Structural impedance based damage diagnosis by piezo‐transducers

Although structural mechanical impedance is a direct representation of the structural parameters, its measurement is difficult at high frequencies owing to practical considerations. This paper presents a new method of damage diagnosis by means of changes in the structural mechanical impedance at high frequencies. The mechanical impedance is extracted from the electro‐mechanical admittance signatures of piezoelectric‐ceramic (PZT) patches surface bonded to the structure using the electro‐mechanical impedance (EMI) technique. The main feature of the newly developed approach is that both the real as well as the imaginary component of the admittance signature is used in damage quantification. A complex damage metric is proposed to quantify damage parametrically based on the extracted structural parameters, i.e. the equivalent single degree of freedom (SDOF) stiffness, the mass, and the damping associated with the drive point of the PZT patch. The proposed scheme eliminates the need for any a priori information about the phenomenological nature of the structure or any ‘model’ of the structural system. As proof of concept, the paper reports a damage diagnosis study conducted on a model reinforced concrete (RC) frame subjected to base vibrations on a shaking table. The proposed methodology was found to perform better than the existing damage quantification approaches, i.e. the low‐frequency vibration methods as well as the traditional raw‐signature based damage quantification in the EMI technique. Copyright © 2003 John Wiley & Sons, Ltd.     

刚玉陶瓷膜管-金属粘接试样显微组织的实验研究

选用新型耐腐蚀、耐酸碱HT812高温结构胶对刚玉陶瓷膜管-20﹟钢进行连接,在常温和700 ℃下对粘接试样进行了抗拉强度测试,用XRD、SEM等方法对刚玉陶瓷膜管/胶粘剂/金属粘合部分的微组织结构进行了表征.结果表明:刚玉陶瓷膜管与金属套接接头界面镶嵌致密,无缝隙气孔.在常温下抗拉强度达到17.57 MPa;在700 ℃下为22.50 MPa,高温下粘接试样的抗拉强度比常温下提高4.93 MPa.这说明在常温及高温工况下均可达到理想的使用效果.     

陶瓷基复合材料及其制造工艺

就陶瓷基复合材料的增韧机理、基体和增强增韧纤维的选择、陶瓷基复合材料的制造工艺,尤其是ＣＶＩ工艺作了较为全面的总结和介绍,并提出了陶瓷基复合材料亟待解决的问题和发展方向。     

Revisiting the Lowrie–Fuller test: alternating field demagnetization characteristics of single-domain through multidomain glass–ceramic magnetite

This paper reports the alternating field demagnetization characteristics of glass–ceramic magnetite assemblages carrying weak-field thermoremanent magnetization (TRM), weak-field anhysteretic remanent magnetization (ARM), and saturation remanence (J_rs). Average grain sizes vary from less than 0.1 μm to approximately 100 μm, and hysteresis parameters indicate that these assemblages encompass single-domain (SD) through truly multidomain (MD) behavior. In all assemblages, weak-field TRM and weak-field ARM are more stable to alternating field demagnetization than is (J_rs). This response is especially remarkable in the 100 μm assemblage, which otherwise displays truly MD behavior. Although the SD samples pass the Lowrie–Fuller test for SD behavior, calculations presented here show that populations of noninteracting, uniaxial SD grains should behave in just the opposite sense to that reported originally by Lowrie and Fuller. This discrepancy could indicate that SD, glass–ceramic magnetite populations are more affected by magnetic interactions than would be expected for magnetite crystals that nucleated individually from a silicate matrix. This interpretation is supported by the SD assemblages failing the ‘Cisowski' test: that is, the curves for acquisition and AF demagnetization of (J_rs) intersect well below the 50% mark. However, a second and intriguing explanation of the SD-like results obtained from all samples is that alternating field demagnetization characteristics reflect a strong dependence of local energy minimum domain state, and its associated stability, on the state of magnetization.     

