並列タイトル等FBGセンサーを用いたCFRPのその場損傷検知 : 縫合複合材と剛性の不整合を有する薄板積層材
一般注記This thesis provides a comprehensive understanding of the capability of optical fiber sensor systems, namely fiber Bragg grating sensor (hereafter, ‘FBG sensor’), to monitor damage behavior in composite materials and structures under mechanical loading. The FBG sensor is embedded in two types of composite systems: (i) stitched laminate materials, (ii) thin composite structure with stiffness mismatch. The composite systems are subjected to two load cases, i.e. static tension and three-point-bending. The stitched laminate materials, which have through-thickness reinforcement in the form of stitch threads, exhibit a complex failure mechanism. Thin composite structures with stiffness mismatch exhibit secondary bending moment due to the shift of neutral-axis. This neutral-axis shift eventually causes delamination, which is generated by high peel stresses at the edge of a stiffener. Cohesive zone model and classical lamination theory combined with first ply failure criteria are performed to determine the preferred area for FBG sensor installation before manufacturing. Experiments were conducted to determine load distribution and failure mode within the specimen. Some non-destructive inspection, such as acoustic emission test and ultrasonic C-scan inspection, are conducted. Micro-structure microscopy is performed to observe the damage in detail. And during the static test, FBG sensor was lit using a broadband light source then the spectrum behavior will retrieve until specimen broken. In this research, a close understanding between the mechanical behavior as finite element analysis result and experimental results are obtained. FBG sensor has successfully detected, monitored and characterized some kinds of damage caused by both loading cases. Multi-peak occurrence is used to interpret the damage growth when specimen experienced with non-linear strain, while is experienced linear strain then wavelength broader is used. FBG sensor combined with C-scan inspection can predict the damage growth. A spectrum graph of the FBG sensor results can be used to replace a stress-strain mechanical graph for use in composite structural health monitoring. However, the additional riveting process can potentially introduce delamination near the holes in post manufacturing. It can be seen that the original spectrum changes. Finally, recommendation on how to establish the structural health monitoring is given. This thesis has proven that FBG sensor is an effective tool to detect damage in composite materials and structures. FBG sensor has a great potential to change the conceptual design and the maintenance process of the aircraft.
首都大学東京, 2014-03-25, 博士(工学), 甲第446号
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