对位芳纶及其复合材料综述并产业化发展思考

对位芳纶由于其出色的性能,在宇宙探索、航空航天、国防军工、民用建筑等领域有大量的应用,尤其是芳纶复合材料已成为高科技领域必不可少的基础材料。对位芳纶复合材料具有轻质高强等突出特点,因此在节约减排方面具有显著效果,随着全球低碳经济的到来,芳纶及其复合材料的发展前景会越来越好。本文根据对位芳纶发展及应用的最新情况,详细介绍了对位芳纶的种类、性能、应用以及发展概况,并结合多年的对位芳纶研发及产业化经验,分析探讨了我国现有对位芳纶及其复合材料产业化发展方面存在的问题,指出我国在技术、生产效率、生产能力、设备、市场等方面与国外的差距,并据此提出对位芳纶及其复合材料今后的发展方向和研究重点。最后从科学发展观和低碳经济的角度,指出我国对位芳纶及其复合材料产业化发展的必要性和紧迫性。     

Carbon aerogel composites prepared by ambient drying and using oxidized polyacrylonitrile fibers as reinforcements

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m(-1) K(-1) at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system.     

Bio-inspired tapered fibers for composites with superior toughness

The toughness of fiber-reinforced composites largely relies on crack bridging. More specifically, intact fibers left behind the tip of a propagating crack are progressively pulled out of the matrix, dissipating energy which translates into toughness. While short fibers are traditionally straight, recent work has showed that they can be shaped to increase the pullout strength, but not necessarily the energy to pullout. In this work we have modeled, fabricated and tested short fibers with tapered ends inspired from a high-performance natural material: nacre from mollusc shells. The main idea was to duplicate a key mechanism where a slight waviness of the inclusion can generate strain hardening and energy dissipation when the inclusion is pulled out. We have incorporated a similar feature to short fibers, in the form of tapered ends with well defined opening angles. We performed pullout tests on tapered steel fibers in epoxy matrices, which showed that the pullout of tapered fiber dissipates up to 27 times more energy than straight fibers. The experimental results also indicated the existence of an optimum taper angle to maximize work of pullout while preventing the brittle fracture of the matrix. An analytical model was developed to capture the pullout mechanism and the interaction between fiber and matrix. The analytical model can guide the design of tapered fibers by providing predictions on the influence of different parameters.     

Forming composites based on mineral fibers

The effect of aluminum sulfate additives on the structure of a composite material based on basalt fibers has been studied using electron microscopy and IR spectroscopy. The introduction of aluminum sulfate leads to the appearance of outgrowths fastening mineral fibers to each other at their intersection contacts. This is accompanied by the appearance of an absorption band in the IR spectra, which is attributed to hydrogen-bonded hydroxy groups. Estimates of the hydrogen bond lengths are obtained from an analysis of the IR absorption band shape.     

纤维混杂复合材料研究进展

介绍了近年来国内外纤维混杂复合材料的研究发展,从混杂比、混杂方式和界面三个方面分析了影响纤维混杂复合材料性能的因素,并介绍了纤维混杂复合材料在冲击性能、剪切性能、压缩性能、热性能、声学性能、透波性能方面的研究进展,并对我国纤维混杂复合材料今后研究提出相关建议.     

Buckling of fibers in fiber-reinforced composites

Elastic stability of fibers in fiber-reinforced composite materials subject to compressive loading is studied. The transversal buckling mode is considered, and two limiting cases, the dilute and non-dilute composites are analyzed. In the case of a non-dilute composite, the cylindrical model and the lubrication approximation are applied. The original problem is reduced to a problem of stability of a rod on elastic foundation. Through the solution of this problem a simple formula for the buckling load is obtained. In the case of a dilute composite, the solution of a problem of stability of a compressed rod in elastic plane is used. On the basis of the obtained solutions in two limiting cases the interpolation formulae are derived. These formulae describe buckling of fiber in the fiber-reinforced composite for any value of the fiber volume fraction. Comparison with known numerical and experimental results is carried out, and the sufficient accuracy of the derived formulae is demonstrated.     

