A Study of the Interphase Region in Carbon Fibre/Epoxy Composites using Dynamic Mechanical Thermal Analysis

We have examined the effect of fibre addition on the glass transition temperature (T_g) of two epoxy resin systems (an amine cured and an anhydride cured epoxy system) using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The presence of fibres changes the glass transition temperature (T_g) of an anhydride cured epoxy resin but does not affect that of an amine cured epoxy. The data suggest that two counteracting mechanisms are responsible for these changes: firstly, the presence of fibres causes a restriction of the molecular motion in the resin system, and secondly, the presence of carboxyi and keto-enol groups on the fibre surface inhibit curing of the resin close to the fibre, i.e. in the interphase region. The former increases the T_g and is a long range effect whereas the latter decreases the T_g and is a localised phenomenon. Changes in the dynamic properties of the interphase region are only detected when the samples are loaded in the longitudinal direction and not in the transverse direction where bulk matrix properties dominate. Sizing the fibres before their incorporation into the epoxy resin eliminates the variation in interfacial properties arising from differences in fibre surface chemistry.     

The Use of Dynamic Mechanical Methods to Study the Effect of Absorbed Water on Temperature-dependent Properties of an Epoxy Resin-Carbon Fibre Composite

Dynamic mechanical methods were used to study the effect of absorbed moisture on the properties of an epoxy resin matrix CFRP. The glass transition temperature (T_g)of the matrix resin, determined as the onset of the characteristic fall in dynamic modulus with increasing temperature, was found to decrease with increasing moisture content. Maximum shifts in T_g of 80 to 90°C, relative to the dry material, were observed for a resin moisture content of 5.2% by weight. The effects of sample geometry, fibre orientation, and frequency of oscillation, on the dynamic mechanical properties are discussed. Results are given of an analysis of the observed dependence of T_g on water content using two theoretical models.     

树脂含量对碳布/环氧复合材料力学性能的影响

主要研究了不同树脂含量下，碳布／环氧复合材料的径向拉伸和纬向压缩性能，并初步探讨了树脂含量对复合材料拉伸、压缩性能的影响机理。试验结果表明：树脂含量对复合材料力学性能的影响较大，当树脂质量含量在42％－45％之间时，拉伸、压缩性能较好。     

The Effect of Fibre Surface Treatment on the Failure of Continuous Carbon Fibre/Epoxy Resin Composites

The failure mechanisms of a composite, consisting of continuous, aligned, high strength, polyacrylonitrile (PAN) based carbon fibre in an epoxy resin, under uniaxial tension, have been studied. In order to study the effect of the interphase/interface strength, six different levels of an electrochemical fibre surface treatment were used. Single tows containing approximately 12,000 treated carbon fibres were impregnated to produce composite rods with a fibre volume fraction of 0.55. Lengths of this impregnated tow were also set in the centre of glass-fibre/epoxy resin composite coupons which were used to study the mechanisms of failure of the embedded tows. Acoustic emission was used to monitor all samples and bundle failure was found to occur after a build-up of sub-critical damage events as previously modelled.¹ Microdebond tests demonstrated an initial increase of interfacial strength which levelled out at the higher levels. In impregnated samples with high surface treatments, catastrophic failure occurred with the crack propagating approximately perpendicular to the fibre direction. However, in samples with lower fibre surface treatments, longitudinal splitting (not accounted for in current models), occurred, meaning that a greater length of composite was involved in the final failure process. Acoustic emission has been shown to have an approximately direct relation with the predicted number of single fibre breaks in composite test-pieces; however, there was no significant difference attributable to the different surface treatments. The hybrid test coupons allow a detailed assessment of the failure mechanisms within the impregnated carbon tow. The failure strains of the embedded tow is some 5% higher than that of unsupported tow. The Weibull modulus is of the same order.     

The Effect of Fibre Surface Treatment on the Failure of Continuous Carbon Fibre/Epoxy Resin Composites

