- 學位論文
以光纖光柵感測器監測碳纖維複材經衝擊/疲勞破壞/貼片修補之缺陷發展
Development of Defects of Monitoring Carbon Fiber Composite after Impact /Fatigue Damage/Patch Repair by Using Fiber Bragg Grating Sensors
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摘要
碳纖維強化複合材料(Carbon fiber reinforced plastics，CFRP)具有良好的機械性質，已廣泛的使用在工程結構中。結構在使用過程中，常因本身運作條件與外在環境因素的影響而遭受破壞，如疲勞及衝擊等破壞。因此，有必要做即時的監測，以確保結構在可靠與安全的情況下使用。因光纖具有低損失、小尺寸、重量輕、敏感度高等優點，適合運用在感測器上。其中布拉格光纖光柵(Fiber Bragg Grating，FBG)由於尺寸小，平行CFRP之纖維方向埋入對其強度影響小且相容性佳。故本研究利用內埋於CFRP之FBG來監測遭受衝擊破壞及衝擊後疲勞破壞的發生與發展情況，以及進行貼片膠合修補之時機及其成效。由實驗結果可知，當CFRP受到衝擊破壞時，FBG反射頻譜之波形由兩個波峰劈裂成多個峰值、最高峰值能量強度下降且波形寬度明顯變寬。受衝擊後疲勞破壞且破壞持續發展時，隨著疲勞週期增加，波形持續改變且最高峰值能量強度會持續下降、背景光源能量抬升，最終甚至導致波峰消失。過程中，最高峰值能量強度由穩定緩慢下降到突然大幅度下降時，即為進行修補較佳時機的指標。貼片膠合修補若達成效，則隨著疲勞週期增加，波形幾乎不改變且最高峰值能量強度下降幅度也很小。埋/貼於補片之FBG，波峰波長隨負載增加成固定比例飄移。換言之，可透過FBG反射頻譜波形變化的特徵，監測CFRP經衝擊/疲勞破壞/貼片修補之缺陷發展，進一步掌握到貼片膠合修補之良窳。
並列摘要
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.
參考文獻
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