Hybrid carbon-glass fiber vinyl ester resin composites

Hybrid carbon-glass fiber composites of novolak epoxy-based vinyl ester resins have been investigated. The chemical resistance, the thermo-oxidative stability and the mechanical properties such as tensile strength and tensile modulus, as well as flexural strength and flexural modulus, interlaminar shear strength (ILSS) and impact strength have also been estimated. The combination of glass and carbon fibers in the hybrid turns out to be an excellent mix. These composites have good tensile and flexural properties as well as the good chemical resistance of the carbon fibers and the high impact strength of the glass fibers and also the thermo-oxidative stability of highly aromatic vinyl ester resins based on novolak epoxy.     

Electrocatalytic hydrogenation of phenol in aqueous solutions at a Raney nickel electrode in the presence of cationic surfactants

The electrocatalytic hydrogenation (ECH) of phenol at a Raney nickel cathode was studied in aqueous solutions. At 30 °C, without surfactants, cyclohexanol was obtained with low or medium yields. The best results were observed in alkaline solutions (pH 9). At pH 2 the efficiency of the hydrogenation reaction is significantly improved by low amounts of didodecyldimethylammonium bromide (DDAB). This surfactant effect is studied in relation to the substrate and hydrogen adsorption phenomena.     

Pulsed electrodeposition of Zn in the presence of surfactants

The preparation of Zn deposits has been performed by galvanostatic pulsed electrolysis, from acidic zinc sulphate solutions, on a stainless steel substrate. The influence of the surfactants (cetyl trimethyl ammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and octylphenolpoly(ethyleneglycolether)_n, n = 10, Triton X-100) on the voltammetric behaviour, structural and morphological characteristics of the deposits have been investigated. The characterization of the samples was made by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDS). The experimental data shows that the presence of surfactants affects the zinc deposition process. The electrodeposits are mainly composed by Zn with different texture, crystal shape and size (grain size ranging from 40 to 20 nm). The obtained results led us to conclude that the Zn deposits prepared in the absence of surfactants and in the presence of SDS are more crystalline and with a higher grain size than the ones obtained in the presence of CTAB and Triton X-100. These facts may be justified by the increase on the overpotential deposition as the electrochemical studies confirm.The XRD results show that the deposits prepared, in the absence of surfactant and in the presence of SDS, contain ZnSO₄ and Zn₄SO₄(OH)₆ as oxidation products. ZnO is also detected on the deposits obtained in the presence of CTAB and Triton X-100.     

The stability of sodium hypochlorite in the presence of surfactants

Studies were made on the stability of NaOCl at 40°C in the presence of sodium alkanesulfonate or alkylarenesulfonate anionic surfactants, and in the presence of a nonionic surfactant,N-octylpyrrolidinone. The results were compared with NaOCl stability in the absence of additives and in the presence of nonsurfactant short-chain sodium alkylbenzenesulfonates. The data indicated that the rate of NaOCl loss is greatly dependent upon the pH of the solution, even at alkaline pHs. At initial pHs below 11, in the absence of additive, there is significant disproportionation of OCl⁻ to ClO ₃ ⁻ , accompanied by decrease in the pH of the solution, within a period of several days. Even at an initial pH of 11.3, in the presence of the surfactants investigated, there is significant disproportionation of OCl⁻ and decrease in the pH of the solution in the first several days. When the initial pH of the solution is 13.5, there is no significant decrease in pH of the solution for at least two months in the presence of the surfactants studied. NaOCl stability in the presence of surfactant decreases in the order: sodium linear alkanesulfonate > sodium linear alkyldiphenylethersulfonate > sodium linear alkylbenzenesulfonate >>N-octylpyrrolidinone. Stability was greater in the presence of linear alkylarenesulfonates than in the presence of branched alkylarenesulfonates. It is suggested that the differences in stability observed are due to the greater ease of oxidation of tertiary carbon atoms compared to primary or secondary atoms.     

Measurement of fiber and matrix orientations in fiber reinforced composites

Short glass fiber reinforced polypropylene was employed in a study to determine the effect of molding and mold design variables on the distrubution of fibers and their orientations, and consequently, on the distributions of mechanical properties in the molded article. In this paper, a variety of experimental techniques were employed to evaluate the distributions of fibers and their orientations. Moreover, techniques were developed to evaluate the orientation and crystallization of the matrix. The results yield significant information regarding the development and control of both the microstructure and the properties of short fiber reinforced composites.     

