镀银织物双层叠放模式与电磁屏蔽效能增量研究

电磁辐射是四大环境污染之一,通过不同电磁屏蔽体的叠加组合能够有效提高屏蔽效能。研究了镀银织物以紧密叠放、夹空气层和夹角叠放3种模式构造,采用小窗法屏蔽效能测试系统实测了0～18 GHz宽频段内双层织物的电磁屏蔽效能的增量问题。结果表明：镀银织物双层紧密叠加有利于电磁屏蔽效能提升,其屏蔽效能可达70 dB,明显高于单层织物,紧密叠放更有利于双层织物的屏蔽效能;夹空气层双层织物在0～6.5 GHz频段的屏蔽效能有所提高,而在其他频段其屏蔽效能呈下降趋势,尤其不利于高频电磁波的屏蔽;夹角叠放双层织物屏蔽效能均达到60 dB以上,大夹角叠放(90°)时使双层织物的屏蔽效能降低。建立了双层织物电磁屏蔽效能的增量模型,为电磁屏蔽效能分析提供了一个新的视角,通过结构优化方式探索屏蔽体构造的最佳配置,对电磁屏蔽体的设计、生产及使用具有一定的参考价值。     

含不锈钢纤维机织物电磁屏蔽机理及其效能的仿真研究

依照电磁屏蔽理论,介绍了金属织物电磁屏蔽的机理。在此基础上,利用多物理场耦合分析软件COMSOL Multiphysics,建立三维仿真模型,分析了不同电磁波极化方向、不同半径和不同嵌织间距的奥氏体304不锈钢长丝,在不同辐射频率下对织物屏蔽效能的影响。仿真结果表明,极化方向、半径大小、嵌织间距和频率,对屏蔽织物都有显著的影响,这对不锈钢长丝防电磁辐射织物的开发和设计提供理论依据。     

不锈钢纤维织物电磁屏蔽效能的研究现状

不锈钢纤维织物具有电磁屏蔽效能良好及防辐射效果持久、透气性好、穿着舒适、加工方便等特点,是当今世界上应用最广泛的高效屏蔽织物.简要描述了不锈钢纤维混纺纱线、不锈钢纤维织物的制备方法及其产品开发现状,重点阐述了不锈钢纤维特性、纱线结构、织物结构及电磁波频率等因素对不锈钢纤维织物电磁屏蔽效能的影响规律.此外,还指出对电磁波屏蔽机理的探索和产品的开发是该材料领域今后的研究重点.     

聚苯胺性状及其含量对镍粉/聚苯胺涂层屏蔽性能的影响

系统分析了金属粉末/聚苯胺复合电磁屏蔽材料中导电聚苯胺的性状,体积分数对微观结构和电磁屏蔽效能的影响.从二次掺杂的导电聚苯胺的电磁性能讨论了聚苯胺对电磁屏蔽效能的贡献.研究了二次掺杂聚苯胺性状对电磁屏蔽涂层微观结构形貌以及与金属粉末的复合效应对电磁屏蔽效能的贡献.研究的结果表明导电聚苯胺的加入有利于增加电磁屏蔽材料对于高频电磁波的电磁屏蔽效能,但是对低频部分的电磁波的屏蔽效能与纯金属粉末电磁屏蔽材料相比有所降低,这可能是由于聚苯胺加入导致的导电组分分布不均匀所引起的.实验结果表明胶状体聚苯胺和粉末状聚苯胺在电磁屏蔽涂料基体树脂中具有完全不同的形态,分析了对电磁屏蔽效能的影响.     

掺石墨/碳纤维电磁屏蔽砂浆的研究

以石墨和碳纤维为电磁屏蔽功能基元材料,将其添加到砂浆中,部分取代砂浆中的砂,调节电磁屏蔽功能材料的含量,使砂浆对电磁波具有屏蔽和吸收功能。研究了电磁屏蔽功能基元材料含量对砂浆电磁屏蔽效能的影响。结果表明添加石墨和碳纤维电磁屏蔽功能基元材料的电磁屏蔽砂浆,在30～200MHz频率范围内,电磁屏蔽效能SE较大,随着频率增加,屏蔽效能SE迅速降低。在200MHz～1.8GHz频率范围内,电磁屏蔽效能SE值趋于平缓,屏蔽效能较低。在1.8GHz附近,碳纤维电磁屏蔽砂浆的SEmin最大,为10dB。     

掺石墨和羰基铁涂料的低频电磁屏蔽性能研究

以石墨和羰基铁作为电磁屏蔽涂料的功能材料,替代一部分涂料填料,并调节各功能材料的含量,使涂料具有对电磁波的屏蔽和吸收功能.通过对不同样品的电磁屏蔽传输系数曲线和最大电磁屏蔽效能的对比,分析了石墨和羰基铁的含量对涂料低频电磁屏蔽效能的影响.并通过涂层表面微观形貌的分析,进一步探讨了涂层表面结构对电磁屏蔽性能的影响机理,为设计高性能低频电磁屏蔽涂料提供参考依据.在1MHz～1.8GHz低频区域,涂料最大电磁屏蔽效能达到了6.029dB.     

