Fracture toughness of structural components: influence of constraint

In this paper, in- and out-of-plane constraint are considered in the process of fracture toughness determination. A three parameter approach—J_IC, Q and T_z is utilized. The plane strain fracture toughness J_IC must be determined experimentally according to valid standards. It is the only quantity measured experimentally except for the classical uniaxial stress-strain curve determined for the material tested. Two additional parameters should be computed numerically using 2D and 3D FE analysis for the structural member which is actually analyzed. The T_z function is the generalized Poisson's ratio for elastic–plastic materials. The general model proposed allows for fracture toughness determination in two cases—when one fracture mechanism dominates the fracture process or two or more mechanisms are active simultaneously. To apply the model the fracture toughness for the particular fracture mechanisms should be known. In the paper simple models to determine these quantities are proposed both for cleavage and ductile fracture. In the latter case a distinction is made between fracture mechanisms along the shear lips and in the central part of the specimen.     

Tape Cast Multilayer Composite of Nano Zirconia with High Toughness

During the last decade, worldwide attention of researchers has focused on nano-ceramic composites with superior mechanical behavior and improved reliability for structural applications. Here we report the development of a multi-layer composite (MLC) of tape cast nano zirconia with high failure energy. The MLC samples were fabricated by thermocompression of green tapes prepared from 3 mole % yttria stabilized zirconia (3-YSZ) powder with a primary crystallite size of 27 nm. Depending on the number of layers, the MLC samples exhibited failure energy (238.97 KJm^-3) more than two times higher than that of the single tape (≈107 KJm^-3) with a reasonably high bi-axial flexural strength (≈630 MPa), high hardness (≈ 13 GPa at 49 N), and indentation fracture toughness nearly four times as high as that of the single tape. In addition, these MLC materials showed the presence of a R-curve behavior.     

PRACTICE GREEN ENGINEERING,KEEP THE JUNKYARDS CLEAR

This paper discusses the fracture prevention aspects of lifetime prediction. Initially, it is pointed out that lifetime can be determined by factors such as obsolescence and consumer rejection. Lifetime is then related to acceptable risk in order to make it compatible with advances in design philosophy for large welded structures. Accident statistics are cited and the argument made that the major opportunities for lifetime improvement are revealed by failure analysis, and are shown to lie in design and production. However, there are some structures, e.g. boilers and pressure vessels, where the construction rules are so well established that failures occur mainly because of operational errors. Based on the results of the Battelle/NBS Cost of Fracture Study, attention is focused on the effect of material–property reproducibility in driving failure probability. Little evidence could be found regarding reproducibility improvements of fatigue lifetime and brittle fracture toughness in production lots of alloys over time.     

用计算机图象处理技术重建三维金属断口

本文利用图象处理技术提出了一种简单、实用、非破坏性地获得断口表面三维信息的方法。籍此可获得目前其它手段无法得到的断日真实表面积。这些三维信息的准确程度与激光扫描显微镜所选用的放大倍数、截面间距有关。如果能把本文所采用的平行截面法融人激光扫描显微镜的软件中，有可能实现三维微观信息的实时动态观察。     

An optimal algorithm for the on-line closest-pair problem

We give an algorithm that computes the closest pair in a set ofn points ink-dimensional space on-line, inO(n logn) time. The algorithm only uses algebraic functions and, therefore, is optimal. The algorithm maintains a hierarchical subdivision ofk-space into hyperrectangles, which is stored in a binary tree. Centroids are used to maintain a balanced decomposition of this tree.These authors were supported by the ESPRIT II Basic Research Actions Program, under Contract No. 3075 (project ALCOM).This author was supported in part by the National Science and Engineering Research Council of Canada.     

金丝生产中的断口分析

通过断口分析,讨论金丝在拉制过程中断裂的主要原因,并提出改进生产工艺的有益意见。     

城市历史形态与水环境——湖北省阳新县城市发展变迁剖析

通过对湖北省阳新县城址变迁历史的追溯及其城市形态基本特征的分析,将县城址的变迁、县城布局基本特征等与县域水环境的具体情况相联系,并引用中国古代城市关于城市选址的有关论述,提出"顺应自然,趋利避害"的原则,探索了中国古代城市的发展与特定水环境之间的关系.     

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目前,由于缺少直接测量水力裂缝长度及导流能力等重要参数的手段,而地下水力裂缝的存在总要反映到油气井压力与产量的变化上来,特别是压力与产量随时间的变化速度与水力裂缝的长短、导流能力的大小等参数有直接关系。在常规压裂井试井分析过程中,所使用的数据主要是停泵后的压降数据,而岩石发生破裂到停泵前这一段压裂施工压力数据则没有得到有效利用;同时,在压裂施工作业过程中也不能对裂缝的延伸状况进行动态监测。文章提供了裂缝模型的诊断技术,通过对岩石发生破裂到停泵前这一段压裂施工压力数据进行分析,确定裂缝参数随压裂时间的变化关系。这样,就可以实时地知道裂缝发育、发展和闭合的过程,对于正确指导压裂施工作业以及获得优质裂缝具有十分重要的意义。     

基于综合脉冲与孔径技术的多基地"无源"定位系统

本文根据综合脉冲／孔径雷达采用多个天线同时向全空域辐射多个载频信号,而在接收端通过信号处理获得发射方向图的特点,提出一种新的多基地“无源”定位雷达系统。该系统既利用在岩上发射,在舰船上接收而构成岩－舰多基地雷达,又由于在接收站不发射信号而相当于无源定位系统,本文介绍该系统的基本组成,工作原理及其与常规地波超视距雷达、双／多基地雷达相比的显著特点,给出计算机模拟结果;最后讨论了该雷达需解决的关键问题。     

关于"可移动Agent系统位置透明通信的一种实现"的一点注记

王红等人的文章“可移动Agent系统位置透明通信的一种实现”的结论是值得商榷的。文中指出该文的不足及欠明晰之处,对其结论进行了澄清。