Analytical study of tensile behaviors of UHMWPE/nano-epoxy bundle composites

Ultra-high molecular polyethylene (UHMWPE) fiber reinforced nano-epoxy and pure epoxy composites in bundle form were prepared and tested for tensile properties. UHMWPE fiber composites are well known for their superior tensile performance, and this work was conducted to assess the effect of adding nanoadditives to the resin and to evaluate possible enhancements or degradations to that attribute. The results showed that tensile tests on various types of UHMWPE fibers/nano-epoxy bundle composites resulted in an increase in modulus of elasticity due to the addition of small amounts of reactive nanofibers (r-GNFs) to epoxy matrix. It was observed that the modulus of elasticity of the composite bundles depended on both volume fractions of the matrix and the weight percent (wt%) of r-GNFs in the matrix. A non-linear relationship was established among them and an optimal modulus was determined by calculation. A three-dimensional surface plot considering these two parameters has been generated which gives an indication of change in modulus of elasticity with respect to volume fraction of matrix and wt% of r-GNFs in the matrix. A Weibull analysis of tensile strengths for the various bundle composites was performed and their Weibull moduli were compared. The results showed that presence of r-GNFs in the composites increased the strength effectively, and 0.3 wt% r-GNFs based composites showed the highest strength. An important ancillary finding is that optimum tensile values are a function not only of the above parameters, but also strongly influenced by the addition of diluents which control the viscosity of the blend.     

Thermal-mechanical properties of a graphitic-nanofibers reinforced epoxy

We previously developed a series of reactive graphitic nanofibers (r-GNFs) reinforced epoxy (nano-epoxy) as composite matrices, which have shown good wetting and adhesion properties with continuous fiber. In this work, the thermal-mechanical properties of the nano-epoxy system containing EponTM Resin 828 and Epi-cure Curing Agent W were characterized. Results from three-point bending tests showed that the flexural strength and flexural modulus of this system with 0.30 wt% of reactive nanofibers were increased by 16%, and 21% respectively, over pure epoxy. Fracture toughness increased by ca. 40% for specimens with 0.50 wt% of r-GNFs. By dynamic mechanical analysis (DMA) test, specimens with 0.30 wt% of r-GNFs showed a significant increase in storage modulus E' (by ca. 122%) and loss modulus E" (by ca. 111%) with respect to that of pure epoxy. Also thermo-dilatometry analysis (TDA) was used to measure dimensional change of specimens as a function of temperature, and then, coefficients of thermal expansion (CTE) before and after glass transition temperature (Tg) were obtained. Results implied that nano-epoxy materials had good dimensional stability and reduced CTE values when compared to those of pure epoxy.     

超高分子量聚乙烯纤维的液相氧化改性及其环氧树脂基复合材料的力学和摩擦性能

为增强超高分子量聚乙烯(UHMWPE)纤维与环氧树脂(EP)基体之间的界面粘结强度,采用重铬酸钾溶液对UHMWPE纤维进行表面改性并制备UHMWPE纤维/EP复合材料。结果表明,UHMWPE纤维经液相氧化后表面刻蚀痕迹明显,表面粗糙度明显增加,结晶度增加了11.3%,与乙二醇的接触角减小了14.12°。与纯环氧树脂相比,纤维含量为0.4%的未改性UHMWPE纤维/EP复合材料的拉伸强度降低18.04%,纤维含量为0.6%的液相氧化改性UHMWPE纤维/EP复合材料的拉伸强度降低51.55%,未改性UHMWPE(纤维含量0.5%)和液相氧化改性UHMWPE(纤维含量0.4%)纤维/EP复合材料的冲击强度分别提升了3.29%和4.39%。当纤维含量为0.3%时,液相氧化改性UHMWPE纤维/EP复合材料的弯曲强度比纯环氧树脂增加6.55%,比未改性UHMWPE纤维/EP复合材料增加19%。当纤维含量由0增大到0.5%时,改性和未改性UHMWPE纤维/EP复合材料的摩擦系数先增加后减小。     

