Status of the JET control and data acquisition system CODAS

This paper presents the current status of the JET Control and Data Acquisition System (CODAS). This system is the result of the effort of the whole CODAS team.     

厦门国际会展中心大跨悬臂钢结构设计

介绍了厦门国际会展中心主楼大跨度、双向悬臂钢结构设计．通过设计方案比较,计算分析和模型试验,较好地解决了由于结构悬挑大、跨度大及体型复杂给结构设计带来的一些难题．     

慢反应聚脲材料的开发及喷涂工艺研究

通过选用反应活性低的原材料制备了一种慢反应聚脲材料,并考察了施工工艺对材料性能的影响,试验结果显示慢反应聚脲能够采用低压喷涂施工工艺,拓展了聚脲材料在小面积、低施工成本工程方面的应用。     

Synthesis of Si3N4/SiC reaction-bonded SiC refractories: The effects of Si/C molar ratio on microstructure and properties

Si₃N₄/SiC reaction-bonded SiC refractories have been fabricated on the basis of the microstructure design concept by introducing a binary-phases binding system. The influence of Si/C molar ratio on phase transformation, microstructure and mechanical properties was studied systematically. Thermodynamic analysis result proved the microstructure design was feasible under 0.03 MPa pressure of N₂ and the selected sintering temperature. In-situ grown SiC nano-whiskers/granule and lamellar Si₃N₄ were both observed in the matrix. The specimen with 2:1 Si/C molar ratio possessed highest cold modulus of rupture (28.27 MPa) but showed low toughness. The strength and toughness of such materials were controlled by two main factors, such as SiC grain boundary binding morphology and in situ grown of SiC in the matrix. The different mechanisms occurred predominantly to meet diverse practical cases and caused to various mechanical properties of final products. The corresponding strengthening and toughening mechanisms were explained in this paper.     

A dispersed polycrystalline phase boundary constructed in CaZrO3 modified KNN based ceramics with both excellent piezoelectric properties and thermal stability

In this paper, the ceramics with composition of (0.98-x)(K_0.5Na_0.5)(Nb_0.96Sb_0.04)O₃-0.02(Bi_0.5Na_0.5)(Zr_0.8Ti_0.2)O_3-xCaZrO₃ (abbreviated as (0.98-x)KNNS-0.02BNZT-xCZ, x = 0, 0.01, 0.015, 0.02, 0.025, 0.03) were prepared by a traditional solid-state reaction method. The effect of the additional amount of CaZrO₃ on the phase structure, microstructure, dispersion index, domain structure and piezoelectric properties of ceramics was systematically studied. Finally, the piezoelectric properties and thermal stability of ceramics could be controlled by adding different amounts of CaZrO₃. The addition of CaZrO₃ transferred the phase structure of the ceramics from orthogonal-tetragonal (O-T) coexistence phase to rhombohedral-orthogonal (R–O) coexistence phase, which could be demonstrated by XRD test, temperature-dependent Raman spectra and ε_r‐T plot analysis. And when x = 0.02, the ceramics possessed the best piezoelectric and dielectric properties (d₃₃ = 253 pC/N, ε_r = 1185, tanδ = 0.044). Such excellent electrical properties could be originated from the heterogeneous domain structure and small-size nano-domains of the ceramics. Moreover, with the increase of CaZrO₃ doping amount, the dispersion index of ceramics gradually increased from 1.404 to 1.871, which showed more obvious dispersion phase transition characteristics and improved the thermal stability of ceramics. Particularly, when x = 0.02, after annealing at a high temperature of 220 °C (close to its Curie temperature), the d₃₃ tested at room temperature remained above 85% of that without annealing. The results indicated that (0.98-x)KNNS-0.02BNZT-xCZ ceramic was a promising lead-free piezoelectric ceramic system.     

复杂交通环境激励下西安城墙模态参数识别与分析

结构的模态参数识别一直是结构健康监测的基础和重点,其能评估结构状态、识别结构损伤,对结构的后续维护具有重要意义,对古建筑结构亦是如此。西安城墙属于中国第一批重点文物保护单位,其模态参数识别更是需要重视。在西安城墙瓮城处城墙布设速度与加速度动力特性监测系统,通过现场动力测试试验,获取复杂交通环境激励下城墙振动响应数据;通过特征系统实现算法(ERA)、随机子空间法(SSI)和峰值法(PP)3种模态识别方法相结合,对响应数据进行结构模态参数识别,获取该区域城墙模态参数;结合城墙数值有限元模型,对比3种方法所得的模态参数,建立有效的结构动力模型。结果表明:3种方法均可以在环境激励下有效识别结构的模态频率并最终得出振型,验证了该3种模态识别方法对古城墙模态参数识别的可行性。     

氧化镁铁铝尖晶石耐火材料的制备

以铁铝尖晶石和镁砂为原料,采用烧结法制备了氧化镁铁铝尖晶石耐火材料.检测了各烧后试样的体积密度、显气孔率和常温耐压强度,利用应力应变法检测了烧后试样的弹性模量,利用X射线衍射(XRD)检测了烧后试样的物相组成,采用扫描电子显微镜(SEM)观察和分析了烧后试样的显微结构.研究结果表明: 1600 ℃时各试样体积密度最大,显气孔率最小,试样达到了烧结;镁砖中加入铁铝尖晶石会引起材料常温强度降低,铁铝尖晶石加入量在3%～4%为宜;铁铝尖晶石以颗粒形式加入的试样的弹性模量比以细粉形式加入的试样要大,所以铁铝尖晶石以颗粒形式加入的试样的抗热震性相对较好;热力学计算表明:当加热温度高于182 ℃时, MgO与FeAl_2O_4开始反应生成MgAl_2O_4;从显微结构照片也可以看出, MgO与FeAl_2O_4中的FeO发生互扩散,FeO扩散进镁砂颗粒中,MgO扩散进铁铝尖晶石内部,与Al_2O_3反应生成MgAl_2O_4,在镁砂颗粒周围形成MgAl_2O_4环,并伴有微裂纹产生.     

采用重稀土改善焊缝韧性的研究

用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X 射线能谱仪(EDAX)研究了重稀土元素对低合金钢焊缝金属韧性的影响.结果发现,采用适当的焊条药皮配方和焊接工艺可使重稀土元素微量过渡到焊缝金属中(约10ppm),减少了夹杂物的面密度和面积百分数,显著提高了焊缝金属的低温韧性。夹杂物的减少和低温韧性的提高有很好的对应关系,因此可以认为,重稀土元素对焊缝金属的净化和变质作用是提高焊缝低温韧性的主要原因。此外,还对焊缝金属中夹杂物的类型进行了较深入的鉴别。     

Controlled growth of gold nanoparticles in zeolite L via ion-exchange reactions and thermal reduction processes

The growth of gold nanoparticles in zeolite can be controlled using ion-exchange reactions and thermal reduction processes. We produce a number of different sizes of the gold nanoparticles with the particle size increasing with increased temperature of the final heat treatment.