Paper number 443


C Y Wei1, S W James2, C C Ye2, N D Dykes1 R P Tatam2, and P E Irving1

1Damage Tolerance Group, School of Industrial and Manufacturing Science
2Optical Sensors Group, Centre for Photonics and Optical Eng., School of Mech. Eng.
Cranfield University, Cranfield, Bedford MK43 0AL, UK

Summary This paper determines the performance of Fibre Bragg Grating (FBG) sensors for strain sensing applications in carbon fibre composite materials. Carbon fibre laminates in either cross-plied or quasi-isotropic stacking sequences were fabricated using T300/Hexcel 914 prepregs. The FBG optical sensors were either surface attached, or embedded within the laminates. The sensor orientation was aligned either parallel or transverse to the adjacent carbon fibre layers. The sensor was also bonded to the surface of an aluminium plate using a high failure strain adhesive to allow the maximum failure strain of the sensor to be determined. The composite structures with integrated FBG sensors were subjected to static tensile loading. A scanning fibre Fabry-Pérot filter was used to monitor the reflected Bragg wavelengths. The optical sensor embedded between two 90° carbon fibre plies shows a high sensitivity to multi-site cracking formed in the transverse plies. The embedding in 90° plies seems to change the local stress distributions and to become a source of crack initiation. Efficient stress transfer from the host materials to the sensors is dependent upon incorporation methods, the thickness of the adhesive layers, and the location of the sensors.
Keywords fibre Bragg grating sensor, strain sensor, smart materials.

Theme : Smart Materials and Smart Manufacturing

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