航空有机玻璃环境—应力开裂的研究：2.取向的影响

本文对比了定向和非定向三号航空有机玻璃在乙醇作用下的应力－溶剂银纹临界应力σｃ，银纹形貌及吸水和紫外光辐照对这两种材料的影响，并就取向对航空有机玻璃抗环境－应力开裂能力的影响及机理进行了分析。     

航空有机玻璃的疲劳性能

通过对航空有机玻璃进行拉伸疲劳试验得到了不同应力水平下的拉伸疲劳S-N曲线以及条件疲劳强度,研究了应力比对有机玻璃拉伸疲劳性能的影响。结果表明:该有机玻璃在应力比为0.4,0.1,-0.1条件下的疲劳强度分别为63.0,57.3,48.4MPa,其对应的拉伸疲劳S-N曲线随着应力比的增加整体上移;在相同应力水平下,应力比越大,该有机玻璃的拉伸疲劳寿命越长。     

航空有机玻璃环境-应力开裂的研究3.介质对有机玻璃缓慢拉伸行为的影响

本文对三号航空有机玻璃在不同介质气氛中的缓慢拉伸行为进行了研究，并对断口的形貌进行细致的观察。结果表明介质气氛对有机玻璃缓慢拉伸行为的影响是与其溶度参数有关。在空气及水气氛中，银纹出现在较高的应力水平下，来不及稳定扩展便引起断裂。在甲醇和乙醇气氛中，银纹在较低的应力水平下形成，然后转变为裂纹并稳定扩展引起断裂，使强度和断裂延伸率和断裂能大大降低     

航空有机玻璃环境——应力开裂的研究：1.环境因素对应力——溶剂银…

用多种有机溶剂测定了三号航空有机玻璃（简称ＹＢ－３，化学成分主要是ＰＭＭＡ的应力－溶剂银纹临界应力ａ。发现ａ基本上随溶剂与ＰＭＭＡ溶度参数之差的增加而增加。同时也研究了吸水，紫外光辐照等单一因素的作用以及吸水／紫外光辐照／应力－溶剂银纹的作用。认为水主要起增塑作用，紫外光主要引起分子主链断裂，两者都导致ａ下降；而多因素的循环作用对ＹＢ－３的破坏作用远远大于任何单一因素的作用。后者是特别值得引起注意     

温度与加载应力对双轴取向聚甲基丙烯酸甲酯蠕变行为的影响

考察了不同试验温度下YB-DM-11航空有机玻璃的拉伸性能,基于拉伸性能研究结果,在加载应力不超过对应温度下有机玻璃屈服强度的情况下,研究了蠕变温度和加载应力对有机玻璃蠕变行为的影响。结果表明,温度从25℃升至115℃,有机玻璃的屈服强度从85.69 MPa下降到9.89 MPa,降幅达88%。有机玻璃蠕变行为是温度、应力耦合作用的结果,升高温度或增加加载应力均能较大地提高有机玻璃的蠕变速率;通过降低蠕变温度或减小加载应力能有效地将有机玻璃蠕变过程控制在前2个阶段。采用广义蠕变方程和有效时间理论的蠕变模型对YB-DM-11航空有机玻璃前2个阶段的蠕变曲线进行拟合,所得拟合曲线与实验结果具有较高的重合度。     

航空有机玻璃环境—应力开裂的研究──1．环境因素对应力—溶剂银纹临界应力的影响

用多种有机溶剂测定了三号航空有机玻璃（简称ＹＢ－３，化学成分主要是ＰＭＭＡ的应力—溶剂银纹临界应力σ_ｃ。发现σ_ｃ基本上随溶剂与ＰＭＭＡ溶度参数之差的增加而增加。同时也研究了吸水，紫外光辐照等单一因素的作用以及吸水／紫外光辐照／应力—溶剂银纹的循环作用。认为水主要起增塑作用，紫外光主要引起分子主链断裂，两者都导致σ_ｃ下降；而多因素的循环作用对ＹＢ－３的破坏作用远远大于任何单一因素的作用。后者是特别值得引起注意的。     

航空有机玻璃失效与寿命预估可视化

在航空有机玻璃构件的力学行为和失效分析的基础上建立了表明应力状态及由此导致的应力银纹，疲劳，蠕变等失效过程的计算机视觉化仿真模型，以Ｗｉｎｄｏｗｓ环境下ＭＡＴＬＡＢ和ＶＣ语言为平台，开发了用于构件应力水平评价和使用状况与寿命预估的计算机可视化系统，为构件工作状况评价的自动化提供辅助工具，以利于此类构件工作状况和使用寿命预估的自动化。     

