Kevlar纤维表面改性对PA6/KF复合材料力学性能与破坏形态的影响

用挤出和注塑的方法加工了PA 6/K ev lar纤维(KF)复合材料,研究了其拉伸、弯曲和冲击性能以及破坏形态。结果表明,KF表面酰氯化、己内酰胺封端并经阴离子接枝尼龙6处理的PA 6/KF 1复合材料的拉伸强度和弯曲强度均得到明显提高,弯曲模量基本不变,冲击强度则有所下降。由断面形态可知,PA 6/KF 0拉伸破坏呈界面脱粘破坏形态,而PA 6/KF 1复合材料呈部分非界面脱粘破坏。弯曲和冲击破坏时PA 6/KF 1复合材料的断口纤维粘附大量尼龙6树脂,而PA 6/KF 0复合材料粘附尼龙6量很少。界面粘接良好导致PA 6/KF 1复合材料冲击性能下降。     

橡胶改性对硼纤维/环氧单向复合材料力学性能的影响

对环氧树脂进行液体丁腈橡胶改性, 并采用缠绕无纬布层压成型工艺制备了硼纤维/环氧单向复合材料。测试了环氧树脂液体丁腈橡胶改性前后硼纤维/环氧单向复合材料的力学性能, 研究了硼纤维/环氧单向复合材料的纵向拉伸破坏模式。结果表明, 基体中的10%液体丁腈橡胶使硼纤维/环氧单向复合材料的拉伸强度、 弯曲强度、 层间剪切强度和断裂延伸率分别提高了18.42%、 13.39%、 28.45%和43.40%, 但其拉伸和弯曲模量稍有下降。基体中含10%液体丁腈橡胶的硼纤维/环氧单向复合材料的纵向拉伸破坏模式为界面层的内聚破坏和脱黏破坏共存的混合破坏。      

三维浅交弯联机织复合材料拉伸性能的有限元分析

本文通过绘图软件PRO/E5.0构建了用于拉伸性能研究的三层浅交弯联机织复合材料的数字化结构模型。借助大型有限元分析软件ANSYS Workbench对复合材料在1mm的拉伸变形下复合材料、纤维增强体及树脂基体的拉伸应力、应变分布情况进行模拟、计算,并对1mm拉伸位移下复合材料的破坏行为和破坏机理进行分析。结果表明:复合材料承受拉伸载荷时,纤维增强体起主要承载作用,树脂基体起次要承载作用;平行于拉伸方向的纬纱比垂直于拉伸方向的经纱承受更大的载荷作用;1mm拉伸位移下,复合材料破坏行为主要为纤维拉伸变形、纤维与树脂间脱粘及树脂的破碎。     

铁基非晶条带-玻璃纤维混杂复合材料力学特性

针对铁基非晶条带-玻璃纤维混杂增强树脂基复合材料,研究了表面处理、热处理对非晶条带力学性能的影响,在此基础上选取了适宜的树脂基体,制备了混杂复合材料,测试了基本力学性能并分析了破坏模式。结果表明：酸蚀表面处理对条带的拉伸性能影响很小,但改变了条带的表面形貌和表面能,从而提高了条带与树脂的粘结性能;混杂复合材料纵向拉伸弹性模量符合混合定律,横向拉伸弹性模量主要由非晶条带贡献,并且非晶条带的承载对混杂复合材料的横向拉伸强度起到了一定的作用;弯曲破坏和剪切破坏均产生受压侧纤维层与非晶条带的分层以及纤维断裂。     

灰粉比对苯丙乳液基水泥复合材料静态力学性能及破坏形态的影响

对不同灰粉比的苯丙乳液基水泥复合材料进行定伸、拉伸和剪切试验,通过测量弹性恢复率、拉伸剪切力学性能指标、变形性能指标、能耗性能指标和负荷位移,研究了灰粉比对苯丙乳液基水泥复合材料定伸黏结性能、拉伸力学性能、剪切力学性能及破坏形态的影响,结合FESEM试验和压汞测孔(MIP)试验结果,分析了灰粉比对苯丙乳液基水泥复合材料力学性能及破坏形态影响规律的微观机制。结果表明:适当增大灰粉比能够改善苯丙乳液基水泥复合材料的微观形貌,优化孔隙结构,提高密实度,显著增强了复合材料的力学性能;随着灰粉比的增大,苯丙乳液基水泥复合材料的定伸黏结性能逐渐降低,拉伸剪切力学性能不断增强,拉伸剪切变形性能和能耗性能均先提升后降低。灰粉比为30%~35%时,苯丙乳液基水泥复合材料的拉伸剪切力学性能最佳;灰粉比为45%时,苯丙乳液基水泥复合材料的拉伸剪切变形性能和能耗性能均低于灰粉比为20%的苯丙乳液基水泥复合材料。随着灰粉比的增大,苯丙乳液基水泥复合材料能够承受的拉伸和剪切负荷位移均先增大后减小,其破坏形态逐步由“内聚破坏”转为“黏结破坏”。      

