马来酸酐刻蚀芳纶纤维/尼龙6复合材料的制备及性能

使用马来酸酐（MAH）对芳纶纤维（AFs）进行刻蚀处理,以期改善其与尼龙6（PA6）的界面相容性,进而提高AFs/PA6复合材料的力学性能。将不同时间梯度处理后的AFs与PA6经均匀共混、注塑制成AFs/PA6复合材料标准试样。采用FE-SEM、XPS、XRD和DSC研究了AFs表面形貌和元素含量以及AFs/PA6复合材料的冲击断面形貌、晶型、晶粒和结晶度。结果表明:经过3 h的刻蚀,AFs表面粗糙程度最大且表面含氧量最高。刻蚀AFs的加入有利于PA6晶粒细化并且形成α 晶型。相对于纯PA6,AFs/PA6复合材料试样的内部更易形成α 晶型,同时结晶度也得到提高。加入经表面处理的AFs有利于提高AFs/PA6复合材料的拉伸强度和弯曲强度,当加入刻蚀时间为3 h的AFs时,AFs/PA6复合材料的力学性能达到最佳。      

混杂比对碳/芳纶纤维混杂纬编双轴向多层衬纱织物增强复合材料力学性能的影响

利用层内混杂的方式制备碳/芳纶纤维混杂纬编双轴向多层衬纱织物,通过对材料进行拉伸、三点弯曲等实验研究该织物增强复合材料的力学性能及混杂比对其力学性能的影响。结果表明,按照一定的混杂比加入芳纶纤维后复合材料的拉伸性能提高,表现出积极的混杂效应。由于延伸性好的芳纶纤维的加入,使复合材料的拉伸断裂伸长率明显提高,材料破坏模式出现了完全脆性断裂模式(C12材料破坏形式)和“扫帚”形纤维断裂模式(C8A4,C6A6材料破坏形式)。此外,按照一定的混杂比加入芳纶纤维也有效改善了碳纤维增强复合材料的破坏韧性,碳/芳纶纤维混杂MBWK织物增强复合材料的弯曲强度和弯曲模量随混杂比的提高而呈下降趋势,当复合材料中芳纶含量从42%(体积分数,下同)(C6A6)到59.2%(C4A8)的变化过程中,弯曲强度和弯曲模量的降低率较高。0°试样在混杂比为59.2%(C4A8)时,弯曲挠度最大,达到7.49 mm,远高于纯芳纶纤维或纯碳纤维增强的复合材料。所有90°混杂复合材料试样的弯曲挠度均高于纯芳纶纤维或纯碳纤维增强的复合材料,表现出积极的混杂效应。     

平纹织物复合材料横向力学性能研究

通过对平纹织物复合材料的横向拉压试验, 分析了产生各种破坏现象的微观机理。横向压缩过程中,在与水平面成45°方向剪切破坏的同时还出现层间裂纹。由于两个方向上纱线的弯曲程度不同, 破坏形式有很大差异, 不同自由边处的纱线界面存在不同程度的剪切破坏, 并表现出不同的边缘效应。借助显微镜观察和基于代表体积单元的数值模拟对这些现象进行了分析, 发现高度不均匀的内部波纹纱线结构在横向压缩下产生的层间剪切应力是出现横向裂纹的主要原因。      

Fabrication and mechanical properties of fine-tungsten-dispersed alumina-based composites

The mechanical properties and microstructure of fine-tungsten-dispersed alumina-based composites, which were fabricated by hot pressing a mixture of fine α-Al2O3 and W powders, have been investigated. Small W particles of approximately 140 nm average size were located within the Al2O3 matrix grains. The mechanical properties were influenced by the metal content and sintering conditions. When the appropriate W content and sintering condition were selected (typically 5–10 vol% W and sintered at 1400°C), the fracture strength was enhanced compared with that of monolithic Al2O3. The metal content dependence of Young's modulus and the Vickers hardness did not obey the rule of mixtures. This may be attributed to the presence of localized residual stress caused by the incorporation of fine W dispersion into Al2O3. On the other hand, high-temperature (1600°C) sintering caused degradation in the properties of the composites due to the grain growth and chemical reaction of W dispersion, which was revealed by X-ray photoelectron spectroscopy analysis. The relations between fabrication condition and mechanical properties are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fabrication and mechanical properties of well-dispersed multiwalled carbon nanotubes/epoxy composites

Multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites were fabricated by using ultrasonication and the cast molding method. In this process, MWCNTs modified by mixed acids were well dispersed and highly loaded in an epoxy matrix. The effects of MWCNTs addition and surface modification on the mechanical performances and fracture morphologies of composites were investigated. It was found that the tensile strength improved with the increase of MWCNTs addition, and when the content of MWCNTs loading reached 8 wt.%, the tensile strength reached the highest value of 69.7 MPa. In addition, the fracture strain also enhanced distinctly, implying that MWCNTs loading not only elevated the tensile strength of the epoxy matrix, but also increased the fracture toughness. Nevertheless, the elastic modulus reduced with the increase of MWCNTs loading. The reasons for the mechanical property changes are discussed.     

Fabrication of toughened Cf/SiC whisker composites and their mechanical properties

In this paper, dense short carbon fiber reinforced silicon carbide matrix composites had been fabricated by hot-pressed (HP) sintering using Al₂O₃ and La₂O₃ as sintering additives. The results showed that the combination of Al₂O₃ and La₂O₃ system was effective to promote densification of short cut carbon fiber reinforced silicon carbide composites (Cf/SiC). The whisker structure of silicon carbide was formed during the annealed treatment at 2023 K for 1 h. However, it was noted that this structure was not observed in the as-received HP material. The mechanism of forming whisker structure was not clear, but this kind of whisker structure was helpful to improve mechanical properties. The combination of grain bridging, crack deflection and whisker debonding would improve the fracture toughness of the Cf/SiC composites.     

The interfacial properties of aramid/epoxy model composites

Many attempts have been made to measure, evaluate and improve the level of interfacial adhesion in aramid/epoxy composites. Different surface treatments have been developed in order to promote chemical bonding between the fibre and the matrix but it is found that most of the surface treatments developed have shown little or no improvement in the level of interfacial adhesion. The interfacial properties of a model composite are often determined by measuring the interfacial shear strength using micromechanical test methods that employ different loading configurations. However, the values of interfacial shear strength determined using different test methods are found to be dependent upon the variation of localized stress in the samples due to the different loading configurations and often give different results. Using Raman spectroscopy it is shown that the strain-dependent shift of the 1610 cm^–1 aramid Raman band can be used to determine the point-to-point variation of axial fibre strain along aramid fibres embedded in epoxy resin matrices from which the interfacial properties can be derived. The interfacial properties of aramid/epoxy model composites have been determined using Raman spectroscopy where the properties of the fibre, including different surface treatments, and the matrix have been changed systematically. The results are reviewed here and compared to those obtained using conventional micromechanical test methods. It is also demonstrated that the Raman technique can be used to characterize the interfacial properties of aramid/epoxy model composites deformed using different micromechanical test methods. In this way the interfacial properties can be determined at different loading levels enabling the progressive failure of the fibre/matrix interface to be monitored and defined accurately.     

甘蔗渣纤维增强聚丙烯复合材料的制备和力学性能

利用注射成型制备了甘蔗渣纤维增强聚丙烯复合材料, 分析了纤维质量分数、 注射成型条件以及添加物对复合材料力学性能的影响。结果表明, 随着纤维质量分数的增加, 材料的弯曲模量呈递增趋势。由于甘蔗渣纤维热降解的发生, 材料的力学性能随筒体温度的增加呈下降趋势。在模具温度90℃、 注射间隔时间30s、 不同的筒体温度185℃和165℃的成型条件下, 材料的弯曲性能和冲击强度分别呈现最大值。添加了马来酸酐改性聚丙烯后, 材料的弯曲强度和冲击强度得到了提高。      

Fabrication and mechanical properties of steel–steel composites

Metal matrix composites based on a low carbon steel matrix reinforced with high carbon steel wires have been fabricated by a combined cold and hot rolling process. Both continuously and discontinuously aligned composites have been produced. A subsequent heat treatment allowed the formation of martenisitc, bainitic or pearlitic wires in a ferrite predominantly matrix. The optimum wire microstructure giving a composite with high strength and reasonable ductility was found to be bainitic — martensitic wires were found to contain microcracks that gave poor composite strengths and ductilities. The discontinuous wire composites produced similar strengths to the continuous composites only when they were deformed to give a wire aspect ratio greater than 20. The strengths of both types of composites showed a good fit to the rule of mixtures as the volume fraction of fibers was increased.     

