Strain Monitoring in Thermoplastic Composites with Optical Fiber Sensors: Embedding Process,Visualization with Micro-tomography,and Fatigue Results

Abstract

This study investigates the possibility of using optical fibers with Bragg gratings for measurements under fatigue loading conditions. Detailed information is given on the principle of optical fiber measurements, the embedding process, and the fatigue tests. To verify the strain derived from the optical fiber, the strain is compared with extensometer measurements. A special design of the blades of the extensometer is presented, since the standard blades suffer from a loss of grip on the surface of the specimen. Furthermore, X-ray micro-tomography is discussed and used for the visualization of the optical fibers and damage in the composite material. The material used for this study is a carbon fiber-reinforced polyphenylene sulfide. It can be concluded that the optical fiber survives over half a million loading cycles, without de-bonding of the fiber. Furthermore, the resolution of the microtomography is high enough to visualize not only the optical fiber, but also damage in the material.

Keywords

fiber Bragg grating thermoplastic composite fatigue microtomography.

References

De Waele, V. , Degrieck, J. , Moerman, W. , Taerwe, L. and De Baets, P. (2003). Feasibility of Integrated Optical Fibre Sensors for Condition Monitoring of Composite Structures — Part I: Comparison of Bragg-Sensors and Strain Gauges, Insight, 45(4): 266—271.

Degrieck, J. , De Waele, W. and Verleysen, P. (2001). Monitoring of Fibre Reinforced Composites with Embedded Optical Fibre Bragg Sensors, With Application to Filament Wound Pressure Vessels, NDT & E International, 34(4): 289—296.

Doyle, C. , Martin, A. , Liu, T. , Wu, M. , Hayes, S. , Crosby, P.A. , Powell, G.R. , Brooks, D. and Fernando, G.F. (1998). In-situ Process and Condition Monitoring of Advanced Fibre-Reinforced Composite Materials Using Optical Fibre Sensors, Smart Materials & Structures, 7(2): 145—158.

Shin, C.S. and Chiang, C.C. (2006). Embedded Fibre Bragg Grating Sensors for Internal Fatigue Damage Monitoring in Polymeric Composites, Advanced Nondestructive Evaluation I, Pts 1 and 2, Proceedings Key Engineering Materials, 321—323: 230—233.

Shin, C.S. and Chiang, C.C. (2006). Fatigue Damage Monitoring in Polymeric Composites Using Multiple Fiber Bragg Gratings, International Journal of Fatigue, 28(10): 1315—1321.

De Baere, I. , Van Paepegem, W. , Degrieck, J. , Sol, H. , Van Hemelrijck, D. and Petreli, A. Comparison of Different Identification Techniques for Measurement of Quasi-Zero Poisson's Ratio of Fabric Reinforced Laminates, Composites Part A, 38(9): 2047—2054.

Malo, B. , Albert, J. , Hill, K.O. , Bilodeau, F. and Johnson, D.C. (1994). Effective Index Drift from Molecular Hydrogen Diffusion in Hydrogen-loaded Optical Fibres and its Effect on Bragg Grating Fabrication, Electronics Letters, 30: 442—443.

Patrick, H.J. , Gilbert, S.L. , Lidgard, A. and Gallagher, M.D. (1995). Annealing of Bragg Gratings in Hydrogen-Loaded Optical Fiber, Journal of Applied Physics, 78: 2940—2945.

Grattan, K.T.V. and Meggitt, B.T. (2000). Optical Fibre Sensor Technology: Fundamentals , Kluwer Academic Publishers, Boston /Dordrecht/London.

10.

Chojetzki, C. , Rothhardt, M. , Müller, H.-R. and Bartelt, H. (2005). Large Fibre Bragg Grating Arrays for Monitoring Applications — Made by Drawing Tower Inscription, IPHT, Jena, Germany & FOS&S, Geel, Belgium.

11.

Vlassenbroeck, J. , Cnudde, V. , Dierick, M. , Masschaele, B. , Van Hoorebeke, L. and Jacobs, P. (2006). Software Tools for Quantification of X-Ray Microtomography at the UGCT, 10th International Symposium on Radiation Physics, Coimbra, Portugal, 17—22 September 2006.