基于压电阻抗技术的结构损伤识别的实验研究

探究利用压电阻抗技术对结构微小损伤的识别。采用安捷伦精密阻抗分析仪测试自由压电片的电导纳,分析自由压电片的特性。以结构裂缝发展为例,对损伤前和损伤后裂缝深度发展下的电导纳信号进行了分析,引入损伤指标(RMSD)对其损伤程度进行定量分析,并研究温度的影响。结果表明在不同裂缝深度下电导的RMSD可以定量识别损伤的程度。     

压电阻抗法识别管道裂纹试验研究

在运营条件下对油气管道的裂纹损伤进行有效识别是实现油气管道健康监测的重要内容之一,实时探测识别油气管道的损伤有利于建立管道健康监测系统。本文利用压电阻抗技术,对油气管道裂纹损伤进行了识别试验。试验分四种工况,通过量测不同深度裂纹损伤的油气管道的压电阻抗谱,分析了油气管道裂纹损伤与压电阻抗谱变化的规律,并利用统计特征指标RMSD和MAPD进一步评估损伤。试验结果表明:损伤的发展会导致电导纳实部频谱曲线向左偏移,频谱曲线峰值频率减小;随着损伤程度的增大,RMSD和MAPD指标呈线性增长。由此实现了对油气管道裂纹损伤程度的有效判别。因此,压电阻抗技术可应用于油气管道的损伤识别,研究结果可为油气管道结构健康监测提供借鉴。     

基于压缩感知理论重构压电阻抗信号的钢结构损伤识别

基于压电阻抗(electromechanical impedance, EMI)技术,针对结构损伤识别提出了阻抗/导纳数据压缩与重构的方法,利用随机矩阵将监测系统中的原始阻抗数据向量进行线性映射,并将映射后的向量输入到接收系统中;基于压缩感知理论将重构原始数据的问题转化成非确定性多项式问题,并基于凸优化(convex optimization, CO)理论求解;在损伤识别阶段,利用均方根偏差(root mean square deviation, RMSD)统计指标对重构阻抗数据的识别效果进行评估,并与使用原始阻抗数据的效果进行对比。利用简支钢梁的局部损伤识别试验采集的阻抗数据证明所提出方法的有效性。结果表明：基于重构阻抗数据能够有效识别结构损伤,基系数矩阵的稀疏度随着测量数的减少而降低,一致球集合对应的稀疏度区间低于其他测量矩阵,阻抗数据重构效果随着压缩率的增加而减弱,当压缩率高于2.0时,部分使用重构阻抗数据识别结构损伤的误差将大于20%,损伤识别精度降低。     

基于神经网络方法的EMI结构损伤识别

介绍了利用机电阻抗法对铝板的结构损伤诊断,然后建立BP神经网络模型对铝板的不同损伤状态进行识别。将压电陶瓷片PZT粘贴在铝板的中心,利用压电陶瓷的动态特性和压电系统的耦合作用,用阻抗分析仪测得铝板在不同损伤状态下的阻抗变化曲线。实验采用了三个频率范围进行扫描,经比较后,采用300~450kHz。建立BP神经网络模型,将实测的阻抗曲线数据的一部分作为输入参数,对构建的BP网络进行了训练和验证,然后将剩余的数据用于网络的测试。结果表明,网络收敛且具有较好的识别能力。     

基于压电阻抗的隧道管片结构螺栓松动损伤识别试验

基于压电阻抗(EMI)的损伤检测技术应用于大型结构健康监测目前仍十分少见。本文通过试验研究了EMI技术在大型隧道管片结构螺栓松动损伤检测中的有效性,探求了传感器的有效监测范围。首先粘贴不同位置的压电传感器实测压电导纳频谱曲线,分析不同位置压电传感器量测的结构谐振峰值特征。通过设置连接管片的螺栓松动损伤,以传感器的导纳频谱变化规律定性识别该损伤,并通过计算损伤指标RMSD量化损伤,采用其变化率衡量传感器敏感度。研究表明压电传感器能有效捕捉螺栓松动损伤的发展,EMI技术用于大型结构损伤检测是可行的;贴于螺栓上比贴于混凝土管片对损伤检测更为有效,随着损伤程度的增大,近距离传感器的损伤指标较远距离传感器变化更为明显,传感器敏感度与其同损伤的距离成反比例线性关系。     

