램파의 분산성과 파 반사가 시간반전과정에 미치는 영향의 이해 = Understanding the Effects of the Dispersion and Reflection of Lamb Waves on a Time Reversal Process

국문 초록 (Abstract)

이 연구에서는 얇은 판형구조물의 손상탐지에 널리 사용되어오는 램파에 시간반전(time reversal)개념의 적용성을 이론적으로 규명한다. 고전적 시간반전 음향학에 의하면, 센서에서의 출력신호를 시간영역에서 반전 후 재입사시켜 원래의 가진점으로 돌려보내면, 그 가진점에서 원래 입력신호가 복원된다. 그러나 램파에 시간반전과정을 적용하게 되면 램파 고유의 분산성과 판 경계에서의 파 반사로 인해 시간반전성이 복잡한 양상을 띠게 된다. 이러한 램파의 시간반전성을 보다 잘 이해하기 위해 이 연구에서는 램파의 시간반전과정을 이론적으로 규명한다. 특히, 램파의 내부모드분산, 다중모드분산, 그리고 판 경계면에서의 램파의 반사가 시간반전성에 미치는 영향을 정식화하였다 간단한 수치예제를 통해 이 연구에서 제시된 이론적 발견들의 타당성을 검증한다.

다국어 초록 (Multilingual Abstract)

This study investigates the applicability of the time reversal concept in modem acoustics to the Lamb waves, which have been widely studied for defect detection in plate-like structures. According to conventional time reversal acoustics, an input signal can be reconstructed at an excitation point if an output signal recorded at another point is reversed in the time domain and emitted back to the original source point. However, the application of a time reversal process(TRP) to Lamb wave propagations is complicated due to velocity and amplitude dispersion characteristics of Lamb waves and reflections from the boundaries of a structure. In this study, theoretical investigations are presented to better understand the time reversibility of Lamb waves. In particular, the effects of within-mode dispersion, multimode dispersion, amplitude dispersion, and reflections from boundaries on the TRP are theoretically formulated. Simple numerical case studies are conducted to validate the theoretical findings of this study.

참고문헌 (Reference)

1 Sohn, H., "Wavelet-Based Active Sensing for Delamination Detection in Composite Structures" 13 : 153-160, 2004

2 Rose, J.L., "Ultrasonic Waves in Solid Media" Cambridge University Press 472-, 1999

3 Giurgiutiu, V., "Tuned Lamb wave excitation and detection with piezoelectric wafer active sensors for structural health monitoring" 16 (16): 291-305, 2005

4 Fink, M., "Time-reversed acoustics" 281 (281): 91-97, 1999

5 Ing, R. K., "Time-reversed Lamb waves. IEEE Transactions on Ultrasonics" 45 (45): 1032-1043, 1998

6 Park, H.W., "Time reversal active sensing for health monitoring of a composite plate" 302 (302): 50-66, 2007

7 Ing, R. K., "Time recompression of dispersive Lamb waves using a time reversal mirror: Application to flaw detection in thin plates" 659-663, 1996

8 "Smart Material Corp."

9 Prada, C., "Separation of interfering acoustic scattered signals using the invariants of the time-reversal operator, Application to Lamb waves characterization" 104 (104): 801-807, 1998

10 Kazakov, V. V., "Sensitive imaging of an elastic nonlinear wave- scattering source in a solid" 81 (81): 646-648, 2002

11 Ing, R. K., "Self-focusing and time recompression of Lamb waves using a time reversal mirror" 104 (104): 801-807, 1998

12 Raghavan, A., "Review of Guided- wave Structural Health Monitoring" 39 (39): 91-114, 2007

13 Sohn, H., "Reference-free damage classification based on cluster analysis" 23 : 324-338, 2008

14 Viktorov, I.A., "Rayleigh and Lamb Waves: Physical Theory and Applications" Plenum Press 1967

15 Scalea, F.L.D., "Propagation of ultrasonic guided waves in lap-shear adhesive joints: Case of incident A0 Lamb wave" 115 (115): 146-156, 2004

16 Moulin, E., "Piezoelectric transducer embedded in a composite plate: application to Lamb wave generation" 82 (82): 2049-2055, 1997

17 "Piezo Systems, Inc."

18 Johnson, E. A., "Phase IIASC-ASCE structural health monitoring benchmark problem using simulated data" ASCE 130 : 3-15, 2004

19 Wilcox, P., "Lamb and SH wave transducer arrays for the inspection of large areas of thick plates, in: Review of Progress in Quantitative NDE 19B" AIP 1049-1056, 2000

20 Kim, S.B., "Instantaneous reference- free crack detection based on polarization characteristics of piezoelectric materials" 16 : 2375-2387, 2007

21 Mindlin, R.D., "Influence of rotatory inertia and shear on flexural motions of isotropic, elastic plates" 18 : 31-38, 1951

22 Su, Z.Q., "Guided Lamb waves for identification of damage in composite structures: A review" 295 (295): 753-780, 2006

23 Fung, Y.C., "Foundation of Solid Mechanics" Prentice-Hall, INC. 525-, 1965

24 Kessler, S. S., "Experimental application of optimized Lamb wave actuating/sensing patches for health monitoring of composite structures" Stanford University 429-436, 2003

25 Giurgiutiu, V., "Embedded NDE with Piezoelectric Wafer Active Sensors in Aerospace Applications, Journal of Materials"

26 Sohn, H., "Effects of Environmental and Operational Variability on Structural Health Monitoring" 365 (365): 539-560, 2007

27 Sohn, H., "Damage detection in composite plates by using an enhanced time reversal method" ASCE 20 (20): 141-151, 2007

28 Paget, C.A., "Damage assessment in composites by Lamb waves and wavelet coefficients" 12 (12): 393-402, 2003

29 Sohn, H., "Combination of a time reversal process and a consecutive outlier analysis for baseline-free damage diagnosis" 18 (18): 335-346, 2007

30 Kim, S. B., "Application of time- reversal guided waves to field bridge testing for baseline-free damage diagnosis" 2006

31 Kim, S.B., "Application of a Time Reversal Process for Baseline-Free Monitoring of a Bridge Steel Girder" 2005

32 Fink, M., "Acoustic time-reversal mirrors" 17 : R1-R38, 2001

33 Wang, C.H., "A computerized time-reversal method for structural health monitoring" 2003

34 Sohn, H., "A Review of Structural Health Monitoring Literature: 1996-2001" Los Alamos National Laboratory Report 301-, 2003