光学非均匀纤维复合材料对径受压圆盘应力分布－光学关系研究

本文报道利用显微激光分析仪研究微透明实际纤维复合材料对径受压圆盘径向应力分布的新尝试。结果表明,从I-θ曲线中提取出来的傅里叶变换四次基波的模A_‖4等于均质双折射材料在暗场下的等色线亮度的1/2.当用传统方法无法再获得实际纤维复合材料的条纹图象时,仍然可以利用显微激光分析仪得到A_‖4,且借助于A_‖4,可通过作图法求出对径受压圆盘的径向应力分布,所得结果与H.Okabo的理论计算相吻合。实验表明,采用上边方法可对透光度低达万分之六(0.06%)的实际纤维复合材料进行测试。      

复合材料中增强粒子与基体中微观应力和残余应力分析

按球对称模型对粒子增强复合材料中热膨胀差(DCTE)热应力和残余应力进行了弹-塑性分析。结果表明,热应力或残余应力具有短程分布特点;粒子内部为常水静应力,界面和基体中径向应力与粒子内部同号,切向和周向应力与径向应力符号相反。存在一个基体发生初始屈服的临界温差t_P,屈服范围随温差|t|而扩大。单程变温产生的残余应力与热应力完全相同;经过一个热循环后,若温差小于t_P则残余应力为零;若大于t_P,则在粒于和基体中产生残余应力。讨论了粒子形状和尺寸对残余应力和基体塑性变形对复合材料性能的影响。     

Al2O3-SiO2纤维增强ZL108合金复合材料的强度特性

用低成本的Al₂O₃-SiO₂系纤维作为增强相,通过加压铸造法制作ZL108合金复合材料,并对该复合材料和ZL108合金进行不同温度下的时效处理和压缩试验。通过DSC、EPMA和TEM分析认为:经488K、0.5h时效处理(T6处理)的V_f 20%的复合材料在573K以下的压缩屈服强度低于ZL108合金,是由于基体中的Mg与Al₂O₃-SiO₂纤维在加压铸造过程中起化学反应而生成MgAl₂O₄,损耗了基体中的大量Mg,导致基体铝合金时效硬化效果很差,所以压缩屈服强度低下。623K、720h保温后的V_f 20%的复合材料的压缩屈服强度比ZL108合金要高得多,是由于在这种温度环境下对ZL108合金来说是过时效,所以纤维的增强怍用显得明显。在高温(673K)下V_f 20%的复合材料的屈服强度比ZL108台金高一倍左右。不论在什么温度场合下V_f5%的复合材料的屈服强度比V_f 20%的复合材料都低。     

短纤维增强透气性莫来石/铁(A3S2/Fe)复合材料烧结特性的研究

本文研究了A₃S₂/Fe复合材料的烧结特性、透气性和纤维增强效果,分析了烧结过程中材料宏观结构和微观组织的形成机理.实验结果表明:纤维增强A₃S₂/Fe复合材料在900～1000℃具有良好的烧结性能,烧成后表层存在一定厚度的硬化层;纤维增强效果显着.材料抗压强度达17～23MPa,相对透气系数为4.30～9.69cm3/(cm2·s·atm).已能满足实际应用的需要.     

复合材料热膨胀性能研究

本文研究了单向纤维增强复合材料的热膨胀性能。引进界面粘结系数C,利用热弹性理论推导出经C修正后的线膨胀系数计算公式。由MOM型综合热分析仪测量了玻璃纤维和碳纤维复合材料在不同界面情况及不同纤维体积含量时的线膨胀系数。理论计算值与实测值相当接近,相对误差小于10%。     

CF/PEEK复合材料界面层结构与性能关系研究

本文根据聚醚醚酮(PEEK)在碳纤维表面形式的横晶层的结构特征分析,建立了CF/FEEK复合材料界面层微观力学性能的理论方程,计算了界面层的杨氏模量.通过超声浸渍法测量复合材料的力学性能验证了计算结果,证明所进行的分析合理.计算结果表明,PEEK界面横晶层在垂直于纤维方向的杨氏模量E_r随PEEK结晶度的增大,或随横晶中PEEK晶片长度的增大而增大,并随晶片厚度的增大而减小.该界面层的上述模量值始终高于界面层附近球晶的模量值E_s,两者之间的比值E_T/E_s;依赖于横晶及球晶中的晶片长度b、厚度c和宽度a.由于界面层的模量高于非界面层的模量,当复合材料中纤维表面形成横晶时,复合材料将有较高的刚性.     