The failure mechanisms of a composite, consisting of continuous, aligned, high strength, polyacrylonitrile (PAN) based carbon fibre in an epoxy resin, under uniaxial tension, have been studied. In order to study the effect of the interphase/interface strength, six different levels of an electrochemical fibre surface treatment were used. Single tows containing approximately 12,000 treated carbon fibres were impregnated to produce composite rods with a fibre volume fraction of 0.55. Lengths of this impregnated tow were also set in the centre of glass-fibre/epoxy resin composite coupons which were used to study the mechanisms of failure of the embedded tows. Acoustic emission was used to monitor all samples and bundle failure was found to occur after a build-up of sub-critical damage events as previously modelled.¹ Microdebond tests demonstrated an initial increase of interfacial strength which levelled out at the higher levels. In impregnated samples with high surface treatments, catastrophic failure occurred with the crack propagating approximately perpendicular to the fibre direction. However, in samples with lower fibre surface treatments, longitudinal splitting (not accounted for in current models), occurred, meaning that a greater length of composite was involved in the final failure process. Acoustic emission has been shown to have an approximately direct relation with the predicted number of single fibre breaks in composite test-pieces; however, there was no significant difference attributable to the different surface treatments. The hybrid test coupons allow a detailed assessment of the failure mechanisms within the impregnated carbon tow. The failure strains of the embedded tow is some 5% higher than that of unsupported tow. The Weibull modulus is of the same order.     

碳纤维／超高相对分子质量聚乙烯复合材料的热性能研究

研究了碳纤维/超高相对分子质量聚乙烯复合材料的热性能变化。结果表明：加入少量的乙烯-丙烯酸共聚物（EAA）及炭黑后,可使复合材料的热变形温度明显提高;此外,不同的加工工艺对复合材料的热性能也有一定的影响。     

Physico-Chemical Characterisation of the Influence of Moisture on the Fibre/Matrix Interaction in Epoxy/Anhydride Composites

The effect of moisture on the fibre/matrix interaction in epoxy/anhydride composites is investigated and explained through the characterisation of the matrix cure in the interphase. The fibre/matrix interaction is inferred from ILSS measurements on the composite, which are compared with a recently-introduced DSC interaction parameter. The matrix cure in the bulk as well as in the interphase is characterised through FT-IR microspectroscopy. Complementary information is gained by measuring the overall T_g value. Moisture is shown to lower the fibre/matrix interaction if the prepreg (= composite precursor) is stored at room temperature or lower prior to final cure. This is due to the reduced crosslink density of the matrix. For PE prepreg stored in ordinary atmospheric conditions, moisture from the surroundings lowers the fibre/matrix interaction sharply. If the prepreg is stored in a dry environment, nearly no effect of the storage is detected on the fibre matrix interaction in PE (polyethylene) fibre composites, while for PVAL (polyvinylalcohol) fibre composites a strong decrease is still found, caused by water adsorbed at the more hydrophilic fibre surface.     

The Effect of Low Power Nitrogen Plasma Treatment of Carbon Fibres on the Interfacial Shear Strength of Carbon Fibre/Epoxy Composites

Type II (high strength) carbon fibres have been given a low power nitrogen plasma treatment. It is shown that this plasma treatment has no effect on the fibre diameter, no detrimental effect on fibre strength and can significantly improve fibre/resin adhesion. It is proposed that this improvement is due to chemical interaction via amine/epoxy bonding at the edge sites together with the interaction of the epoxy with activated basal planes present on the fibre surface. This improvement is only achieved if the fibres are immersed in resin before being exposed to air. Exposing the treated fibres to air drastically reduces fibre/adhesion due to the adsorption of moisture from the environment. Heating these latter fibres in a vacuum at 130°C for one hour allows some recovery of the interfacial strength. It is also demonstrated that the interfacial shear strength falls dramatically when the nitrogen-containing functional groups are completely removed from the fibre surface.     

The Effect of Low Power Nitrogen Plasma Treatment of Carbon Fibres on the Interfacial Shear Strength of Carbon Fibre/Epoxy Composites

Type II (high strength) carbon fibres have been given a low power nitrogen plasma treatment. It is shown that this plasma treatment has no effect on the fibre diameter, no detrimental effect on fibre strength and can significantly improve fibre/resin adhesion. It is proposed that this improvement is due to chemical interaction via amine/epoxy bonding at the edge sites together with the interaction of the epoxy with activated basal planes present on the fibre surface. This improvement is only achieved if the fibres are immersed in resin before being exposed to air. Exposing the treated fibres to air drastically reduces fibre/adhesion due to the adsorption of moisture from the environment. Heating these latter fibres in a vacuum at 130°C for one hour allows some recovery of the interfacial strength. It is also demonstrated that the interfacial shear strength falls dramatically when the nitrogen-containing functional groups are completely removed from the fibre surface.     

Effect of Fiber Acid Treatment on the Dynamic Mechanical Properties of Unsaturated Polyester/Carbon Fiber Unidirectional Composites

In this study, the surface modification of carbon fiber by sulfuric acid is investigated. Atomic Force Microscopy was employed to capture the corresponding changes in the surface roughness of the carbon fiber. Moreover, using treated and untreated fibers, unsaturated polyester unidirectional composite rods were prepared and their flexural properties were determined by three-point bending and dynamic mechanical thermal analysis.

