古代大铜锅和大铜缸(续前)

叙述了古代大铜锅和大铜缸的有关情况。在现存的26口古代大铜锅中,重点介绍了其中6口大铜锅的尺寸、铸造年代、功用、特点和存放地。而现存的165口古代大铜缸,都是明、清两代铸造的,绝大多数都存于北京故宫,本文较详细地介绍了其中5口大铜缸的有关情况。     

古代大铜锅和大铜缸(待续)

叙述了古代大铜锅和大铜缸的有关情况。在现存的26口古代大铜锅中,重点介绍了其中6口大铜锅的尺寸、铸造年代、功用、特点和存放地。而现存的165口古代大铜缸,都是明、清两代铸造的,绝大多数都存于北京故宫,本文较详细地介绍了其中5口大铜缸的有关情况。     

大吨位六面顶液压机大垫块的结构分析

对六面顶液压机现有大垫块的三种结构进行分析,确定外凸式大垫块为大吨位压机的最佳结构。     

斜轧穿孔机的大锥辊与大导盘对比分析

对大锥形辊与大导盘在斜轧穿孔机中应用的优缺点进行了对比，认为大锥形辊综合性能优于大导盘。     

古代大铁炮

阐述了我国古代大铁炮的发展历程和现况,叙述了现存的若干古代大铁炮的名称、尺寸、铸造年代及其特点,并附有它们的照片。还介绍了我国古代铸造大炮的3种方法。     

镁合金大塑性变形的研究进展

综述镁及镁合金大塑性变形的近期发展现状,分析了大塑性变形的技术原理。介绍了大塑性变形方式对变形镁合金晶粒细化和织构控制的影响。通过对现有镁合金大塑性变形研究结果的总结与归纳,得出了镁合金大塑性变形技术未广泛应用的原因所在,并指出开发生产效率高、成本低、工艺简单的一道次成型即可显著细化晶粒和控制织构的新型大塑性变形技术将会是未来变形镁合金领域中的研究重点。     

科学发展 实现大跨越

2008年,围绕跨越式可持续发展目标,我们做出了"三年打基础,五年大发展"的工作部署。2008～2010年重点是打基础。在夯实基础的条件下,"十二五"期间,要实现大转型、大跨越、大发展。     

大磁致伸缩执行器

本文阐述了大磁致伸缩材料的特性和大磁致伸缩材料在执行器中应用情况。大磁致伸缩执行器作为新一代小型强力执行器,被应用于低频声纳、新型马达、流体传动系统以及抗振系统等。大磁致伸缩执行器将有远大的发展前景。     

大并不是伟大

大公司是规模大,但并不一定是伟大。有很多公司,例如美国的三大汽车制造商,动辄成千亿美金的销售额,但充其量是规模大而已,连年亏损,市场价值往往连一些中小公司都不如,谈不上伟大。这些巨无霸,移动缓慢,就如中古世纪的恐龙,成为化石是迟早的事。看看他们的供应链,却又是惊人的一致。     

大并不是伟大

大公司是规模大,但并不一定是伟大。有很多公司,例如美国的三大汽车制造商,动辄成千亿美金的销售额,但充其量是规模大而已,连年亏损,市场价值往往连一些中小公司都不如,谈不上伟大。这些巨无霸,移动缓慢,就如中古世纪的恐龙,成为化石是迟早的事。看看他们的供应链,却又是惊人的一致。     

Mechanical behaviour of overlap joints of titanium

Abstract

Increasing demand for lightweight vehicles as well as for laser welding for automotive technologies in high rate production have pushed the automotive industry to consider the use of expensive lightweight materials with high specific mechanical properties and, as for example titanium, high corrosion resistance. Butt welds have too stringent requirements in relation to laser positioning and clamping methods, so the move to overlap joints is justified. The changes in welding design have to be requalified, in order to determine the geometries that allow the optimum exploitation of the bearing properties of a material. In this paper, the mechanical properties of overlap joints of thin sheets of titanium Grade 2 and of an α/β alloy Ti–6Al–4V are investigated. The results presented allow a very precise classification of the two materials and should help engineers by indicating the optimum material for any given purpose. Ti–6Al–4V offers, for example, the highest strength when statically loaded, while, in contrast, the high notch sensibility results in a very poor fatigue limit when it is used for overlap joints, which is comparable to the low strength titanium Grade 2 in the same configuration.     

Modeling of diffusion processes during carburization of alloys

A Model was developed for the finite-difference calculation of carburization profiles in high-temperature alloys. The method includes the ternary crossdiffusion effect due to substitutional alloying elements that are preferentially oxidized. It can be used to treat cases such as carburization of preoxidized alloys or simultaneous oxidation and carburization. Up to three distinct types of carbide precipitation reactions can be included in the calculations. The solubility product is computed for each reaction and the amount of C that reacts is removed from the diffusion process. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. For comparison, under protective conditions carburization profiles were obtained for preoxidized alloys using C¹⁴ radioactive tracer. The application of the model yields values for the diffusivities of C in the alloys tested. Under nonprotective conditions, the predictions of the model were compared to carburization profiles reported for pack carburization tests. The method is able to predict maximum carbide levels and penetration depths for different alloys in various conditions and can be used in the selection and design of high-temperature alloys for use in carburizing environments.     

