Fiber Bundle Pushout: A Technique for the Measurement of Interfacial Sliding Properties

An experimental technique for the measurement of interfacial sliding properties in fiber-reinforced materials is presented. The technique involves pushing a bundle of fibers simultaneously through a thin section of the composite. Using this technique, sample averages are immediately available, eliminating the need for repeated single-fiber tests. The technique is particularly useful for composites that contain small-diameter fibers. Salient features of the technique are demonstrated through tests on a CAS/SiC composite.     

聚丙烯纤维增强水泥基复合材料界面过渡区的纳米力学性能

研究了不同水灰比条件下聚丙烯纤维增强水泥基复合材料界面过渡区(ITZ)的纳米力学性能。通过纳米压痕试验测试界面过渡区及其附近区域的载荷–深度(P–h)曲线,运用Oliver-Pharr方法得到各测点弹性模量和压痕硬度,采用高倍显微镜成像与扫描电子显微镜技术绘制了界面过渡区微结构表征云图。利用反褶积法对水泥基体及界面过渡区的弹性模量及压痕硬度进行多峰拟合,得到了各相的频率分布。结果表明:不同水灰比条件下界面过渡区的厚度均处于10~20μm之间,且其弹性模量和压痕硬度均低于水泥基体的;随着水灰比的变化,界面过渡区水化产物的成分及体积分数也产生相应改变。     

Influence of Fiber and Interfacial Properties on Fracture Behavior of Fiber-Reinforced Ceramic Composites

The fracture and fracture resistance behaviors of zirconmatrix composites uniaxially reinforced with either uncoated or BN-coated silicon carbide fibers are studied by performing experiments in three-point flexure and by analyzing results analytically using a cohesive crack model that incorporates crack bridging and fiber pullout mechanisms. A comparison of experimental results with the model predictions demonstrates good agreement. This analytical approach is then used in a parametrical study to demonstrate the role of fiber and fiber-matrix interfacial properties on the mechanical behavior of fiber-reinforced ceramic-matrix composites. Material parameters that enhance ultimate strength and ductility or toughness are elucidated.     

亚麻纤维增强复合材料湿热环境中界面性能研究

为了全面研究植物纤维增强复合材料界面的湿热行为,亚麻纤维增强环氧树脂复合材料以亚麻纤维作为增强材料,环氧树脂作为基体材料,采用真空辅助树脂传递模塑(RTM)成型工艺制备复合材料层合板,通过探究亚麻/环氧复合材料在湿热环境条件下的吸水率和界面剪切强度的变化,并借助扫描电子显微镜(SEM)、傅里叶红外光谱仪(FTIR)等材料表征设备,分析了植物纤维增强高分子基复合材料在湿热条件下微观结构的变化,揭示了植物纤维增强高分子复合材料在湿热环境下其界面性能下降的机理,为植物纤维增强复合材料的应用与界面改性提供了大量的理论依据。     

碳纤维粉-钢渣水泥基复合材料的力学性能和导电性能研究

本文研究了碳纤维粉和钢渣对水泥基复合材料力学性能和导电性能的影响,结合SEM分析了水泥基复合材料的微观结构.试验结果表明:碳纤维粉的加入会提高试件的力学性能,当碳纤维粉掺量为0.5％时,钢渣替代量为45％时,3d抗折强度达到6.3 MPa,28 d抗折强度达到8.4 MPa;3 d抗压强度达到28.1 MPa,28 d抗压强度达到44.6 MPa;碳纤维粉和钢渣加入后,促进导电网络的形成,也会提高水泥基复合材料的导电性能;SEM分析表明,适量的碳纤维粉能均匀分散在体系内,形成密实的结构,从而促进体系力学性能和导电性能的提高.     