二甲基硅油及其表面活性剂在化纤生产中的应用

综述了二甲基硅油及其表面活性剂在化纤油剂中的应用 ,化纤油剂应具有的高平滑性、高耐热等特性 ;介绍了改善油剂的综合性能及硅油表面活性剂用来提高纤维的可纺性等性能的方法。建议我国应尽快开发研制含硅油的化纤油剂     

Fracture of fiber reinforced composites

Characteristics of the fracture of fiber reinforced plastic composites are described in terms of the elastic stress distribution at the crack tip, the mechanism of crack tip damage, and the modes and conditions of final fracture. The three-dimensional, stress field at the tip of a sharp crack in a laminate is presented and contrasted to traditional two-dimensional models. The response of the material in the form of inter- and intraply damage formation and growth under increasing load is characterized, and its effect in blunting the main crack is examined. The final fracture conditions, which may range from quasi-brittle to notch insensitive, are discussed and related to the damage zone extension. Observed and anticipated effects of various material and geometric parameters are also discussed.     

Fracture modes in off-axis fiber composites

Criteria have been developed for identifying, characterizing, and quantifying fracture modes in high-modulus graphite-fiber/resin unidirectional composites subjected to off-axis tensile loading. Procedures are described which use sensitivity analyses and off-axis data to determine the uniaxial strength of fiber composites. It was found that off-axis composites failed by three fracture modes, which produce unique fracture surface characteristics. The stress that dominates each fracture mode and the load angle range of its dominance can be identified. Linear composite mechanics is adequate to describe quantitatively the mechanical behavior of off-axis data are comparable to those measured in uneasily tests.     

涂层法制备镍纤维

采用改进型螯合溶胶凝胶法分别制备出Ni-EDTA和Ni-CA两种溶胶,将溶胶连续地涂覆于国产连续碳纤维上,通过原位还原法制得涂层型金属镍纤维,并分别对所制备的溶胶和镍纤维微观结构与性能进行了系统研究。研究表明制备溶胶的最佳配方为:n(Ni)∶n(EDTA)=2∶1或n(Ni)∶n(CA)=1∶2(溶液pH值分别为6 7、2 7)时,所得溶胶稳定性最好,溶胶在陈化2 5h、超声时间为0 5h时涂层效果好,改变溶胶黏度和超声时间可调节涂层厚度。制得的镍纤维连续、柔顺有光泽、纯度高,涂层厚度为160～200nm,涂层后T300碳纤维的单丝力学强度提高了10.7%。     

碳纤维复合材料在汽车工业中的应用

节能减排是当前汽车工业可持续发展迫切需要解决的问题,采用碳纤维复合材料等轻质材料使汽车轻量化是一个有效的解决办法。介绍了碳纤维复合材料的性能特点和在汽车上的应用现状,从材料、设计和成型工艺3个方面分析了其在国内汽车工业应用中的问题,提出了促进碳纤维复合材料广泛应用的发展建议,并展望了其在汽车工业中的应用前景。     

The anomalous codeposition of tungsten in the presence of nickel

Deposition of tungsten-rich alloys from plating baths that do not contain ammonia is reported. Alloys with nominal composition of NiW and even NiW₂ have been formed for the first time by electroplating. It was shown in this paper, and in our previous work [Electrochem. Solid-State Lett. 3 (2000) 543; Proc. Advanced Metalization Conf. (AMC 2000) p. 337; Langmuir 17 (2001) 8270; J. Electrochem. Soc. 149 (2002) C100; J. Appl. Surf. Sci. 200 (2002) 1], that alloys of tungsten and nickel having any composition between a few a/o and 67 a/o of tungsten can be electroplated, by suitable choice of the experimental conditions. The most important factors among these are the concentrations of citrate, which acts as the complexing agent, the ratio of concentrations of nickel and tungstate ions and the pH of the solution. New indirect evidence for the existence of a mixed metal complex of the type [(Ni)(WO₄)(Cit)(H)]²⁻ was obtained by: (a) the pH dependence of the composition of the alloy and (b) by the linear dependence of the partial current density for deposition of tungsten on the calculated concentration of this complex, over a wide range of solution compositions. Removing ammonia from the plating bath allows the deposition of tungsten-rich alloys, but this is achieved at the cost of a substantial reduction in Faradaic efficiency.     

连续玄武岩纤维在复合材料中应用

连续玄武岩纤维是绿色环保材料,是国家鼓励开发与应用的纤维材料.本文对玄武岩基本情况和连续玄武岩纤维制作等工艺的介绍,根据连续玄武岩纤维的特点,列举出玄武岩纤维长纤增强LFT、玄武岩直接无捻粗纱增强纤维和玄武岩纤维SMC无捻粗纱增强纤维的应用特点和情况,并对连续玄武岩纤维复合材料作了展望,期待有更大的应用范围.     

