激励电压对压电阻抗法检测灵敏度的影响

研究了锆钛酸铅压电陶瓷(lead zirconate titanate piezoelectric ceramic,简称PZT)传感器的激励电压与压电阻抗法(electro-mechanical impedance,简称EMI)结构健康监测技术灵敏度之间的关系.借助WK 6500B精密阻抗分析仪及自行搭建的高激励电压电阻抗测试系统(high excitation voltage electrical impedance measurement system,简称HEVEIMS),在0.01～20 V之间8种不同激励电压下,对尺寸为1250 mm×100 mm×3 mm铝梁结构上距离PZT传感器1 000 mm的直径为1.2,2.5和3.5 mm的通孔损伤进行了检测.研究结果表明,激励电压与检测灵敏度之间的关系是非单调的.在1～10 V范围内,提高激励电压能够显著增大EMI方法的检测灵敏度.高激励电压下PZT电阻抗信号中非线性成分增多是导致EMI方法检测灵敏度升高的主要原因.研究结果不但为EMI检测中激励电压的选取提供了参考,也为明确激励电压与检测灵敏度之间的相关关系提供了数据支持.     

碳纤维复合材料层合板损伤的压电阻抗法检测研究

为了验证压电阻抗(Electro-Mechanical impedance,EMI)技术在复合材料结构无损检测中的适用性,搭建损伤检测实验平台,设置不同的工况,测量不同损伤状态下PZT的电导曲线。利用均方根偏差RMSD对电导曲线进行分析,得出了损伤程度、损伤位置与RMSD值之间的关系:损伤程度增大,PZT测得电导曲线的偏移量增大,体现为RMSD值增大;与损伤位置间距越小的PZT测得电导曲线的RMSD值越大。验证了压电阻抗法应用于复合材料结构的适用性,并利用损伤距离与RMSD值之间的关系进行初步定位实验,得到精度较高的定位拟合曲线。     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance, 简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer, 简称PZT)进行主动激励，通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态；然而EMI方法容易受到环境工况变化的影响，导致结构损伤的误报。针对此问题，采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征，将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列，根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性，开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明，协整消除了动态应力对EMI方法的影响，当铝梁内存在持续变化的应力时，仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响，及时准确地进行结构损伤识别。     

压电阻抗技术用于智能螺栓的实验研究

针对工程结构中的螺栓连接件易松动的问题,进行了基于压电阻抗技术(EMI)的螺栓松动监测实验。实验将锆钛酸铅压电陶瓷材料(PZT)直接粘贴在螺栓和螺母上,通过万能试验机对螺栓施加不同的拉力来模拟螺栓预紧力的变化,采用精密阻抗分析仪提取不同螺栓和螺母上压电材料的导纳信号,引入基于电导纳的均方根偏差(RMSD)损伤指标,建立螺栓松动程度和预紧力之间的对应关系。试验结果表明,不同型号的螺栓和螺母上安装的压电材料都可以感知预紧力的变化;得到了损伤指标(RMSD)和预紧力之间的定量对应关系;通过分析损伤指标和预紧力之间的关系可得到螺栓的松动情况,并且可直接定位松动的螺栓。研究表明基于压电阻抗技术的智能螺栓(智能螺母)可以实现松动自检测。     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance,简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer,简称PZT)进行主动激励,通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态;然而EMI方法容易受到环境工况变化的影响,导致结构损伤的误报。针对此问题,采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征,将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列,根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性,开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明,协整消除了动态应力对EMI方法的影响,当铝梁内存在持续变化的应力时,仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响,及时准确地进行结构损伤识别。     

基于激光多普勒技术的PZT薄膜压电性能测试研究

应用基于激光多普勒技术的微小形变分析方法,并引入数字锁相技术,成功实现了PZT(Pb(Zr,Ti)O₃)铁电薄膜的压电性能测试。对商用压电陶瓷在小信号激励下的压电性能测试表明,数字锁相技术的引入能有效抑制系统噪声,并提高激光多普勒系统的位移检测分辨率,使其达到皮米量级。此外,研究了用溶胶-凝胶技术和溶胶-电雾化技术制备得到的PZT薄膜的电压-位移曲线和压电位移"蝴蝶线",实验结果表明:在5 V直流偏置下测得两种方法制备得到的PZT薄膜的d₃₃压电系数分别为218.7 pC/N和215.8 pC/N,相应的标准偏差分别为12.7和28.6。     

基于51单片机和AD5933的便携式电阻抗测试系统设计

针对商用阻抗分析仪存在的价格昂贵、设备笨重等缺点,借助51单片机、AD5933芯片及辅助电路构建了一套便携式电阻抗测试系统。该测试系统可以在0.1～100 kHz频率范围内以0.2～2 V的激励电压对PZT传感器进行电阻抗测量。使用该系统对一维梁结构上宽度为0.5 mm的裂纹损伤扩展过程进行了检测;研究结果表明,所构建的测试系统对于一维梁结构的初始损伤具有很高的灵敏度,对于随后的扩展损伤也能进行有效的检测。     

螺栓无损检测方法综述!