Influence of Residual Stresses, Interface Roughness, and Fiber Coatings on Interfacial Properties in Ceramic Composites

Fiber pushout tests are performed on zircon-matrix composites especially fabricated with a variety of silicon carbide reinforcing fibers and fiber coatings in order to create samples with different interfacial properties, surface roughness, and possibly in different states of residual stress to demonstrate their role on the interfacial and mechanical properties of fiber-reinforced composites. The data obtained from fiber pushout tests are analyzed using linear, shear-lag, and progressive debonding models to extract important interfacial properties, residual stresses, and surface roughness. The nature and magnitude of residual stresses in composites are independently characterized by measuring the coefficient of thermal expansion of the fiber, the matrix, and the composite for comparison with similar values measured using the fiber pushout tests. These results are then compared for self-consistency among different ways of analyzing data and with independently measured and calculated values. The results have shown that independent and complementary methods of data acquisition and analysis are required to fully understand interfacial properties in ceramic composites. In particular, independent measures of the coefficient of thermal expansion, residual stresses, and surface roughness are required to confidently interpret interfacial properties obtained by different analytical approaches and then relate them to the overall mechanical response of composites. It is also shown that composites with optimum mechanical response can be created by suitably engineering the interface using multiple fiber coatings.     

纳米粒子增强碳纤维复合材料界面性能的研究进展

详细介绍了纳米粒子改性碳纤维的方法、原理及其在增强碳纤维复合材料界面性能方面的研究进展,并指出了纳米粒子改性碳纤维复合材料界面性能存在的相应问题,为提高碳纤维复合材料界面性能的研究提供了参考。     

Effect of Interfacial Roughness Parameters on the Fiber Pushout Behavior of a Model Composite

The effect of interfacial roughness on the frictional sliding in composites has been studied using fiber pushout and pushback tests on a model composite of Plexiglas rods in an epoxy matrix. Different extents of roughness were introduced on the Plexiglas rods and the resulting roughness profiles measured. The roughness profiles were characterized using six different roughness parameters. An attempt was made to find a correlation between the sliding resistance and the selected roughness parameters. A parameter defined as the maximum coefficient in the Fourier transform of the roughness profile was found to yield the best correlation. If the roughness introduced is periodic, then the pushout traces exhibit periodic dips, but the magnitude of this periodic dip is significantly smaller than the seating drop obtained from pushback tests.     

Interfacial Sliding Friction in Silicon Carbide–Borosilicate Glass Composites: A Comparison of Pullout and Pushout Tests

Interfacial sliding friction stress (τ_f) was assessed using both pushout and pullout tests on SiC-borosilicate glass composite specimens. Single-filament composite specimens were fabricated by heating to 950°C in argon borosilicate glass rods with fine-diameter (250-μm) capillary in which SiC filaments were inserted. The composite specimens prepared in this manner showed only frictional bonding. The maximum frictional sliding loads for pushout and the initial frictional sliding loads in pullout were measured as functions of the embedded length of the filament in the glass rods. The nonlinear variations of the frictional loads were analyzed using shear-lag models that include corrections for the effects of Poisson expansion or contraction on the sliding friction stress. It is shown that under identical conditions of composite fabrication the two tests give nearly identical properties for the interfaces. Pushout tests on hotpressed bulk composite specimens, however, showed both chemical bonding and a higher sliding friction stress relative to the single-filament capillary specimens. The presence of compressive residual stress on the filaments was independently confirmed by evidence of stress-induced birefringence.     

Control of Interfacial Properties through Fiber Coatings: Monazite Coatings in Oxide–Oxide Composites

Fiber pushout tests were used to quantify the effects of fiber coating thickness on the mechanical properties of two model composite systems: a monazite-coated (LaPO₄-coated) alumina (Al₂O₃) fiber in an Al₂O₃ matrix and a LaPO₄-coated yttrium aluminum garnet (YAG) fiber in an Al₂O₃ matrix. Interface properties were quantified using the Liang and Hutchinson (LH) pushout model and mechanistically rationalized by considering the change in residual thermal stresses with changes in the coating thickness. Measures of the pure Mode II interfacial fracture energy, the coefficient of friction, and a radial clamping pressure are extracted by fitting the LH equations to the experimental results. Using the approach that has been developed herein, a methodology is available for measuring the interfacial properties, predicting the effect of coating thickness, and selecting the coating thickness to     