Escherichia coli adhesion to abiotic surfaces in the presence of non-ionic surfactants

Escherichia coli adhesion to the silica gel surface in the presence of non-ionic surfactants was investigated. E. coli adhesion to silica gel begins with long-range, non-specific van der Waals interactions, followed by short-range, specific Lewis acid-base interactions. When surfactants were introduced to the system before E. coli, the amounts of attached E. coli to silica gel surfaces corresponded to interactions between E. coli and silica gel, which were determined by surface properties of both E. coli and silica gel, as well as the intervening medium. When surfactants were introduced after E. coli colonization, the amounts of attached E. coli desorbed from silica gel surfaces corresponded to interactions between lipopolysaccharides and silica gel, which were determined by surface properties of both lipopolysaccharides and silica gel, as well as the intervening medium.     

Strength properties of discontinuous fiber composites

The longitudinal strengths of unidirectional discontinuous fiber composites have been calculated based on the concept of perturbation effect and the distortional energy criterion, utilizing the finite-element method. The theoretical results thus obtained are compared with the experimental data as well as the results of shear lag analysis for tungsten-copper, boron-aluminum, glass-epoxy and boron-epoxy composites. Based on the Jackson-Cratchley equations, modified for discontinuous fibers, a formula is also proposed for calculating the strengths of randomly oriented discontinuous fiber composites. The results calculated from this formula are compared with the experimental data for aluminum oxide-aluminum-silicon and glass-epoxy composites.     

Photographed impact of continuous fiber composites

Instrumented falling weight impact is conducted on eight different continuous carbon fiber composites. During impact, photography of the tension surface of the specimens enables crack propagation to be monitored. One photograph per specimen is taken. Measurements of integral crack length is related to corresponding absorbed energies during impact. These results enable an apparent value of G_c to be determined. These are tabulated for the eight advanced composite samples.     

Stamping of continuous fiber thermoplastic composites

Despite demonstrated success in low volume aerospace and defense applications, structural composites remain at the periphery of high volume industries such as construction, automotive, and consumer goods because of long cycle times. Stamping provides a means of making composite sheet products at rates ten to a hundred times faster than any existing continuous fiber processes. However, to make composites stamping a viable process, one must understand how the combination of fabric architecture, tool design, and process conditions interact to produce a part free of wrinkling and tearing. In this paper, the effect of temperature, stamping rate, and boundary constraints on the material deformation is presented. The focus of this study is a co‐mingled glass/polypropylene fabric, in the form of a layer of unidirectional yarns held together by stitches. The results show that temperature variations have the greatest effect on deformation. In addition, a finite element model of parallel strips with linear constraints was shown to successfully simulate the sliding deformation or draw‐in of the stitched unidirectional material.     

The interphasial regions in interlayer fiber composites

The interaction between the fiber and matrix in a fiber-reinforced material plays an important role in determining the mechanical behavior of the composite. An efficient technique to simultaneously improve fiber-matrix interfacial shear strength and impact behavior of the composite is to deposit a flexible interlayer onto the fiber. This results in the creation of three bulk phases, the fiber, matrix, and the interlayer and two interphasial regions. A phenomenological model that defines the variation of the fiber-interlayer interphase and that of the interlayer-matrix interphase has been developed. In the model, the elastic moduli of these regions vary continuously, so as to bridge the two bulk phases on either side of the interphase. The interaction between the bulk phases is also taken into consideration. The model has the potential for the use of dynamic mechanical analysis to obtain, relatively, adhesion/interaction parameters of different fiber-interlayer-matrix systems. These parameters can be used to determine the optimum interlayer thickness for improved toughness and good stress transfer efficiency.     

Mechanism of the reverse dissolution of zinc in the presence of nickel

Cyclic voltammetry and impedance measurements were used to investigate the influence of an additive, triethyl-benzyl-ammonium chloride, on the kinetics of zinc deposition in acidic sulphate electrolytes containing Niu²⁺ ions able to induce the reverse dissolution of zinc deposits. It is shown that the adsorbed additive inhibits both the nucleation and growth of zinc deposits. By competing with the formation of a nickel-containing surface compound responsible for a stimulation of hydrogen evolution, the additive adsorption also inhibits hydrogen evolution and thereby stabilizes the galvanostatic deposition of zinc.