阐述了螺栓结构完整性破坏的两种形式及其成因,并着重介绍了超声波螺栓检测法、磁粉检测法、磁记忆检测、压电阻抗技术、固有频率法以及其他新兴的螺栓检测方法的工作原理和近期进展。根据各种检测方法的检测效果及优劣势,结合当前行业发展现状,从多样化、精准化、标准化及系统化4个方面展望了螺栓无损检测的未来研究方向。     

流延法制备0-3型PZT/PVDF压电复合膜的微观结构及性能

采用流延法制备了不同配比的0-3型PZT/PVDF压电复合膜材料,利用扫描电镜观察微观组织,用X射线衍射仪进行物相分析,并研究了PZT与PVDF的配比对压电复合膜材料压电性能的影响。结果表明:流延法制备的0-3型PZT/PVDF压电复合膜材料的结构均匀致密,无杂质相,PZT的分散性良好;随着PZT体积分数的增加,PZT/PVDF压电复合膜材料的压电常数、介电常数、介电损耗、机械品质因数均逐渐增大;在1kHz的测试频率下,当PZT体积分数达到70%时,复合材料综合性能最佳。     

基于PZT结Lamb波方向算法的损伤定位方法

基于Lamb波在板中的传播特性,针对复合材料的损伤检测,提出一种新型的损伤定位方法。该方法采用3个压电陶瓷片( piezoelectric transducers,简称PZT)组成PZT结,通过从各PZT中提取出损伤散射信号,找到其损伤波包到达的时间差,并依据Lamb波的传播速度得到位移差。首先,结合PZT结中各PZT的几何位置,具体推导出损伤方向算法,运用方向算法找到Lamb波在损伤位置发生散射后的其中一个传播方向,通过传播方向的交点来实现损伤位置的判定;其次,分析了互相关理论的基本原理,并运用互相关算法提取出损伤散射信号;最后,在碳纤维增强树脂基复合材料薄板上对该算法进行实验验证,求出了损伤方向以及损伤位置。验证结果表明,该方法能够对复合材料损伤进行有效的定位。     

珩架型构造物损伤检测的研究

对大型机械设备的机械结构进行快速诊断和损伤检测,经济价值和效益明显.在对珩架型构造物的机械结构的阻抗进行实验测试的同时,对检测材料的固有频率进行了理论推导,对分辨率的选择及分辨率对测试结果的影响进行了深入分析.这为珩架型构造物的机械结构损伤评价,打下了坚实的科学基础.     

基于阻抗技术的压电元件自损伤检测-

为了保证结构健康监测系统的有效运行,基于压电阻抗技术原理,提出了一种压电传感、驱动元件自损伤检测方法.通过研究压电元件等效电容值(压电元件导纳虚部数值)的变化,判别压电元件是否破损及其与主体结构之间是否剥离,并在悬臂梁结构上进行压电元件自损伤检测试验.结果表明,相比压电元件完好的情况,各频率下压电元件电纳值随脱粘部分面积的增加而上升,随破裂部分面积的增加而下降,并且损伤程度和等效电容变化量成比例关系,与理论分析结果吻合较好.     

Modeling of EMI response of damaged Mindlin–Herrmann rod

To ensure high sensitivity to incipient damages, electromechanical impedance (EMI) is measured at high frequencies for damage detection. In the working high-frequency range, very high vibration modes, of the order of the thousandth mode or higher, of a structural member are likely to be activated. This imposes a great difficulty on the accurate modeling of EMI response of a structure. In this paper, the reverberation matrix method (RMM) is adopted to study the dynamics of a Mindlin–Herrmann rod with surface piezoelectric patches. The rod is inhomogeneous along the axial direction so that damage-induced reduction of cross-section or Young's modulus could be easily incorporated in the model. A piecewise-homogeneous rod model is subsequently introduced to approximate the inhomogeneous rod, along with a shear lag model of interfacial bonding between the lead zirconate titanate (PZT) patches and the host rod. An analytical expression for the electric impedance (or admittance) of the coupled model of PZT patch-bonding layer-host rod system is derived. Comparison with other established results is presented. Parametric investigations are also performed to show the dynamic properties of the coupled smart structural system. The analysis in this paper provides necessary theoretical basis for damage detection of rod via the EMI signatures.     