The results indicated that the carbon fiber surface roughness increases in all samples. It is also found that treating the fiber decreases the magnitude of loss modulus. Besides, the flexural strength of composites made of the treated carbon fiber significantly increased.     

Transient Thermal Deformations of the Interphase in Polymer Composites

Heterodyne micro-interferometry was utilized to measure out-of-plane transient displacements in the interphase due to thermal cycling. In-situ measurements were made on single carbon fiber/epoxy samples with interphases of varying glass transition temperature. Interphase properties were tailored such that one set of samples had fibers which were coated with a low T_g resin, another set had a higher T_g coating, and in the third set the fibers were uncoated. The interferometric data demonstrated that interphase T_g has a significant effect on the rate and magnitude of the thermal deformations at the fiber/matrix interface. The presence of a low T_g interphase caused an increase in the magnitude of the thermal displacements due to a local softening of the matrix and increase in coefficient of thermal expansion. In addition, the rate at which the displacements increase was also higher due to the reduction in T_g. Samples with untreated fibers (no tailored interphase) behaved as if a low T_g interphase had formed. Experimental displacement profiles were also compared with finite element predictions to assess the behavior of the tailored interphases.     

化学处理方法对剑麻纤维/环氧树脂固化反应动力学的影响

通过采用非等温DSC方法．研究了不同化学处理方法对剑麻纤维/环氧树脂固化体系的固化反应动力学的影响,计算了固化反应的活化能,为共混体系的固化反应机理的研究提供了依据。     

Improving Mechanical Properties of Carbon/Epoxy Composite by Incorporating Functionalized Electrospun Polyacrylonitrile Nanofibers

Electrospun functionalized polyacrylonitrile grafted glycidyl methacrylate (PAN‐g‐GMA) nanofibers are incorporated between the plies of a conventional carbon fiber/epoxy composite to improve the composite's mechanical performance. Glycidyl methacrylate (GMA) is successfully grafted onto polyacrylonitrile (PAN) polymer powder via a free radical mechanism. Characterization of the electrospun PAN and PAN‐g‐GMA nanofibers indicates that the grafting of GMA does not significantly alter the tensile properties of the PAN nanofibers but results in an increase in the diameter of nanofibers. Statistical analysis of the mechanical characterization studies on PAN‐carbon/epoxy hybrid composites conclusively shows that the composite reinforced with functionalized PAN nanofibers has greater mechanical properties than that of both the neat PAN nanofiber enriched hybrid composite and control composite (without nanofibers). The improved performance is attributed to the grafted glycidyl groups on PAN, leading to stronger interactions between the nanofibers and the epoxy matrix. PAN‐g‐GMA nanofiber reinforced composite outperforms their neat PAN counterparts in tensile strength, short beam shear strength, flexural strength, and Izod impact energy absorption by 8%, 9%, 6%, and 8%, respectively. Compared to the control composite, the improvements resulting from the PAN‐g‐GMA nanofiber incorporation are even more pronounced at 28%, 41%, 32%, and 21% in the corresponding tests, respectively.

     

海军舰炮弹药用碳布增强环氧复合材料热老化寿命预测

研究了热老化对海军舰炮弹药用碳布增强环氧复合材料力学性能的影响,并利用回归分析方法对复合材料热老化寿命进行了预测。结果表明,碳布增强环氧复合材料分别在温度110,120,130,140℃热空气条件下老化2000 h,材料的各项力学性能总体呈下降趋势,但降幅很小,甚至在整个试验过程中会出现性能升高的情况,说明材料具有优异的力学性能。以90%作为材料失效判据点,碳布增强环氧树脂基复合材料常温贮存条件下贮存寿命为20年。     

