Structure Damage Identification Technique Based on OPCM Sensors and Gabor wavelet

1. Structure Damage Identification Technique Based on OPCM Sensors and Gabor wavelet Y. Luo R.R. Gong J.Z. Gu G.Q. Zhao Faculty of Science, Jiangsu University, Zhenjiang，Jiangsu,212013, P.R.China

2. Introduction • SHM (Structure Health Monitoring) • Significance • Crack-growth detection and monitoring • AET (Acoustic Emission Technique) • Prominent advantage • real time monitoring • dynamic monitoring • convenience • covering large areas • acquiring original damage information by AE sensors

3. PZT sensors • Advantage • high sensitivity • wide bandwidth • high measure precision • stabilization • acquiring original damage information by AE sensors • Disadvantage • have uniform sensitivity to orthotropic stress waves • sensing signal easily influenced by transverse stress wave • influence the damage identification

4. Model and characteristics of OPCM sensors Fig.1 The model of OPCM sensor

5. The coupling relation equation between induced strain and the deformation of piezoelectric phase is • From above equation, the obvious orthogonality can be seen because longitudinal and traverse piezoelectric strain constants, is commonly.

6. CharacteristicsOPCM sensor • good flexibility • high intensity • large strain • light weight • its orthotropic characteristics to stress wave • distinguish stress wave of different components on the same surface • Research prove orthotropic characteristics by computation with FEM and experiment

7. Comparing between PZT and OPCM Fig.2 The numerical simulation result of FEM

8. Comparing between PZT and OPCM Fig.3 FFT of experiment result

9. Under pulse load • OPCM sensor is only sensitive to the longitudinal wave for its orthotropic sensing characteristics. • PZT sensor is more complex in resonance characteristics and haven’t the different direction sensitivities for its isotropy.

10. Location method • Structure damage identification Fig.4 One dimensional AE source location • The distance between sensor A and AE source is

11. Discussion • as , 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 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. • Structure damage identification

12. signal processing technique • Gabor wavelet • presenting a signal in the time-frequency domain • better resolution in the time-frequency domains compared with other wavelets • Research • Based on OPCM single sensitivity and Gabor wavelet time-frequency analysis, damage identification technique is also discussed in this paper.

13. Consider two harmonic waves of equal unit amplitude propagating in the x-direction • Gabor wavelet time-frequency analysis • Gabor function is • Its Fourier transform is

14. Gabor wavelet transform result is • Gabor wavelet time-frequency analysis • It indicates that the magnitude of the WT takes its maximum value frequency and time

15. Improved location method----transmission method • Structure damage identification • The distance between sensor A and AE source is ( 1 ) • Where is time difference between the first two-peak values of received signal.

16. Experiment setup • Experiment research • a OPCM sensor • infiniium54820A oscillograph • two steel rods show as follows Fig.5 Integrated steel rod Fig.6 Steel rod with defect

17. Experiment result and signal processing • Experiment research Fig.7 Signal processing of integrated steel rod

18. According to the time difference Δt & 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 relative error is 2.3% and 5.5%

19. Experiment result and signal processing • Experiment research Fig.8 Signal processing of steel rod with defect

20. Experiment research • Experiment result and signal processing • Dynamic damage identification • The AE source location result is respectively 449.9mm and 464.1mm and the relative error is 2.3% and 5.5%. • Static defect identification • The change section location (thought as static defect in this work) result is 240.6mm and the relative error is 10%.

21. (1) The orthotropic characteristics of OPCM sensor are demonstrated by FEM and experiment. • (2) Compared with 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 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). • Conclusions

22. In locating defect of two-dimension structure using traditional acoustic emission (AE) technique, 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, avoid false location in traditional triangular location, and qualitatively analyze whether there is a static defect in structural materials, furthermore. • Other research in our workshop

23. Acknowledgements • National Natural Science Foundation of China supports the research under contract number: 50375069. Thanks!