【作者】 王强；

【导师】 袁慎芳；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2009， 博士

【摘要】 主动Lamb波结构健康监测方法由于对结构中的裂纹、复合材料脱层等小损伤敏感,是目前被认为最有效的板结构损伤监测方法。然而Lamb波传播存在着频散及多模特性,同时待测结构往往较为复杂,尤其是复合材料结构,结构特性及损伤机理分析困难,主动Lamb波结构健康监测研究中还存在信号信噪比低下、损伤辨识方法简单、监测效率不高等诸多问题。本文研究了Lamb波自适应时间反转聚焦,并将这一原理应用于主动Lamb波复合材料结构健康监测技术的改进研究。主要研究工作包括以下几方面:首先,介绍了结构健康监测以及主动Lamb波技术的研究背景和意义,给出了本文的研究方向和内容;第二,采用弹性力学理论,讨论了Lamb波传播频散方程及基于压电元件的Lamb波激励和传感模型;在Lamb波传播特性分析基础上,分析了时间反转方法的基本原理,以及基于压电元件的Lamb波信号的时间反转聚焦过程;第三,研究提出了基于时间反转聚焦过程的主动Lamb波损伤直接时反成像技术,分析了该方法和合成时反成像方法的异同点和适用性;提出了采用波包重建方法,克服波包混叠现象引起的成像显示精度低问题;第四,基于时间反转聚焦原理,提出了基于信号峰值和基于损伤散射信号的两种监测技术中的信号增强方法,给出了方法的具体实施过程,并进行了实验验证;第五,针对主动Lamb波健康监测中通过参考信号方式获取损伤信息的方法实用性差问题,研究了无参考损伤成像监测方法,提出双元压电传感阵列和时间窗函数截取监测信号中的结构内部散射信号,并采用合成损伤成像方法实现对损伤的监测;在此基础上,初步研究实现了对加筋复合材料板的无参考损伤监测。第六,结合某无人机机翼盒段结构件地面验证实验,在该盒段结构上进行了主动Lamb波健康监测应用研究,设计了压电夹层规范传感器阵列的电气特性、安装和布线工艺,在盒段结构件螺钉松动监测实验中,验证了基于时反聚焦方法对监测信号的增强效果;最后,对全文进行了总结,并对研究中发现的问题和进一步研究方向进行了阐述。更多还原

【Abstract】 Lamb wave based active diagnosis method is one of the most effective Structural Health Monitoring (SHM) techniques due to its sensitivity to small defects in plate-like structures, such as crack and composite delamination. However, the analysis and interpretation of Lamb waves are complicated due to their dispersive and multimodal natures. Because of the complicated structures, especially the composite, it is difficult to analyze the structural character and its damage. There also existed some problems in the applications of the Lamb wave based diagnosis method, including low signal-to-noise rate, simple damage information detection and low monitoring effective. Time reversal focalization of Lamb wave is researched in this paper. Improvements have been done for the Lamb wave based active diagnosis method based on the time reversal technique. Main contents as follows: Firstly, it was summarized on research background and significance of SHM and Lamb wave based active diagnosis method. And research direction was confirmed;Secondly, the propagation dispersive equations of Lamb wave and the modeling of PZT actuating and sensing have been analyzed using elasticity theory. After that, the principle of time reversal theory was discussed, and the processes of Lamb wave time reversal focusing with PZT elements were analyzed and researched experimentally;Thirdly, directly time reversal imaging technology was proposed for active Lamb wave method based on time reversal focusing. This method was compared with synthetic time-reversal imaging method in detail. Wave rebuilding method was proposed to overcome Lamb wave modes confusing which caused low precision of the damage image. In the presented method, narrower pulse was used to rebuild the sensing signals;Fourthly, signal enhancing methods based on time reversal theory were researched and proposed for signal peak value based and damage scattering signal based damage monitoring methods. Implementary details about the methods were given and validated by experiments.Fifthly, because active Lamb wave monitoring method based on reference signal had low practicability, baseline free damage imaging method was researched and proposed. New double elements PZT array and time window function were presented to intercept structural inner scattering signals from sensing. Synthetic time-reversal imaging method was adopted to detect and show the damages. After that, baseline free damage monitoring for composite plate with stiffeners was presented.Sixthly, during the fatigue tests of UAV wing box structure, application research works of Lamb wave based active diagnosis method were done on the box. PZT layer was designed to normalize the electric character, wiring and setting of the PZT array. Time reversal focusing method for signal-to-noise improvement was validated in the bolts loosing monitoring experiments.Lastly, summary of the whole works was drawn. The problems meted in the research and the continuing directions were presented.更多还原