Cement-based composites containing functionalized carbon fibers

Carbon fibers can be used to improve both mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. To guarantee both a good dispersion in water and a strong interaction with cement, surface functionalization of carbon fiber surface by reaction with acid was preferred to the use of a dispersing agent. The best oxidation conditions were chosen by using a Taguchi approach, and the samples contained the treated fibers were subjected to both mechanical and electrical tests, to determine flexural strength, toughness, compressive strength and electrical conductivity. It was shown that a not-too-strong oxidation by piranha solution was very effective to obtain well-dispersed fibers and a cement-composite with improved mechanical properties (in particular toughness) and electrical conductivity.     

石油沥青基炭纤维的制备

利用元素分析、TG、DSC、FT—IR、XRD和STM等手段研究了各向同性沥青和各向异性沥青基炭纤维的不熔化、炭化和石墨化工艺过程，对不熔化过程的反应机理进行了推导，并计算出不熔化反应的动力学参数。同时还研究了石墨化过程中，纤维的力学性能和结晶参数的变化。研究结果表明，在制备沥占基炭纤维工艺过程中，各向同性沥青纤维(APF)的最佳氧的质量分数为19.63％，而各向异性沥青纤维(APF)的最佳氧的的质量分数为8.03％。各向同性沥青基石墨纤维(IPGF)的d002，Lc，La分别为0.3432nm、3.432nm和8．053nm，而各向异性沥青基石墨纤维(APGF)的d002、Lc、La分别为0.3391nm、25．69nm和53．05nm。IPGF的拉伸强度和模量分别为596MPa和58GPa，而APGF的拉伸强度和模量分别为2956MPa和632GPa。     

Carbon based conductive polymer composites

Composite material has attracted increasingly remarked interest over the last few decades and set it apart in its own class due to its distinct properties. World annual production is over 10 million tonnes and the market has in recent years been growing at 5–10% per annum. Among these materials, one subgroup, conductive polymer composite, has figured out and its importance is increasing in years to come. When used as conductive material, it possesses the merits of light weight, ease of manufacturing and chemical resistance. This review focuses on the electrical properties of carbon based conductive polymer composites. Special emphases are placed on the percolation phenomenon, the factors that affect the percolation threshold as well as related theoretical research work. Then mechanisms of electric conduction and factors influencing conductive properties are addressed.     

Carbon fibers modified with carbon nanotubes

Carbon nanotubes were used to modify a polyacrylonitrile (PAN) polymer solution before the manufacture of the carbon fiber precursor. The modified PAN fibers were spun from a dimethylformamide solution containing a small amount of single-walled carbon nanotubes. The fibers were characterized by thermogravimetry and optical and scanning electron microscopy. Structure, morphology, and selected properties of the composite polymeric fibers and the fibers after carbonization are characterized. The mechanical properties of the fibers are examined. It is found that nanotubes in the PAN solution have a strong tendency to form agglomerates that inhibit suitable macromolecular chain orientation of the carbon fiber precursor. Fibers manufactured from such a solution have similar mechanical properties to those from a pure PAN precursor, and after carbonization the resultant carbon fibers are very weak. A comparison of pure carbon fibers and those containing nanotubes reveals slight differences in their structural ordering.     

First pseudo-grain failure model for inelastic composites with misaligned short fibers

This paper presents a new model and an experimental investigation of the elastic–plastic flow until failure in short-fiber reinforced thermoplastics typically produced by injection molding. The distribution of fiber orientations and lengths is reproduced statistically within a representative volume element (RVE) of the composite microstructure. Then, the RVE is decomposed fictitiously into pseudo-grains (PGs) inside of which the fiber orientation and aspect ratio are unique. An incremental Mori–Tanaka model is used to predict the phase averages of the stresses and strains inside each PG. Damage intervenes in a second homogenization step: the macroscopic stress accounts for the fact that PGs fail one after the other in function of the fiber orientation and the applied strain mode. Hence, the model is called “first pseudo-grain failure model” by analogy with the “first ply failure model” in laminated composites. An evaluation of the proposed model against experimental data is conducted for short-glass-fiber reinforced polyamide 6,6 (PA6,6). It is shown that the model yields satisfactory predictions of the response under uniaxial tension of composite samples with different fiber contents cut under various directions relative to the main injection flow direction.     

