The effect of oxygen-plasma treatment on Kevlar fibers and the properties of Kevlar fibers/bismaleimide composites

The effect of oxygen-plasma treatment for Kevlar fibers on the interfacial adhesion and typical macro-properties of Kevlar fiber/bismaleimide composites was intensively studied. It is found that oxygen-plasma treatment significantly affects the interfacial adhesion by changing the chemistry and morphology of the surfaces of the fibers, and thus leading to improved interlaminar shear strength, water resistance and dielectric properties of the composites. However, the improvement is closely related to the treatment power and time. The best condition for treating Kevlar fiber is 70 W for 5 min. Oxygen-plasma treatment provides an effective technique for overcoming the poor interfacial adhesion of Kevlar fiber based composites, and thus showing great potential in fabricating high performance copper clad laminates.     

Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, –COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23–27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.     

Improving the performance of conventional glass fiber epoxy matrix composites by incorporating nanodiamonds

Multiscale glass fiber epoxy matrix composites containing nanodiamonds were fabricated using vacuum bagging technique. Three different loadings of nanodiamonds were incorporated in epoxy resin after their functionalization through ozone-treatment, i.e., 0.1, 0.3 and 0.5 wt%. The functionalization of nanodiamonds was confirmed by infrared spectroscopy, which improved the dispersion of nanodiamond in epoxy resin thus improving the mechanical properties. Tensile, compression, flexural and interlaminar shear properties of the composites were improved. The tensile, compression and flexural strengths improved up to 36, 56 and 30% by the addition of 0.5 wt% nanodiamonds while the corresponding moduli increased to 30, 125 and 46%, respectively. An improvement of 38% in interlaminar shear strength was observed. The microscopy of the composites was performed using optical and electron microscopy and proper impregnation of glass fibers and the absence of the agglomerates of nanodiamonds were ensured. The homogeneous dispersion of nanodiamonds and their adhering role at fiber/matrix interface improved the mechanical properties of the composites. The developed composites are ideal candidate materials for engineering applications demanding high specific mechanical properties.     

Surface Modification of Para-Aramid Fiber by Direct Fluorination and its Effect on the Interface of Aramid/Epoxy Composites

Surface modification of a para-aramid fiber (DAFIII) was performed by direct fluorination. The properties of treated and untreated fibers were characterized and compared in detail by mechanical testing, Fourier transform infrared (FTIR) spectroscopy characterization, X-ray photoelectron spectroscopy (XPS) analysis and static contact angle measurements. The results showed that little damage of the fiber occurred after direct fluorine treatment, and the content of polar groups on the fibers surfaces were increased significantly, which resulted in a lower value of contact angle. The interlaminar shear strength (ILSS) of DAFIII fiber/epoxy composites and the tensile strength of NOL-ring specimens increased by 33% and 12%, increasing to 56.2 MPa and 2340 MPa, respectively, which indicated that the interfacial adhesion between the matrix and the aramid fiber was improved significantly by the fluorination treatment. Further tests showed that the durability of the direct fluorination treatment on the aramid fiber was also satisfactory.     

Fiber-matrix adhesion mechanism of pitch-based carbon fiber composites

The fiber-matrix adhesion mechanism in high modulus pitch-based carbon fiber-epoxy matrix composites has been studied. The surface morphology and chemistry of the carbon fibers were examined by microscopic (SEM, STM), thermodynamic and spectroscopic (XPS, Raman) techniques. The interlaminar shear strength and transverse tensile strength of the composites made from surface-treated and untreated fibers were also obtained. In the microscopic analysis, there was no difference in the surface roughness between the surface-treated and untreated fibers. In the thermodynamic and spectroscopic analyses, surface treatment of the carbon fibers increased the amount of surface oxygen. The results indicated that the major role of the surface treatment on the carbon fiber-epoxy resin adhesion is not the mechanical interlocking effect by the surface roughness. The formation of surface oxygen-containing functional groups is assumed to account for the increase in fiber-matrix interfacial adhesion.     

UV grafting of extended chain polyethylene fibres

A bench-scale continuous fibre treatment line has been built to modify polyethylene fibre surfaces using UV radiation-induced grafting. It is shown that grafting does indeed take place and that the grafts adhere well to the resin. Single-fibre pullout behaviour, interlaminar shear strength, and flexural behaviour were observed to improve considerably. The loss of tensile properties due to treatment was investigated and found to be small in the range of useful treatments. The interlaminar shear strength of the UV-treated fibre is as high as 38 MPa (5.5 ksi) as compared with the untreated fibre value of 10 MPa (1.5 ksi). The most important process parameters are identified and trends established.     