Cosmic radiation shielding tests for UHMWPE fiber/nano-epoxy composites

Cosmic radiation shielding properties are important for spacecraft, and hydrogenous materials such as polyethylene have been shown to be effective in shielding against galactic cosmic rays and solar energetic particles. Ultrahigh molecular weight polyethylene (UHMWPE) fibers, which are effective in such shielding, also have advanced mechanical and physical properties, which potentially are very valuable for NASA space missions both as a radiation shield and as vehicle structure. In our previous studies, we fabricated a nano-epoxy matrix with reactive graphitic nanofibers that showed enhanced mechanical (including strength, modulus and toughness) and thermal properties (higher T_g, stable CTE, and higher ageing resistance), as well as wetting and adhesion ability to UHMWPE fibers. In this work, the radiation shielding performance of the UHMWPE fiber reinforced nano-epoxy composite was characterized by radiation tests at the NASA Space Radiation Laboratory at Brookhaven National Laboratory. The results showed that the high radiation shielding performance associated with UHMWPE was not degraded by the addition of graphitic nanofibers in the matrix. Together with the previous studies showing higher mechanical properties, these new studies validate the importance of the UHMWPE fiber/nano-epoxy composite for potential applications in more durable space composites and structures, and offer reduced manufacturing costs and wider design applications through avoidance of specialized and in some cases ineffective UHMWPE fiber surface treatment processes.     

Treatment of functionalized graphitic nanofibers (GNFs) and the adhesion of GNFs-reinforced-epoxy with ultra high molecular weight polyethylene fiber

Though ultra high molecular weight polyethylene (UHMWPE) fiber made of carbon and hydrogen has superior mechanical properties and effective cosmic shielding properties, it shows weak composite properties due to poor interfacial adhesion between UHMWPE fibers and polymer matrix. In this study, functionalized graphitic nanofibers (GNFs) were treated further using the sonication method. High-level sonication with a series of conditions was employed for the treatment of functionalized GNFs. submicron particle size analyzer and transmission electron microscope (TEM) were used to study effects on the length and morphology of treated nanofibers by sonication conditions. The sonication conditions were optimized for preparation of a nano-epoxy matrix containing well-dispersed, reactive, functionalized graphitic nanofibers. The adhesion ability of the nano-epoxy to UHMWPE fiber was investigated. Bundle fiber pullout specimens with single and double-ends were designed and prepared for study of the adhesion property of the nano-matrix with UHMWPE fiber. Test results showed that the nano-epoxy matrix could effectively improve interfacial adhesion property with UHMWPE fiber.     

基于纤维束/环氧树脂复合材料试验的单向层合板横向拉伸强度预测方法

实验研究表明,纤维束/环氧树脂复合材料试件的横向拉伸强度与工程上常用的单向层合板横向拉伸强度在趋势上具有很好的相关性,但是数值上存在一定差距。本文使用两种碳纤维和两种环氧树脂制备了三种纤维束/环氧树脂复合材料和单向层合板,并分别测量了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度,以及环氧基体的拉伸强度。在实验基础上,应用Griffith断裂强度理论建立了纤维束/环氧树脂复合材料和单向层合板的横向拉伸强度的关系模型,通过两种复合材料实验的结果拟合了该模型中的参数。利用第三种复合材料实验进行校验,发现该模型预测的单向层合板横向拉伸强度与实测强度之间达到很好的一致性,相对偏差为9%。采用本文提出的方法,可以用较为简单的纤维束/环氧树脂复合材料和环氧基体拉伸试验预测单向层合板的横向拉伸强度。     

芳纶纤维和超高分子量聚乙烯纤维制备工程用纤维/水泥复合材料的适用性

研究了两种高强合成纤维在工程用纤维/水泥复合材料制备过程中的适用性,其中,芳纶纤维的表面为亲水性,超高分子量聚乙烯（UHMWPE）纤维的表面为憎水性。研究结果表明:工程用芳纶纤维/水泥复合材料拉伸破坏过程中无应变硬化能力且表现为单裂纹破坏现象;工程用UHMWPE纤维/水泥复合材料拉伸破坏过程中表现出良好的应变硬化能力和多裂纹开裂特性。因此,两种纤维相比,UHMWPE纤维适宜于工程用纤维/水泥复合材料的制备。随着水胶比的降低,工程用UHMWPE纤维/水泥复合材料抗拉强度增大,但应变硬化能力降低,因此,在制备工程用UHMWPE纤维/水泥复合材料的过程中,应协调纤维抗拉强度和基体与纤维之间界面过渡区的品质。      

Effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites

The effect of fiber loading on the properties of treated cellulose fiber-reinforced phenolic composites was evaluated. Alkali treatment of the fibers and reaction with organosilanes as coupling agents were applied to improve fiber–matrix adhesion. Fiber loadings of 1, 3, 5, and 7 wt% were incorporated to the phenolic matrix and tensile, flexural, morphological and thermal properties of the resulting composites were studied. In general, mechanical properties of the composites showed a maximum at 3% of fiber loading and a uniform distribution of the fibers in such composites was observed. Silane treatment of the fibers provided derived composites with the best thermal and mechanical properties. Meanwhile, NaOH treatment improved thermal and flexural properties, but reduced tensile properties of the materials. Therefore, the phenolic composite containing 3% of silane treated cellulose fiber was selected as the material with optimal properties.     

超高分子量聚乙烯纤维复合表面改性及其橡胶基复合材料的力学性能

针对超高分子量聚乙烯(UHMWPE)纤维与基体之间界面结合强度低的问题,采用超声波结合铬酸溶液氧化的复合工艺对UHMWPE纤维进行表面处理,并将处理后的纤维加入到天然橡胶(NR)中制备短切UHMWPE纤维/NR复合材料。结果表明:复合改性工艺可有效增加纤维表面粗糙度及表面含氧官能团含量,最佳改性工艺条件为:按照重铬酸钾、水及浓硫酸的质量比7∶12∶150配置铬酸溶液,将含有一定质量UHMWPE纤维的铬酸溶液放入35℃的超声波清洗仪中氧化5min,其中超声波频率为100kHz。与纯NR样品相比,在UHMWPE纤维与NR的质量比为0~6∶100范围内,随着处理后短纤维含量的增加,复合材料的拉伸强度逐渐减小,最大损失量达到50%;复合材料的硬度不断增大,最大增加量达到96%;复合材料的撕裂强度先增大后减小,在UHMWPE纤维与NR的质量比为5∶100时达到最大值,最大增加量达到49%。     

弹道防护用超高分子量聚乙烯纤维增强热塑性树脂基复合材料的拉伸力学行为

以弹道防护用超高分子量聚乙烯(Ultra-high molecular weight polyethylene,UHMWPE)纤维增强热塑性树脂基复合材料作为研究对象,通过热压工艺制备单向正交结构的复合材料层压板。基于自主设计的拉伸试验装置,开展UHMWPE纤维增强热塑性树脂基复合材料在宏观尺度和准细观尺度上的面内拉伸试验,研究其面内拉伸力学性能及失效模式。研究结果显示：弹道防护用UHMWPE纤维增强热塑性树脂基复合材料在准细观尺度上的面内拉伸力学性能是其本征性能;随着偏轴角度的增加,拉伸断裂强度呈现指数型下降,这是由于失效模式由纤维的拉伸断裂破坏转变为纤维-树脂基体的界面破坏;此外,其在宏观尺度上的拉伸破坏强度比在准细观尺度上的拉伸断裂强度降低了50.52%,这是由于宏观尺度上的面内拉伸力学响应是其面内拉伸变形和层间分层破坏的耦合结果,即层压板的叠层效应。     

三维编织超高分子量聚乙烯纤维/碳纤维/环氧树脂混杂复合材料力学行为及混杂效应

采用复合处理工艺对三维混杂超高分子量聚乙烯纤维/碳纤维编织体进行表面处理, 通过RTM工艺制备了环氧树脂基混杂复合材料（UHMWPE/CF/ER）, 并研究了其力学性能及混杂效应。结果表明, 在纤维总体积分数一定的情况下, 随着超高分子量聚乙烯纤维/碳纤维混杂比的减小, 复合材料的弯曲强度、 弯曲模量及压缩强度增大, 而其纵向剪切强度及冲击韧性降低。三维编织混杂复合材料的断裂机制由混杂纤维的混杂比及其性质决定, 通过调节混杂比可实现对复合材料力学性能的有效调控。      

