Structural Damage Location with Fiber Bragg Grating Rosettes and Lamb Waves

Abstract

The aim of this study is to present the results of testing a damage detection and damage localization system based on fiber Bragg grating sensors. The objective of the system is to detect and locate damage in structures such as those found in aerospace applications. The damage identification system involves Bragg gratings for sensing ultrasound by detecting the linear strain component produced by Lamb waves. A tuneable laser is used for the interrogation of the Bragg gratings to achieve high sensitivity detection of ultrasound. The interaction of Lamb waves with damage, e.g., the reflection of the waves at defects, allows the detection of damage in structures by monitoring the Lamb wave propagation characteristics. As the reflected waves produce additional components within the original signal, most of the information about the damage can be found in the differential signal of the reference and the damage signal. Making use of the directional properties of the Bragg grating the direction of the reflected acoustic waves can be determined by mounting three of the gratings in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the reflection, i.e., the damage, by taking the intersection of the directions given by each rosette. A genetic algorithm (GA) can be used to calculate that intersection and to account for any ambiguities from the Lamb wave measurements. The performance of the GA has been studied and optimized with respect to the localization task. Initial experiments are carried out on an aluminum structure, where holes were drilled to simulate the presence of damage. The results show very good agreement between the calculated and actual positions of the damage.

Keywords

fiber optical sensors damage detection damage localization ultrasonic testing Lamb waves fiber bragg gratings

Get full access to this article

View all access options for this article.

References

Chang, F.-K. (2003). Structural Health Monitoring 2003: Proceedings of the 4th International Workshop on Structural Health Monitoring, Lancaster: DESTech Publications, Inc.

Balageas, D.L. (2002). Proceedings of the first European Workshop on Structural Health Monitoring 2002, Lancaster: DEStech Publications.

Buderath, M. (2002). Maintaining ageing military aircraft using the Tornado fighter as an example. In: Balageas, D.L. (ed.), Proceedings of the First European Workshop on Structural Health Monitoring 2002, Paris: DEStech Publications, pp. 76—96.

Hellier, C.J. (2001). Handbook of Non-destructive Evaluation, New York: McGraw-Hill .

Shull, P.J. (2002). Nondestructive Evaluation: Theory, Techniques, and Applications, New York: Marcel Dekker, Inc.

Staszewski, W.J. , Boller, C. and Tomlinson, G.R. (2004). Health Monitoring of Aerospace Structures: Smart Sensor Technologies and Signal Processing, Chichester: John Wiley & Sons Inc., pp. 288.

Kehlenbach, M. and Das, S. (2002). Identifying damage in plates by analyzing Lamb wave propagation characteristics. Presented at Smart Structures and Materials, San Diego.

Betz, D.C., Thursby , G., Culshaw , B. and Staszewski, W.J. (2003). Acousto-ultrasonic sensing using fiber Bragg gratings . Smart Material and Structures, 12, 122—128.

Betz, D.C. (2004). Application of Optical Fibre Sensors for Structural Health and Usage Monitoring. Dissertation. de Berlin.

10.

Timoshenko, S.P. and Goodier, J.N. (1987). Theory of Elasticity, 3rd edn, New York: McGraw-Hill 1970, 1987.

11.

Betz, D.C. , Thursby, G. , Culshaw, B. and Staszewski, W.J. (2003). Lamb wave detection and source location using fiber Bragg grating rosettes. Presented at Smart Structures and Materials 2003: Sensory Phenomena and Measurement Instrumentation for Smart Structures and Materials, San Diego, CA, USA.

12.

Seydel, R. and Chang, F.-K. (2001). Impact identification of stiffened composite panels: I. system developments. Smart Material and Structures, 10, 354—369.

13.

Seydel, R. and Chang, F.-K. (2001). Impact identification of stiffened composite panels: II. implementation studies. Smart Material and Structures , 10, 370—379.

14.

Staszewski, W.J. , Worden, K. , Tomlinson, G.R. and Ball, A. (1997). Optimal sensor locations for impact detection on a composite panel. In: Proceedings of the 2nd International Workshop on Damage Assessment Using Advanced Signal Processing Procedures — DAMAS 97, Sheffield, UK.

15.

Worden, K. and Staszewski, W.J. (2000). Impact location and quantification on a composite panel using neural networks and a genetic algorithm. Strain 2000, 36, 61—70.

16.

Coverley, P.T. and Staszewski, W.J. (2002). Impact damage location in composite structures using optimised sensor triangulation procedure. Smart. Mater. Struct.

17.

Goldberg, D.E. (1989). Genetic Algorithms in Search, Optimisation, and Machine Learning. Boston: Addison-Wesley.