Shin Chow-Shing, Lin Tzu-Chieh, Huang Shun-Hsuan
Department of Mechanical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
Sensors (Basel). 2024 Dec 25;25(1):36. doi: 10.3390/s25010036.
Adhesive joining has the severe limitation that damages/defects developed in the bondline are difficult to assess. Conventional non-destructive examination (NDE) techniques are adequate to reveal disbonding defects in fabrication and delamination near the end of service life but are not helpful in detecting and monitoring in-service degradation of the joint. Several techniques suitable for long-term joint integrity monitoring are proposed. Fiber Bragg grating (FBG) sensors embedded in the joint are one of the promising candidates. It has the advantages of being close to the damage and immune to environmental attack and electromagnetic interference. Damage and disbonding inside an adhesive joint will give rise to a non-uniform strain field that may bring about peak splitting and chirping of the FBG spectrum. It is shown that the evolution of the full spectral responses can closely reveal the development of damages inside the adhesive joints during tensile and fatigue failures. However, recording and comparing the successive full spectra in the course of damage is tedious and can be subjective. An energy modulation interrogation technique is proposed using a pair of tunable optical filters. Changes in the full FBG spectral responses are modulated by the filters and converted into a conveniently measurable voltage output by photodiodes. Monitoring damage development can then be easily automated, and the technique is well-suited for practical applications. Filter spectrum width of 5 nm and initial overlap with the FBG spectrum to give 40% of the maximum output voltage is found to be optimal for measurement. The technique is tested on embedded FBGs from different adhesive lap-joint specimens and successfully reflected the severity of changes in the full spectral shapes during the course of tensile failure. Moreover, the trends in these PD outputs corroborate with the value previously proposed to describe the qualitative change in FBG spectral shape.
粘结连接存在严重的局限性，即粘结层中出现的损伤/缺陷难以评估。传统的无损检测（NDE）技术足以揭示制造过程中的脱粘缺陷以及使用寿命末期附近的分层情况，但对于检测和监测接头在役期间的退化并无帮助。人们提出了几种适用于长期接头完整性监测的技术。嵌入接头中的光纤布拉格光栅（FBG）传感器是很有前途的候选技术之一。它具有靠近损伤部位、不受环境侵蚀和电磁干扰影响的优点。粘结接头内部的损伤和脱粘会产生不均匀的应变场，这可能导致FBG光谱出现峰值分裂和啁啾现象。结果表明，全光谱响应的演变能够密切揭示粘结接头在拉伸和疲劳失效过程中内部损伤的发展情况。然而，在损伤过程中记录和比较连续的全光谱既繁琐又可能存在主观性。提出了一种使用一对可调谐光学滤波器的能量调制询问技术。FBG全光谱响应的变化由滤波器调制，并通过光电二极管转换为便于测量的电压输出。这样，监测损伤发展就可以轻松实现自动化，该技术非常适合实际应用。发现5 nm的滤波器光谱宽度以及与FBG光谱的初始重叠度能给出最大输出电压的40%时，测量效果最佳。该技术在不同粘结搭接接头试样的嵌入式FBG上进行了测试，并成功反映了拉伸失效过程中全光谱形状变化的严重程度。此外，这些光电二极管输出的趋势与先前提出的用于描述FBG光谱形状定性变化的值相符。
