| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 100 === Carbon fiber reinforced plastics have many mechanical properties that are superior to conventional structural materials and are becoming more and more widely used. However, this material is prone to in service damages such as foreign object impact and cyclic loading fatigue. The latter is especially detrimental if it follows an foreign object impact that has created internal defects in the material. To improve structural reliability, it will be helpful if on-line monitoring of the existence and development of internal defects is possible. In this work, we propose to use optical fiber Bragg grating (FBG) sensor for this purpose. Optical fiber sensor is small in size, light weighted, sensitive has good long term stability and most importantly it is highly compatible with polymeric composites and can be easily embeddable inside the structure. We employed FBG to monitor the occurrence of internal defects due to impact of foreign objects, the development of these defects in the ensuing cyclic loading and after patch repairing. The reflected spectrum from an FBG in an undamaged composite laminate consists of a well-defined peak. On suffering impact damage, the spectrum broadened and become splitted while the peak intensity dropped. If the impact was followed by cyclic fatigue damage, the peak intensity continued to drop while that of the background wavelength rise. Eventually the characteristic reflect spectrum of the FBG will become totally submerged in background noise. If patch repairing was applied in the course of the damage, the above drop in peak intensity and change in reflected spectrum will be arrested if the repair was successful. The above showed that it is possible to use the FBG sensor to monitor the occurrence and development of impact-fatigue damage and
to check whether a patch repair has attained its purpose.
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