Threshold and growth mechanism of fatigue cracks under mode II and III loadings

ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔK_IIth. The relationship ΔK_IIth > ΔK_Ith caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack.     

一种基于PWM的半桥型开关电源

主要介绍了由SG3525组成的半桥型开关稳压电路的结构和工作原理，阐述了PWN集成电路SG3525的特性和主要功能。实践表明：该系统工作稳定，运行效果良好。     

神经网络分类器的快速构造算法

使用ＢＰ算法训练多层网络的速度很慢而且事先难于确定隐节点和隐层的适当数目。本文提出一个有效的算法，先构造决策树，然后将构造的决策树转换为神经网。文中使用一个全局准则函数控制决策树的增长，它较好地匹配了树的复杂性和训练样本量及错分率界。实验结果，本文的算法比用ＢＰ算法训练多层网络要快，而其分类精度不低于用ＢＰ算法训练的多层神经网。     

实验应变／应力模态分析若干问题的进展评述

本文评述了实验应变／应力模态分析进展的若干基本问题。主要是：应变响应与位移响应的关系；应变频响函数矩阵的特点及其测量方法；应变模态的加权正交性及其识别方法；以及其他问题。     

The TDCPR Management Mode of Engineering Equipment

The Three Gorges Project is a very large project,and its structure is very complex.Interna-tional advanced engineering equipment is broadly used.The state of equipment running directly influ-ences project building qualities and limited time.According to the factud conditions of the Three Gor-ges Project,the characteristics of engineering equipment are analyzed.At the same time ,some theories about equipment management are induced ,and the TDCPR management mode of engineering equip-ment of the Three Gorges Project is put forwared in order to gain the aim of managing and using equip-ment well and speeding up the project construction.     

钠冷快堆中喷雾钠火的计算分析

根据钠冷快堆中喷雾钠火的特点建立了理论模型，编制了SSPRAY程序。该程序模拟钠喷雾燃料过程中钠滴的运动、钠和氧气的燃烧反应、热量传递和质量传递等瞬态过程。用该程序计算了气体和墙壁温度、气体压力、氧气摩尔份额、喷雾流燃烧速率和热量热递速率等主要参数。利用AI实验数据和美国SPRAY－3A的计算结果对程序进行了验证，结果符合较好。     

分子振动态及其跃迁的激光相干控制

讨论了激光合成相干叠加态的原理及其性质 ,针对 XY2 型分子 ,证明了合成局域模振动的可行性 ,然后给出相干叠加态的跃迁几率特征 ,发现它仍表现出相干的特性 ,对之进行分析研究表明 ,分子的振动态具有可控性 ,态跃迁几率具有可控性。     

A bidding decision index for construction contractors

Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors.     

气体绝缘封闭电器的高速瞬变过程和现场试验

随着ＧＩＳ的工作电压不断提高和发展，一系列新的现象和问题也同时出现。从国外一些科研，设计，制造部门所研究发表的内容看，大致有隔离开关操作和高速瞬变过程，粒子影响和对干扰定位的技术，元件的监督，现场试验等课题，本文对以上问题加以综合介绍。     

耦合腔行波管慢波结构的工作模式及其特性

耦合腔行波管慢波结构可工作于三种不同模式：正常模、简并模和反向模。应用改进的等效电路法计算了正常模腔通带和槽通带。求得的简并模耦合槽张角与实验值相符。最后讨论了反向模耦合腔行波管诱人的特点。