碳纤维-钢纤维水泥基复合材料电学性能试验研究

为优化水泥基复合材料的电学性能,以碳纤维(CF)和钢纤维(SF)为导电材料,通过抗压强度试验、交流阻抗测试、扫描电镜测试和升温试验,研究了碳纤维和钢纤维的体积掺量对水泥基复合材料抗压强度和电学性能的影响。结果表明,碳纤维-钢纤维水泥基复合材料的抗压强度随碳纤维掺量增大呈先增大后减小的趋势。碳纤维、钢纤维的渗滤阈值分别为0.35%和0.6%(均为体积分数),复掺碳纤维和钢纤维使水泥基复合材料的导电性能大幅增强,产生了明显的正向混杂效应,碳纤维和钢纤维体积掺量达到渗滤阈值后,继续增大纤维掺量对导电性能的提升作用不大。用ZSimp Win软件拟合得到等效电路各电路元件数值,并结合SEM照片分析了导电机制。碳纤维-钢纤维水泥基复合材料具有良好的电热性能,当输入功率为7.9 W,通电30 min、60 min、90 min后,其平均温度可达到33℃、43℃、50℃,通过曲线拟合得到了温度随时间变化的回归方程。     

Comparative Studies of Mechanical and Interfacial Properties Between Jute Fiber/PVC and E-Glass Fiber/PVC Composites

Composites (50 wt% fiber) of jute fiber reinforced polyvinyl chloride (PVC) matrix and E-glass fiber reinforced PVC matrix were prepared by compression molding. Mechanical properties such as tensile strength (TS), tensile modulus (TM), bending strength (BS), bending modulus (BM) and impact strength (IS) of both types of composites was evaluated and compared. Values of TS, TM, BS, BM and IS of jute fiber/PVC composites were found to be 45 MPa, 802 MPa, 46 MPa, 850 MPa and 24 kJ/m², respectively. It was observed that TS, TM, BS, BM and IS of E-glass fiber/PVC composites were found to increase by 44, 80, 47, 92 and 37.5%, respectively. Thermal properties of the composites were also carried out, which revealed that thermal stability of E-glass fiber/PVC system was higher. The interfacial adhesion between the fibers (jute and E-glass) and matrix was studied by means of critical fiber length and interfacial shear strength that were measured by single fiber fragmentation test. Fracture sides after flexural testing of both types of the composites were investigated by Scanning Electron Microscopy.     

Regeneration of Interfacial Adhesion in Fiber Reinforced Composites

Our studies of the regeneration of interfacial adhesion in micro-composites have shown that fiber/thermoplastic (aramid/polycarbonate) bonds can be completely regenerated, the degree of regeneration depending on both time and temperature of heating. Complete regeneration requires high temperatures, suggesting that mechanical interlocking resulting from flow of heat-softened resin into fiber surface crevices may be the primary mechanism of bond strength regeneration. Only partial regeneration of fiber/thermosetting resin (epoxy with aramid and carbon fibers) bond strength has been achieved, and this appears to be independent of fiber and reheating time. Apparently, the viscoelastic behavior of the resin is a critical factor in bond strength regeneration.     

Residual Stresses in Silicon Carbide–Zircon Composites from Thermal Expansion Measurements and Fiber Pushout Tests

Coefficients of thermal expansion (CTE) in the axial direction of two types of SiC fibers, monolithic zircon, monolithic SiC, and several SiC_f-zircon composites were measured in the temperature range of 50 to 1380C. The measured CTE values of composites were compared with values predicted by the rule-of-mixtures approach, and a small difference in measured and calculated values was ascribed to the nature of interfacial bonding and assumptions implicit in the rule-of-mixtures approach. Fiber pushout tests were performed on these composites and the residual stresses were extracted from the analysis of the load–displacement plots in terms of the shear-lag and progressive debonding models. The radial and axial residual stresses arising from the mismatch in CTE were calculated and compared with values obtained from the fiber pushout tests. The fiber pushout tests in general produced lower values of the residual stresses, but the residual stresses obtained using shear-lag analysis were in good agreement with the calculated values based on the CTE mismatch in composites with lower values of the interfacial shear stress. The influence of anisotropic fiber expansion in the radial and axial directions on the radial and axial residual stresses in composites were also examined.     

