The effect of doubly tapered strut morphology on the plastic yield surface of cellular materials

Although the literature on the mechanics of cellular materials is vast, there is no theoretical model to account for the effects of axial yielding of struts aligned to the applied loading direction on the plastic yield surface under multiaxial loading conditions. An anisotropic hexagonal model having tapered strut morphology is developed to show these effects on the plastic yield surface under multiaxial tensile loading condition. This model covers several types of cellular structure such as two-dimensional (2D) hexagonal and square cellular materials, and three-dimensional (3D) hexagonal and rhombic cellular materials of rod-like columnar structure. A tetrahedral element with tapered strut morphology is also used for a foam model to illustrate these effects on the yield surface under axisymmetric loading condition. Plastic collapse due to bending moment in the inclined struts is a dominant mode. However, under multiaxial tensile loading, the collapse due to axial yielding of struts parallel to the loading direction is found to be an important mode. The shape of plastic yield surface was found to depend not only on relative density but also on the strut morphology.     

土工合成材料在防汛抢险中的应用

土工合成材料具有整体性强、抢险速度快、适应性强、储运方便、造价低、经久耐用和可废物利用的优点，在防汛抢险中主要起到排水、反滤和防渗的作用，常用于堤岸崩塌、基础管涌、堤身跌窝与漏洞、背水坡散浸、背水面脱坡、洪水浸顶和防风浪淘刷、涵闸及堵口等方面，可及时排队险情。     

PTC热敏电阻的现状与发展趋势(续一)

基于对1995年以来,国内外PTC热敏电阻的研究,介绍了PTC热敏电阻用原料(BaCO3、TiO2、BaTiO3、SrCO3、PbO、Pb3O4、SrTiO3、PbTiO3、Y2O3、Nb2O5、CaCO3、SiO2等);材料(BaTiO3系、V2O3系及高分子);生产技术(瓷粉制造、烧成、芯片制造、质量评定、理化分析、片式PTC生产);重点产品(消磁、马达启动、限流及加热等用)以及基础研究(相变应力模型、表面势垒模型)等方面的现状及今后的发展趋势。     

Deformation of Rodlike Elements of Composite Materials Subjected to Uniform Compression

On the basis of generalization of the results of investigation of the operation of rodlike elements of composite materials, we make a conclusion that the influence of various factors on the deformability of these elements is studied incompletely. The comparison of the stress-strain states for different models of concrete and reinforced-concrete elements makes it possible to describe the effect of longitudinal reinforcement (coefficient of reinforcement, strength and deformation characteristics) on the critical level of strains in the cross section. According to the results of our investigations, we give recommendations concerning the evaluation of the critical value of the coefficient of reinforcement above which one may observe the effect of reinforcement on the deformability of the analyzed sections. It is shown that the compression strength of the brittle base of the composite with inhomogeneous structure decreases as a result of the fracture processes. It is also demonstrated that the existing procedure used for the evaluation of the indicated decrease in strength requires significant improvement. The problem of evaluation of the ultimate value of the coefficient of reinforcement is also analyzed.     

粉末冶金法制备PSZ/Mo复合材料的研究

本文采用粉末冶金法制备了不同成分的PSZ/Mo复合材料。并对其密度、弹性模量和热膨胀系数进行了测量和分析 ,用XRD进行了物相分析。实验结果表明 :纳米氧化锆的烧结性能比金属钼好 ;弹性模量估算选用简单混合法则进行计算时应进行修正 ;钼和氧化锆在烧结时不发生化学反应。通过热压PSZ/Mo功能梯度材料的断口扫描分析发现 :虽然金属钼和纳米氧化锆具有一定增韧作用 ,但材料断裂方式仍以脆性断裂为主     

Single‐Source Precursors For Synthesizing Bifunctional Periodic Mesoporous Organosilicas

A new class of bifunctional periodic mesoporous organosilicas (PMOs) composed of organosilicate building blocks with two different silicon sites have been synthesized from the single‐source bifunctional organosilica precursors tris(triethoxysilylethyl)ethoxysilane and bis(triethoxysilylethyl)diethoxysilane, respectively denoted MT³‐PMO and DT²‐PMO. The synthesis of these PMOs is achieved by the co‐assembly of a triblock‐copolymer Pluronic P123 template with the bifunctional organosilica precursor under acid‐catalyzed and inorganic‐salt‐assisted conditions. After template removal through solvent extraction, the MT³‐PMO and DT²‐PMO so obtained show well‐ordered mesopores and display large pore diameters (6–7 nm) and pore volumes (0.6–0.8 cm³ g^–1) with a narrow pore‐size distribution and high surface areas (700–800 m³ g^–1).     

碳素材料超声检测的信号处理方法

针对碳素材料超声无损检测存在信噪比较低的问题,从自相关性出发分析了典型超声检测信号的组成成分,提出了在自相关分析的基础上的小波去噪思想,探讨了自相关分析和小波分析相结合的信号处理方法。利用此方法进行实际超声信号分析效果良好。     

Highly Efficient Orange and Green Solid‐State Light‐Emitting Electrochemical Cells Based on Cationic IrIII Complexes with Enhanced Steric Hindrance

Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂ sb]PF₆ in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W^–1) at 2.5 V, and 7.1 % and 26.2 lm W^–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.     

Effect of Synergistic Anticorrosion Treatments on Cycling Stability of Mg-Based Hydrogen Storage Electrode

In this paper, any two of the three anticorrosion agents, that is emulsifier (OP-10), soluble glass (Na2O·nSiO2) and glycerin (C3H8O3), were treated simultaneously on the surface of amorphous (a-) MgNi+5% Ml2Mg17 (Ml denotes the lanthanum-rich mish metal) electrode and the electrolyte. Effect of the synergistic anticorrosion treatment on charging/discharging cycle stability of the electrode was investigated. Contrasted with single treatment method, the cycling stability of the electrodes was further improved. The desirable synergistic anticorrosion method was that the electrode was treated by the soluble glass, and that OP-10 was added into the electrolyte. The cyclic voltammogram (CV) results of the electrode show clearly that the anticorrosion agent can change the electrochemical activity and mechanism of the electrode. The concentration of the anticorrosion agent in the electrolyte treated by the synergistic anticorrosion method was also investigated. The appropriate concentration of the anticorrosion agents in the electrolyte is 0.143%.     

Facile modifications of polyimide via chloromethylation: II. Synthesis and characterization of thermocurable transparent polyimide having methylene acrylate side groups

From chloromethylated polyimide, a useful starting material for modification of aromatic polyimides, a thermocurable transparent polyimide having acrylate side groups was prepared. In the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene, chloromethylated polyimide was esterified with acrylic acid to synthesize poly(imide methylene acrylate). The polymer was soluble in organic solvent, which makes it possible to prepare a planar film by spin coating. The polymer film became insoluble after thermal treatment at 230 °C for 30 min. Optical transparency of the film at 400 nm (for 1 µm thickness) was higher than 98 % and not affected by further heating at 230 °C for 250 min. Adhesion properties measured by the ASTM D3359‐B method ranged from 4B to 5B. Preliminary results of planarization testing showed a high degree of planarization (DOP) value (>0.53). These properties demonstrate that poly(imide methylene acrylate) could be utilized as a thermocurable transparent material in fabricating display devices such as TFT‐LCD. Copyright © 2004 Society of Chemical Industry