Fabrication,characterization and mechanical properties of SiC-whisker-reinforced Y-TZP composites

The microstructure and mechanical properties of hot-pressed yttria-stablized tetragonal zirconia polycrystals (Y-TZP) reinforced with up to 30 vol % SiC whiskers were investigated. The homogeneously dispersed and fully dense SiC whisker/Y-TZP composites were fabricated by wet-mixing the constitutents and uniaxially hot-pressing the resulting powder. The grain size of the matrix depended on the whisker volume fraction and the hot-pressing temperature. The significant increase of fracture toughness of about MPa m^1/2 at 10 Vol % SiC and a small increase in strength were achieved by uniformly dispersing the whiskers in the Y-TZP matrix. Fracture surfaces revealed evidence of toughening by the mechanisms of crack deflection, pullout, and crack bridging by the whiskers and also a phase transformation of ZrO₂. The observed increase in the fracture toughness of Y-TZP due to the addition of SiC whiskers was correlated with existing models of toughening mechanisms. Good agreement was achieved between the theoretical predictions and the experimental toughness values, obtained from the Y-TZP/SiC_w composites.     

短切芳纶纤维/聚硅氧烷-甲基丙烯酸锌复合材料的结构与性能

为提高聚硅氧烷-甲基丙烯酸锌(ZDMA)树脂材料的性能,采用短切通用型芳纶纤维与聚甲基乙烯基硅氧烷-ZDMA复合并在高温下交联固化,得到短切芳纶纤维/聚硅氧烷-ZDMA复合材料.采用SEM、FTIR、拉伸和压缩试验方法、霍普金斯压杆试验方法,表征了短切芳纶纤维/聚硅氧烷-ZDMA复合材料的结构和静态力学性能,研究了芳纶...     

碳纤维-Ni/尼龙66复合材料的制备与性能表征

为制备低电阻率的尼龙66基复合材料,以碳纤维和镍粉(Ni)填充尼龙66制备碳纤维-Ni/尼龙66高导电复合材料。研究填料表面改性和含量对碳纤维-Ni/尼龙66复合材料导电性能和力学性能的影响。结果表明:KH550改性碳纤维和Ni有助于降低碳纤维-Ni/尼龙66复合材料的电阻率。碳纤维-Ni/尼龙66复合材料的电阻率随着碳纤维和Ni含量的增加而减小,且碳纤维和Ni填充尼龙66的导电逾渗阈值均为20wt%,此时制备的碳纤维-Ni/尼龙66复合材料的电阻率为455Ω·cm,熔融温度为202.2℃。碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度随着碳纤维或Ni含量的增加而先增大后减小。当Ni含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度在碳纤维含量分别为20wt%和10wt%时达到最大值,分别为98MPa和70 MPa;当碳纤维含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度则在Ni含量为30wt%和20wt%时达到最大值,分别为120 MPa和67 MPa。     

Tuning the mechanical properties of SWNT/nylon 6,10 composites with flexible spacers at the interface

We have prepared nylon 6,10 nanocomposites using functionalized single wall carbon nanotubes and our interfacial in situ polycondensation method. The specific functional groups -(CH2)nCOCl [n = 4 and 9] on the sidewalls of SWNT were designed to covalently link nanotubes to the nylon matrix via alkyl segments. The composites with functionalized SWNT show significant improvements in tensile modulus, strength, and toughness relative to nylon and nylon modified with non-functionalized SWNT. The alkyl linkages at the SWNT/nylon 6,10 interface contribute significantly to improving the toughness of the composites.     

