial properties in carbon fibre/epoxy matrix composites

Carbon fibres with different degrees of surface oxidation, as well as epoxy-sized fibres, were used to prepare epoxy composites in order to compare the effects of the fibres surface chemistry on the interfacial properties. X-ray photoelectron spectroscopy, water vapour adsorption measurements and contact angle examination were applied to characterize the carbon fibre surfaces. A correlation was found between the content of primary adsorption sites on the fibre surface and interlaminar shear strength (ILSS) of the composites. Higher values of ILSS obtained for the oxidized fibres containing composites are proposed to be due to the higher concentration of carboxylic groups created on the oxidized fibres surface and to the creation of chemical bonds at the fibre/epoxy matrix interface. Enthalpy of cure, reaction peak temperature and glass transition temperature of the composites were determined by differential scanning calorimetry.     

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.     

尼龙无纺布结构化增韧层增韧碳纤维/环氧树脂复合材料的湿热力学性能

采用尼龙无纺布(PNF)作为结构化增韧层,制备了PNF层间增韧改性的U3160碳纤维增强3266环氧树脂(U3160-PNF/3266)复合材料,研究了U3160-PNF/3266复合材料的面内力学性能及湿热老化后的力学性能变化,并分析了复合材料湿热老化前后的层间形貌。结果表明:PNF增韧层的引入并未导致复合材料面内力学性能的下降,与未增韧的U3160碳纤维增强3266环氧树脂(U3160/3266)复合材料相比,增韧复合材料U3160-PNF/3266的90°拉伸性能有所提高。而湿热老化处理对U3160-PNF/3266复合材料的基体和界面性能影响相对明显,尤其是尼龙纤维与树脂基体之间的界面结合性能,湿热老化处理后增韧复合材料的90°压缩和层间剪切性能保持率均明显低于未增韧复合材料的。     

Characterisation of carbon fibres recycled from carbon fibre/epoxy resin composites using supercritical n-propanol

Three different PAN based carbon fibres (Toray T600S, T700S and Tenax STS5631) were recycled from epoxy resin/carbon fibre composites using supercritical n-propanol. The recycled carbon fibres were characterised using single fibre tensile tests, SEM, XPS and micro-droplet test. The tensile strength and modulus of the recycled carbon fibre was very similar to the corresponding as-received carbon fibres. However, the surface oxygen concentration decreased significantly, which caused a reduction of the interfacial shear strength with epoxy resin.     

超高模量聚乙烯纤维-碳纤维混杂复合材料冲击性能的研究

本工作以平面Charpy冲击、缺口与非缺口Charpy冲击全面地研究了本实验所制备的超高模量聚乙烯(UHMPE)纤维-碳纤维混杂增强环氧复合材料的冲击性能。同时根据试样在冲击过程中的载荷-时间曲线以及试样在冲击破坏后的形貌对该类混杂复合材料的冲击破坏过程与冲击破坏模式进行了分析。结果表明,将UHMPE纤维与碳纤维相混杂,复合材料的冲击性能呈现出明显的正混杂效应。     

An evaluation of acoustic emission from fibre-reinforced composites

An analysis of acoustic emission(AE) from epoxy matrices of different amounts of hardener and model composites containing a glass bead, carbon and glass fibres has been carried out to identify the sources of emission. A few AE events generated by microcracking were observed for epoxy matrix near the final fracture strain. From microscopic and emission observations it was found that the emission was generated by interfacial debonding at the pole for the model composite containing a single particle of the glass bead, and that the source of AE bursts for a continuous single carbon fibre/epoxy composite was succeeding fibre fractures along fibre length. The high AE activity due to fibre fracture was observed for a composite consisting of a bundle of glass fibres. The total of AE events was in agreement with the number of fibre fracture counted with the aid of a microscope in a carbon/epoxy composite. The shear strength at the carbon/epoxy interface was evaluated by a critical length of the fractured fibres using the AE results.     