弹道防护用先进复合材料弹道响应的研究进展

本文对弹道防护用先进复合材料的弹道响应研究及其在工程领域的应用现状进行了综述。首先,基于工程应用研究的试验结果,对超高分子量聚乙烯(UHMWPE)纤维、对位芳香族聚酰胺(PPTA)纤维、芳Ⅲ纤维、聚对苯撑苯并双噁唑(PBO)纤维和聚酰亚胺(PI)纤维等高性能纤维的防弹性能及其复合材料在弹道防护工程领域的应用现状进行了概述,近年来先进复合材料的防弹性能随着纤维力学性能的突破而逐渐提高;其次,讨论了先进复合材料弹道响应的影响因素及其作用机制,发现先进复合材料的塑性拉伸变形是其抵挡弹丸侵彻的主要防弹机制;最后,对弹道防护用先进复合材料的研究方向进行了展望。      

纳米增韧三维正交玻璃纤维机织物增强环氧树脂复合材料的力学性能

为研究纳米改性对复合材料力学性能的影响,以纳米黏土改性环氧树脂与固化剂混合胶液为基体,以三维正交机织玻璃纤维织物为增强体,利用真空辅助树脂传递模压工艺（Vacuum assisted resin transfer molding,VARTM）,制备纳米增韧三维正交玻璃纤维机织物增强环氧树脂复合材料。分别测试不同质量分数（1wt%、2wt%、3wt%、4wt%）纳米黏土改性复合材料沿0°和90°方向的弯曲和拉伸性能。结果表明:当纳米黏土质量分数为1wt%时,复合材料弯曲强度最大,沿0°和90°方向的弯曲强度分别增大了约7.21%和13.71%,弯曲模量分别增大了约5.69%和16.64%。当纳米黏土质量分数为3wt%时,复合材料拉伸强度最大,沿0°和90°方向的拉伸强度分别增大了约24.96%和27.93%,拉伸模量分别增加了约21.35%和13.26%。这是由于纳米黏土呈纳米尺度以片层状分散于环氧树脂中,增加了两相间的接触面积,提高纤维/树脂界面的结合力,进而增强了复合材料的力学性能。      

Processing and properties of poly(methyl methacrylate)/carbon nanofiber composites

Single wall carbon nanotubes, multiwall carbon nanotubes, as well as carbon nanofibers (CNF) are being used for reinforcing polymer matrices. In this study, poly(methyl methacrylate) (PMMA) nanocomposites have been processed by melt blending, containing two different grades (PR-21-PS and PR-24-PS) of CNF manufactured by Applied Sciences Inc. The amount of nanofibers used was 5 and 10% by weight, respectively. The PMMA/CNF composites were processed into 4 mm diameter rods and 60 μm diameter fibers using the small-scale melt processing fiber spinning equipment. At 5 wt% CNF, composite rods as well as fibers show over 50% improvement in axial tensile modulus as compared to the control PMMA rod and fibers, respectively. The reinforcement efficiency decreased at 10 wt% CNFs. The PMMA/CNF nanocomposite fibers also show enhanced thermal stability, significantly reduced shrinkage and enhanced modulus retention with temperature, as well as improved compressive strength. CNF reinforcement efficiency has been analyzed using the modified Cox model.     

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.     

Multi-scale study of the adhesion between flax fibers and biobased thermoset matrices

The environmental impact of composite materials made with a thermoset matrix can be reduced in two ways. First, glass fibers can be replaced by natural fibers. Second, petrochemical components from the matrix can be replaced by biobased renewable equivalents. The quality of the interface between the matrix and the fibers has a strong influence on the composite mechanical properties. In this study, tensile performances of flax fibers and commercially partly biobased epoxy and polyester matrices have been investigated and corresponding unidirectional composites were elaborated. Their mechanical performances are in accordance with fiber and matrices properties, taking into account fiber dispersion. Then, at the microscopic scale, the debonding test was used; a great adhesion between flax fiber and thermoset matrices was highlighted. Finally, tensile tests on ±45° laminates were carried out to create an in-plane shear at the macroscopic scale. Interestingly, the results obtained at the macroscopic scale are well correlated to the ones given by the debonding test at the microscopic scale.     