Improved mechanical properties of carbon fiber reinforced PTFE composites by growing graphene oxide on carbon fiber surface

The mechanical properties of carbon fiber reinforced polymer composites depend upon fiber-matrix interfacial properties. To improve the mechanical properties of ?bers/PTFE composites without sacri?cing tensile strength of ?bers, graphene oxide (GO) was introduced onto the surface of CFs by chemical vapour deposition (CVD). This hybrid coating increased the wettability and surface roughness of carbon fibers, which led to improved affinity between the carbon fibers and PTFE matrix. The resulting hybrid-coated carbon fiber-reinforced composites showed an enhancement in the short beam strength compared to un-coated carbon fiber composites. Meanwhile, a signi?cant increase of interlaminar shear strength (ILSS), interface shear strength tests (IFSS) and impact property were achieved in the 5-min-modi?ed CFs.     

Preparation of High-Quality Polyacrylonitrile Precursors for Carbon Fibers Through a High Drawing Ratio in the Coagulation Bath During a Dry-Jet Wet Spinning Process

Excellent poly(acrylonitrile-co-itaconic acid) (99/1) (PAI) nascent fibers, which have an important role in preparing high-quality precursors for carbon fibers, were prepared by a dry-jet wet spinning process. Their structures were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and an ultrasound solvent etching method, as well their properties being determined by a strength and extension meter and a fineness meter, both designed specifically for fibers. When a high drawing ratio, over 300%, was applied to the fibers in the dry-jet wet spinning coagulation bath, the molecular chains were easy to orient and regularly arrange, resulting in the relative crystallinity, crystal size and amorphous orientation degree of the nascent fibers being improved. The fibrils with large diameter were formed, increasing the bulk density with the overall porosity and pore numbers decreasing. Therefore, the nascent fibers had smaller diameters, higher strength, higher rupture elongation and smaller coefficients of variation. The optimum high performance PAI precursor fibers, with 0.59dtex in titer, 7.51cN/dtex in tensile strength, 7.9% in rupture elongation and the final carbon fiber with 5.54GPa in tensile strength, were obtained through a post-spinning treatment in which they were subjected to a high coagulation bath draw ratio and carbonization.     

The effect of the microstructure of porous alumina films on the mechanical properties of glass-fiber-reinforced aluminum laminates

The glass-fiber-reinforced aluminum laminates were obtained by anodizing aluminum alloy under anodizing voltage of 10, 20, and 30?V in the 200?g/L H₃PO₄ electrolyte. Scanning electron microscopy (SEM), short beam, and tensile tests were employed to determine the surface morphology, interlaminar shear strength (ILSS) and tensile strength of laminates, respectively. The results also show that the epoxy penetrates into the pores of the anodic films, and this is the mechanism of adhesion. The ILSS and tensile strength of the anodized specimens (under 20?V) respectively increased by approximately 50 and 15% comparing with those of the non-anodized specimens. This increase of mechanical properties results from the porous surface of aluminum providing greater mechanical interlocking to epoxy. The ILSS and tensile strengths of the anodized specimens increased with the increase of anodizing voltage from 10 to 20?V; however, it decreased when the voltage further increased to 30?V. It is considered that the microstructure evolution of the porous films has a significant effect on the mechanical properties of the laminates.     

Improvement of aramid fiber III reinforced bismaleimide composite interfacial adhesion by oxygen plasma treatment

Domestic Aramid Fiber III (DAF III) was modified by oxygen plasma treatment. The effects of oxygen plasma treatment power on fiber surface and DAF III reinforced bismaleimides (BMI) composite interfacial properties were investigated, respectively. The fiber surface characteristics were analyzed by X-ray photoelectron spectroscopy, Scanning Electron Microscopy, Atomic Force Microscopy and Dynamic Contact Angles Analysis, respectively. The results showed that oxygen plasma treatment introduced new oxygen containing groups such as C=O and –COO on to the fiber surfaces, changed the fiber surface morphologies and enhanced surface roughness by oxidative reactions and plasma etching. Finally, the fiber surface wettability was effectively improved. The total free energy increased from 49.8 to 71.7 mJ/m2 at maximum with 300 W oxygen plasma treatment. The composite interlaminar shear strength (ILSS) was evaluated by short beam shear measurement. The ILSS value increased from 49.3 to 59.8 MPa (by 21.3%) within 300 W plasma treatment.     

