Optical fiber sensor systems for simultaneous monitoring of strain and fractures incomposites

Abstract

In this paper, a fiber optic health monitoring system was proposed and applied to thesensing of strain and fracture behaviors of composites. In order to detect strain andfracture signals simultaneously, we combined a white light interferometer with an intensitydemodulator in an EFPI (extrinsic Fabry–Perot interferometer) sensor. Both abroadband light source and a narrowband filter such as an FBG (fiber Bragg grating)and a Fabry–Perot filter were coupled in an EFPI sensor imbedded in compositespecimens. This paper compares the performance of two fracture sensing units withdiffering intensity demodulating filters and describes the implementation of thetime–frequency analysis of STFT (short time Fourier transform) for the detection of thefracture signals like matrix cracking. From the test of tensile load monitoring usingthe optical fiber sensor system, the measured strain agreed with the value of anelectric strain gage, and the fracture sensing unit could detect matrix crackingwith high sensitivity to recognize the onset of the micro-crack fracture signals.