Effects of various environments on fatigue crack growth in Laser formed and IM Ti–6Al–4V alloys

The fatigue crack growth behaviors of Laser formed and ingot metallurgy (IM) Ti–6Al–4V alloys were studied in three environments: vacuum, air and 3.5% NaCl solution. Taking the Unified Fatigue Damage Approach, the fatigue crack growth data were analyzed with two intrinsic parameters, stress intensity amplitude ΔK and maximum stress intensity K_max, and their limiting values ΔK^* and . Fatigue crack growth rates da/dN were found increase with stress ratio R, highest in 3.5% NaCl solution, somewhat less in air and lowest in vacuum, and higher in IM alloy than in Laser formed one. In 3.5% NaCl solution, stress corrosion cracking (SCC) was superimposed on fatigue at R=0.9 for where K_max>K_ISCC, the threshold stress intensity for SCC. This and environment-assisted fatigue crack growth were evidenced by the deviation in fatigue crack growth trajectory (ΔK^* vs. curve) from the pure fatigue line where . Furthermore, the fractographic features, identified along the trajectory path, reflected the fatigue crack growth behaviors of both alloys in a given environment.     

Calibration of the Weibull stress scale parameter, σu, using the Master Curve

This work proposes that the Weibull stress scale parameter, σ_u, increases with temperature to reflect the increasing microscale toughness of ferritic steels caused by local events that include plastic shielding of microcracks, microcrack blunting, and microcrack arrest. The Weibull modulus, m, then characterizes the temperature invariant, random distribution of microcrack sizes in the material. Direct calibration of σ_u values at temperatures over the DBT region requires extensive sets of fracture toughness values. A more practical approach developed here utilizes the so-called Master Curve standardized in ASTM Test Method E1921-02 to provide the needed temperature vs. toughness dependence for a material using a minimum number of fracture tests conducted at one temperature. The calibration procedure then selects σ_u values that force the Weibull stress model to predict the Master Curve temperature dependence of K_Jc values for the material. At temperatures in mid-to-upper transition, the process becomes more complex as fracture test specimens undergo gradual constraint loss and the idealized conditions of high-constraint, small-scale yielding assumed in E1921-02 gradually degenerate. The paper develops the σ_u calibration process to incorporate these effects in addition to consideration of threshold toughness effects and the testing of fracture specimens with varying crack-front lengths. Initial illustrations of the calibration process for simpler conditions, i.e. 1T crack-front lengths, use the temperature dependent flow properties and a range of toughness levels for an A533B pressure vessel steel. Then using the extensive fracture toughness data sets for an A508 pressure vessel steel generated recently by Faleskog et al. [Engng. Fract. Mech., in press], the paper concludes with calibrations of both m and σ_u over the DBT region and assessments of the Master Curve calibration approach developed here.     

基于Z曲线的SARS冠状病毒特征的研究

刺突（Spike）蛋白是SARS（Severe Acute Respiratory Syndmme）冠状病毒表面最重要的膜蛋白，它通过与被感染细胞的受体结合来作为感染的媒介。受此启发，该文利用Z曲线方法，对S蛋白及SARS受体序列进行探究，捕捉到一种SARS病毒的可视化特征。大量序列比对的结果证明该特征是SARS病毒所特有的。将这种特征图谱应用到SARS病毒的检测中，可以提供一种非标准的、简单、直观的检验方法，能够诊断一些利用标准方法难以判断的SARS病例。由此可见，Z曲线作为一种基因序列的几何学研究途径是一种有效的研究方法。     

基于椭圆曲线的多银行电子现金支付协议的研究

椭圆曲线密码体制以其特有的优越性被广泛用于进行数据加密、数字签名，同样也可用来构建盲签名协议和电子现金协议。本文设计出了多银行电子现金支付协议。上述协议都是基于椭圆曲线离散对数表示问题的，其安全性是基于椭圆曲线离散对数的安全性。     

环境会计目标探讨

可持续发展论的提出 ,环保意识的增强 ,要求会计创新其研究领域。传统会计目标已不能适应环境变化的需要。我国有必要引进环境会计。环境会计目标体系包括 2个层次 ,其基本目标是实现经济效益、环境效益和社会效益的多目标协调 ;其具体目标是提供环境会计信息和利用环境会计信息。     

Lyocell经弹织物结构相及其与织物弹性的关系

采用纱线形态扫描法对不同经纬配置的Lyocell经弹织物进行了测定。结果表明 Lyocell经弹织物的结构相为6以上,是经支持面织物,这表明经纱的原料对织物的表面性能将有更重要的影响。并捻法生产的经弹织物是非紧密结构织物,在织物的经纬纱交织处存在明显的空隙,空隙和经线屈曲波高的增加均对织物的弹性有利。     

EDXRF方法在土壤重金属污染评价中的应用

高灵敏度CUT-3000型能量色散X射线荧光(EDXRF)分析仪采用低能X光管和同位素源双激发方式，以电致冷半导体探测器作为探测系统，使该分析仪具有分辨率高、检出限低、分析元素多的特点。采用该仪器成功地分析了攀枝花地区土壤中重金属的含量，评价了该区土壤重金属污染的特征，结果表明该区重金属污染主要与工矿活动有关。     

电子电器产品的回收再利用及其关键技术研究

电子电器产品制造业是我国一个庞大的产业领域 ,但废旧电子电器产品的有效回收利用尚没有得到足够的重视。本文结合相关项目的研究 ,阐述了在我国这样一个人均资源占有量很低的国家 ,开展废旧电子电器产品回收利用的重要意义 ,并分析了国内外在废旧电子电器回收利用方面的现状 ;在此基础上 ,探讨了废旧电子电器产品有效回收的途径 ;指出系统地研究废旧电子电器产品的回收过程 ,不仅有利于其产业化、规模化 ,而且可以为电子电器产品的绿色设计提供丰富的数据和知识支持     

基于最优潮流与模糊贴近度的电力系统环境保护研究

在电力市场环境下，对电力系统环境保护问题加以研究，是当前面临的一个重要问题。该文提出一种考虑了多种污染排放指标的最优潮流问题的新算法。该方法把购电成本及多个污染排放指标计入目标函数，由逐次线性规划内点法求得非劣解集，运用模相贴近度的概念，从多个非劣解中找出最贴近于理想解的最优解。该方法只需对最优潮流模型作一定的修改，在不添加环保设备的情况下，能有效地减轻火力发电厂对环境的污染。该方法只需对最优潮流模型作一定的修改，在不添加环保设备的情况下，能有效地减轻火力发电厂对环境的污染。通过对IEEE30节点系统算例的数值分析，验证了算法的有效性。     

医用线阵换能器声场指向性曲线的计算机模拟

本文介绍了基于Visual Basic语言的线阵换能器声场指向性曲线的计算机模拟.