Monitoring Single Lap Joint Integrity with Optical Fiber Grating
Date Issued
2016
Date
2016
Author(s)
Yang, Yi-Jui
Abstract
The performance of adhesives has made great progress in recent years, so now adhesives are not only used for secondary structures but also applied to some primary structures. Although adhesives 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. One of the advantages of fiber Bragg grating (FBG) sensors is its capability of being embedded into the structure. So this thesis adopted FBG to monitor the variation of the strain filed caused by damage around the embedded FBG sensors. This research used single lap joints (SLJ) as the testing specimens. The adherend was 6061-T6 aluminum alloy and the adhesive was epoxy resin E-30CL manufactured by Loctite. At the beginning of the experiment, finite element analysis (FEA) had been carried out to study the stress and strain distribution in the adhesive. The angular sensitivity and embedded position sensitivity were also investigated by experiments. The results show that the FBG which embedded near the edge of the overlap length direction and parallel to the load direction has the best sensitivity to the damage detection.The follow-up experiments including tensile test, fatigue test, fatigue test after tensile damage has occurred, fatigue test after tensile damage has occurred then immersed the specimens into hot water for 30 days, fatigue test after the specimens have been placed in a high temperature and low humidity environment for 30 days then immersed in hot water 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, the test of interactive effect by using FBG as the filter, the dynamic tensile test by using adjustable filter and FBG as the filters, the fatigue test after tensile damage has occurred and raise the load step by step and unloading had all been experimented by using energy modulation method. The conclusions are that the interactive effect could well achieved by using FBG pasted in E-30CL on the top of the adherend, and the modulation voltage will suddenly rise when the damage has occurred because of the strain concentration effect.
Subjects
Single lap joint
Optical fiber grating sensor
Structural health monitoring
Fatigue damage monitoring
Epoxy resin structural adhesive
Type
thesis
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