聚酰亚胺表面处理玻璃纤维/环氧树脂复合材料力学性能

采用浇铸成型工艺制备含0.5wt%、长度分别为1 mm、3 mm、5 mm的短切玻璃纤维/环氧树脂（GF/EP）复合材料,研究含活性酚羟基和不含酚羟基的两种聚酰亚胺（PI）处理GF表面对纤维束拉伸强度及GF/EP复合材料力学性能的影响,并进一步研究PI处理GF对复合材料热性能的影响。研究结果表明,经过PI处理的GF,集束性和拉伸强度得到提高。含活性酚羟基聚酰亚胺（PI1）处理的GF拉伸强度由原丝束的517 MPa提高到1 032 MPa,不含酚羟基聚酰亚胺（PI2）处理的GF提高到986 MPa。当PI1处理的GF长度为3 mm时,GF/EP复合材料的力学性能最好,拉伸强度比未处理的提高23.62%,拉伸模量提高34.03%,弯曲强度提高28.74%,断裂韧性提高13.04%;PI2处理的GF,GF/EP复合材料拉伸强度提高15.87%,拉伸模量提高23.70%,弯曲强度提高14.11%,断裂韧性提高4.05%。此外,PI处理GF对GF/EP复合材料热性能也有一定程度的提高。     

Fabrication and characterization of fully biodegradable natural fiber-reinforced poly(lactic acid) composites

Polymer composites were fabricated with poly(lactic acid) (PLA) and cellulosic natural fibers combining the wet-laid fiber sheet forming method with the film stacking composite-making process. The natural fibers studied included hardwood high yield pulp, softwood high yield pulp, and bleached kraft softwood pulp fibers. Composite mechanical and thermal properties were characterized. The incorporation of pulp fibers significantly increased the composite storage moduli and elasticity, promoted the cold crystallization and recrystallization of PLA, and dramatically improved composite tensile moduli and strengths. The highest composite tensile strength achieved was 121 MPa, nearly one fold higher than that of the neat PLA. The overall fiber efficiency factors for composite tensile strengths derived from the micromechanics models were found to be much higher than that of conventional random short fiber-reinforced composites, suggesting the fiber–fiber bond also positively contributed to the composites’ strengths.     

Heat treatment effects on SiC fiber

The Wright Laboratory Materials Directorate at Wright-Patterson AFB has been spearheading the development and evaluation of a new class of metal matrix composites based upon continuous SiC fiber reinforcement of orthorhombic phase containing titanium aluminide matrices. These composites (O TMCs) will be subjected to thermal exposures during primary and secondary component processing, and possibly also during heat treatments to optimize matrix-dominated mechanical performance. Such thermal excursions must not degrade the SiC fiber reinforcement, hence compromising resulting composite properties. Therefore, the effects of heat treatment on the room temperature tensile strength of continuous SiC fibers were studied. The fibers examined included: Trimarc 1®, SCS-6, Ultra SCS and an experimental large diameter version of Ultra SCS. The fibers were heat treated below and above the beta solvus temperature of the orthorhombic matrix alloy utilized for this study, Ti-22Al-23Nb (at%). The fibers were evaluated for ambient temperature tensile strength in the following conditions: (1) as-received: (2) heat treated in vacuum; and (3) consolidated into Ti-22Al-23Nb, heat treated in vacuum, and chemically extracted. Fiber microstructure and fracture analysis was accomplished via secondary scanning electron microscopy (SEM). Chemical reactions between fiber core and the SiC, and between the SiC fiber and the Ti-22Al-23Nb matrix, were also studied by SEM.     

TDI改性苎麻纤维增强PE复合材料的性能

以苎麻原麻、纱线、苎麻粗绳、苎麻布为原料,用甲苯-2,4-二异氰酸酯(TDI)进行接枝改性,然后制备出不同苎麻纤维与树脂PE的复合材料。采用扫描电镜(SEM)、电子万能拉伸试验机等分析测试手段对复合材料力学性能和断口进行了测试分析。结果表明:苎麻纤维经过TDI接枝改性后,其复合材料界面性能明显改善。接枝后原麻/PE复合材料复合拉伸性能略有下降,而苎麻绳和苎麻布/PE复合材料拉伸性能明显提高。