以內埋式光纖光柵感測器監測碳纖維複合材料之疲勞損傷

Abstract

Carbon fiber reinforced plastics (CFRP) are used in various fields due to their high specific strength and specific modulus. It is important to monitor the damage occurrence and development to make CFRP materials reliable and safe. Current methods for internal defect examination in polymeric composites are time consuming and often cannot provide real time monitoring while the components concerned are in use. We propose to use optical fiber sensors for real time monitoring of internal defect development under fatigue loading. Optical fiber has a small diameter, is unaffected by electro-magnetic interference and is reasonably temperature resistant. It may be embedded inside a composite material and comes close to the internal defects. The current work aimed at exploring the use of embedded fiber Bragg grating (FBG) to monitor fatigue damage evolution in a Graphite/Epoxy composite. The on-set and development of the fatigue damage was assessed through changes in the shape of the optical spectrum and shift in wavelengths in the optical fiber sensors. The evolution in light spectrum during fatigue may be divided into four stages. The test specimens were also examined using X-ray radiography, ultrasonic scan, modulus degradation and optical microscopy to reveal the type and extents of the defects at different stages of fatigue damage. Comparison with conventional examination results shows that changes in the light spectrum are associated with (1) matrix cracking in the 90o lamina; (2)splitting along the fiber direction in the ±45o laminae; (3) splitting along the fiber direction in the 0o lamina ; and (4) delamination. As a conclusion, embedded fiber grating sensors appears to have the potential to be developed into a useful tool for on-line structural health monitoring of composite structures.