CALL混杂复合材料裂纹尖端损伤区实验研究

本文用以高密度光栅技术为基础的云纹干涉法对带双边裂纹的CALL混杂复合材料进行了拉伸实验研究,得到了在纤维方向和垂直纤维方向拉伸时双边裂纹尖端损伤区的形状及其应变场分布。结合对试件断口形貌的扫描电镜观察,分析了两种拉伸试件的破坏模态。所得实验结果为进一步深入研究CALL混杂复合材料的损伤和破坏机理提供了重要依据。     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

碳纤维/环氧单向复合材料的统计强度和破坏准则

本文运用了纤维损伤的随机临界核理论及混合法则 ,对碳纤维 /环氧单向复合材料受纵向拉伸时的统计强度及破坏准则作了理论分析与实验研究     

高温炭化处理对三维五向碳/酚醛编织复合材料拉伸性能的影响

对未经炭化和经不同温度炭化处理后的三维五向碳/酚醛编织复合材料进行了纵向和横向拉伸实验, 获得了拉伸应力-应变曲线, 并确定了材料的拉伸强度、 拉伸模量、 破坏应变和泊松比等主要力学性能, 分析了这类材料经不同温度炭化处理后拉伸力学性能的变化规律。对试件拉伸实验后的破坏断口进行了宏观和微观分析, 探讨了材料的变形和破坏机理。实验结果表明: 随炭化处理温度的增加, 三维五向碳/酚醛编织复合材料的纵向、 横向拉伸强度和拉伸模量均呈先降后升的趋势, 存在一个转折温度, 超过该温度, 材料的拉伸强度和拉伸模量从下降变为上升, 但拉伸模量的变化幅度较小; 但是, 随着炭化温度的升高, 材料的破坏应变是逐渐降低的。通过形貌观察和树脂热分解机理分析, 认为在不同的炭化处理温度下, 材料的细观组织结构演变存在明显的差异, 因此造成了材料力学性能的变化。      

高强高模聚酰亚胺纤维/环氧树脂复合材料力学性能与破坏机制

以高强高模聚酰亚胺（PI）纤维为增强体,以航空级环氧树脂（EP）为基体,通过热熔法制备预浸料并采用热压罐成型技术制备了PI/EP复合材料层合板,对其力学性能和破坏形貌进行了分析。结果表明:高强高模PI纤维与EP具有良好的界面结合力,PI/EP复合材料的层间剪切强度为65.2 MPa,面内剪切强度为68.6 MPa;良好的界面结合状态能充分发挥PI纤维优异的力学性能,PI/EP复合材料的纵向拉伸强度达1 835 MPa,弯曲强度为834 MPa;PI/EP复合材料纵向拉伸破坏模式为散丝爆炸破坏,同时由于高强高模PI纤维还具有优异的韧性和较高的断裂伸长率,PI/EP复合材料从受力到失效断裂的时间较长;PI/EP复合材料纵向压缩破坏模式为45°折曲带破坏。高强高模PI/EP复合材料为航空航天先进复合材料增加了一个全新的选材方案。      

Assessing the effect of fibre extraction processes on the strength of flax fibre reinforcement

A number of factors impede the direct translation of fibre properties from plant crop species to natural fibre composites. Commercially available fibre extraction processes introduce defects and degrade the mechanical properties of fibres. This study reports on a novel image based approach for investigating the effect of fibre extraction processes on flax fibre bundle strength. X-ray micro Computed Tomography (μCT) was coupled with uniaxial tensile testing to measure the in-situ fibre bundle cross-section area and tensile strength in flax plant stems. The mean tensile strength result was 50% higher than that of the fibres extracted through the standard commercial process. To minimize fibre damage during fibre extraction, a pre-treatment was proposed via saturating flax plant stems in 35% aqueous ammonia solution. By environmental scanning electron microscopy (ESEM), it was evident that ammonia treatment significantly reduced the extent of damage in flax fibre knots and the optimum treatment parameter was identified.     

