离心法制备环氧树脂/不锈钢短纤维梯度功能复合材料的电性能研究

本文选用机械振动切削法制得的不锈钢金属短纤维（SSSF）为增强材料，采用离心法制备了环氧树脂基纤维梯度功能材料。通过沿离心力方向上试样密度分布估算纤维含量梯度分布情况。研究了离心旋转速率、时间、粘度等工艺参数对复合材料中纤维分布梯度的影响。试验表明，随着离心速率的增大，不锈钢金属短纤维分布厚度变窄，纤维浓度梯度增加。导电性的研究发现，纤维体积浓度在4．5％－5．5％为阈值，高于此阀值的部分是导电体；低于此阈值的部分几乎不导电。阈值与纤维网络的形成相对应。     

功能梯度材料制备方法的研究进展

功能梯度材料作为一种新型的复合材料,因其优异性能得以广泛应用.本文回顾了功能梯度材料的发展历史,综述了功能梯度材料的制备方法,其中包括粉末冶金法、等离子喷涂技术、粉末冶金法、电沉积法以及气相沉积法等,并提出了今后功能梯度材料的研究重点.     

梯度功能材料的研究现状与展望

本文简要介绍了梯度功能材料的基本要领及其设计思想和研究内容。着重对梯度功能材料的研究现状和发展前景作了比较全面的综述。     

离心法制备气孔梯度氧化铝陶瓷

选用两种粒径大小不同的氧化铝粉体,通过选择分散工艺配制了适合离心成型的流变性好的浆料.用此浆料以离心成型工艺成功制备了具有气孔梯度的材料,并对材料的微观形貌、气孔率以及孔径分布进行了分析.结果表明:引入分散剂后pH值为9～10时,粉体的zeta电位绝对值最大,此时浆料流变性能最好.用此浆料制得的陶瓷样品经过1400℃烧制后具有梯度分布的粒径和气孔,样品底部气孔率为29.2%,气孔尺寸在0.2～1.0 μm左右;顶部气孔率只有18.6%,而气孔尺寸则小于0.2μm.     

聚合物基梯度功能材料研究进展

对正在兴起的聚合物基梯度功能材料的研究状况，特别是其制备技术的研究和开发进行了综述，并对其潜在的应用价值进行了展望。利用物质传输原理制备梯度功能材料的方法包括了基于质量传输的溶液扩散、互穿网络、相转变和溶胶一凝胶等方法；而基于能量传输的制备方法涉及到了利用电场能、磁场能、热能、重力势能、辐射能、光能以及化学能等多种方法。同时还对界面聚合、纤维排列、组分含量连续调控、复合共挤、逐层浇注、静电喷涂等基于构造原理所开发的制备技术作了简要介绍。     

PSZ—Mo系梯度功能材料的热应力缓和设计与制备

对ＰＳＺ－Ｍｏ系梯度功能材料在制备过程中的热应力缓和性能进行了优化设计，用有限元方法解析了ＰＳＺ－Ｍｏ系两层叠层材料（即非梯度功能材料）在制备过程中的热应力分布情况。同时解析了ＰＳＺ－Ｍｏ系ＦＧＭ在制备过程中的热应力分布及缓和规律。揭示了ＰＳＺ－Ｍｏ系ＦＧＭ在制备过程中的热应力大小与组成分布形状指数Ｐ的关系，对所研究的体系通过热应力缓和最佳时的Ｐ值，同时，对ＦＧＭ的制备工艺进行了研究，用粉末法分别     

功能梯度材料及其复合电镀制备现状与进展

综述了功能梯度材料的概念、性能、研究动态及最新进展。总结了功能梯度材料的各种制备方法。重点探讨了采用复合电镀技术制备功能梯度材料的方法。该方法成本低,易于操作,所得镀层孔隙率低,结合力好,耐磨,耐蚀性好,具有广阔的应用前景。     

碳纤维/改性环氧树脂复合材料的制备与表征

采用手糊成型工艺制作碳纤维复合材料(CFRP),选用T-700碳纤维为增强体,用气相氧化法对其进行表面处理,选用双马来酰亚胺(BMI)改性的耐高温环氧树脂为树脂基体。结果表明,碳纤维经过表面处理后,其表面与基体树脂的接触角由116.8°下降到50.5°,并且表面出现条纹沟槽,改善了碳纤维表面对基体树脂间的界面性能。同时,玻璃化转变温度提高了4.0%,热分解温度提高了1.9%。     

