1、Structure Damage Identification Technique Based on OPCM Sensors and Gabor waveletY. Luo R.R. Gong J.Z. Gu G.Q. ZhaoFaculty of Science, Jiangsu University, Zhenjiang，Jiangsu,212013, P.R.China1AET (Acoustic Emission Technique) Prominent advantage real time monitoring dynamic monitoring convenience cov

2、ering large areas acquiring original damage information by AE sensors Introduction SHM (Structure Health Monitoring)SignificanceCrack-growth detection and monitoring 2PZT sensors Advantage high sensitivity wide bandwidth high measure precision stabilization acquiring original damage information by A

3、E sensors Disadvantage have uniform sensitivity to orthotropic stress waves sensing signal easily influenced by transverse stress wave influence the damage identification3Fig.1 The model of OPCM sensorModel and characteristics of OPCM sensors 4The coupling relation equation between induced strain an

4、d the deformation of piezoelectric phase is From above equation, the obvious orthogonality can be seen because longitudinal and traverse piezoelectric strain constants, is commonly. 5Characteristics OPCM sensorgood flexibilityhigh intensitylarge strainlight weightits orthotropic characteristics to s

5、tress wavedistinguish stress wave of different components on the same surface Research prove orthotropic characteristics by computation with FEM and experiment 6Comparing between PZT and OPCM Fig.2 The numerical simulation result of FEM 7Comparing between PZT and OPCMFig.3 FFT of experiment result 8

6、 OPCM sensor is only sensitive to the longitudinal wave for its orthotropic sensing characteristics. PZT sensor is more complex in resonance characteristics and havent the different direction sensitivities for its isotropy. Under pulse load9Structure damage identification Location method Fig.4 One d

7、imensional AE source location The distance between sensor A and AE source is 10Structure damage identification Discussionas , AE source location is at the middle of two sensors;as , AE source location is at the position of sensor A; as , AE source location is at the position of sensor B.when the AE

8、source locates outside of the two sensors, time difference will be and induce to false location result that AE source will be located at sensor A or sensor B. 11signal processing technique Gabor waveletpresenting a signal in the time-frequency domain better resolution in the time-frequency domains c

9、ompared with other wavelets Research Based on OPCM single sensitivity and Gabor wavelet time-frequency analysis, damage identification technique is also discussed in this paper.12Gabor wavelet time-frequency analysis Consider two harmonic waves of equal unit amplitude propagating in the x-direction

10、Gabor function isIts Fourier transform is 13Gabor wavelet time-frequency analysis Gabor wavelet transform result is It indicates that the magnitude of the WT takes its maximum valuefrequencyand time14Structure damage identification Improved location method-transmission method The distance between se

11、nsor A and AE source is Where is time difference between the first two-peak values of received signal. ( 1 ) 15Experiment research Experiment setupFig.5 Integrated steel rod Fig.6 Steel rod with defecta OPCM sensor infiniium54820A oscillograph two steel rods show as follows16Experiment research Expe

12、riment result and signal processingFig.7 Signal processing of integrated steel rod 17According to the time difference t & the group velocity 4579m/s gained from experiments.The distance the AE source and OPCM sensor can be worked out by Eq.1. The result Is respectively 449.9mm and 464.1mm and the re

13、lative error is 2.3% and 5.5%18Experiment research Experiment result and signal processingFig.8 Signal processing of steel rod with defect 19Experiment research Experiment result and signal processing Dynamic damage identificationThe AE source location result is respectively 449.9mm and 464.1mm and

14、the relative error is 2.3% and 5.5%. Static defect identificationThe change section location (thought as static defect in this work) result is 240.6mm and the relative error is 10%. 20Conclusions (1) The orthotropic characteristics of OPCM sensor are demonstrated by FEM and experiment.(2) Compared w

15、ith locating source using traditional one-dimension location method of acoustic emission, transmission wave method only uses one sensor and can avoid the influence of threshold setup and different sensitivities of sensors on damage location.(3) Transmission wave method can give qualitative analysis

16、for the isotropic elastic rod with change section (it is thought as static defects in this paper, in practical engineering such as change section by erosion or other factors). 21Other research in our workshop In locating defect of two-dimension structure using traditional acoustic emission (AE) tech

17、nique, its accuracy mainly depends on the following factors: threshold setup of sensor passages, different sensitivities among various sensors, and static defects. In order to solve these problems, new approaches of planar location will be presented based on the research of OPCM sensor, the dispersive characteristics of Lamb wave and signal processing method of Gabor wavelet time-frequency analysis. These methods can reduce the number of sensors in planar location, av