Ti-Al-Nb合金的热变形与动态再结晶行为研究

目的 建立本构方程及动态再结晶模型,描述热变形条件对Ti-Al-Nb合金动态再结晶以及合金软化的影响规律。方法 基于热模拟压缩变形试验,获得Ti-Al-Nb系合金在不同热变形工艺参数下的应力应变曲线。采用双曲正弦模型表征流动应力,通过线性回归等数据处理方式求得各参数的具体数值。结果 求得动态再结晶活化能Q=197.626 kJ/mol,材料常数A的平均值为3.173×10⁶,建立流动应力本构方程。Z/A为无量纲参数,通过最小二乘线性拟合求得ε^*=344×10⁵(Z/A)^0.495,εc=16.15(Z/A)^0.24。结论 Ti-Al-Nb系合金在峰值应力出现之前均发生了动态再结晶:当应变速率较高时,在流动稳定前会发生强烈的软化,曲线显现双峰;当应变速率较低时,在加工硬化和软化作用达到平衡后逐渐进入稳定阶段,此时曲线显现单峰。研究结果将为Ti-Al-Nb系合金的精密塑性成形提供一定的技术参考和理论依据。     

(Al2O3)f/Al复合材料在强界面结合下的疲劳损伤模式

在拉-拉载荷下测定了(Al₂O₃)_f/Al复合材料的疲劳寿命(S-N)曲线。通过夭折试验以及SEM疲劳断口和纵截面组织结构分析,研究了复合材料的疲劳损伤模式。研究结果表明,(Al₂O₃)_f/Al复合材料的疲劳极限为750MPa,远高于SCS-6碳化硅纤维增强钛基复合材料。该复合材料兼有钛基和树脂基纤维复合材料疲劳损伤的特点,高应力下由单个裂纹的起源和生长导致复合材料的失效;低应力下,疲劳损伤模式包括纤维劈裂、众多基体裂纹和单个基体裂纹的横向扩展。其中纤维劈裂是主控机制。其更高的疲劳极限可归因于低应力下纤维的纵向劈裂。     

用溶胶－凝胶法在碳纤维表面涂覆Al2O3

本文研究用溶胶-凝胶方法在碳纤维表面涂覆Al₂O₃,的工艺对涂层性能、结构及对纤维强度、抗氧化性能等的影响。结果表明:所配溶胶质量好,涂覆工艺合适,可在纤维表面得到均匀、连续的Al₂O₃,涂层;该涂层不仅改善了纤维的抗氧化性能,而且还能保持纤维原有的强度;改善与熔铝的润湿性,为复合材料的制备提供方便。     

复合材料的Ⅰ型层间断裂韧性

本文采用铰链式双悬臂梁试件对碳/双马来酰亚胺复合材料的Ⅰ型层间断裂韧性进行了研究,分析比较了层间断裂韧性G_IC的表达方法,用三次多项式和幂函数拟合实验柔度的方法得到的结果比较满意,实验结果表明纤维桥连对单向层合板的G_IC的影响是显着的,用刀片切割桥连纤维后G_IC值下降百分之二十,分散性也有显着下降。另外发现G_IC值随试件厚度增加而增大。     

Natural fibres-based polymers: Part I—Mechanical analysis of <Emphasis Type="Italic">Pine needles</Emphasis> reinforced biocomposites

Lack of resources and increasing environmental pollution has evoked great interest in the research of materials that are friendly to our health and environment. Polymer composites fabricated from natural fibres is currently the most promising area in polymer science. Keeping in view the various advantages of natural fibres, in current series of green composites a study on natural fibre reinforced polymer composites has been made. This paper presents the results of an experimental series designed to assess the possibility of Pine needles as reinforcing material in polymer composites. First of all, urea-formaldehyde resin was synthesized and optimized by evaluating its mechanical properties. Optimized resin was reinforced with employing Pine needles of different dimensions such as particle reinforcement, short fibre reinforcement and long fibre reinforcement. Experimental results obtained shows that mechanical properties such as tensile strength, compressive strength and wear resistance of UF resin increases to a considerable extent when reinforced with Pine needles. Further it has been observed that particle reinforcement is more effective as compared to short fibre and long fibre reinforcement. These results suggest that Pine needles can be potential candidates for use in natural fibre reinforced polymer composites. Thermal and morphological studies of these composites have also been carried out.     

