Effects of emulsion sizing with nano-SiO<Subscript>2</Subscript> on interfacial properties of carbon fibers/epoxy composites

Nano-SiO₂ particles were used to modify epoxy emulsion sizing of carbon fibers to improve the interfacial properties of carbon fibers reinforced epoxy composites. The mechanical interfacial strength between fibers and matrix was investigated by the single fiber fragmentation test and the 3-point short beam shear test, respectively. Dynamic contact angle analysis (DCAA), X-ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM) were performed on the carbon fibers with unmodified sizing and nano-SiO₂ modified sizing. The results indicated that modified sizing with nano-SiO₂ slightly increased the surface energy, the hydroxyl functional group and the surface roughness of carbon fibers compared to unmodified sizing, so that the interfacial shear strength (IFSS) of the single fiber composites and the interlaminar shear strength (ILSS) of composites were enhanced. SEM images of fracture sections of composites proved powerfully that the interfacial adhesion between fibers and matrix was improved after nano-SiO₂ modified emulsion sizing treatment.     

Effect of nano-SiO2 modified emulsion sizing on the interfacial adhesion of carbon fibers reinforced composites

The influence of nano-SiO₂ modified epoxy emulsion sizing on the interfacial adhesion properties of carbon fibers reinforced composites was investigated. The interfacial interaction between carbon fibers and the matrix was characterized by X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM) and three-point short-beam shear testing. The results showed that the amount of hydroxyl groups was slightly increased on the carbon fibers surface after treatment with nano-SiO₂ modified sizing. Compared to the unsized composites, the interlaminar shear strength (ILSS) values for the composites with unmodified sizing and nano-SiO₂ modified sizing were increased by 9% and 14%, respectively. The holes and carbon fibers pullout were not observed in their fracture sections. Surprisingly, the fracture section of the composites with nano-SiO₂ modified sizing was more compact and the fiber debonding was more difficult.     

混杂比对碳纤维-玄武岩纤维混杂增强环氧树脂基复合材料弯曲性能的影响

将玄武岩纤维置于混杂铺层的压缩侧,研究了碳纤维-玄武岩纤维混杂增强环氧树脂基复合材料的弯曲性能及混杂比对其弯曲性能的影响。通过对试样进行三点弯曲试验得到了材料的弯曲性能,并通过扫描电子显微镜观察材料的失效模式。与纯碳纤维增强环氧树脂基复合材料相比,当混杂比为16.7%和33.3%时,混杂复合材料的弯曲强度明显提升,弯曲强度分别提高12.4%和15.2%,但是其弯曲模量随着混杂比的提升而降低。混杂后的材料及玄武岩纤维增强环氧树脂基复合材料的失效位移都高于碳纤维增强环氧树脂基复合材料,断裂韧性明显提升。从侧面观察可以发现不同铺层在压缩侧、拉伸侧和中间层有不同的失效形式。      

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。     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

A Study on flexural properties of wildcane grass fiber-reinforced polyester composites

The main objective of this study is to introduce a new natural fiber as reinforcement in polymers for making composites. Wildcane grass stalk fibers were extracted from its stem using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were intentionally reinforced in a polyester matrix unidirectionally, and the flexural properties of the composite were determined. The fibers extracted by retting process have a tensile strength of 159 MPa, modulus of 11.84 GPa, and an effective density of 0.844 g/cm³. The composites were formulated up to a maximum fiber volume fraction of 0.39, resulting in a flexural strength of 99.17 MPa and flexural modulus of 3.96 GPa for wildcane grass fibers extracted by retting. The flexural strength and the modulus of chemically extracted wildcane grass fiber composites have increased by approximately, 7 and 17%, respectively compared to those of composites made from fibers extracted by retting process. The flexural strength and the modulus of KMnO₄-treated fiber composites have increased by 12 and 76% over those of composites made from fibers extracted by retting process and decreased by 3 and 48% over those of composites made from fibers extracted by chemical process, respectively. The results of this study indicate that wildcane grass fibers have potential as reinforcing fillers in plastics in order to produce inexpensive materials with high toughness.     