Influence of γ-ray radiation grafting on interfacial properties of aramid fibers and epoxy resin composites

This research used Co⁶⁰ γ-ray radiation to modify Armos fibers in 1,2-epoxy-3-chloropropane. After the treatment, the interlaminar shear strength (ILSS) values of aramid/epoxy composites were improved by about 20%. Surface elements of Armos fibers were determined by XPS analysis, which indicated that the oxygen/carbon ratio was increased. The surface of the fibers treated was rougher than that of the untreated fibers when examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Fourier transform infrared (FT-IR) spectra confirmed that the epoxy group was grafted onto the fibers. The wettability of the fibers' surface was also enhanced by the treatment. Nanoindentation technique analysis showed that the nanohardnesses of the various phases (the fiber, the interface and the matrix) in the composite, whose fibers were treated, were correspondingly higher than those in the composite, whose fibers were untreated. The results indicate that γ-ray irradiation grafting technique, which is a suitable batch process for industrialization, can modify the physicochemical properties of Armos fibers and improve the interfacial adhesion of its composite.     

Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

基于可见与近红外光谱联用的柑桔黄龙病快速无损检测研究

黄龙病是柑桔果树的毁灭性病害,对柑桔产业危害巨大。基于模型平均理论,探讨联用可见与近红外光谱技术,提高柑桔黄龙病快速无损检测精度的可行性。采集记录柑桔叶片的可见与近红外光谱,经实时荧光定量PCR鉴别黄龙病叶片为轻度、中度和重度三类,缺素和正常样品也经PCR鉴定,共五类叶片。基于光谱直接拼接、光谱归一化拼接和模型平均三种不同策略,结合偏最小二乘判别分析(PLS-DA)和多元线性回归(MLR)方法,分别建立了柑桔黄龙病可见与近红外光谱联用无损检测模型。经比较发现,光谱联用模型的检测精度均高于可见或近红外单一检测模型,且经导数处理后的光谱直接拼接PLS-DA模型检测精度最高,模型预测相关系数为0.97,预测均方根误差为0.67,模型总误判率为3%,其原因是导数消除了光谱的基线漂移。光谱归一化拼接的PLS-DA模型检测精度次之,模型总误判率为7%。可见与近红外模型平均的检测精度最低,模型总误判率为7.2%。实验结果表明,联用可见与近红外光谱,结合光谱拼接方法,提高了柑桔黄龙病无损检测模型的检测精度,研究可为其他领域的光谱联用提供参考依据。     

高体分SiC_p/Al复合材料螺纹性能的测试

从SiCp/Al复合材料性能分析着手,讨论了预置件法、焊接法和粘接法等在空间遥感器研制中常用的联接方法的优缺点,提出了在高体积分数（体分）SiCp/Al复合材料上直接加工螺纹,并加装钢丝螺套的方法来改善螺纹联接性能。对在某高体分SiCp/Al复合材料上加工的M4、M5螺纹进行了拉伸测试,结果表明：加装钢丝螺套前,复合材料螺纹有被拉脱现象;加装钢丝螺套后,M4螺纹、螺杆在3 000～4 000 N被拉断;M5螺纹、螺杆在8 000～9 000 N被拉断,测试后两种规格的螺纹状态良好,可以满足实际应用对该材料拉伸强度的要求,其已应用于工程项目中。     

Interfacial characterisation and mechanical properties of heat treated non-woven kenaf fibre and its reinforced composites

This paper reports on the comprehensive characterisation of heat treated kenaf fibre (KF) and its composites. The kenaf fibres were modified by heating for 2.5–12.5 h inside a drying oven. Heat treatment produces an increase in the crystallinity index and fibre strength of KF. The highest value of KF strength was recorded by applying heat treatment of 10 h on KF. The heat treatment results in the partial removal of impurities/extractives on the KF surface which is detected by scanning electron microscopy and X-ray photoelectron spectroscopy. Atomic force microscopy results signify the decrease of roughness, the increase in peak area density and the increase of the adhesion force on the surface area of heat treated KF. The effect of the heat treatment in enhancing the interface bonding characteristics between the KF and unsaturated polyester matrix can be reflected by the interlaminar shear strength (ILSS) and dynamic mechanical analysis value of the composites. The flexural properties of the composites showed a similar trend to ILSS. However, the fracture toughness revealed contrasting results. Water absorption induced a drastic loss of the mechanical properties of the composites albeit better retention of properties was observed in the case of heat-treated KF composites.     