聚合物基功能梯度复合材料的研究进展

介绍了聚合物基功能梯度材料的概念和分类,综述了其制备研究进展(包括非平衡溶胀法,扩散共聚法,电场诱导法,离心法,纤维排列法)及其在航空,生物医学,光学工程领域的应用,并对其发展趋势作出了展望。     

Cu基功能梯度复合材料的发展及研究现状

Cu具有优良的性能,仅次于银的导电和导热性,容易塑性变形等,但铜的强度、硬度较低,耐腐蚀、耐氧化、耐磨性差等大大限制了其应用,要求既具有高导电、导热低温延展性,同时具有高强度、耐腐蚀、氧化等性能,Cu基功能梯度材料的出现满足了材料这种高导电率、高强度以及更高的性能要求,目前有Cu-Mo,Cu-WC等功能梯度材料,在导电导热性、等离子体材料等有广泛的应用。重点综述了Cu基功能梯度复合材料的各种制备方法、应用,并对其未来发展及前景进行了展望。     

Attaining a controlled graded distribution of particles in polymerizing fluid for functionally graded materials

The precise control on concentration profile of dispersion in functionally graded material (FGM) is essential for obtaining a desired material. A suitable simulation of parameters and an appropriate model that describes the motion of particles in the fluid can predict various aspects those are needed to produce FGM, by gravity sedimentation or centrifugation technique. Simulation was conducted to observe the changes in concentration profile, while using the following equations applicable to polymerizing fluid, and to determine the terminal velocities (V_m) of particles; V_m = {D²(ρ_s ? ρ_l)g*(1 ? ?_s)^4.65}/(18μ₀e) for gravity sedimentation and V_m = {D²(ρ_s ? ρ_l)rω²(1 ? ?_s)^4.65}/(18μ₀ e) for centrifugation, where D is the diameter of the spherical particle, ρ_s the density of solid particles, ρ_l the density of fluid, μ the viscosity of fluid, g* the acceleration due to gravity, ?_s is the volume fraction of particles, and t_c is the elapsed time of curing of thermosetting resin. b is a constant, r is the radius, and ω is the angular velocity. This simulation demonstrates that the time of centrifugation/sedimentation, particle size, distribution of particle size, and centrifugal/gravitational forces can be effectively utilized to attain a desired concentration profile in graded materials. Simulation also revealed that there exist the possibility of two graded profiles, namely low concentration profile and high concentration profile, in one sample of graded material, made either by centrifugation or sedimentation. Low concentration profile is more sensitive to particle size distribution as compared to high concentration profile. The present simulation method is also sensitive to concentration‐measuring methods. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Electrochemical processing of porosity gradients for the production of functionally graded materials

The present paper lays the theoretical foundations of a new production process for functionally graded materials (FGMs). The process is based on the evolution of porosity gradients in porous electrodes which undergo electrochemical dissolution or deposition. The electrodes with graded porosity serve as preforms for the production of graded composites by infiltration processing. A one-dimensional macroscopic model of the porous electrode has been used for the prediction of the porosity gradients. A numerical approach allows utilization of experimentally determined current–potential curves for nonporous electrodes, with the incorporation of changes of the pore structure during the course of the electrode reaction, to predict the porosity gradients. For porous copper cathodes and anodes the results of this model are compared with experimentally observed polarization behavior and porosity distributions for different current densities and electrolyte conductivities.     

Processing and mechanical behavior of carbon black graded rubber compounds

Functionally graded rubber compounds (FGRCs) were prepared by construction based method. The matrix used was natural rubber (NR). Amorphous carbon black (N‐330) was used as grading material. The gradation of nanoparticles in a rectangular geometry comprised the variation of particle volume fraction along thickness direction. Its performance was evaluated for structural application through various mechanical and surface properties like tensile strength, modulus, tear strength, elongation at break, hardness, fracture surface by scanning electron microscopy, etc. At the same percentage of nanofiller loading, FGRCs show enhanced properties, i.e., modulus and tear strength (in some grades) compared to uniformly dispersed rubber compounds (UDRCs). Modulus of FGRCs, for a given particular stacking sequence of the layers, increases as much as by 275% compared to UDRCs. The ultimate properties like tensile strength and elongation at break made up for the modulus enhancement that decreases to as minimum as 50 and 80%, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Study on mixed‐mode fracture characterization in functionally graded materials