Biocomposites from Musa textilis and polypropylene: Evaluation of flexural properties and impact strength

Abaca (Musa textilis)-reinforced polypropylene composites have been prepared and their flexural mechanical properties studied. Due to their characteristic properties, M. textilis has a great economic importance and its fibers are used for specialty papers. Due to its high price and despite possessing very distinctive mechanical properties, to date abaca fibers had not been tested in fiber-reinforced composites. Analysis of materials prepared showed that, in spite of reduced interface adhesion, flexural properties of the PP composites increased linearly with fiber content up to 50 wt.%. Addition of a maleated polypropylene coupling agent still enhanced the stress transfer from the matrix to the reinforcement fiber. As a result, composites with improved flexural properties were obtained. The mechanical properties of matrix and reinforcing fiber were evaluated and used for modelling both the flexural strength and modulus of its composites. In addition, the impact strength of materials was evaluated. Comparison with mechanical properties of composites reinforced with fiberglass points out the potentiality of abaca-reinforced polypropylene composites as suitable substitutes in applications with low impact strength demands.     

Flexural behavior of geopolymer composites reinforced with steel and polypropylene macro fibers

Like ordinary Portland cement concrete, the matrix brittleness in geopolymer composites can be reduced by introducing appropriate fiber reinforcement. Several studies on fiber reinforced geopolymer composites are available, however there is still a gap to understand and optimize their performance. This paper presents the flexural behavior of fly ash-based geopolymer composites reinforced with different types of macro steel and polypropylene fibers with higher aspect ratio. Three types (length-deformed, end-deformed and straight) of steel fibers and another type of length-deformed polypropylene fiber with optimum fiber volume fraction of 0.5% are studied. The effects of different geometries of the fibers, curing regimes (ambient cured and heat cured at 60 °C for 24 h) and concentration of NaOH activator (10 M and 12 M) on the first peak strength, modulus of rupture and toughness of the geopolymer composites are investigated. The quantitative effect of fiber geometry on geopolymer composite performance was also analyzed through a fiber deformation ratio. The compressive strength, splitting tensile strength and flexural toughness are significantly improved with macro fibers reinforcement and heat curing. The results also show that heat curing increases the first peak load of all fiber-reinforced geopolymers composites. End-deformed steel fibers exhibit the most ductile flexural response compared to other steel fibers in both heat and ambient-cured fiber reinforced geopolymer composites.     

Optimal design for the flexural behaviour of glass and carbon fibre reinforced polymer hybrid composites

A study on the flexural behaviour of hybrid composites reinforced by S-2 glass and T700S carbon fibres in an intra-ply configuration is presented in this paper. The three point bend test in accordance with ASTM D790-07 at various span-to-depth ratios was simulated using finite element analysis (FEA). For the purpose of validation, specimens of selected stacking configurations were manufactured following the hand lay-up process and tested in a three point bend configuration. The validated FEA model was used to study the effects of fibre volume fractions, hybrid ratio and span-to-depth ratio. It is shown that flexural modulus increases when the span-to-depth ratio increases from 16 to 32 but is approximately constant as the span-to-depth ratio further increases. A simple mathematical formula was developed for calculating the flexural modulus of hybrid composites, given the moduli of full carbon and full glass composites, and the hybrid ratio. Flexural strength increases with span-to-depth ratio. Utilisation of hybridisation can improve the flexural strength. A general rule is in order to improve flexural strength, the fibre volume fraction of glass/epoxy plies needs to be higher than that of carbon/epoxy plies. The overall maximum hybrid effect is achieved when the hybrid ratio is 0.125 ([0_G/0_7C]) when both V_fc and V_fg are 50%. The strength increases are 43.46% and 85.57% when compared with those of the full carbon and glass configurations respectively. The optimisation shows that the maximum hybrid effect is 56.1% when V_fc = 47.48% and V_fg = 63.29%.     

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。      

Effects of nano-SiO2 particles on the mechanical and microstructural properties of ultra-high performance cementitious composites

In this research the effects of nano-SiO₂ particles on the mechanical performance, hydration process and microstructure evolution of ultra-high performance cementitious composites were investigated by different methods. The results showed that the compressive and flexural strength increased with the increase of the nano-SiO₂ content up to 3% and due to agglomeration of nano-SiO₂ particles, the mechanical properties decreased slightly when the nano-SiO₂ content was more than 3%. The hydration process was accelerated by the addition of nano-SiO₂. The porosity and the average pore diameter decreased with the increase of the nano-SiO₂ content and aging. The microstructure was more homogenous and dense for nano-SiO₂ specimens as compared to the control specimen. All of these improvements could be mainly attributed to the pozzolanic and filler effects of nano-SiO₂.     

