三维多向编织复合材料有效弹性模量的细观计算力学分析

编织复合材料性能预报与材料优化设计研究是纺织复合材料研制开发的重要环节,本文在已建立的三维多向编程复合材料单胞几何模型的基础上,研究建立了含多相介质单元的有限元分析方法,结合实例预报了碳／环氧四向编织复合材料的有效性能并和实验结构进行了对比。     

铜和石墨对铁基含油自润滑复合材料机械及摩擦学性能的影响

采用粉末冶金工艺制备了铁基含油自润滑复合材料,考察了Cu与石墨的含量对铁基含油自润滑复合材料的机模样性能、摩擦学性能及组织结构的影响,并利用X射线衍射仪、扫描电子显微镜及光学显微镜等对材料的组分、显微组织形态和结构以及磨损表面形貌等进行了系统的观察和分析,结果表明：添加适量Cu的Fe-Cu二元系材料的机械性能和摩擦学性能明显优于Fe系材料,这主要是因为Cu的加入改变了材料的微观结构。添加适量石墨的Fe-Cu-石墨三元系材料比Fe-Cu二元系材料具有更优异的摩擦学性能,但机械性能有所下降,这主要是由于石墨与油的协同润滑效应和石墨的加入改变了材料的微观结构所致。     

刹车速度对C／C复合材料制动摩擦性能的影响

在MM－1000型摩擦磨损试验上考察了碳布叠层结构的C／C复合材料在不同速度下的制动摩擦磨损行为,并用扫描电子显微镜观察分析了试样磨损表面形貌,结果表明：随着刹车速度的增大,摩擦系数增大,在20－25m/s速度范围出现峰值;当刹车速度增大至28－30m/s时,摩擦系数仍保持较高,体现了优良的高能摩擦特性;磨损量在低速时较小,当刹车速度大于15m/s,磨损量迅速增大,低速时磨损表面由一层薄的磨屑层所覆盖,当速度大于15m／s,大量的磨屑形成一层较厚的磨屑层,高速时由于剧烈的氧化和剪切作用,很多基质碳被氧化剥落,炭纤维被磨断、拔出,使磨损增大。     

Preparation of Core‐Sheath Composite Nanofibers by Emulsion Electrospinning

Summary: Uniform core‐sheath nanofibers are prepared by electrospinning a water‐in‐oil emulsion in which the aqueous phase consists of a poly(ethylene oxide) (PEO) solution in water and the oily phase is a chloroform solution of an amphiphilic poly(ethylene glycol)‐poly(L ‐lactic acid) (PEG‐PLA) diblock copolymer. The obtained fibers are composed of a PEO core and a PEG‐PLA sheath with a sharp boundary in between. By adjusting the emulsion composition and the emulsification parameters, the overall fiber size and the relative diameters of the core and the sheath can be changed. A mechanism is proposed to explain the process of transformation from the emulsion to the core‐sheath fibers, i.e., the stretching and evaporation induced de‐emulsification. In principle, this process can be applied to other systems to prepare core‐sheath fibers in place of concentric electrospinning and it is especially suitable for fabricating composite nanofibers that contain water‐soluble drugs.

Schematic mechanism for the formation of core‐sheath composite fibers during emulsion electrospinning.     

A Composite Polymer Film with both Superhydrophobicity and Superoleophilicity

Summary: A composite film composed of porous polyurethane (PU) and polystyrene (PS) microspheres with both superhydrophobicity and superoleophilicity has been prepared. In this film, the dual‐scale structure enhances both the hydrophobicity and oleophilicity of the surface material. The composite film with such an ‘intelligent’ wettability property can be utilized to separate oil and water systems efficiently.

The composite film can be used to separate diesel oil and water.     