EP/SiO_2/CF复合材料的动态热力学分析

为了研究纳米级SiO_2、碳纤维(CF)对环氧树脂(EP)基复合材料动态热力学性能的影响,制备了不同用量(分别为EP质量的0%和4%)纳米SiO_2、不同体积分数(分别为5%,10%,15%,20%)CF增强EP基复合材料弯曲试样,对试样进行了多频扫描动态热力学分析(DMA),研究了纳米SiO_2和CF对复合材料玻璃化转变温度(Tg)、储能模量、表观活化能和最大损耗因子的影响。结果表明,总体上添加4%的纳米SiO_2后复合材料的Tg下降2~6℃;100℃之前,测试频率对复合材料的储能模量影响较小,且未含SiO_2的试样储能模量曲线比含SiO_2的试样较为平坦;当CF体积分数分别为10%,15%,20%时,添加4%纳米SiO_2的EP/CF复合材料的在40℃下的储能模量较未加纳米SiO_2时提升31.2%,135.5%,13.6%,表明纳米SiO_2和CF展现出很好的协同效应从而提升了复合材料储能模量,而最大损耗因子分别下降3.7%,6.5%,14.8%,表明纳米级SiO_2有助于增强复合材料的刚性;当纳米SiO_2用量为EP质量的4%,CF体积分数为15%时,复合材料内部作用力最大,表观活化能达到569 k J/mol,呈现了很好的协同效果。     

Mechanical Properties of Thermoplastic Butadiene–Styrene (SBS) and Oxidized Short Carbon Fibre Composites

This work reports on some results of research conducted on composite materials consisting of a butadiene–styrene (SBS) thermoplastic elastomer matrix filled with short carbon fibres previously subjected to oxidative treatment to increase the surface functionality. Scanning electron microscopy confirms the existence of interactions between the matrix and the fibre, which are not observed for commercial fibre fillers and which translate into mechanical strength increments, in terms of the Young’s modulus, tensile and tear strengths for the oxidized fibre composites. The stress–strain curves of the composites show yield point phenomena as strain is applied longitudinally to the main fibre orientation. In oxidized fibre composites the stress and strain coordinates are a function of the degree of oxidation (greater strain for more strongly oxidized fibre) and fibre strength (lower stress for longer treatment times). © 1997 SCI.     

多壁碳纳米管在国产碳纤维增强环氧树脂复合材料中应用

研究了一种简易有效的多壁碳纳米管(MWNTs)分散入环氧树脂的方法,对树脂的工艺性进行试验研究;使用碳纤维复丝的力学性能来表征纤维/树脂界面性能和纤维强度转化效果,制备了含MWNTs的环氧树脂/碳纤维预浸料,并对使用此预浸料制备的复合材料单向板进行力学性能测试。结果表明,当MWNTs的用量为E–51的0.5%时,二者混合球磨8 h后配制的树脂溶液适用期大于24 h,黏度小于0.8 Pa·s,树脂浇铸体拉伸强度78 MPa,弯曲强度106 MPa,断裂伸长率4.3%;添加MWNTs之后纤维/树脂结合良好,复合材料单向板拉伸强度提升了7.2%,弯曲强度提升了9.73%,压缩强度提升了6.82%,层剪强度提升了11.54%。     

表面处理对碳/酚醛材料层间性能影响的研究

本文分别研究了在有氧与无氧状态下表面处理对碳／酚醛材料界面特性的改善，尤其是在高温环境下的变化。通过扫描电镜(SEM)、电子能谱(XPS)研究了不同状态处理下的碳布，测试了碳／酚醛复合材料的剪切强度。研究表明，在500～600％有氧状态下处理的碳／酚醛材料层间性能最佳。     

PE-HD/CF/HGB三元复合材料的制备及力学性能

以高密度聚乙烯(PE-HD)为基体、碳纤维(CF)为增强材料,采用双辊塑炼工艺制备了PE-HD/CF复合材料,力学性能测试结果表明该复合材料的拉伸和弯曲性能随CF含量的增加而增大,但缺口冲击强度逐渐下降。在该复合材料基础上添加空心玻璃微珠(HGB)制得PE-HD/CF/HGB三元复合材料,力学性能测试结果表明当HGB用量为10份且CF用量为15份时,三元复合材料的拉伸强度、弯曲强度和缺口冲击强度均达到最大,分别为46.98 MPa,45.69 MPa和8.17 kJ/m2,较未加HGB的PE-HD/CF复合材料分别提高了7.19%,4.17%和10.4%。扫描电子显微镜结果表明,HGB主要通过其变形和破坏来吸收冲击能量,从而提高复合材料的韧性。     

接枝炭黑/聚乙烯导电复合材料正电阻温度系数(PTC)效应研究

用接枝炭黑作导电粒子研究了在聚乙烯基材中的正 (电阻 )温度系数 (PTC)效应。结果发现 ,甲基丙烯酸甲酯接枝的炭黑在高密度聚乙烯中能表现出较好的 PTC效应。从实验现象分析 ,接枝炭黑的 PTC效应是结晶熔融和体积膨胀双重变化共同作用的结果。