The fracture characterizations on mixed‐mode crack of functionally graded materials (FGMs) are investigated using digital speckle correlation method (DSCM). The stress intensity factors at mixed‐mode crack tip are obtained from digital speckle displacements fields. In combination with finite elements simulation results, the influences of gradient coefficients on fracture behavior of mixed‐mode cracks are analyzed. All the results show that the influence of gradient coefficients on fracture modes is not noticeable, and the stress intensity factor at the crack tip in graded materials are clearly influenced by the gradient coefficients, i.e., the stress intensity factors decrease with the increasing of gradient coefficients. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal residual stresses in adhesively bonded in-plane functionally graded clamped circular hollow plates

This study investigates the effects of in-plane compositional gradient exponent and direction on the thermal residual stress and deformations in adhesively bonded functionally graded clamped circular plates. The material composition was assumed to vary with a power law along an in-plane direction not through the plate thickness direction. The transient heat conduction and Navier equations in polar coordinates describing the two-dimensional thermo-elastic problem were discretized using finite-difference method, and the set of linear equations were solved using the pseudo-singular-value method. The material composition direction is designed as Ceramic-Metal (CM)–CM, CM–Metal-Ceramic (MC), MC–CM, and MC–MC for the inner and outer plates. The temperature decreased radially along the plates, but exhibited a sharp decrease across the adhesive layer. The compositional gradient exponent and direction affected evidently temperature levels and heat transfer period. The compressive radial and shear strains are more effective on the deformation in the adhesive layer and the plate regions near the plate–adhesive interfaces. The adhesive layer is subjected to considerable shear deformations. The equivalent strain and stresses are very low in a large region of the plates but exhibit sharp peaks on the plate regions near the plate–adhesive interfaces, and decrease towards the adhesive interfaces. These stress and strain peaks in the plates and adhesive layer are affected by the compositional gradient and direction. For an outer edge flux, the largest equivalent strain and stresses are observed in the CM–MC joint but the lowest levels occur in the MC–CM or secondly CM–CM joint. In addition, an inner edge flux results in the lowest and highest peak strains and stresses in the MC–CM and CM–MC joints, respectively. The MC–MC and CM–CM joints result in lower temperature, stress and strain levels around the adhesive layer and along the adhesive interfaces for outer and inner edge fluxes, respectively.     

碳纤维增强复合材料的应用现状

碳纤维复合材料以其优异的综合性能成为当今世界材料学科研究的重点。介绍了碳纤维的概念及其性能,简述了碳纤维复合材料作为结构型复合材料、结构功能型复合材料及功能型复合材料的一些具体应用。     

碳纤维产业现状及发展前景

碳纤维是一种力学性能优异的新材料,被誉为"黑色黄金",是指含碳量高于90%的无机高分子纤维。本文主要结合碳纤维的特性及用途,简述了碳纤维的国内外生产现状及我国发展碳纤维产业的措施及建议。     

Free vibration analysis of an adhesively bonded functionally graded double containment cantilever joint

In this study, Genetic Algorithms (GAs) combined with the proposed neural networks were implemented to the free vibration analysis of an adhesively bonded double containment cantilever joint with a functionally graded plate. The proposed neural networks were trained and tested based on a limited number of data including the natural frequencies and modal strain energies calculated using the finite element method. GA evaluates a value generated iteratively by an objective function and this value is calculated by the finite element method. The iteration process restricts us apparently to use directly the finite element method in our multi-objective optimisation problem in which the natural frequency is maximised and the corresponding modal strain energy is minimised. The proposed neural networks were used accurately to predict the natural frequencies and modal strain energies instead of calculating directly them by using the finite element method. Consequently, the computation time and efforts were reduced considerably. The adhesive joint was observed to tend vertical bending modes and torsional modes. Therefore, the multi-objective optimisation problem was limited to only the first mode which appeared as a bending mode. The effects of the geometrical dimensions and the material composition variation through the plate thickness were investigated. As the material composition of the horizontal plate becomes ceramic rich, both natural frequency and modal strain energy of the adhesive joint increased regularly. The plate length and plate thickness were more effective geometrical design parameters whereas the support length and thickness were less effective. However, the adhesive thickness had a small effect on the optimal design of the adhesive joint as far as the natural frequencies and modal strain energies are concerned. The distributions of optimal solutions were also presented for the adhesive joints with fundamental joint lengths and material compositions in reference to their natural frequencies and corresponding modal strain energies.