Impact monitoring of smart composites using stabilized fiber bragg grating sensor system

Abstract

This research focuses on the development of impact damage assessment system of smart composite structures using fiber Bragg grating (FBG) sensors. From the viewpoint of hardware development of an FBG sensor system, research on stabilized a high frequency demodulation technique must be performed in order to constantly maintain the sensitivity of the FBG acoustic sensor. Moreover, a multiplexing scheme for a high-speed demodulation should be developed to improve the system efficiency for the construction of the multipoint AE sensing array of impact damage assessment system for a large structure. In this research, a high frequency detectable multiplexing demodulator using the FFP filter with a narrow free spectral range (FSR) was proposed, which can demodulate the input signals of two FBG sensors simultaneously without the loss of measurable frequency range. In addition, an active stabilization control system was constructed to avoid sensitivity fadeout problems and to maintain the maximum sensitivity of the FBG vibration sensors. In the proposed FBG sensor system, the filtering wavelength of the demodulator is continuously adjusted to the operation point of the FBG spectrum where the slope is the steepest. Because the attenuation of AE signal in composite materials is relatively higher than that of metallic materials and FBG sensor has directional sensitivity variation for the vibration signals of longitudinal mode, it is necessary to develop damage assessment technique less affected by the boundary condition in composite structures. In this research, the damage assessment technique using the sharing percentage of the wavelet detail components was proposed, and a low-velocity impact test was conducted on composite laminates using FBG sensors to confirm the feasibility of the proposed signal processing method. The proposed damage assessment method correctly discriminated the impact damage without being influenced by the signal attenuation and the directivity of th...