Mechanical properties of natural fibre reinforced polymer composites

During the last few years, natural fibres have received much more attention than ever before from the research community all over the world. These natural fibres offer a number of advantages over traditional synthetic fibres. In the present communication, a study on the synthesis and mechanical properties of new series of green composites involving Hibiscus sabdariffa fibre as a reinforcing material in urea-formaldehyde (UF) resin based polymer matrix has been reported. Static mechanical properties of randomly oriented intimately mixed Hibiscus sabdariffa fibre reinforced polymer composites such as tensile, compressive and wear properties were investigated as a function of fibre loading. Initially urea-formaldehyde resin prepared was subjected to evaluation of its optimum mechanical properties. Then reinforcing of the resin with Hibiscus sabdariffa fibre was accomplished in three different forms: particle size, short fibre and long fibre by employing optimized resin. Present work reveals that mechanical properties such as tensile strength, compressive strength and wear resistance etc of the urea-formaldehyde resin increases to considerable extent when reinforced with the fibre. Thermal (TGA/DTA/DTG) and morphological studies (SEM) of the resin and biocomposites have also been carried out.     

Fabrication and characterization of <Emphasis Type="Italic">S. cilliare</Emphasis> fibre reinforced polymer composites

In the recent times, there has been an ever-increasing interest in green composite materials for its applications in the field of industries, aerospace, sports, household etc and in many other fields. In this paper, fabrication of Saccharum cilliare fibre reinforced green polymer composites using resorcinol formaldehyde (RF) as a novel matrix has been reported. A systematic approach for processing of polymer is presented. Effect of fibre loading on mechanical properties like flexural, tensile, compressive and wear resistances has also been determined. Reinforcing of the RF resin with Saccharum cilliare (SC) fibre was done in the form of particle size (200 micron). Present work reveals that mechanical properties of the RF resin have been found to increase up to 30% fibre loading and then decreases. Morphological and thermal studies of the resin, fibre and particle reinforced (P-Rnf) green composites have also been studied.     

Fibre orientation of novel dynamically sheet formed discontinuous natural fibre PLA composites

This paper describes work carried out to fabricate and to assess the fibre orientation in PLA reinforced by aligned discontinuous harakeke and hemp fibre mats produced using a dynamic sheet former (DSF). These mats were combined with PLA sheets to make composites with fibre contents of 5–40 wt% using a hot press. It was found that the fibre orientation factors (K_θ) for both harakeke and hemp fibre composites were higher than those values seen in the literature for composites prepared using injection moulding and hot pressed using randomly oriented fibre mats, but slightly lower than the highest values obtained with aligned fibre nonwoven preform composites utilising more processing stages. The highest K_θ values for harakeke and hemp fibres in this work were found to be 0.58 and 0.44 respectively. K_θ decreased, reflecting increased fibre misalignment as fibre content increased, believed to be due to fibre agglomeration and the higher pressure required during processing.     

The compression strength of composites with kinked,misaligned and poorly adhering fibres

Experiments carried out on pultruded fibre reinforced polyester resins show that, at moderate fibre volume fractions, the compressive strength of aligned fibre composites depends linearly on the volume fraction. The strength falls off when the fibre volume fraction,V _f=0.4 with Kevlar and high strength carbon fibres. The effective fibre strength atV _f<0.4 is much less than the tensile strength but it is close to the tensile strength with E-glass fibres and high modulus carbon fibres. Poor adhesion between fibres and matrix reduces the compressive strength, as does kinking the fibres when the fibre radius of curvature is reduced to below 5 mm. Misalignment of the fibres reduces the compressive strength when the average angle of misalignment exceeds about 10° for glass and carbon fibres. However, with Kevlar no such reduction is observed because the compression strength of Kevlar reinforced resin is only a very little better than that of the unreinforced resin.     