玻璃纤维表面纳米SiO_2改性对GF/PCBT复合材料力学性能的影响

为研究玻璃纤维(GF)表面纳米SiO2改性对GF增强树脂基复合材料力学性能的影响,利用真空辅助模压(VAMP)工艺制备了不同含量的纳米SiO2表面改性GF增强聚环状对苯二甲酸丁二醇酯(PCBT)复合材料。分析了GF表面改性对GF/PCBT复合材料力学性能的影响,研究了纤维表面改性对GF/PCBT复合材料抗湿热老化性能的影响规律。纤维拔出试验结果表明:经表面处理的GF/PCBT复合材料的界面剪切强度提高了1.16倍;采用含量为0.5wt%和2wt%(与树脂质量比)的纳米SiO2处理GF表面后,复合材料的三点弯曲强度分别提高1.5倍和1.67倍,弯曲模量分别提高1.03倍和1.17倍。SEM结果显示:当纳米SiO2用量为2wt%时,破坏后的纤维表面被树脂完全覆盖,树脂与纤维粘结良好。在湿热条件下,由于纳米SiO2颗粒的存在,水分子很难通过界面相扩散到改性后的材料内部,其抗湿热性能提高。     

混杂工艺对椰壳-大麻/聚丙烯复合材料力学性能的影响

采用正交分析法,讨论混杂工艺和复合工艺对椰壳-大麻/聚丙烯（PP）复合材料力学性能的影响。结果表明,混杂处理后的椰壳-大麻/PP复合材料的力学性能均比相同复合工艺条件下的大麻/PP复合材料有较大程度的改善。椰壳纤维与大麻纤维质量比对混杂椰壳-大麻/PP复合材料力学性能影响最大,且混杂椰壳-大麻/PP复合材料的力学性能随椰壳纤维含量的增加而线性增大;混杂针刺毡中PP纤维质量分数对混杂椰壳-大麻/PP复合材料的抗弯强度影响较大,最初混杂椰壳-大麻/PP复合材料的抗弯强度随PP纤维质量分数的增加而减小,随后又随PP纤维质量分数的增加有一定程度的增大,而混杂椰壳-大麻/PP复合材料的抗拉强度则随PP纤维质量分数的增大而线性减小;混杂椰壳-大麻/PP复合材料的力学性能随复合层压温度的升高呈下降趋势。      

Effects of different nanomaterials on hardening and performance of ultra-high strength concrete (UHSC)

Nanomaterials have attracted much interest in cement-based materials during the past decade. In this study, the effects of different nano-CaCO₃ and nano-SiO₂ contents on flowability, heat of hydration, mechanical properties, phase change, and pore structure of ultra-high strength concrete (UHSC) were investigated. The dosages of nano-CaCO₃ were 0, 1.6%, 3.2%, 4.8%, and 6.4%, by the mass of cementitious materials, while the dosages of nano-SiO₂ were 0, 0.5%, 1.0%, 1.5%, and 2%. The results indicated that both nano-CaCO₃ and nano-SiO₂ decreased the flowability and increased the heat of hydration with the increase of their contents. The optimal dosages to enhance compressive and flexural strengths were 1.6%–4.8% for the nano-CaCO₃ and 0.5%–1.5% for the nano-SiO₂. Although compressive and flexural strengths were comparable for the two nanomaterials after 28 d, their strength development tendencies with age were different. UHSC mixtures with nano-SiO₂ showed continuous and sharp increase in strength with age up to 7 d, while those with nano-CaCO₃ showed almost constant strength between 3 and 7 d, but sharp increase thereafter. Thermal gravimetry (TG) analysis demonstrated that the calcium hydroxide (CH) content in UHSC samples decreased significantly with the increase of nano-SiO₂ content, but remained almost constant for those with nano-CaCO₃. Mercury intrusion porosimetry (MIP) results showed that both porosity and critical pore size decreased with the increase of hydration time as well as the increase of nanoparticles content to an optimal threshold, beyond which porosity decreased. The difference between them was that nano-CaCO₃ mainly reacted with C₃A to form carboaluminates, while nano-SiO₂ reacted with Ca(OH)₂ to form CSH. Both nano-CaCO₃ and nano-SiO₂ demonstrated nucleation and filling effects and resulted in less porous and more homogeneous structure.     

