有机/LRH复合体的合成及荧光性质研究

通过均匀沉淀法制备了硝酸根型层状铕氢氧化物（NO3--LEuH）,采用离子交换法将层间阴离子NO3-交换为苯丙氨酸（PHE）,得到了PHE/LRH复合体,并研究了其荧光性质.前躯体和复合体均有Eu3＋的5 D0-7FJ跃迁发射峰,在室温下发射出Eu3＋的特征红光,发射光谱峰位基本一致,但与NO3--LEuH相比,PHE/LRH复合体的发射峰强度大大减弱,表明将PHE引入LEuH层间对Eu3＋的荧光有猝灭作用.     

C/C-SiC复合材料的制备及其湿式摩擦磨损性能研究

采用T700炭纤维针刺毡,经超声振动渗硅、化学气相沉积(CVD)、硅化处理及液相浸渍/炭化新工艺制备SiC呈"岛状"分布的C/C-SiC复合材料,利用偏光显微镜和扫描电子显微镜观察其微观组织结构并分析其形成机制,在MM-1000型湿式摩擦磨损试验机上研究C/C-SiC复合材料的摩擦磨损性能.结果表明:在初始转速恒定的条件下,动摩擦系数随制动比压的增加而逐渐减小;当制动比压恒定时,摩擦系数随初始转速的增加呈现出先增大而后降低的趋势;在本文试验条件下,摩擦系数稳定在0.088～0.126之间;在300次磨损试验后,其磨损量检测值为0.     

Propagation of longitudinal elastic waves in composites with a random set of spherical inclusions (effective field approach)

The work is devoted to the problem of plane monochromatic longitudinal wave propagation through a homogeneous elastic medium with a random set of spherical inclusions. The effective field method and quasicrystalline approximation are used for the calculation of the phase velocity and attenuation factor of the mean (coherent) wave field in the composite. The hypotheses of the method reduce the diffraction problem for many inclusions to a diffraction problem for one inclusion and, finally, allow for the derivation of the dispersion equation for the wave vector of the mean wave field in the composite. This dispersion equation serves for all frequencies of the incident field, properties and volume concentrations of inclusions. The long and short wave asymptotics of the solution of the dispersion equation are found in closed analytical forms. Numerical solutions of this equation are constructed in a wide region of frequencies of the incident field that covers long, middle, and short wave regions of propagating waves. The phase velocities and attenuation factors of the mean wave field are calculated for various elastic properties, density, and volume concentrations of the inclusions. Comparisons of the predictions of the method with some experimental data are presented; possible errors of the method are indicated and discussed.     

A PREDICTIVE APPROACH TO THE IN-PLANE MECHANICAL PROPERTIES OF STITCHED COMPOSITE LAMINATES

This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching,and to predict the in-plane effective tensile strength of the stitched composite laminates.The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties.A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching.The undistorted region,the fiber distortion region,the resin-rich pocket and the through-thickness reinforcement section are taken into account.The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters,the distortion width and maximum misalignment.It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors,the stitch hole and inhomogeneous fiber content.The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite.The model is used to predict the tensile strength of the [0/45/0/-45/90/45/0/-45]_(2s) T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations,showing an acceptable agreement with experimental data.     

纤维复合材料透射式光弹性方法中的偏振光学问题

本文总结了用显微激光分析仪对一般纤维增强复合材料进行透射式光弹性研究的近期工作。针对纤维复合材料违反传统光弹理论的偏振光学行为,讨论了纤维、基体的双折射率不同以及由纤维与基体的界面两侧出射的光在Airy斑重叠区发生干涉等问题,从更一般的角度探讨了最近的文章中所提出的新光弹公式中所含两个滞后量的存在性。      

厚热塑性复合材料AS4/PEEK角铺设层合板的层间应力分析

将表征热塑性复合材料AS4 /PEEK非线性行为和应变速率相关行为的三维弹塑性模型通过程序加以实现。将程序计算结果和文献实验结果相比较可以发现,二者吻合较好,验证了所生成程序的有效性。计算了厚的AS4 /PEEK角铺设层合板[±25]s4在不同界面上的层间应力。由层间应力的三维分布图,分析了不同界面上层间应力的分布特征,并说明了可能引起层间分层的主要因素。     

On the problem of interfacial damage in fibre-reinforced composites under variable loads

In this paper, the theoretical background for the failure analysis of fibre-reinforced composites under variable repeated loads in the framework of direct methods is presented. It is based on a local shakedown analysis in a representative volume element of the composite and the use of averaging techniques to study the influence of each component (matrix, fibre and interface) on the macroscopic response of such composite.     

EVOLUTION OF THE MICROCRACKS IN WHISKER TOUGHENING CERAMIC MATRIX COMPOSITES

The modified equivalent inclusion theory by the authors and the internalvariable theory are employed to investigate the evolution of the microcracks in whiskertoughening ceramics and the influence of the microcracks on the mechanical propertiesof the material. The effect of residual thermostrain, whisker content and aspect ratio isconsidered. The modulus, initial nonlinear load, strength and nonlinear constitutiverelation are calculated and some important conclusions are given.     

Infiltration of Liquid Metals in Porous Compacts: Modeling of Permeabilities During Reactive Melt Infiltration

Reactive infiltration is a fast and cost-effective technique for manufacturing ceramic-matrix composites (CMCs). CMCs are used in elevated temperature applications like rocket engine casings, jet nozzles, gas turbine blades and nuclear cladding. There is an urgent need for minimizing experimental costs as well as optimizing process parameters during manufacture, so that we have minimized manufacturing costs and reduced infiltration times. Towards this end, the objective of this research was to develop an integrated micro-macro model of reactive flow of molten silicon in a porous preform consisting of carbon-coated silicon carbide fibers and then optimize process parameters computationally. The overall objective of the research was to arrive at a modified equation of Darcy's law for flow through a porous medium with the help of numerical/computational modeling. This paper deals with the flow of silicon through porous carbon at the macro level. The macro flow of silicon was integrated with an available micro model by determining the transient porosity from the micro model and using it in Darcy's law written for the macro flow of silicon. From the results of this study, we recommend suitable process parameters such as initial temperature of the solid reactant and the specific kind of reactants to be used for achieving complete infiltration. These conclusions are drawn after observation of the rate of decrease of permeability with more reaction.     

纤维增强金属基复合材料整体蠕变性能的细观力学分析

高温下金属基复合材料的蠕变主要由基体蠕变和界面扩散蠕变两部分构成,以往的研究中常常只考虑其中一种蠕变机理,从而导致得到的规律具有较大的局限性．本文提出了一种可预测金属基复合材料整体蠕变性能的细观力学方法,同时考虑了基体蠕变和界面扩散蠕变两种蠕变机理,导出了具有张量形式并满足不可压缩性的界面扩散蠕变应变表达式．采用Mori-Tanaka法和自洽法二者结果的平均以便更准确地计算纤维中的应力,揭示了两种蠕变机理相互影响的竞争关系．研究了恒定双轴荷载下的总体蠕变和固定位移约束下的应力松弛这两种常见蠕变问题,探究了基体蠕变与界面扩散蠕变两种蠕变机理在总蠕变中发挥的作用,考察了不同加载条件和不同纤维体积分数对复合材料整体蠕变行为的影响．