Effects of fibre surface silanisation on silica fibre/phenolics composites produced by resin transfer moulding process

Abstract

The effects of fibre surface silanisation on silica fibre/phenolics composites produced by the resin transfer moulding (RTM) solution impregnation route were investigated. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and micro-Wilhelmy method were used to evaluate the surface properties of silanised silica fibre. The interlaminar shear strength (ILSS) measurements and morphological observations of the silica fibre/phenolics composites were also performed. The interactions occurring between silica fibre and the components of phenolic resin solution affect the dynamic adsorption behaviour of phenolic resin onto fibre reinforcement. The competitive adsorption of ethanol as solvent onto silica fibre suppresses that of phenolic resin. Fibre surface silanisation by γ-aminopropyl-triethoxysilane (γ-APS), γ-glycidoxypropyl-trimethoxysilane (γ-GPS) and γ-methacryloxypropyl-trimethoxysilane (γ-MPS) leads to the improvement of mechanical interfacial properties of silica fibre/phenolics composites on one hand and decreases the inhomogeneities of resin distribution and mechanical interfacial properties at different regions of the RTM product on the other hand.     

High temperature acidic stress corrosion of glass fibre composites: Part I Effect of fibre type

The stress corrosion characteristics of uniaxial glass fibre reinforced thermosetting resin composites have been examined in hydrochloric acid at 80°C. A simple technique based on linear elastic fracture mechanics (LEFM) is presented for characterizing crack growth in these materials subjected to hostile acidic environments. The environmental stress corrosion cracking is investigated both for different types of resin and different types of glass fibre reinforcements. Two matrices were used: DERAKANE* 411-45 epoxy vinyl ester resin (based on Bisphenol-A epoxy resin) and DERAKANE 470-30 epoxy vinyl ester resin (based on epoxidized novolac resin). Two glass fibre types were employed: standard E-glass fibre and ECRGLAS®, a special type of E-glass with superior acid resistance. Model experiments using a modified double cantilever beam test with static loading have been carried out on unidirectional composite specimens in 1 M hydrochloric acid solution at 80°C. The rate of crack growth in the specimen depends on the applied stress, the temperature and the environment. Consequently, the lifetime of a component or structure made from glass fibre reinforced plastics (GRP) subjected to stress corrosion conditions, could be predicted provided the dependence of crack growth rate on stress intensity at the crack tip is known. Scanning electron microscope studies of the specimen fracture surfaces have identified the characteristic failure mechanisms. The most important finding of this work is that the selection of DERAKANE epoxy vinyl ester resins reinforced with ECRGLAS® fibre exhibited superior resistance to crack growth at 80°C compared to similar E-glass reinforced composites at room temperatures.     

The fracture toughness of bast fibre reinforced polyester composites Part 1 Evaluation and analysis

Hemp and jute fibre reinforced polyester composites were fabricated to various fibre volume fractions (V _f) up to 0.45. Laminates reinforced with a chopped strand mat (CSM) glass fibre were also manufactured. The tensile properties of these materials were evaluated. Fracture toughness was assessed, using linear elastic fracture mechanics (LEFM) principles, under quasi-static loading conditions. At equivalent V _f (0.2) it was found that the fracture toughness (K _Ic) of the CSM glass fibre reinforced material was approximately 3 times greater than that of the natural fibre reinforced laminates and an order of magnitude greater than the unreinforced polymer alone. Critical strain energy release rates (G _c) and plastic zone radii were computed. The G _c of the natural fibre reinforced laminates was approximately an order of magnitude lower than that of the CSM reinforced material at the same V _f. It was hypothesised that the size of the crack-tip plastic zone influences the energy absorbing capacity of the material. By comparing the relative volumes of the plastic zones, implications regarding the toughening mechanisms operative in natural fibre reinforced composites have been made. The applicability of LEFM to characterise toughness in these materials is discussed.     

Influence of fibre surface oxidation treatment on mechanical interfacial properties of carbon fibre/ polyarylacetylene composites

Abstract

In the present work, the mechanical interfacial properties of carbon fibre (CF) reinforced polyarylacetylene (PAA) resin composites were modified through the surface oxidation treatment of carbon fibres by ozone. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy showed that oxidation treatment could increase the amount of elemental oxygen on the fibre surface markedly by introducing more oxygen groups. Atomic force microscopy (AFM) images indicated that weak surface regions of fibres had been etched and removed, and the degree of fibre surface roughness was increased. The interlaminar shear strength (ILSS) and the interfacial shear strength (IFSS) of CF/PAA composites were both improved notably (no less than 50%). It could be concluded that an improvement of fibre surface chemical activity, better wettability of resin on the carbon fibre surface, and stronger mechanical joining between fibres and resin all resulted in the modification of interfacial properties of carbon fibre reinforced PAA composites. The influences of temperature, ozone concentration, and treatment time on the oxidation results were studied, and optimal treatment parameters determined.