X射线荧光分析仪用靶自动控制系统的设计

X射线荧光分析仪用靶自动控制系统主要由步进电机及其控制电路、光电检测电路、靶盘和齿轮传动五部分组成。该系统采用了单片机控制步进电机,从而驱动靶盘按要求转动相应的角度,并通过光电检测电路进行闭环控制,最终实现能量色散X射线荧光分析中靶的自动更换,解决了长期以来依靠人工更换靶的问题,提高了工作效率和安全性。该控制系统的靶中心点定位偏差不大于1 mm,并能满足能量色散X射线荧光测量工作中的测量要求。     

井底钻具组合纠偏技术在新疆YX-1油井的应用

在易斜地层中钻进，降斜保直一直是一个重要的研究课题。介绍了井底钻具组合纠偏技术及其在新疆YX-1油井中的应用。     

宝石识别展教系统公众展示载体应用创新研究——基于非接触检测与步进电机控制技术的集成系统

本文以宝石识别展教系统为对象,针对其现状及存在的问题,同时考虑公众体验需求,将宝石识别知识通过现代工业集成技术,引入到具象演示系统的研制中,采用知识体系与展示载体相融合的传播模式,解决技术集成创新应用的问题,再现宝石识别方法的重要步骤和相关现象,最终研究形成了基于非接触检测技术与步进电机控制技术的集成系统,并提交关键技术应用创新研究的具象解决方案,为宝石识别展教系统公众展示载体的应用创新提供了新的设计思路和开发实例。     

EXPERIMENTAL VERIFICATION OF BOUNDED-FORCE CONTROL METHOD

An efficient and simple non-linear active control method called Bounded-Force Control (BFC) method has been developed. The theoretical development and application examples of the BFC method has been presented in several publications where it was shown that the BFC is more efficient than the Linear Quadratic Regulator (LQR) method in terms of maximum control force and power requirements when applied to an Active Tuned Mass Damper (ATMD) system. Following a brief review of the fundamental concept of the BFC and a discussion of its main advantages, the results of an experimental investigation using a three-storey shear building model excited by a shaking table and controlled by an electromagnetic linear motor are presented. The experimental results were in perfect agreement with the analytical results, thus confirming the validity of the proposed BFC algorithm.     

Experimental study on earthquake‐induced pounding between structural elements made of different building materials

The phenomenon of earthquake‐induced structural pounding has attracted the researchers' attention for several years now. The aim of this paper is to show the results of two experiments concerning interactions between elements made of different building materials, such as steel, concrete, timber and ceramic. The first experiment was conducted by dropping balls from different height levels onto a rigid surface, whereas the second one was focused on pounding‐involved response of two tower models excited on a shaking table. The results of the impact experiment show that the value of the coefficient of restitution depends substantially on the prior‐impact velocity as well as on the material used. Based on these results, the appropriate formulations have been suggested to be applied in the numerical simulations. The results of the shaking table tests show a considerable influence of the material used for colliding elements on the behaviour of structures during earthquakes. Copyright © 2009 John Wiley & Sons, Ltd.     

面向机动车出行OD监测的目标路段选择算法

机动车在感兴趣区域（例如景点或小区）之间的出行起始和结束（Origin-Destination,OD）信息反映了居民使用机动车出行的活动需求分布,是建立城市智能交通系统中交通需求分析与管理的基础信息之一。数量充足的监测设备能够收集的机动车出行信息更为精细,最终构建的OD信息可用性更强。然而在实际应用中,设备数量往往因为预算情况而存在限制。在设备数量有限的情况下,分析如何选择监测路段来实现OD信息可用性的最大化具有重要应用价值。考虑到感兴趣区域的空间精细程度直接影响监测设备的需求,首先采用层次聚类思想调整感兴趣区域的空间精细程度;然后,根据道路交叉口车流量守恒原则,探测冗余监测路段来进一步降低对监测设备的需求。本研究基于上述2步操作来实现给定数量设备监测能力的最大化。该算法以摄像头为例,在深圳市大鹏半岛区域进行了实验。结果显示,该算法能够支持在不同摄像头数量限制的情况下制定监测路段的选择方案,表明了算法的有效性。