芳纶捆绑对纬编双轴向多层衬纱织物增强环氧树脂复合材料层间性能的影响

将芳纶作为捆绑纱制备纬编双轴向多层衬纱(MBWK)织物增强环氧树脂复合材料，研究了MBWK织物增强环氧树脂复合材料层间性能及芳纶捆绑纱对其层间性能的影响。通过三点弯曲和短梁剪切测试，得到MBWK织物增强环氧树脂复合材料的弯曲性能和层间剪切性能，并通过Aramis V6三维场应变测量系统观察实验过程中层间应变变化。与传统涤纶低弹丝捆绑的MBWK织物增强环氧树脂复合材料相比，芳纶捆绑MBWK织物增强环氧树脂复合材料的弯曲性能和层间剪切性能明显提升，弯曲强度和层间剪切强度分别提高了14.21%和12.70%；弯曲模量提高了25.49%。芳纶捆绑MBWK织物增强环氧树脂复合材料在受到面外载荷时，纵向应变(Epsilon X)和层间剪切应变(Epsilon XZ)在中性面区域内较大，且在受到面外载荷时，芳纶捆绑纱起到有效抑制复合材料分层的作用。      

The dielectric properties of nylon 6,6/aramid fibre microcomposites in the presence of transcrystallinity

Dielectric spectroscopy was applied in the present work for the first time to polymeric composite materials containing transcrystallinity, wherein the dielectric properties of pure nylon 6,6 and of aramid fibre-reinforced nylon 6,6 microcomposites were examined over wide frequency and temperature ranges. The temperature behaviour of the dielectric losses of the materials indicated three polarization processes, related to either local or collective molecular mechanisms of motion. In addition, interfacial polarization of the Maxwell–Wagner–Sillars type was observed. The dielectric response was found to be sensitive to the presence of transcrystallinity in the microcomposites. It was found that the activation energy of the α, β and γ relaxations exhibits typical variations in the presence of reinforcement and transcrystallinity. The dielectric strength, calculated from fitting of the relaxation spectra to the Havriljak–Negami empirical term for all the relaxation processes, was found to be very sensitive to the morphology of the systems. The specific values at 1 MHz of the dielectric constant, dielectric loss and dielectric loss tangent as a function of temperature for the transcrystalline layer were retrieved from the composites data using the rule-of-mixtures. A comparison was conducted between the values of the transcrystalline layer and those of the bulk matrix to determine the effect of the transcrystalline layer on the dielectric properties.     

Fabrication and mechanical properties of PLA/HA composites: A study of in vitro degradation

The adverse effects of stress shielding from the use of high-modulus metallic alloy bio-implant materials has led to increased research into developing polymer–ceramic composite materials that match the elastic modulus of human bone. Of particular interest are poly-l-lactic acid–hydroxyapatite (PLA/HA)-based composites which are fully resorbable in vivo. However, their bioresorbability has a deleterious effect on the mechanical properties of the implant. The purpose of this study is to investigate, from a micromechanistic perspective, the in vitro degradation behavior of such composites manufactured using a simple hot-pressing route for two different hydroxyapatite particles: a fine-grained (average particle size ∼5 μm) commercial powder or coarser whiskers (∼ 25–30 μm long, ∼ 5 μm in diameter). We observed that composites with ceramic contents ranging between 70 and 85 wt.% have mechanical properties that match reasonably those of human cortical bone. However, the properties deteriorate with immersion in Hanks' Balanced Salt Solution due to the degradation of the polymer phase. The degradation is more pronounced in samples with larger ceramic content due to the dissolution of the smaller amount of polymer between the ceramic particles.     

纳米石墨微片/聚氯乙烯复合材料的制备与性能

利用超声作用制备纳米石墨微片(nano-Gs), 并采用混酸对其进行表面活化, 最后通过熔融共混法制备nano-Gs/聚氯乙烯(PVC)复合材料。通过FTIR、 SEM对nano-Gs的结构进行表征, 并研究了nano-Gs对nano-Gs/PVC复合材料导电性能和力学性能的影响。FTIR分析表明: nano-Gs经混酸处理后表面活性官能团含量明显升高, 并与PVC 分子链发生一定程度的氢键作用; SEM图片显示: nano-Gs 厚度为30～80 nm, 其微片宽度为4～20 μm, 在PVC 树脂基体中呈无规状均匀分布; 导电性能测试表明: 随着nano-Gs 含量升高, nano-Gs/PVC复合材料的体积电阻率呈非线性降低趋势, 最低为103 Ω·cm, nano-Gs 的逾渗阈值为10%(质量分数); 力学性能测试表明, 随着nano-Gs含量升高, nano-Gs/PVC复合材料的拉伸强度及缺口冲击强度均先升高后降低, nano-Gs质量分数为1%时, 复合材料的拉伸强度及缺口冲击强度均达到最大值, 相比纯PVC分别升高约14%和38%。