以分佈式布里淵光纖感測系統監測碳纖維複材受衝擊後內部損傷之應用

Abstract

碳纖維強化複合材料(Carbon fiber reinforced plastics，CFRP)具有優異的機械性質，因此在眾多領域中被大量應用，然而易受外物衝擊造成損傷。有鑑於此，當複材內部結構因受衝擊損傷時，為避免往後造成更大規模的結構破壞，如何有效地監測即為一重要議題。研究中將分佈式感測光纖內埋於複材試片中，利用布里淵光相關域分析(Brillouin optical correlation domain analysis，BOCDA)系統，控制泵波(Pump wave)與探測波(Probe wave)之間的相關性，以達到分佈式量測。 為了建立後續實驗之最佳參數，對BOCDA系統做調校與優化，使其在至少50cm之量測距離內擁有至少2cm之空間解析度。而為了探討BOCDA系統對於內埋光纖複材監測之可行性，進行複材彎曲與衝擊測試：首先，試片在一定彎曲負載內進行四點彎曲測試，發現內埋光纖之布里淵頻率漂移量(Brillouin frequency shift，BFS)會隨著彎曲負載增加有線性變化，且只會對內部產生暫時性受損情況；施予衝擊後，可由內埋光纖布里淵增益頻譜(Brillouin gain spectrum，BGS)之變化，定位出衝擊點之位置；而衝擊後疲勞測試中，可知經一定疲勞週期後，複材受損將導致內埋光纖受影響進而失去量測功能。此研究成功地利用BOCDA系統，並以超音波C-Scan驗證試片受損情況，證明其在監測複材受損上之應用潛力。

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.