Enhancing the interfacial strength of glass/epoxy composites using ZnO nanowires

This paper investigated the application of ZnO nanowires (ZnO NW) to enhance the interfacial strength of glass/epoxy composites. ZnO NW were grown on glass fibers by hydrothermal method, tensile properties of bare and ZnO NW coated fibers were measured by single fiber tensile testing, wettability of fiber with resin was studied by contact angle measurements and finally the interfacial strength and mechanisms were determined by single fiber fragmentation testing of glass/epoxy composites. The surface coverage of ZnO NW on glass fibers was fairly uniform without formation of major clusters. The coating of ZnO NW slightly reduced the tensile strength and improved the tensile modulus of fibers. Wettability tests showed reduction in contact angles for ZnO NW coated fibers because of enhanced wetting and infiltration of epoxy resin into nanowires. In fragmentation testing of microcomposites, smaller and concentrated interfacial debonding zones for ZnO NW coated fibers indicated good stress transfer and strong interfacial adhesion. A new form of crossed and closely spaced stress patterns were observed for nanowires of high aspect ratios. The interfacial strength of ZnO NW coated fibers increased by at least 109% and by 430% on average, which was attributed to the increased surface area and mechanical interlocking provided by ZnO NW.     

7050铝合金等通道转角挤压过程中显微结构和力学性能演化的小角x射线散射研究

采用三种等通道转角挤压（ECAP）与热处理相结合的工艺制备了超高强度细晶7050铝合金， 应用小角x射线散射技术定量地分析了ECAP过程中显微结构参数的变化情况，合理地解释了E CAP过程中力学性能的变化，揭示了合金强化机理. 研究发现，“固溶淬火＋ECAP＋时效” 工艺是获得高性能7050铝合金的合适工艺，可以使7050铝合金的抗拉强度提高到677 MPa， 延伸率保持在15％左右. 关键词： 7050铝合金 小角x射线散射 显微结构 力学性能     

子孔径拼接检测非球面时调整误差的补偿

针对在子孔径拼接测量非球面的过程中干涉仪与待测非球面相对位置存在的对准误差,提出了一种基于模式搜索迭代算法的调整误差补偿方法。该方法可以很好地从测量的子孔径相位数据中消除由拼接测量位置没有对准带来的调整误差,实现多个子孔径的精确拼接。对该方法的基本原理和实现步骤进行了分析和研究,建立了子孔径拼接测量的调整误差补偿模型。对口径为230 mm×141 mm的离轴碳化硅非球面反射镜进行了调整误差补偿和相位数据拼接,得到了精确的全口径面形分布。作为验证,对待测非球面进行了零位补偿检测,结果显示两种测试方法的面形PV值和RMS值的相对偏差仅为0.57%和2.74%。     

Composites of Hydroxyapatite Whiskers/poly(L-lactide-co-glycolide) with High Tensile Plasticity

Hydroxyapatite whiskers (HAW) with a maximum aspect ratio of 20 were employed to improve the toughness of poly(L-lactide-co-glycolide) (PLGA). 3-Aminopropyltriethoxysilane (AMEO) was grafted on the surface of the hydroxyapatite whiskers (g-HAW) to improve its wetting in the PLGA matrix. Composites based on HAW, g-HAW, and PLGA were prepared. The structure and properties of the composites were subsequently investigated by powder X-ray diffraction (XRD), scanning electron microscopy, differential scanning calorimetry, and tensile testing. The g-HAW were distributed homogenously in the PLGA matrix because of improved wetting of g-HAW while the HAW were aggregated. The stronger interfacial bonding also gave rise to improved mechanical properties of the g-HAW/PLGA composites. The HAW/PLGA and g-HAW/PLGA composites failed in a tough manner with intensive plastic deformation. The g-HAW/PLGA composite (5 wt% g-HAW) failed at a maximum elongation of 366%, although the tensile strength dropped slightly. The g-HAW/PLGA composite (1 wt% g-HAW) maintained the initial tensile strength of neat PLGA but failed at an equally high elongation of 347%, whereas PLGA failed at an elongation of 11%.