Development of Metallic Structure Fatigue Cracks by Composite Patch Repair Using Pre-embedded Fiber Bragg Grating Sensors
Date Issued
2012
Date
2012
Author(s)
Chen, Yi-Chun
Abstract
Fatigue is a common failure mechanism in aircraft structures. Composite patching is a recent technique for repairing fatigue cracked structures. However, it is not easy to know whether the crack underlying the composite patch is still growing or not. In this paper, we investigate the possibility of using optical fiber sensor for monitoring the fatigue crack under a composite repair patch. Optical fiber sensing system has the advantage of small size, high sensitivity, long term stability and immunity to electrical noise. Moreover it is also highly compatible with polymeric composites. Optical fiber can be embedded inside the polymers matrix composite material to be an intelligent repair patch that can repair and monitor the development of metallic structure fatigue crack meanwhile.
This study proposes to use the Fiber Bragg Grating (FBG) to monitor the growth of cracks. For the fatigue crack growth test, the growth of cracks could be known by FBG located vertical cracks, according to the peak wavelength shift of the reflected light spectrum. For the composite patches repair test, when the crack tip grew past the grating, the degree of FBG placed parallel cracks split would decrease. While the FBG placed vertical to cracks, it was easy to know the growth of cracks, according to the peak wavelength shift of the reflected light spectrum. The FBG spectrum would remain unchanged, which is the same as the case for a arrested crack. Hence FBG can be used detect the growth of a crack if special FBG arrangement in the patch layout is employed. With its use, the reliability of large-sized structure can be greatly improved.
Subjects
Fatigue Test
Metallic Crack Growth Monitoring
Fiber Bragg Grating
Composite Patch Repair
Non-destructive Detecting
Type
thesis
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