The effect of fibre content on the mechanical properties of hemp and basalt fibre reinforced phenol formaldehyde composites

In this study, mechanical properties such as tensile, flexural and impact strengths of hemp/phenol formaldehyde (PF), basalt/PF and hemp/basalt hybrid PF composites have been investigated as a function of fibre loading. Hemp fibre reinforced PF composites and basalt fibre reinforced composites were fabricated with varying fibre loading i.e. 20, 32, 40, 48, 56 and 63 vol%. The hybrid effect of hemp fibre and basalt fibre on the tensile, flexural and impact strengths was also investigated for various ratio of hemp/basalt fibre loading such as 1:0, 0.95:0.05, 0.82:0.18, 0.68:0.32, 0.52:0.48, 0.35:0.65, 0.18:0.82 and 0:1. Total fibre loading of the hybrid composites was 40 vol%. The results showed that the tensile strength and elongation at break increase with increasing fibre loading up to 40 vol% and decrease above this value for hemp fibre reinforced PF composite. Similar trend was observed for flexural strength and the maximum value was obtained for 48 vol% hemp fibre loading. Impact strength of hemp/PF composite showed a regular trend of increase with increasing fibre loading up to 63 vol%. Tensile strength, flexural strength and impact strength values of basalt/PF composites were found to be lower compared to hemp/PF composites. The tensile strength and elongation at break of basalt/PF composite increased by incorparation of basalt fibre up to 32 vol% and decreased beyond this value. Flexural strength of basalt/PF composite decreased linearly with fibre loading. However, the maximum impact strength was obtained for 48 vol% basalt fibre loading. For hemp/basalt hybrid PF composite, the tensile strength decreased with increasing basalt fibre loading. On the other hand, the flexural and impact strengths showed large scatter. The maximum flexural strength value was obtained for 0.52:0.48 hemp/basalt ratio. Corresponding value for impact strength was obtained for 0.68:0.32 hemp/basalt fibre ratio.     

The effect of fibre content on the mechanical properties of glass fibre mat/polypropylene composites

Glass fibre mat was prepared by the fibre mat-manufacturing machine developed in our laboratory. Glass fibre mat reinforced polypropylene (PP) composites were fabricated with the variation of glass fibre content. Tensile, flexural and high rate impact test was conducted to investigate the effect of glass fibre content on the mechanical properties of the glass fibre mat/PP composite. Deformation and fracture behaviour of the glass fibre mat/PP composites was investigated to study the relationship with the mechanical property data. The tensile and flexural modulus increased with the increment of glass fibre content. However, the tensile and flexural strengths exhibited maximum values and showed a decrease at the higher glass fibre content than this point. The impact absorption energy also exhibited a similar result with the tensile and flexural property data.     

Polyoxymethylene composites with natural and cellulose fibres: Toughness and heat deflection temperature

Cellulose and abaca fibre reinforced polyoxymethylene (POM) composites were fabricated using an extrusion coating (double screw) compounding followed by injection moulding. The long cellulose or abaca fibres were dried online with an infrared dryer and impregnated fibre in matrix material by using a special extrusion die. The fibre loading in composites was 30 wt.%. The tensile properties, flexural properties, Charpy impact strength, falling weight impact strength, heat deflection temperature and dynamic mechanical properties were investigated for those composites. The fibre pull-outs, fibre matrix adhesion and cracks in composites were investigated by using scanning electron microscopy. It was observed that the tensile strength of composites was found to reduce by 18% for abaca fibre and increase by 90% for cellulose fibre in comparison to control POM. The flexural strength of composites was found to increase by 39% for abaca fibre and by 144% for cellulose fibre. Due to addition of abaca or cellulose fibre both modulus properties were found to increase 2-fold. The notched Charpy impact strength of cellulose fibre composites was 6-fold higher than that of control POM. The maximum impact resistance force was shorted out for cellulose fibre composites. The heat deflection temperature of abaca and cellulose fibre composites was observed to be 50 °C and 63 °C higher than for control POM respectively.     