碳纤维增强聚醚醚酮的非等温结晶行为与力学性能

利用聚酰亚胺(PI)作为碳纤维(CF)界面改性剂,制备了界面改性碳纤维增强聚醚醚酮(MCF/PEEK)复合材料。采用差示扫描量热仪(DSC)讨论了CF及其界面改性对PEEK非等温结晶行为的影响机制与作用规律,并基于莫志深法研究了MCF/PEEK的非等温结晶动力学;借助DSC和小角X射线散射仪(SAXS)表征不同降温速率下PEEK基体的结晶结构,采用万能试验机评价了MCF/PEEK的力学性能。结果发现:CF对PEEK的结晶有较为明显的异相成核促进作用,经过PI界面改性之后成核作用有所下降,但结晶行为仍较纯PEEK更容易发生,整体结晶速率更快;随冷却速率的增大,基体结晶度、片晶厚度与长周期均减小,MCF/PEEK的拉伸强度与模量也显著减小,层间断裂韧性提高。     

玻纤浸润剂组分对环氧基复合材料界面性能的影响

通过测定复合材料NOL环层间剪切强度,研究了增强型玻纤浸润剂中常用的几类成膜剂、润滑剂对玻纤增强环氧基复合材料界面层剪性能的影响。聚酯、环氧、聚氨酯成膜剂种类中,用于玻璃纤维增强环氧树脂基复合材料时,环氧成膜剂的复合材料界面性能最佳;不论干润滑剂,还是湿润滑剂,其复合材料的界面性能均较成膜剂弱,阳离子酰胺类润滑剂相对其他润滑剂略好。     

小应力下碳纳米管/碳纤维水泥基材料压敏特性研究

测试了碳纳米管/碳纤维水泥基材料的抗压强度,研究了其在小应力范围内循环载荷下电阻率的变化特性.结果表明,当碳纳米管掺量控制在0.2％到1.0％之间,碳纳米管其有利于增强水泥基材料抗压强度、线性度和可逆性,从而提高水泥基材料压敏性能.碳纳米管/碳纤维水泥基材料作为压力传感器用于车辆检测、动态称重计量和车速检测等工程实际有非常好的前景.     

聚乙烯醇纤维在水泥基复合材料中的分散性表征及调控

为了建立聚乙烯醇(PVA)纤维在水泥基复合材料(FRCC)中的分散性表征技术和调控方法,采用荧光光谱仪和荧光显微镜+图像分析软件分别对PVA纤维的荧光特性及其在FRCC中的荧光图像进行获取和分析,再研究搅拌工艺、纤维长径比及体积掺量、分散剂对PVA纤维分散性的影响。结果表明:PVA纤维最佳激发和发射波长范围分别为415~460 nm及480~540 nm,荧光图像获取时应选择绿色荧光蛋白(GFP)滤波器;基于荧光图像分析,建立荧光分析技术,利用纤维分散系数和有效利用率两个评价指标对PVA纤维的分散性能进行定量表征;采用同掺法搅拌6 min后,再掺入分散剂可使PVA纤维(长度12 mm、直径27μm、体积掺量0.3%)在FRCC中的有效利用率较基准提高了32.9%。     

碳纤维/聚芳基乙炔复合材料界面改性方法的研究

为了改善碳纤维/聚芳基乙炔复合材料的界面性能,采用表面氧化、表面接枝、偶联剂、表面涂层等方法对碳纤维进行表面处理,探讨了各种方法对非极性聚芳基乙炔树脂基复合材料的界面改性效果。研究表明,纤维表面氧化处理后有利于碳纤维/聚芳基乙炔复合材料界面性能的改善,在此基础上通过表面接枝及表面偶联剂处理在纤维表面引入可与基体树脂发生反应的基团,可以达到非极性树脂基复合材料界面改性的目的。极性的高碳酚醛树脂可以更好地浸润氧化后的纤维表面,并且与聚芳基乙炔树脂在结构上相似,因此作为涂层处理纤维表面后可以明显提高材料的界面性能,该方法适于进行3D织物的改性处理,是较为理想的处理方案。