共混/填充高分子复合材料界面力学行为实验研究进展

本文首先介绍了高聚物复合材料界面微观结构的特点和界面破坏的微观形式, 在此基础上,详细回顾了粒子填充高分子复合材料和共混高分子合金两类材料的界面力学性能实验研究的进展,总结了研究粒子/基体界面力学性能的实验方法和用这些方法获得的实验结果。介绍的实验方法从宏观拉伸实验到细观在位拉伸实验, 从定性的断口形貌分析到定量的界面强度和粘结能计算, 从不同层次和角度阐述了研究界面性能各种方法的优缺点。最后, 作者根据综合分析的结果, 指出了实验研究界面力学性能遇到的主要困难来自实验仪器的局限性和实验方法的匮乏性。为了获得可靠的界面性能, 一方面应该设计出利于表征的界面, 另一方面需要在实验技术上有所创新。相信该文对于深入了解和研究共混/填充高分子复合材料的界面问题, 以及其它类型材料的界面问题具有一定的借鉴意义。      

压电压磁复合材料中一对平行裂纹对弹性波的散射

利用Schmidt方法对压电压磁复合材料中一对平行对称裂纹对反平面简谐波的散射问题进行了分析,借助富里叶变换得到了以裂纹面上的间断位移为未知变量的对偶积分方程．在求解对偶积分方程的过程中,裂纹面上的间断位移被展开成雅可比多项式的形式,最终获得了应力强度因子、电位移强度因子、磁通量强度因子三者之间的关系．结果表明,压电压磁复合材料中平行裂纹动态反平面断裂问题的应力奇异性与一般弹性材料中的动态反平面断裂问题的应力奇异性相同,同时讨论了裂纹间的屏蔽效应．     

Rheological Investigations in Understanding Shear‐Enhanced Crystallization of Isotactic Poly(propylene)/Multi‐Walled Carbon Nanotube Composites

A novel experimental technique to follow the crystallization processes of poly(propylene)/MWCNT composites that experience a steady shear deformation using dynamic melt rheometry is described. The effects of heterogeneous nucleation, temperature, and preshear on the crystallization behaviors were determined. A quantitative evaluation of crystallization kinetics difference between quiescent and preshear conditions could be achieved. By combining rheology with POM, we demonstrate that two different crystallization processes account for the shear‐enhanced crystallization at low and high temperatures, respectively.

     

The Twist-Bending Behavior of Forward Swept Wings: A Case Study of a Glass/Carbon Hybrid Composite Structure

The behavior of the wing of an aircraft is characterized by the complex interaction among dynamic (distribution of the masses), elastic (ownership of the materials) and aerodynamic (shapes, forces and moments) phenomena. As a rule it is expected from us that the aerodynamic actions damp the oscillations (natural or forced) of the wing. However, above given speeds a lot of undesired aero-elastic phenomena, among which the divergence of the wings, occur and became of considerable importance in view of safety. To potentially prevent dangerous situations, generally the speed of the aircraft is limited; a possible alternative is to endow the “system wing” of proper devices (passive or active, i.e. controls) in order to prevent that the energy transfer of aerodynamic actions amplifies its instability. The forward swept wings are extremely efficient in terms of aerodynamics performance (stall and supersonic behavior) and therefore of maneuverability of the aircraft, even if, unfortunately, they are extremely critic under the profile of the aero-elastic stability. The solution of the technical-scientific and technological problems associated with the use of innovative configurations of wings prefigures a meaningful breakthrough in the international aerospace sector. Within this work the authors aim to determine a particular configuration of composite material for the realization of a forward swept wing in such a way that, under the action of the effective aerodynamic loads, the wings structural response provides a coupled bending-torsion deformations with stability effects. It will be shown that by using a recursive analysis of the composite lay-up one can tailor the overall bending/torsion deformation ratio value.     

Flexural Properties of Glass Fibre Reinforced Composite with Partially Biodegradable Polymer Matrix

Summary: The aim of this study was to evaluate flexural properties of a partially biodegradable glass fibre reinforced composite after water immersion and dehydration. In addition water sorption and solubility was determined. E-glass fibres were preimpregnated with a biodegradable biopolymer of poly(hydroxyproline) amide (PA). The preimpregnated fibres were then further-impregnated with Bis-GMA–TEGDMA-resin and light polymerized (n = 6). There was also specimen made of plain polymer and FRC without PA. After water immersion and/or dehydration, the specimens were tested by the three-point bending test. The flexural strength and Young's modulus was increased in most cases after water immersion and dehydration except for PA containing specimens. The water sorption was <50 µg/mm³ for all studied specimens and solubility was 20 µg/mm³ for specimens without PA and 35 µg/mm³ for specimens with PA.