Control of interfaces in Al-C fibre composites

The interface of Al-C fibre composite was modified by coating a silver layer on the surface of carbon fibres prior to making composites, in an attempt to improve the wettability between molten aluminium and carbon fibres during infiltration. An electroless plating technique was adopted and perfected to provide a homogeneous silver coating on the carbon fibre surface. Al-C fibre composites were prepared using a liquid infiltration technique in a vacuum. It was found that silver coating promoted the wetting between aluminium and carbon fibres, particularly with polyacrylonitrile-base carbon fibres. However, due to rapid dissolution of silver in molten aluminium, it was believed that the improved infiltration was not due to the wetting behaviour between molten aluminium and silver. The cleaning of the fibre surface and the preservation of the cleaned carbon surface with silver coating was considered to be the prime reason for the improved wettability. Interfacial reactions between aluminium and carbon fibres were observed. Amorphous carbon was found to react more with aluminium than graphitic carbon. This is believed to be because of the inertness of the graphitic basal planes.     

Abrasive wear of epoxy composites filled by abrasive particles and reinforced by polyamide fibres

Abrasive wear caused by sandy soil of steel coated by epoxy resin was investigated. Experiments were carried out using an abrasive wear tester developed to simulate the wear of the tillage tools under controlled testing conditions. Epoxy coatings were filled by abrasive particles such as aluminium oxide, silicon carbide and silicon oxide of different particle size. Also, epoxy coatings were reinforced by polyamide fibres of different diameters. The test results showed that, relatively lower wear values were displayed by epoxy coatings filled by silicon oxide particles of 5 wt% content. The wear values performed by silicon oxide of (10–20) μm particle size were lower than that displayed by uncoated steel surface. Solid lubricant such as graphite and molybdenum disulphide as filling material caused significant increase in wear due to the weak adhesion between epoxy/solid lubricant layers. Wear of epoxy reinforced by polyamide fibres showed the minimum wear values. Orientation of fibres much affected wear. Parallel fibres represented higher wear than perpendicular ones. The minimum wear was observed for cross plied coatings where shorter wear tracks and higher tensile strength in both perpendicular and parallel directions were existed. The minimum wear values which were lower than that displayed by uncoated steel test specimens were displayed by 0.1 and 0.3 mm polyamide fibre diameters. This observation confirmed the application of the polyamide fibres as reinforcement in epoxy coatings.     

Behaviour of coatings on reinforcements in some metal matrix composites

Coating on reinforcements affects the interface bonding of a composite, and is therefore usually used for improving the composite's properties. The behaviour of SiC coating on carbon fibre in reinforced aluminium metal castings, Fe on carbon fibre-reinforced copper and alumina coating on K₂O · 6TiO₂ whisker-reinforced aluminium composites were investigated, respectively, by modern techniques such as TEM, SEM etc. with the goal of controlling the interfacial interaction and wettability of reinforcement with the matrices. SiC coating produced by a polycarbosilane solution process effectively improved the strength because it successfully controlled oxidation of the carbon fibres themselves and the harmful reaction between the carbon fibres and molten aluminium during the fabrication process and heating process of the composites. The metal coating, Fe, made by electrical plating, strengthened the bonding of carbon fibres with copper by changing the bonding state of the interface from a mechanical one to a partly chemical one. Therefore the strengths of the resulting composites were improved. The alumina coating on K₂O · 6TiO₂ also controlled the diffusion of the K element from the whiskers into the aluminium matrix and altered the reaction with aluminium, and led to the optimization of interfacial bonding between the whiskers and a superior composite.     

Nickel- and copper-coated carbon fibre reinforced tin-lead alloy composites

Nickel and copper were deposited over brominated, surface treated, and pristine P-100 carbon fibres using cementation and electroplating techniques. The fibres were brominated by bromine vapour for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment of the fibres involved electrochemical etching in a dilute sodium hydroxide electrolyte for 3 min. Electroplated coated fibres showed better tensile properties than cementation coated fibres. In addition, nickel coating exhibited better bonding with the carbon fibres compared to copper coating. The effect of bromination and surface treatment was improved adhesion between coating and fibres. Nickel- and copper-coated fibres, which were brominated, anodically oxidized, and pristine, reinforced tin-lead alloy composites were fabricated by squeeze casting. The composites containing coated treated carbon fibres had higher tensile and shear strength than the ones containing coated pristine carbon fibres. Moreover, the composite with coated brominated carbon fibres had better tensile strength and shear strength than the surface treatment. The results also showed the composites containing nickel-coated fibres had higher tensile and shear strength than the ones containing copper-coated fibres.