Mechanical impedance-based technique for steel structural corrosion damage detection

The electromechanical impedance (EMI) technique has gained acceptance for structural health monitoring, due to its merits of model-free, high frequency detection and fast response features. This paper presents an innovative mechanical impedance-based technique to monitor the development of corrosion damage on steel structure, which is different from the traditional admittance (inverse of impedance)-based EMI technique. Firstly, structural mechanical impedance (SMI) which directly manifests the structural properties is theoretically deprived. Secondly, by measuring the raw admittance signature, the sensitivity of SMI is investigated in the experiment of steel structural corrosion damage conducted within 117 days. Finally, the corrosion damage quantification is also discussed by calculating the root mean square deviation (RMSD) index. The results indicate that structural mechanical impedance is sensitive to corrosion damage but the detecting range is limited. The real part of SMI can be adopted for an effective indicator of steel structural corrosion damage. The proposed technique is found to be effective in steel structural corrosion damage detection.     

Estimation for bolt fastening conditions of thin aluminum structure using PZT sensors

This work presents a study on PZT impedance-based method, it is one of the NDT(Non-Destructive Technique). We study about assessment of the square-structure health condition by impedance-based technique using PZT patches, associated with longitudinal wave propagation. Health conditions of the square-structure controlled by bolt fastening condition is adjusted by torque wrench. In order to estimate the damage condition numerically, we suggest the evaluation method of impedance peak frequency shift.     

热超声键合PZT阻抗和功率动态特性研究

鉴于热超声芯片封装工艺的键合点空间高度局部化和时间瞬态性等特点，通过分析系统前端PZT阻抗和功率的动态变化规律，研究了芯片金球凸点与基板的键合过程及键合质量。结果表明：对于恒压源的键合系统，PZT换能器电流、阻抗及功率信号可表征键合过程的动态变化，且可将金球凸点与基板键合过程分为初始、平稳、结束三个阶段；键合环境的变化反映在PZT阻抗和功率变化之中，且PZT阻抗和功率与键合强度存在直接关系。试验及分析表明，PZT换能器阻抗和功率变化反映了金球凸点与基板键合过程及键合质量的差别，可用以分析整个键合系统。     

A<Emphasis Type="Italic">built-in</Emphasis> active sensing system-based structural health monitoring technique using statistical pattern recognition

A piezoelectric sensor-based health monitoring technique using a two-step support vector machine (SVM) classifier is developed for railroad track damage identification. Abuilt-in active sensing system composed of two PZT patches was investigated in conjunction with both impedance and guided wave propagation methods to detect two kinds of damage in a railroad track (hole-damage 0.5cm in diameter at the web section and transverse cut damage 7.5cm in length and 0.5cm in depth at the head section). Two damage-sensitive features were separately extracted from each method: a) feature I: root mean square deviations (RMSD) of impedance signatures, and b) feature II: sum of square of wavelet coefficients for maximum energy mode of guided waves. By defining damage indices from these two damagesensitive features, a two-dimensional damage feature (2-D DF) space was made. In order to enhance the damage identification capability of the current active sensing system, a two-step SVM classifier was applied to the 2-D DF space. As a result, optimal separable hyper-planes (OSH) were successfully established by the two-step SVM classifier: Damage detection was accomplished by the first step-SVM, and damage classification was carried out by the second step-SVM. Finally, the applicability of the proposed two-step SVM classifier has been verified by thirty test patterns prepared in advance from the intact state and two damage states.     

EXPERIMENTAL RESEARCH ON EVALUATING STRUCTURE DAMAGE WITH PIEZOELECTRIC DYNAMIC IMPEDANCE

A dynamic impedance-based structural health monitoring technique is introduced. According to the direct and the converse piezoelectric property of piezoelectric materials, the piezoceramic ( PZT ) can be used as an actuator and a sensor synchronously. If damages like cracks, holes, debonding or loose connections are presented in the structure, the physical variations of the structure will cause the mechanical impedance modified. On the basis of introducing the principle and the theory, the experiment and the analysis on some damages of the structure are studied by means of the dynamic impedance technique. On the view of experiment, kinds of structural damages are evaluated by the information of dynamic impedance in order to validate the feasibility of the method.     

基于Lamb波时间反转法的复合材料损伤检测

为检测复合材料损伤,利用Lamb波时间反转法的聚焦特性,在复合材料布置压电传感器激励和接收Lamb波。时间反转法无需对比基准信号就能快速准确地实现损伤的判别,提出的改进损伤成像方法可实现损伤情况可视化。实验研究验证了检测方法的有效性和改进损伤成像方法的优越性。