压电阻抗技术在结构损伤监测中的应用

目前基于压电材料的阻抗监测技术仍然处于结构损伤监测的定性分析,对定量损伤监测研究突破较少,并且压电阻抗技术只能对损伤位置局部监测定位和识别分析,需要进一步研究和开发监测精度。基于此,本文查阅大量文献总结了压电阻抗传感技术的工作机理和优点,概括分析了海内外学者基于阻抗传感技术对结构损伤监测所做的科研成果。在此基础上,以监测木材裂纹深度损伤为例,对木材的人工切割裂纹进行监测,通过分析木材的阻抗实部频率谱曲线和阻抗对数频率谱曲线来判断木材的裂纹深度,结果表明:阻抗峰值随裂纹深度加深,相应频率点峰值下降,采用压电阻抗技术能够有效地监测木材裂纹深度损伤。     

基于压电阻抗的钢管混凝土柱界面缺陷检测研究

在介绍基于压电阻抗的缺陷检测基本原理的基础上,利用压电传感器的压电阻抗测量对一大比例不规则多腔钢管混凝土试件中钢管内壁与核心混凝土之间的模拟界面剥离缺陷进行检测试验研究。对压电传感器在不同频段的机电耦合阻抗进行测量,基于压电阻抗测量值差的均方根定义损伤指标。结果表明,基于压电材料机电耦合阻抗测量可以实现属于隐蔽缺陷的钢管混凝土柱界面剥离缺陷的有效检测。     

基于EMI损伤检测技术的温度补偿研究

基于机电阻抗(EMI)方法的健康监测技术近年来迅速发展,但温度对该方法的影响使得EMI技术的发展受到了一定的阻碍。此研究以实验为基础分析了温度对基于EMI的损伤检测技术的影响,随后分别采用有效频率偏移方法和神经网络方法对EMI损伤检测技术做温度补偿,并对比分析了两者的补偿效果。实验研究表明温度的变化会引起EMI方法中导纳曲线的偏移,引起RMSD损伤指标的变化,从而影响对损伤程度的分析判断。通过有效频率偏移方法及神经网络方法作温度补偿后,均得到了比较理想的补偿效果,温度影响明显减小。通过对比得出神经网络方法的补偿效果更加明显。     

基于压电阻抗技术的混凝土剪力墙裂缝损伤监测

简要阐述了基于压电阻抗法的结构损伤监测技术基本原理,指出了该项技术的优点.结合压电阻抗法及混凝土结构的特点,提出了针对混凝土裂缝损伤监测的传感器布置策略.最后,利用有限元软件对基于压电阻抗技术的混凝土裂缝损伤监测技术进行数值模拟研究.在研究中,建立了黏贴有压电陶瓷传感器列阵的混凝土剪力墙模型,模拟了墙体由健康状态逐渐向...     

基于布谷鸟搜索算法的温度驱动损伤识别方法

基于振动的损伤识别方法数据分析过程复杂,且易受环境不确定因素影响,为解决该问题,提出了一种基于布谷鸟搜索算法的温度驱动损伤识别方法。分析中将温度视为结构的可测激励,对基于温度诱导应变的结构损伤参数识别公式进行了推导,进而利用实测的温度诱导响应值与有限元模型计算的温度诱导响应值构造目标函数,基于改进的布谷鸟搜索算法对有限元模型中的损伤参数进行更新,从而实现损伤的准确判别。通过一根两端弹性约束的H型钢梁,以及一榀Benchmark钢框架模型的数值仿真分析,验证了所提方法的损伤识别效果。分析结果表明：基于布谷鸟搜索算法的温度驱动损伤识别方法可对不同程度、不同位置及不同数量的损伤进行有效识别,即使在较高的噪声干扰下,仍能取得较好的识别结果。相比于基于振动的有限元模型损伤参数识别方法,该方法无需施加外部激励,输入与输出数据（温度与温度响应）方便可测,损伤识别所需的数据量较少,受噪声干扰影响小,可对结构的损伤进行有效定位与量化。     