YB-DM-10航空定向有机玻璃疲劳裂纹扩展性能

通过研究定向有机玻璃(YB-DM-10)疲劳裂纹扩展性能,得到该种定向有机玻璃疲劳断裂阈值。发现其疲劳裂纹扩展速率曲线遵循Pairs公式以及Walker公式。研究平面内不同角度、不同频率和应力比对疲劳裂纹扩展的影响;通过对比Paris公式以及Walker公式的回归系数以及断裂表面不同阶段的扫描图像,分析不同参数对疲劳裂纹扩展的影响。结果表明:材料板材平面内,不同切割角度的试样疲劳裂纹扩展速率基本相同;加载频率对疲劳裂纹扩展速率影响不大,但在da/d N-ΔK曲线的第三阶段,数据有分离的趋势;相同的ΔK情况下,应力比增大,疲劳裂纹扩展速率增加。本工作结果为该种定向有机玻璃的应用以及航空座舱透明件损伤容限性能研究奠定了基础。     

航空MDYB-3定向有机玻璃蠕变行为温度效应试验研究

对航空MDYB-3定向有机玻璃不同温度下的蠕变行为进行了试验研究.得到了有机玻璃在20,50℃和75℃和不同应力下的蠕变曲线,结果表明:有机玻璃蠕变分为三个阶段,随着温度和应力的增大,有机玻璃的蠕变速率加快,蠕变断裂伸长增大,抗蠕变断裂时间变短.运用陈化理论,Norton公式和指数公式分别描述了蠕变三个阶段的特性.     

YB-3和YB-4航空有机玻璃疲劳裂纹扩展特性的研究

研究了交变载荷的应力比、频率、材料所吸收水份和湿热老化作用,以及水环境对YB-3和YB-4航空有机玻璃耐疲劳裂纹扩展性能的影响。发现水份,尤其是水环境对两种玻璃耐裂纹性能有良好作用,从而具有重要意义。根据断面显微观察提出了交变载荷作用下有机玻璃裂纹亚临界扩展的微观机理模型。     

Anisotropic organic glasses

While the last decades have seen considerable efforts to control molecular packing in organic crystals, the idea of controlling packing in organic glasses is relatively unexplored. Glasses have many advantageous properties that crystals lack, such as macroscopic homogeneity and compositional flexibility, but packing in organic glasses is generally considered to be isotropic and highly disordered. Here we review and compare four areas of recent research activity showing control over anisotropic packing in organic glasses: (1) anisotropic glasses of low molecular weight organic semiconductors prepared by physical vapor deposition, (2) the use of mesogens to produce anisotropic glasses by cooling equilibrium liquid crystal phases, (3) the preparation of highly anisotropic glassy solids by vapor-depositing low molecular weight mesogens, and (4) anisotropic films of polymeric semiconductors prepared by spin-coating or solution casting. We delineate the connections between these areas with the hope of cross-fertilizing progress in the development of anisotropic glassy materials.     

Al_2O_3对稀土配合物掺杂有机改性凝胶玻璃结构及荧光性能的影响

以γ-缩水甘油氧基三甲氧基硅烷作为有机改性先驱体,采用原位合成技术,用溶胶-凝胶法制备稀土离子(Eu3+或Tb3+)、配位体β-二酮噻吩甲酰三氟丙酮或苯甲酸及协同体1,10-菲啰啉共掺的两种有机改性二氧化硅玻璃,测量它们的发射光谱和红外光谱,并进行X射线衍射分析和扫描电镜观察,探讨Al2O3的掺量对凝胶玻璃结构及性能的影响。结果表明:Al3+对稀土离子发射峰的位置没有明显的影响,并使凝胶在室温时的荧光减弱,但它能使稀土离子及原位合成的配合物在较高温度保持相对稳定,提高凝胶玻璃的热稳定性和荧光强度;在制备较实用的具有较强荧光的含稀土离子的凝胶玻璃时,要根据实际需要选取适宜掺量的Al2O3。     

Anisotropic glass-ceramics produced by extrusion through opposed dies

Oriented glass-ceramics have been produced in two morphologically different systems by extruding the green glasses through opposed dies at temperatures near their respective crystallization temperatures. The principal crystalline phase is a mica for one system and an asbestos for the other and, by using the crystals as markers, it has been possible to explore the pattern of flow and its effect on crystal orientation at various stages of the extrusion process. It is demonstrated that crystal alignment occurs during extensional flow between the dies and is modified by plug flow through the dies. Oriented glass-ceramics are expected to exhibit marked anisotropy in properties and, as far as mechanical properties are concerned, this has been confirmed by measurements of tensional modulus, fracture stress and indentation strength. The oriented crystals remain aligned during subsequent drawing down to fibres and by suitable heat-treatment can be complemented by a population of randomly oriented crystals.     