A BEM formulation for homogenization of composites with randomly distributed fibers

In recent papers by the authors, deterministic models of distribution of fibers in composite structures have been studied. For example, problems related to optimization, homogenization, localization, etc., have been solved. The extended Hashin–Shtrikman (H–S) variational principles served as a starting point (eigenparameters were involved in the formulations), and the comparative medium was introduced. The BEM formulations were then admissible and efficient. The formulations of the above-mentioned problems require the restriction of geometry of the fibers to certain ‘locally reasonable’ structures, e.g. to periodic or pseudo-periodic cells.Since the condition of regular distribution of fibers is violated in applications, and a random distribution is more probable, another extension of the H–S principles is needed. In this paper, the problem is extended to the case of statistically distributed fibers. H–S variational principles are formulated in terms of statistical characteristics in the domain and the eigenparameters are also involved, affected by the statistical values. Following the H–S principles, an integral formulation is stated (again, thanks to the use of the comparative medium such a formulation is admissible) in a representative volume, which contains no longer regular geometry of the fibers. The boundary element method has then a special form, which is advantageous particularly for two-phase media.The above-mentioned formulation of H–S variational principles with randomly distributed fields of fibers can be extended to non-linear problems (plasticity, debonding) by introducing transformation fields (eigenstresses or eigenstrains, which are involved in the formulations for completeness).The results form the research presented in this paper basically apply to homogenization of diaphysal implants. But, there is a wide range of applications of the theory introduced in this paper. Due to results from tests on the bearing composite frame of a bicycle, which has a similar structure for certain types of composites of the diaphysal implants, a typical cross-section of the bearing frame of a bicycle is studied as an example. The frame is built of a graphite-epoxy composite.     

纳米结构的炭钌复合物-一种提高超级电容器性能的电极材料

报道了一种利用氧化硅模板,裂解简单易得的含钌有机物制备纳米结构炭/钌复合物的方法.在该复合物中,钌纳米颗粒均匀地分布在多孔的炭基体中.该复合物被电氧化所得炭/RuO2·xH2O的超级电容性质明显提高(10 mV/s 时229 F/g ).     

Low density polyethylene composites containing cellulose pulp fibers

Unbleached and bleached Kraft cellulose pulp fibers modified with a long chain carboxylic acid, i.e. oleic acid in cold plasma conditions have been used as reinforcements in low density polyethylene (LDPE). The purpose of the modification is to enhance the interfacial adhesion between cellulose and matrix and to increase the dispersability. Composites containing up to 10 wt.% of untreated and modified cellulose pulp fibers with LDPE were prepared by melt mixing. The samples were characterized by processing behavior, mechanical and rheological properties, SEM, contact angle measurements, TGA and DSC. It was found that when the modified pulp fibers were incorporated into composites matrix, most of the properties have been improved.     

几种热带植物纤维在复合材料领域的研究进展

我国热带地区的农作物丰富多样,热带作物的重要性也日趋显著,然而大量的热带农业生物质资源却被当作废料处理,忽视了重要的潜在应用价值。热带农作物含有丰富的天然纤维,如香蕉茎杆、甘蔗渣、木薯渣、菠萝叶、椰壳等。天然纤维在增强复合材料的综合性能中有着广泛的应用,阐述和分析了几种热带植物纤维的理化性质以及利用天然纤维增强复合材料的研究现状,为热带植物纤维的材料化利用提供参考。     

Recent developments in fibers and interphases for high temperature ceramic matrix composites

The long term durability of CMCs is limited by two factors: (1) creep and rupture of the fibers, and (2) environmental degradation of the constituents, primarily in the nonoxide composites. Oxide CMCs are limited by the creep resistance of the fiber at this stage of development and by interphase concepts that are not yet mature. Nonoxide fibers have been developed with excellent creep resistance relative to oxide fibers, but oxidation of the interphase and the interface, particularly at intermediate temperatures, causes embrittlement of these composites. This effect is particularly severe when matrix cracks are present and under cyclic loading conditions.     

Review of applications for advanced three-dimensional fibre textile composites

Current and future potential applications for three-dimensional (3D) fibre reinforced polymer composites made by the textile processes of weaving, braiding, stitching and knitting are reviewed. 3D textile composites have a vast range of properties that are superior to traditional 2D laminates, however to date these properties have not been exploited for many applications. The scientific, technical and economic issues impeding the more widespread use of 3D textile composites are identified. Structures that have been made to demonstrate the possible uses of 3D composites are described, and these include applications in aircraft, marine craft, automobiles, civil infrastructure and medical prosthesis.