| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 100 === Carbon fiber reinforced plastics (CFRP) has outstanding mechanical features and has been widely used in numerous fields. However, it is prone to foreign object impact damage. To avoid larger scale structural damage that might follow from the initial impact damages, efficient monitoring of the damaged defect has become an important issue. This study proposes to use distributed sensing optical fiber embedded in the specimen. By controlling the correlation between pump wave and probe wave in the Brillouin optical correlation domain analysis (BOCDA) system, distributed measurement can be achieved.
To establish the optimum experimental parameters, this study conducted correction and optimization to the BOCDA system which raised spatial resolution to 2 cm within at least a 50cm measuring distance. To investigate the feasibility of the embedded optical fiber for damage monitoring using BOCDA system, bending test, impact test and post-fatigue impact test of CFRP were conducted: First, the specimen was loaded in four-point bending with a range of bending load. It was found that the shift in the Brillouin frequency (BFS) of the embedded optical fiber had the linear change varying with the increment of the bending load. On removing the bending load, the spectrum returned to normal, implying that no damage has been incurred during the bending test. After impact, the impact position can be located by observing the change of the Brillouin gain spectrum (BGS) from the embedded fiber. Then, from the post-impact fatigue test, it was found that after certain fatigue cycles, the damage of the CFRP influenced the embedded fibers, making the measurement cannot be conducted. The correctness of the monitoring is cross-checked with the ultrasonic C-Scan examination. It was proved that the BOCDA system had very good potential for monitoring the damage of the CFRP.
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