FTIR spectral characterization of thin film coatings of oleic acid on glasses: I. Coatings on glasses from ethyl alcohol

Oleic acid was coated on soda lime–silicate, soda-silicate, and silica glasses from ethyl alcohol. The coating properties of oleic acid were related to the structure, composition, and dissolution properties of the glasses. The bonding mechanism between the organic coating and the glass surface for each different composition of the glass was revealed by analysis of the diffuse reflectance infrared Fourier transform (DRIFT) spectra. The metal ions on the soda lime–silicate glass surface produced metal-(Na-, Ca-, and Al-) oleates through the formation of metal–carboxylate complexes. Two different structural types were present for calcium-oleate. Some of the oleic acid coated undissociatively on the glass surface through hydrogen bonding. Oleic acid reacted with the surface of the soda-silicate glass, which possessed less Na2O content than the soda lime–silicate glass did, completely dissociating, producing only sodium-oleate species because of the high diffusion and dissolution rates of Na+ ions. Oleic acid formed only hydrogen bonds with silanol groups on silica glass. The coated organic layer on soda lime–silicate glass possessed a more ordered and compact structure than either on silica glass or in pure oleic acid. The metal ions on the soda lime–silicate glass surface strongly coordinated to COO– ions from the oleic acid and made the alkyl chains of the oleates more rigid and oriented, consequently causing the coated layer to be more ordered and compact. This structural result caused the dimeric pairs of COOH groups of undissociatively adsorbed oleic acid molecules to be closer, possessing stronger hydrogen bonds than occurring on the silica glass surface. These results suggest that the composition of the glass is one of the most important factors for determining the coating mechanism involving oleic acid.     

Cover Picture: Liquid Crystalline Peptide Nanowires (Adv. Mater. 22/2007)

Liquid‐crystalline peptide nanowires consisting of aromatic dipeptides are easily prepared by a sonication in a volatile organic solvent, report Hyotcherl Ihee, Sang Ouk Kim, and co‐workers on p. 3924. The colloidal nematic liquid crystalline phase of the rigid nanowires allows for a macroscopically ordered morphology of the nanowires under an external electric field. The cover image presents a broad field view of nanowires oriented by an electric field between two electrodes.     

Facile method to align crystalline needles composed of organic semiconducting materials using a balance between centrifugal and capillary forces

Methods to align one-dimensional microstructures composed of organic materials have attracted much attention because of their potential applications to devices such as field-effect transistors. Although dip coating is one of the methods (using self-assembly) used for the purpose, its disadvantage is that a larger amount of the material dissolves in the solution than what actually gets deposited on substrate. In this study, we developed a novel method that requires a small amount of precursor solution. By placing a polydimethylsiloxane block on a glass substrate and rotating the substrate using a spin coater, a small amount of the precursor solution was confined in a narrow region along the foot of the block. When we used an organic semiconducting material, 9,10-dibromoanthracene, as a solute, aligned and roughly oriented crystalline needles were precipitated. The thicknesses and lengths of the crystalline needles were controlled by the composition of the solvent and the rotation speed.     

Morphology and optical characterization of organic semiconductor microwires based on tetracyanoquinodimethane

Liquid phase deposition starting from solutions of 7,7′,8,8′ Tetracyanoquinodimethane (TCNQ) is used to grow oriented aggregates consisting of submicron-sized width wires. Spectrophotometric analysis shows that the as-deposited films consist of neutral TCNQ and have polarization dependent optical properties. The TCNQ microstructures react when exposed to organic solvent vapours, forming charge-transfer complexes characterized by a gradual and partial reduction of the organic molecules from the neutral to the monovalent ionic state. The morphology of the solution deposited films before and after the vapour treatment is investigated by means of optical microscopy, and Scanning Electron Microscopy (SEM).     

Comparison of compressive deformation and fracture behaviors of Zr- and Ti-based metallic glasses with notches

Compressive tests on the Zr- and Ti-based metallic glasses with different notches were investigated to compare their shear fracture mechanism and plastic deformation abilities. It is found that the plasticity of the two metallic glasses can be improved by installing two semicircular symmetrical notches even for the Ti-based metallic glass which has nearly zero compressive plasticity. The enhanced plasticity may be ascribed to the easy initiation of shear bands (SBs) around the notches, and the consequent blocking effect of notches on the propagation of shear bands according to the large-scale stress gradient. Additionally, based on a theoretical model originated from the concept of critical steady shear displacement (CSSD), compared with the sizes of smooth regions on the fracture surface, the plasticity difference of the two different metallic glasses was analyzed quantitatively. The current findings might provide an approach to understand and estimate the difference in the plastic deformation abilities on diverse metallic glasses, as well as the ones with large-scale stress gradient.     

硅酸钙-海藻酸钙复合水凝胶膜的制备及表征

将海藻酸钠与硅酸钙共混,经过钙离子交联制备了硅酸钙-海藻酸钙(CaSiO_3-CaAlg)复合水凝胶平板膜,观测了其形貌。对CaSiO_3-CaAlg复合膜进行了FTIR、TG和XRD表征。研究了不同CaSiO_3含量的CaSiO_3-CaAlg复合水凝胶平板膜在湿态下的力学拉伸性能,并研究了其溶胀性能。结果表明,CaSiO_3与CaAlg具有较好的相容性,CaSiO_3的加入改善了CaAlg的热性能。随着CaSiO_3含量的增加,CaSiO_3-CaAlg复合水凝胶膜的极限应力先增加后减小。CaSiO_3-CaAlg复合水凝胶膜制备方法简单,没有用到任何有机溶剂,膜厚度可控且均匀,易批量生产,有望应用于组织工程材料以及医用敷料中。