以內埋光纖光柵監控複材膠合接口技術探討

Abstract

工程結構的各個部件接合一般仰賴:螺栓或鉚釘鎖固、高溫熔融焊接，卻都各有其侷限性，而以結構膠接合相對於傳統接合方式有較輕、改善應力集中與面外彎曲現象，隨著近年來黏膠性能提升，使得膠合接合的應用日趨普遍，關於膠合接口之研究已有許多，但尚缺乏完整性監測的探討。 本研究採用布拉格光纖光柵(fiber Bragg grating, FBG)感測器，利用其可內埋於單搭接膠合接口內與膠的結合力強的優勢來偵測膠合接口，實驗的試片搭接物為碳纖維強化複合材料(Carbon fiber reinforced plastics, CFRP)，黏膠為Loctite所生產之環氧樹脂結構膠E-30CL，由萬能試驗測試機(Material Testing System, MTS)進行拉伸測試、疲勞測試、拉伸至尚未破壞後疲勞測試與拉伸至破壞後疲勞測試，在測試過程中引起的破壞，能釋放結構膠成化時的殘餘應力，並造成膠合結構內不均勻應變場產生，導致FBG感測器頻譜波形產生嚴重變化。接著以浸泡熱水三十天與高溫低濕環境三十天後進行拉伸測試，測試溫濕環境對複材單搭接膠合接口影響，利用水能由複合材料滲入接口之特性，證實FBG感測器頻譜能偵測到因破壞或是水分滲入所造成之應變場改變。在確認以FBG頻譜偵測膠合接口破壞可行性後，接著探討以能量調變法監控FBG感測器經拉伸測試後的頻譜變化，在拉伸至破壞產生時由於應變集中使得FBG頻譜波形變化劇烈，故在接近破壞時檢光器輸出電壓會有突然變化之趨勢，並以計算模擬方法改善實驗上的困難。

For many engineering structure, they generally rely on: bolting, riveting and spot welding. But each has their own limitations. However, adhesive bonded joints promote a more uniform stress distribution and less out-of-plane bending than other methods of joining. With the increase of adhesive properties in recent years, so now adhesives are not only used for secondary structures but also applied to some primary structures. Although adhesive joints are widely used in industries now, the research on monitoring the integrity of adhesive joints is still at an early stage and lack complete study. This research used fiber Bragg grating (FBG) sensor with its advantage, which is its capability of being embedded in to the adhesive single lap joints for monitoring damage. The adherend was carbon fiber reinforced plastic (CFRP) and the adhesive was epoxy resin E-30CL manufactured by Loctite. The experiments including tensile test, fatigue test, fatigue test after tenile damage has not occurred, fatigue test after tensile damage has occurred were test by Material Testing System (MTS). During the testing process, the damage could release the residual stress which was formed by epoxy curing and cause non-uniform stress, resulting in a serious change in FBG reflected spectrum. To improve FBG sensors can monitor humidty damage which caused by moisture and used the advantage of CFRP can be diffused by water. The experiment followed by tensile test after immersed the specimens into hot water for 30 days, tensile test after the specimens have been placed in a high temperature and low humidity environment for 30 days. The conclusion is that the FBG reflected spectrum could detect the change in strain filed caused by tensile, fatigue and moisture damage. After the feasibility of using FBG sensors to detect the damage in the adhesives had been confirmed. Then use energy modulation method to monitor changes of FBG reflected spectrum caused by tensile damage. The modulation voltage will suddenly change when the damage has occurred because of the strain concentration effect. Furthermore, this research used calculation method to simulate the modulation voltage, which could reduce the difficulty of the experiment and improve energy modulation method.