【作者】 乔海燕；

【导师】 林莉； 李喜孟；

【作者基本信息】 大连理工大学 ， 材料无损检测与评价， 2010， 硕士

【摘要】 PZT压电阻抗法具有工作频率较高(30kHz以上),对结构微小损伤变化敏感,受外界环境影响小,不依赖模型,PZT性能稳定等优点。该方法属于结构健康监测技术的一种,与传统无损检测技术相比,实施时不需要预知损伤位置且在检测期间结构不需要停止工作。基于以上特点PZT压电阻抗法已经成为适合大型复杂结构在线监测的热门技术。压电阻抗法的核心问题是PZT片激励及耦合电阻抗(或电导纳)的测量,目前研究中多是借助阻抗分析仪实现。该仪器测试频率范围宽、检测速度快、可测参数全,但同时也存在设备笨重、造价昂贵且驱动电压过低(2V以下)等缺点。当PZT片粘贴于大型结构上进行损伤检测时,不能被充分激励,使所得信号的信噪比降低。因此,亟需开发出一套驱动电压高、测试频率范围宽、成本低廉的小型PZT片激励与阻抗测试系统。同时,由于压电阻抗法不依赖于结构模型,且结构损伤状况存在多样性和复杂性,实现损伤定量表征仍是其研究中的难点。论文针对以上两点对压电阻抗法检测结构损伤的实验系统开发和定量表征方法进行研究。推导出PZT阻抗近似值的计算公式与测量电路,设计搭建一套驱动电压范围更广且造价更低廉,可取代阻抗分析仪进行阻抗测量以检测结构损伤的系统,组成包括能量、频率、电压等参数广泛可调的ARB-1410任意波形发生卡、高测量灵敏度的频谱分析仪及自行设计的阻抗测量电路,系统频率范围在15MHz时对应的驱动电压为10V,频率2MHz时电压可达35V,频率测量精度可达0.1Hz。为了验证该系统对微小损伤检测的灵敏程度,分别在尺寸为206mm×21.5mm×3mm的梁Ⅰ和353mm×17.5mm×5.2mm的梁Ⅱ上制作一系列逐渐扩展的孔洞和裂纹损伤。利用该系统在120kHz-215kHz频率范围内对两种损伤进行检测。在孔洞直径由φ1mm到φ3mm不断扩展并增加孔数量的过程中,以及裂纹深度d由0.5mm到1.5mm逐渐加深,并且裂纹数目增加的过程中,测量频段内阻抗谱峰值向低频方向不断漂移,且测量频率较高时,谱线变化规律更显著。由得到的阻抗谱曲线变化规律可以明显区分各损伤状态,实验证明了该系统检测一维梁微小损伤的有效性。为了研究压电阻抗法对于连续变化的损伤的区分度,选用对数据之间差异敏感的统计参数均方根差RMSD(Root Mean Square Deviation)、平均绝对偏差MAPD(Mean Absolute Percentage Deviation)、协方差Cov(Covariance)和相关系数CC(CorrelationCoefficient)作为损伤指数对损伤进行定量评估,得到以下结果：RMSD和MAPD数值都随着损伤程度发展而增加,前者在两种类型损伤的定量表征中表现得更稳定和准确；Cov和CC随损伤变化规律一致,损伤程度越严重,数值越小,二者相比,CC受到数据本身数值大小影响小,更能准确反映两组状态所有数据点的相关程度；相对损伤系数中R-Cov对损伤的位置最不敏感,不适合损伤的定位。更多还原

【Abstract】 The PZT-based electro-mechanical impedance (EMI) method has been developed as a promising tool for real-time damage assessment of large and complex structures due to the advantages as follows:being sensitive to local minor damages because of high actuating frequency (greater than 30 kHz); not based on any model and can deal with unpredicted failure patterns; excellent features of PZT under normal working conditions; etc. Unlike the conventional non-destructive evaluation (NDE) method, the EMI technique does not need the location of damage previously or temporarily unusable of structures during detection. The core issues of EMI are the excitation of PZT patches and measurement of coupled impedance (or admittance) which are usually achieved by the bulky and expensive Impedance Analyzer. The actuating voltage is low (smaller than 2V) so that the PZT patches could not be excited well and the signal-to-noise ratio of impedance will be decreased correspondingly. Therefore, it is necessitated to develop an EMI system with high exciting voltage, wild operating frequency and low cost. Moreover, it is difficult to obtain the quantitative results due to the complexity and variety of damages.This paper investigated the experimental system and quantitative evaluation for damages on 1-dimensional beams using EMI method. The new impedance-measuring system is composed by an arbitrary waveform generator, an FFT analyzer and a small current measuring circuit. The actuating voltage is 10V with the working frequency range of 15 MHz, while the frequency range is 2MHz, the system could be excited at 35V. The frequency measurement accuracy is 0.1Hz. A series of drilling holes (diameterφ1mm-φ3mm) and cracks (depth 0.5mm-1.5mm) were made on beam I and beam II respectively to prove the efficiency and sensitivity of the new system. In the detecting frequency range of 120kHz-215kHz, the damage states could be distinguished clearly by the variation of impedance spectra. With the increasing degree of injury, the peaks of impedance spectrum shift to lower frequency and the variation were more significant in the higher frequency range. Experimental results show the efficiency of the detection system.Four types of statistics damage metrics:Root Mean Square Deviation (RMSD). Mean Absolute Percentage Deviation MAPD), Covariance (Cov) and Correlation Coefficient (CC) were introduced for quantitative characterization of damages. The values of RMSD and MAPD increased with the development of damage. The performance of RMSD was more stable and accurate in evaluating the damages. Cov and CC showed opposite tendency to RMSD with the increasing degree of injury. The variation of CC was more accurate in reflecting the correlation of two sets of data because of less influence by the values of data itself. Among the relative-damage metrics, R-cov was the least sensitive one in locating the damages.更多还原