Effect of copper and nickel coating on short steel fiber reinforcement on microstructure and mechanical properties of aluminium matrix composites

Commercially pure Al base short steel fiber reinforced composites were prepared by stir casting method and poured into a cast iron mould. Steel fibers were coated with copper and nickel by electroless deposition method. The density, hardness and strength of composites increased as compared to matrix alloy. The mechanical properties of these composites were measured and the results were correlated with the microstructure observation. It was found that copper-coated short steel fiber reinforced composites show considerable improvement in strength with good ductility because copper form a good interface between Al matrix and short steel fiber. Nickel-coated steel fiber reinforced composites showed improvement in strength to a lower extent possibly because of formation of intermetallic compound at the interface. The improvement in strength with uncoated fibers and nickel-coated fibers is on the lower side because of formation of brittle intermetallic compounds like Fe₂Al₅ and FeAl₃. Fracture surface of tensile specimen was examined under SEM, which revealed a ductile fracture. Copper coating on steel fiber improved the strength properties while retaining a high level of ductility due to better interface bonding.     

混杂纤维增强水泥基复合材料的力学性能

研究了化学改性聚丙烯（PP）纤维以及掺加聚丙烯纤维和芳纶纤维混杂比例和混杂效应对水泥基复合材料力学性能的影响,并构建了纤维增强水泥砂浆界面层的物理模型,描述了纤维对水泥砂浆的增强机制。实验表明,聚丙烯纤维经改性后使水泥砂浆前期抗折强度明显提高,聚丙烯纤维和芳纶纤维的混杂使水泥砂浆的后期抗折强度显著提高。改性聚丙烯纤维掺加体积分数为0.56%,芳纶纤维的体积分数为0.24%时,混杂纤维增强水泥砂浆试样较空白试样,3天、28天抗折强度分别提高了18.48%、31.17%,3天、28天抗压强度分别提高了7.16%、5.19%。     

Fabrication of SiCf/SiC composites by chemical vapor infiltration and vapor silicon infiltration

Three-dimensional (3D) silicon carbide fiber reinforced silicon carbide matrix (SiC_f/SiC) composites, employing KD-1 SiC fibers (from National University of Defense Technology, China) as reinforcements, were fabricated by a combining chemical vapor infiltration (CVI) and vapor silicon infiltration (VSI) process. The microstructure and properties of the as prepared SiC_f/SiC composites were studied. The results show that the density and open porosity of the as prepared SiC_f/SiC composites are 2.1 g/cm³ and 7.7%, respectively. The SiC fibers are not severely damaged during the VSI process. And the SiC fibers adhere to the matrix with a weak interface, therefore the SiC_f/SiC composites exhibit non-catastrophic failure behavior with the flexural strength of 270 MPa, fracture toughness of 11.4 MPa·m^1/2 and shear strength of 25.7 MPa at ambient conditions. Moreover, the flexural strength decreases sharply at the temperature higher than 1200 °C. In addition, the thermal conductivity is 10.6 W/mk at room temperature.     

Mechanical and thermal characterization of epoxy composites reinforced with random and quasi-unidirectional untreated Phormium tenax leaf fibers

The present work investigates tensile and flexural behavior of untreated New Zealand flax (Phormium tenax) fiber reinforced epoxy composites. Two series of laminates were produced using the same reinforcement content (20 wt%), arranged either as short fibers or quasi-unidirectional ones. Composites reinforced using quasi-unidirectional fibers showed higher modulus and strength both in tensile and flexural loading, when compared to neat epoxy resin. Short fiber composites, although still superior to epoxy resin both for tensile and flexural moduli, proved inferior in strength, especially as concerns tensile strength. These results have been supported by scanning electron microscopy (SEM), which allowed characterizing fiber–matrix interface, and by acoustic emission (AE) analysis, which enabled investigating failure mechanisms. In addition, thermal behavior of both untreated phormium fibers and composites has been studied by thermogravimetric analysis (TGA), revealing the thermal stability of composites to be higher than for phormium fibers and epoxy matrix alone.     

Study on the friction and wear behavior of basalt fabric composites filled with graphite and nano-SiO2

To improve the friction and wear behavior of basalt fabric reinforced phenolic composites, single graphite or nano-SiO₂ and both of them were incorporated. The tribological properties of the resulting composites under different sliding conditions were investigated systematically on a model ring-on-block test rig. The friction and wear mechanisms of the composites were studied through analyzing the worn surfaces and transfer films by a scanning electron microscopy (SEM). Experimental results showed that graphite (Gr) was more beneficial than nano-SiO₂ in improving the tribological properties of basalt fabric composites (BFC) when they were singly incorporated. It is well worth noting that the friction and wear behavior of the filled composites was improved further when nano-SiO₂ and graphite were added together, indicating that there was a synergistic effect between them. Tribological tests under different sliding conditions revealed that the BFC/Gr/SiO₂ composites seemed to be more suitable for tribological applications under higher sliding speed and load.     

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。