浅析广电数字双向网络改造中的EPON技术应用

以太无源先网络是一个专门应用于接入网的技术.采用点到多点的网络拓扑结构,在一芯光纤上利用上下行两个波传输数据,下行数据采用广播方式的时分复用方式,上行数据采用时分多址接入的方式,达到利用光纤实现数据、语音和视频多种业务接入的目的.     

Optical properties of carbon-containing titanium oxide nanocomposites obtained by the pulsed plasma chemical method

This paper presents the results of an experimental investigation on the optical properties of the TiO₂ and Ti_xC_yO_z nanopowders, produced by the pulsed plasma chemical method. Pulsed plasma chemical synthesis is realized on the laboratory stand, including a plasma chemical reactor (6 l) and TEA-500 electron accelerator. The parameters of the electron beam are as follows: 400–450 keV electron energy, 60 ns half-amplitude pulse duration, up to 200 J pulse energy, and 5 cm beam diameter. In TiO₂ sample, obtained using the pulsed plasma chemical method, the particles can be divided into two groups: 100–500 nm large spherical particles and tiny complex particles (sized less than 100 nm). For TixCyOz sample, the morphology of the particles is mainly presented with irregular fragment shape. The average size of the particles is ranged from 200 to 300 nm. The band gap for all synthesized samples is within 2.94–3.35 eV.     

Crystallographic analysis on small fatigue crack propagation behaviour of a nickel-based single crystal superalloy

In situ observations by scanning electron microscopy show that small fatigue cracks in a nickel-based single crystal superalloy are inclined to the loading direction and propagate in dominant crystallographic manners. In order to evaluate the driving forces for inclined crack propagation, three-dimensional anisotropic linear elastic finite-element analysis is conducted. The plastic zone size on the dominant slip plane has been calculated and proposed to correlate the fatigue crack growth. It is shown that this parameter takes into account both material anisotropy and octahedral fracture modes, and it can effectively characterize small crack propagation behaviour.     

Influence of residual thermal stresses on fatigue crack growth life of discontinuous reinforcements in metal matrix composites

The fatigue life prediction model based on crack propagation from micro-structural features is derived and presented for planar and randomly oriented Discontinuous Reinforced Metal Matrix Composites (DRMMCs). The model contains the influence of micro-structural properties such as aspect ratio, volume fraction of particle/fibre and constraint between particle and the matrix. The effect of residual thermal stresses generated within the matrix during development of composite is considered. The particle/fibre plays a dominant role in the development of the cyclic plastic zone size ahead of the crack tip; moreover, it enhances the cyclic plastic deformation characteristics of DRMMC. The theoretical model-based evaluations for low cycle fatigue in DRMMCs are within the proximity of the experimental results.     

Identification of local cyclic stress‐strain curves at material inhomogeneities on the basis of digital image correlation

Low‐cycle fatigue (LCF) tests on butt‐welded joints revealed that material inhomogeneities become decisive for the fatigue behavior at elastic‐plastic strain amplitudes and the geometrical notch is no longer the failure location – as observed in high‐cycle fatigue (HCF) regime. Digital image correlation techniques enable the measurement of local strains at the surface of the welded region. A new method is proposed that is able to calculate related local stresses and identifies local cyclic material properties in structures of inhomogeneous material and geometry. This method combines strain measurements and Finite Element simulations. It is a fast iteration procedure that is able to perform the identification within less than ten iterative steps at several hundred local points. Transient material behavior is easy to capture and an application at high temperatures is anticipated due to the method is based on materials mechanics.     

基于可持续理念的塑料包装可回收设计策略研究

目的通过设计的力量降低浪费、增进资源应用效率并减少环境污染,探索用可持续理念推动未来塑料包装设计的创新,实现循环经济和可回收的包装设计解决方案。方法从可回收包装设计的基本理念和内涵出发,概括可回收包装设计的基本原则,再结合塑料包装的材料特性、个人案例及优秀塑料包装设计案例,探讨并构建塑料包装可回收设计策略。结论从可回收包装设计的角度出发,探讨塑料包装可持续设计策略,最大限度降低封口与标签等包装精简化设计、消费者可及性设计、激发设计创新、考虑生物降物的材料、消费后回收利用。构建了塑料包装可回收设计策略;有助于包装的设计开发、产品制造商和消费者创造价值,为产业价值链上的每个参与者提供了一个新维度,最终有助于社会可持续理念的普及和实现。     

等通道转角挤压制备超细晶材料的研究与发展

等通道转角挤压(Equal channel angular pressing,ECAP)是大塑性变形制备超细晶材料的方法之一,具有大晶粒尺寸的材料可以在室温下挤压达到超细晶尺度。从ECAP模具参数、工艺条件影响因素、模具及制备方法改进、细化机理、制备的超细晶材料组织稳定性及性能方面进行总结,并结合部分研究结果可知,ECAP模具正在不断被优化和改进,复合挤压技术不断出现,目前已实现超细晶材料的连续ECAP挤压制备技术。等通道转角挤压的晶粒细化主要是由于剪切力的作用和第二相粒子的作用,ECAP晶粒细化机理及组合工艺的研究是目前研究的热点。超细晶材料在不同领域的应用对其性能提出的更高要求,对其大塑性变形制备技术本身也是挑战。     

大塑性变形工艺制备纳米晶过饱和固溶体的研究进展

合金在大塑性变形过程中能够形成纳米晶过饱和固溶体,呈现出不同于传统粗晶材料的微观结构和独特性能。近年来,纳米晶过饱和固溶体的形成机制及其热稳定性已成为国内外的一个研究热点。综述了大塑性变形工艺(如机械合金化法、高压扭转法等)制备纳米晶过饱和固溶体的研究概况,着重讨论分析了大塑性变形诱导纳米晶形成和固溶度扩展的几种机制及其局限性,简要介绍了纳米晶过饱和固溶体的热稳定性及其影响因素,最后对该领域今后的研究方向做出了分析和展望。     

铝合金厚板搅拌摩擦焊焊缝局部金属的塑性流动特征

以0.02mm厚铜箔为标示材料,采用带三角平面圆锥形搅拌针对20mm厚7075-T6铝板进行焊接。通过测试沿焊缝厚度方向上温度场分布及观察标示材料分布状态,分析焊缝局部金属塑性流动行为特征。结果表明,沿焊缝厚度方向上自上而下的金属温度逐渐降低;焊缝上、下表面温度差约为90℃;同一厚度上相对称的两点,位于前进边金属的温度高于返回边约15℃。位于焊核区上部的铜箔呈细小颗粒状均匀分布;下部铜箔则呈层片状分布,且向前进边偏移。焊核区由多个呈纹路状、有序排列的洋葱环结构相互层叠而成,这与焊缝塑化金属沿轴向迁移方式发生变化有关。