Monitoring the strength development in concrete by EMI sensing technique

For any new nondestructive evaluation (NDE) technique, prior to full commercialization and real field application, rigorous studies are needed to address its practicality and reproducibility of the results under nominally the same conditions. Recently, the applicability of electro-mechanical impedance (EMI) sensing technique has been extended to monitoring of concrete curing and strength gain. Experimental investigations of this relatively new NDE technique for damage detection in structures have been successfully demonstrated by many researchers. The objective of the present study is to further develop the application of the EMI sensing technique for in situ monitoring of concrete using the low cost piezoceramic (PZT) patches. In this investigation, resonant frequencies of the surface bonded PZT patches were tracked using an impedance analyzer by sweeping the frequency within the range of 100–400 kHz. The experimental results verify the practicality of the EMI sensing technique for monitoring the strength development in concrete. Using an established empirical relationship, the relative strength gain of concrete can be predicted by monitoring the resonant frequency shift. The quantitative approach based on the statistics metrics such as RMSD, MAPD and CCD to compare the EMI spectra is also presented.     

Damage detection in concrete structures using a simultaneously activated multi-mode PZT active sensing system: numerical modelling

In this study, a structural health monitoring approach that integrates both electromechanical admittance (EMA) and guided wave (GW) techniques is presented. More specifically, the EMA technique is used for local damage identification, by employing a piezoelectric transducer (PZT) as admittance sensor. Simultaneously, the same admittance sensor is disturbed by selected elastic GWs launched by another PZT to monitor the damages located beyond the sensing area of the admittance sensor. The validation of the integrated approach is achieved by identifying the changes in electrical admittance signatures as measured on the surface electrodes of PZTs. These changes occur when damage alters the mechanical impedance of the examined concrete structure and when propagating GWs encounter structural damage. Finite element models of damages occurring in conventional unreinforced, steel-reinforced or fiber reinforced plastics-reinforced concrete specimens are investigated. Results illustrate that the proposed integrated technique is an efficient approach for damage identification of concrete structures.     

Monitoring of the strength gain of concrete using embedded PZT impedance transducer

Piezoelectric lead zirconate titanate (PZT) impedance transducer in the electro-mechanical impedance (EMI) technique has emerged as a potential sensing tool for structural health monitoring. In the EMI technique, PZT acts as both sensor and actuator simultaneously due to its direct and inverse piezoelectric effects. The PZT impedance transducer provides a new alternative for monitoring the compressive strength gain of concrete since the conventional nondestructive detection techniques have many limitations. This paper briefly presents a waterproof process for PZT patches using asphalt lacquer material in order to use PZT patches as embedded transducers into concrete, and also presents a new monitoring technique of concrete strength based on embedded PZT impedance transducers. In the technique, a PZT patch covered with asphalt lacquers are embedded into one of concrete cubes. By monitoring the PZT admittance (inversion of impedance) signals and measuring the compressive strength of concrete cubes in different ages, and by combining with the indexes of the root mean-square deviation (RMSD) and the mean absolute percentage deviation (MAPD), the correlations between concrete strength gain and RMSD as well as its correlation with MAPD are founded. The feasibility of the new EMI method based on embedded PZT transducers for monitoring the concrete strength development in early ages is verified.     

