Debonding monitoring of a composite repair patch using small-diameter FBG sensors

Abstract

This paper presents the health monitoring technique of composite repair patches using small-diameter fiber Bragg grating (FBG) sensors. The composite patch structures consist of carbon fiber reinforced plastic (CFRP) patches, aluminum substrates and adhesive layers. The debonding progressed between aluminum substrate and the adhesive layers under cyclic loading. In this research, two types of the specimen were prepared for evaluation of the debonding size. One is specimen with the patches glued on the both side of the aluminum plate. The other is pre-notched specimen for investigation of the influence of the crack propagation in the substrate. The FBG sensors were embedded into the adhesive layers easily, because the diameter of the sensor was only 52 µm. Reflection spectra from the sensor were measured at various lengths of the debonding. The form of the spectrum changed sensitively with an increase in the debonding size. For confirmation of the measured results, the spectra were simulated theoretically. As a result, the change in the calculated spectrum was consistent with that in the measured spectrum, and the relation between the spectrum and the debonding was clarified. Moreover, the debonding length was evaluated quantitatively by the monitoring of the form of the reflection spectrum.

Online health monitoring and safety evaluation of the relocation of a research reactor using fiber Bragg grating sensors

“…Real-time monitoring provides information on the time, loading condition or other conditions at which damage occurs, thereby facilitating the evaluation of the cause of the damage. Moreover, realtime monitoring provides information as soon as the damage occurs, thus enabling timely repairs or other hazard precaution measures [5][6][7][8][9][10][11][12][13][14][15][16][17].…”

“…One of the most effective sensory devices currently available for structural integrity applications appears to be the fiber optic sensor [5][6][7][8][9][10][11][12][13][14][15][16][17]. Optical fibers were developed for long-distance data transmission in the telecommunications industry.…”

“…The use of optical fibers for applications in the telecommunications industry started in the mid-1960s, and the technology has since undergone tremendous growth and advancement. The development of optical fiber sensors started in 1977, although some isolated demonstrations had taken place prior to this [5][6][7][8][9][10][11][12][13][14][15][16][17]. Compared with the above common NDT methods, fiber optic sensors have many advantages.…”

“…Compared with the above common NDT methods, fiber optic sensors have many advantages. One of the main advantages is that these sensors are very light weight and small enough that they can be embedded in materials in a manner that does not degrade the structural integrity [5][6][7][8][9][10][11][12][13][14][15][16][17]. Fiber optic sensors, and especially the fiber Bragg grating sensors (FBG) in smart structures, are an enabling technology that allows engineers to add a nervous system to their designs, allowing for the detection of damage and the monitoring of the health status of their structures.…”

“…Fiber optic sensors, and especially the fiber Bragg grating sensors (FBG) in smart structures, are an enabling technology that allows engineers to add a nervous system to their designs, allowing for the detection of damage and the monitoring of the health status of their structures. The FBG sensor has been recognized as a new NDE technique suitable for all structural applications [5][6][7][8][9][10][11][12][13][14][15][16][17]. The advantage of using FBG sensors for strain sensing applications is that it is able to measure strain locally with high resolution and accuracy.…”