Al颗粒夹层CFRP复合材料力学及电磁屏蔽性能EI北大核心

CFRP复合材料具有优异的力学性能,在航空航天装备中有广泛应用,但是因其单层铺层内部的结构各向异性,单向纤维铺层对于垂直极化波的电磁屏蔽效能较弱。为应对日益复杂的电磁环境,保护电子元器件不受干扰,增强复合材料的电磁屏蔽效能显得尤为重要,本工作利用非连续Al颗粒在层间面内紧密排列,构建了一种层间面内含连续Al屏蔽层的CFRP复合材料,并研究了不同Al颗粒含量对复合材料电磁屏蔽效能和力学性能的影响规律。结果表明,随着Al颗粒含量的增加,CFRP复合材料的导电性和电磁屏蔽效能也随之增加,当聚合物中Al颗粒质量分数达到33.3%时,复合材料的面内电导率提高了3个数量级,在垂直于纤维方向上对频率为3~17 GHz的电磁波的电磁屏蔽效能提高了10 dB以上。随着Al颗粒含量的增加,复合材料层间剪切强度与弯曲强度出现先上升后下降的变化规律,当树脂中Al质量分数为33.3%时,复合材料的层间剪切性能提高了5.2%达到80.5 MPa,当树脂中Al质量分数为50%时,复合材料的弯曲强度提高了20%至1441.0 MPa,弯曲模量提高了10.2%达到101.83 GPa。由此可见,Al颗粒夹层CFRP复合材料可以实现力学性能和电磁屏蔽效能的同步提升,是一种具有广泛应用前景的结构-电磁屏蔽一体化复合材料。     

多层金属纤维混纺织物的电磁屏蔽效能

金属纤维混纺织物由于具有较好的电磁屏蔽性能得到了广泛应用,但其屏蔽效能受纺织工艺等诸多因素影响,难以建立精确的计算模型。在分析介质平板屏蔽体屏蔽效能的基础上提出等效算法,将金属纤维混纺织物等效为均匀介质平板,以计算多层织物材料的电磁屏蔽效能。通过测试单、双层金属纤维混纺织物的电磁屏蔽效能,验证了等效方法的正确性和可行性,可用于指导复合材料的设计。     

新型功能材料

陕西纺科所设计成功电磁波屏蔽织物由陕西省纺织科学研究所开发的“金属纤维混纺纱及电磁屏蔽织物”项目,近日通过了陕西省技术成果鉴定。项目选用了直径为6微米至8微米的金属纤维、涤纶纤维和棉纤维,开发了金属纤维含量为10％至15％的18.2tex、16.4tex、14.5tex。混纺纱及其系列屏蔽织物、染色织物,产品性能均达到精梳涤棉国标一等品、优等品物理指标要求。据悉,新产品在设计上进行了优化创新,采用等支持面织物结构设计,使织物屏蔽效能各向同性、均匀稳定,在频率150kHz至6GHz范围内电磁能衰减量达到32dB至38dB。通过生物效能实验证明,该电磁波屏蔽织物具有防电磁波辐射保健作用。中国工程院院士邱爱慈研究员认为,该项目达到国内同类产品领先水平。     

不同金属填料对电磁屏蔽涂料屏蔽效能的影响

复合电磁屏蔽材料是一类用于防护电磁波干扰的新型功能材料,作为屏蔽组分主体的金属填料的电磁特性及其在涂料中的分布状态对于材料的屏蔽效能具有显著的影响,同时由于复合材料的结构特点使这类复合电磁屏蔽材料的屏蔽效能与传统金属板材的屏蔽效能计算理论有着较大的差异.在实验研究的基础上讨论了几种典型的金属粉末填料构成的复合电磁屏蔽材料的屏蔽效能的特点,并分析了其与传统屏蔽效能计算理论的差异和形成的原因,为设计高效复合电磁屏蔽材料提供必要的参考.     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...