Accoustic emission crack detection with FBG

Abstract

A Bragg grating based acoustic emission crack detection (AECD) sensor system is developed. The ultimate goal of the sensor system is to provide structural health monitoring of composite structures. Various aspects of the sensor system including the parameters involving the optical filter using a matched fiber Bragg grating have been analyzed. The prototype sensor system was tested using pencil lead break tests and Open-Hole-Tension (OHT) specimens (ASTM D 5766). The fiber Bragg grating sensor was embedded into the composite tension specimen at the mid-plane and outside of the region under strain so as to reduce the effects of unwanted structural strains in the sensor response. Impact tests with the surface mounted sensor system determined the sensitivity of the sensor to the direction of the stress wave. The tests demonstrate the ability of the AECD sensor system to detect a pencil lead break event and actual AE events from a composite specimen both in the near surface and embedded configurations.

Development of smart composite structures with small-diameter fiber Bragg grating sensors for damage detection: Quantitative evaluation of delamination length in CFRP laminates using Lamb wave sensing

“…After the wave propagates in the laminate, the transmitted wave is received by an FBG sensor embedded in or glued on the laminate. Some high-speed FBG demodulation systems have been developed by other researchers [27][28][29][30][31][32]. Since it is difficult to use mechanical moving parts for the systems to detect high-speed change in Bragg wavelength of FBG, the techniques of transformation from the wavelength shift to the optical power are of key importance.…”

“…From the transmitted power ratio of the two waves, the Bragg wavelength can be detected. A uniform FBG or a Fabry-Perot tunable filter was also used for the wavelength filter [30][31][32].…”

Pencil-lead-break transient detecting by phase- optical time domain reflectometer based on coherent detecting

“…As early as 1980, 1-D optical Fourier spectrum analyzer system is used to detect fatigue cracks, as small as 0.5mm fatigue cracks can be tested [3]. Since 1989, the Bragg grating has become the dominant sensor to monitor strains and deformation [4][5]. One remarkable advantage of distributed optical fiber sensors is that the desired measurement can be obtained in a distributed way and spatial profiling can easily be accomplished Distributed sensor corresponds to optical time domain reflectometry (Rayleigh scattering and Fresnel scattering) [6][7].…”

Development of small-diameter optical fiber sensors and high-speed optical wavelength interrogator for damage detection in composite materials

“…FBGs have been used as sensors in a wide range of devices [5][6][7][8] , because they reflect light of a specific wavelength that shifts according to the applied strain or temperature. We developed a FBG sensor with a small-diameter optical fiber whose diameter is less than one-third that of a normal single-mode optical fiber 9) and can thus be embedded in composite materials without inducing any mechanical defects.…”