Jetting and fibre degradation in injection moulding of glass-fibre reinforced polyamides

Injection-moulded glass fibre-reinforced polyamides with up to 50% by weight fibre content were examined for processing behaviour such as jetting and fibre degradation. Jetting was found to be a function of the ratio of the gate depth to mould-cavity depth, fibre length, fibre content and injection ram speed. Contrary to expectation, jetting occurred less frequently as the injection ram speed was increased. Major fibre degradation was experienced during the transport of the melt from the injection machine to the mould cavity. Further fibre degradation due to increases in injection back-pressure was comparatively small. Tensile strength was shown to be sensitive to variations in the fibre length distribution, whereas the elastic modulus remained unaffected.     

Procedural influences on compression and injection moulded cellulose fibre-reinforced polylactide (PLA) composites: Influence of fibre loading,fibre length,fibre orientation and voids

The influence of fibre loading (20, 30, 40 mass%), fibre fineness, and the processing procedure (compression moulding – CM and injection moulding – IM) on the tensile and impact strength of lyocell/PLA composites was examined. The results revealed a significantly higher tensile and impact strength for CM composites compared to IM composites. An increase in strength up to a fibre loading of 40% was determined for CM composites, while for IM composites the highest values were measured at a fibre loading of 30%. Composites were investigated for their void content, fibre orientation, fibre length and process-induced fibre damage. A better fibre/matrix adhesion and compaction of IM composites was found while fibre orientation as well as mechanical properties of extracted fibres show no significant differences between CM and IM composites. The different mechanical characteristics of CM and IM samples are attributed predominantly to the fibre aspect ratio and the distribution of voids.     

Monitoring the micromechanics of reinforcement in carbon fibre/epoxy resin systems

The technique of laser Raman spectroscopy (LRS) was employed to obtain the interfacial shear stress (ISS) distribution along a short high-modulus carbon fibre embedded in epoxy resin at different levels of applied stress. Up to 0.6% applied strain, the ISS reached a maximum at the bonded fibre ends and decayed to zero at the middle of the fibre. At higher applied strains, the maximum value of the ISS distribution shifted away from the fibre ends towards the middle of the fibre. At the point of fibre fracture, fibre/matrix debonding was found to initiate at the fibre breaks. Further increase of applied strain resulted also in debonding initiation at the fibre ends. Current analytical stress-transfer models are reviewed in the light of the experimental data.     

Characterization of functionally gradient epoxy/carbon fibre composite prepared under centrifugal force

Centrifugal force was employed in order to induce a spatial gradient of fibre distribution in the epoxy/carbon fibre system. The gradient structure of the epoxy/carbon fibre composite can be controlled by varying the rotation time and the material parameters, such as fibre length, fibre content and matrix viscosity. The spatial gradient distribution of carbon fibres in an epoxy matrix was achieved by the combined mechanism of packing and settling. The mechanical properties of the functionally gradient epoxy/carbon fibre composite were also investigated. At the same content of carbon fibre, the flexural strength of the functionally gradient composite was higher than that of conventional isotropic composite. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fabrication and characterization of electrospun PVDF-aliquat 336 fibre membrane for removal of cadmium from hydrochloric acid solutions

The use of polyvinylidene fluoride (PVDF) electrospun fibre membrane incorporating aliquat 336 for the removal of cadmium from hydrochloric acid solutions was investigated. Scanning electron microscopy (SEM) was used to determined fibre diameter and to observe the fibre morphology. Energy dispersive spectroscopy (EDS) analysis was carried out to follow the fate of the aliquat 336 in the fibre membrane formed via electrospinning process and to detect the presence of cadmium in fibre membrane after it has acted as an ion exchange media. The amount of cadmium removed by the fibre membranes was determined by flame atomic absorption spectroscopy. The maximum capacity of the PVDF-aliquat 336 electrospun fibre membranes was determined to be 0.46 mg/g.     

The study of model polydiacetylene/epoxy composites

A mode composite system consisting of one polydiacetylene single crystal fibre in an epoxy resin matrix has been subjected to tensile strain parallel to the fibre direction. The strain at all points along the length of the fibre was determined by resonance Raman spectroscopy while that of the matrix was measured by conventional techniques. Comparison of the fibre and matrix strain showed two distinct regions. Below about 0.5% matrix strain the composite followed Reuss-type behaviour with equal stress in the fibre and the matrix. At higher matrix strain the composite followed Voigt-type behaviour with any increase in matrix strain matched by an equal increase in fibre strain. In this region the strain distribution along the length of the fibre could be approximately described by the shear-lag model of Cox. The critical length of the fibre was found to increase linearly with fibre diameter as predicted by that model. Good qualitative agreement was found with the predictions of a calculation based on finite element analysis over the full range of applied stress.