Study of structural heredity in brazing of aluminium alloys

Possibility analysis data of application gas-dynamic sputtering technique to eliminate defects in complex metal objects are covered. It is shown that usage of zinc addition in the powder composition allows for a hermetization problem efficient solution and for defects elimination with the help of DIMET portable equipment for metal coating sputtering.     

飞机二次共固化蒙皮超声检测缺陷信号的识别方法

针对飞机二次共固化蒙皮结构部分位置的典型缺陷,结合CIVA软件理论仿真与实际检测数据的比对,总结出不同类型不同位置缺陷的典型特征。结果可以作为缺陷识别的指导,以便于检测人员更加准确地定性判断缺陷,也验证了CIVA软件仿真可以为检测工艺的制定提供支持。     

大型核电主管道制造技术的发展

美国西屋公司AP1000技术是我国引进的第三代核电技术,由于其设计寿命提高到60年,其主管道制造采用整体锻造技术.接管嘴要求与主管一体锻造而成,而且整根管道(包括弯管部分)不允许有环焊缝,属于典型的形状复杂的异形件锻造,制造难度大.本文阐述了主管道材料和成形制造技术的发展情况,根据AP1000核电主管道整体锻造的要求,...     

连铸过程中电磁流体力学的数值模拟现状及发展趋势

对连铸过程中电磁流体力学的数值模拟的研究现状进行了综合评述。介绍了一种应用于连铸过程中的低频电磁流体力学数值模拟的新方法,并给出了其在圆坯旋转搅拌、CSP薄板坯电磁制动和板坯二冷辊式行波搅拌中的应用实例。该方法特点是分别建立电磁场模型和流场模型,并采用磁感应方程实现电磁场和流场模型之间的耦合。结果表明,目前的方法可较为准确地描述连铸过程中的电磁场分布和电磁流体力学特点,并能够对电磁搅拌参数和连铸工艺过程进行优化。最后,提出了连铸过程中电磁流体力学数值模拟技术的未来发展趋势。     

自适应控制的应用研究综述

文中对国内外自适应控制在工业和非工业领域的应用研究现状进行了较系统的总结。自适应控制成为一个专门的研究课题已超过5O年了,至今,自适应控制已在很多领域获得成功应用,证明了其有效性。存在的问题主要是其通用性和开放性严重不足,导致其推广应用至今仍受限制,但现在已能设计出安全、稳定、快速、有效、对现场操作人员无过高要求的自适应系统。结合神经网络、模糊逻辑等人工智能技术是今后一段时期内可能的理论和应用研究方向。     

Simulations of the dielectric constant of bonding materials and field emission properties of CNT cathodes

The effect of the dielectric constant (k) of bonding materials in a screen-printed carbon nanotube (CNT) cathode on the field enhancement factor was investigated for high-efficiency CNT cathodes using the ANSYS software. The values obtained by a simulation study were compared to the experimental results obtained for screen-printed CNT cathodes. The field enhancement factor increased as the dielectric constant decreased, reaching a maximum value at a dielectric constant of 1, the value for a vacuum. The findings indicate that the larger sheet resistance of the bonding materials, after the firing process, can be attributed to the larger emission current of the CNT cathode. From these results, it was concluded that the best bonding materials for screen-printed CNT cathodes should have a low dielectric constant and a high sheet resistance. This finding can be used as criteria for selecting bonding materials for use in CNT pastes for highly efficient CNT cathodes.     

Preliminary Examination of the Quenching of Titanium Alloys

From the limited experimental data in the literature, preliminary values were derived for the thermal diffusivity of titanium alloys and for the quenching severity of various mediums used in heat treating them. The thermal diffusivity, under quenching conditions, was found to be approximately 0.006 sq in. per sec. The quenching severity H for brine is approximately 8, for water 4, for oil 0.9, for air 0.08, and for argon 0.02 in.^?1 The quenching severity of the Jominy-Boegehold end quench water jet against titanium alloys appeared effectively infinite. Using these results, graphs were prepared showing ideal round sizes and Jominy positions having cooled conditions equivalent to those at the center and surface of titanium alloy rounds, plates, and sheets quenched in various media.     

Effect of FeCl3 on the stability of π-conjugation of electronic polymer

Understanding the chemistry of chemical doping, which is necessary to generate charge carriers in π-conjugated polymers, have become increasingly important for increasing charge carrier mobility, a primary requisite for the development of polymer electronic devices. An evidence for disruption in π-conjugation upon increase in doping is evidenced by changes in characteristics bands in Fourier transform infra-red (FT-IR) spectroscopy, influence of structural damage on morphological changes in atomic force microscopy (AFM) and monitoring the conductivity patterns versus doping concentrations. Quest for finding the reason behind such an unwanted chemistry is uncovered by solution proton nuclear magnetic resonance (¹H NMR) spectroscopy of various combinations of dopant and to be doped species. Knowing the reason of disruption of π-conjugation will prove useful in developing careful doping chemistries, utterly important for polymer electronic devices.