空间谱估计在Lamb波的结构损伤检测中的应用

考虑到阵列信号处理中空间谱估计能得到信号的波达方向的特点,本文将空间谱估计引入到基于Lamb波的结构损伤检测中。选择了最具代表性的多重信号分类算法进行分析,利用其对波达方向的估计对损伤进行定位。首先介绍了多重信号分类算法的特点及Lamb波的基本原理,然后通过在铝板上开小孔模拟损伤进行仿真。选取结构上布置的传感器阵列中的一个压电片激励Lamb波,随后收集阵列中所有传感器的波信号,对接收信号采用多重信号分类算法进行波达方向分析,可以从中比较准确地估计出结构损伤发生的角度,仿真结果表明空间谱估计中对波达方向的估计可以应用于结构的损伤检测中。     

基于小波分析的结构损伤信号奇异性检测

结构发生损伤时,其动力特性会发生突然变化,因此会产生奇异信号。Lipschitz指数是表征信号局部奇异性特征的一种度量,可以用来识别结构损伤的发生。小波变换是一种时频域分析方法,具有多分辨率分析的特点,是奇异性信号分析的合适工具。在突变时刻小波系数出现模极大值,通过小波系数模极大值求得的Lipschitz指数可以作为衡量突变程度的指标,由此可以准确识别结构发生损伤的时刻。通过对一空间结构损伤前后加速度信号的奇异性进行分析,验证本文的相关理论。     

主余震序列作用下钢筋混凝土框架结构损伤分析

一次强震过后通常伴有多次余震发生。由于主震和其后续余震之间的间隔时间较短,使得主震损伤结构未能得到及时修复而进一步遭受余震作用,产生“二次损伤”。为此,以一栋5层按我国相关设计规范设计的钢筋混凝土框架结构为研究对象,对主余震序列对结构造成累积损伤及余震对结构造成的增量损伤进行了研究。选取75条真实主震及其余震记录构成序列型地震动输入。同时,采用真实主余震序列中的主震记录,分别采用重复法和随机法两种人工余震构造方法,构造两组人工主余震序列作为地震输入。采用改进的Park-Ang损伤指数作为结构损伤指标,对结构在主震及其在真实和人工主余震序列作用的损伤进行计算,并对余震产生的结构增量损伤进行评估。进一步以峰值加速度、谱加速度、Arias强度作为主震和余震强度参数,研究了余震与主震强度比与余震增量损伤之间的相互关系。分析结果表明：基于随机法的人工主余震序列会对结构造成最显著的增量损伤;采用余震和主震强度比可以较好地预测余震增量损伤的显著性。     

Application of electro-mechanical impedance sensing technique for online monitoring of strength development in concrete using smart PZT patches

Electro-mechanical impedance (EMI) sensing technique utilizing smart piezoelectric materials has emerged as a potential tool for the implementation of an online monitoring system for structural health monitoring. Many nondestructive methods for strength gain monitoring seem to have limited capabilities in monitoring of the strength gain in a continuous manner. In this study, the feasibility of the EMI sensing technique for the online strength gain monitoring of early-age concrete is investigated. The experimental study is conducted on the piezoelectric patch instrumented concrete specimen. It is found that the EMI signature is very sensitive to the strength gain in early age concrete.     

Wavelet packet based damage detection in beam-like structures without baseline modal parameters

In this paper, a new approach for damage detection in beam-like structures is presented. The method can be used without the need for baseline modal parameters of the undamaged structure. Another advantage of the proposed method is that it can be implemented using a small number of sensors. In the proposed technique, the measured dynamic signals are decomposed into the wavelet packet decomposition (WPD) components, the power spectrum density (PSD) of each component is estimated and then a damage localisation indicator is computed to indicate the structural damage. The proposed method is firstly illustrated with a simulated beam and the identified damage is satisfactory with assumed damage. Then, the method is applied to a steel beam. The effect of damage location and the effects of wavelet type and the decomposition level are examined. The results show that the proposed method has great potential in crack detection of beam-like structures.