Damage detection system

Abstract

A damage detection system including: a optical fiber sensor including a core portion to have a grating portion formed therein, the grating portion having gratings reflecting light, wherein a wavelength band of the reflected light changes when a distance between adjacent gratings changes; a light source to input broadband light into the core portion; two optical filters connected to an output end of the sensor; and an apparatus to perform arithmetic processing on output values of the optical filters, wherein each passband of the optical filters overlaps with the vibration range of the wavelength band, in which a center wavelength of one of the passbands is fixed to an upper area of a vibration center of a center wavelength of the reflected light and that of the other of the passbands is fixed to a lower area thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the scope of the invention, and wherein:

FIG. 1 is a schematic configuration view of a damage detection system according to an embodiment of the present invention;

FIG. 2A is a schematic configuration view of a optical fiber sensor, and FIG. 2B is a diagram showing a refractive index change of a grating portion in a light traveling direction;

FIG. 3A is a configuration view of a optical fiber sensor and a spectrum analyzer connected thereto, and FIG. 3B is a spectrum diagram showing passbands of eight optical filters;

FIG. 4A shows a waveform of an input wave to the optical filter, FIG. 4B is a spectrum diagram showing passbands of two optical filters, and FIG. 4C shows waveforms of output waves from the optical filters;

FIG. 5 is a block diagram showing a control system of the damage detection system according to an embodiment of the invention;

FIG. 6 is a graph showing the relationship between length of damage and DI values;

FIG. 7 is a perspective view of a skin/stringer structure in which optical fiber sensors and piezoelectric elements are embedded;

FIG. 8 is a plan view of a sample for directivity test of a optical fiber sensor;

FIGS. 9A-9C show a series of waveforms of output waves of the spectrum analyzer, obtained in the directivity test of the optical fiber sensor;

FIG. 10 is a graph showing the relationship between θ shown in FIG. 8 and the maximum voltage of the output waves of the spectrum analyzer;

FIGS. 11A-11C are a series of 3D diagrams showing analyzed results for spectrum response of reflected light in the case that sensor length is 10 mm;

FIG. 12A is a plan view of S₀ wave propagating through a structure, and FIG. 12B is a plan view of A₀ wave; and

FIG. 13 is a graph showing the relationship between frequency and propagation velocity of an elastic wave propagating in a cross-wise laminated CFRP board ([0₂/90₂]s, thickness of 1 mm).

Claims

1. A damage detection system comprising: a vibration actuator to apply vibration to a subject to be inspected;a optical fiber sensor including a core portion to have a grating portion formed therein, the grating portion having a plurality of gratings reflecting light, wherein a wavelength band of the reflected light changes when a distance between adjacent gratings changes, and the optical fiber sensor vibrates the wavelength band depending on an elastic wave transmitted from the subject;a light source to input broadband light which includes at least a vibration range of the wavelength band, into the core portion;two optical filters connected to an output end of the optical fiber sensor; andan arithmetic processing apparatus to perform arithmetic processing on output values of the two optical filters, the values being obtained when the vibration actuator applies vibration,wherein each of passbands of the two optical filters overlaps with the vibration range of the wavelength band, in which a center wavelength of one of the passbands is fixed to an upper area with respect to a vibration center of a center wavelength of the reflected light and a center wavelength of the other of the passbands is fixed to a lower area with respect to the vibration center of the center wavelength of the reflected light.

2. The damage detection system according to claim 1, wherein the optical filters are arrayed waveguide grating type optical filters.

3. The damage detection system according to claim 1, wherein the grating portion of the optical fiber sensor has a length not more than one-thirds of a wavelength of the elastic wave transmitted from the subject.

4. The damage detection system according to claim 2, wherein the grating portion of the optical fiber sensor has a length not more than one-thirds of a wavelength of the elastic wave transmitted from the subject.

5. The damage detection system according to claim 1, wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

6. The damage detection system according to claim 2, wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

7. The damage detection system according to claim 3, wherein the arithmetic processing apparatus analyzes a change of output values for a predetermined period output from the two optical filters and calculates a value corresponding to a scale of damage in the subject.

8. A damage detection system comprising: a optical fiber sensor including a core portion to have a grating portion formed therein, the grating portion having a plurality of gratings reflecting light, wherein a wavelength band of the reflected light changes when a distance between adjacent gratings changes;a light source to input broadband light which includes the wavelength band, into the core portion;two optical filters connected to an output end of the optical fiber sensor; andan arithmetic processing apparatus to perform arithmetic processing on output values of the two optical filters,wherein each of passbands of the two optical filters overlaps with the vibration range of the wavelength band, in which a center wavelength of one of the passbands is fixed to an upper area with respect to a vibration center of a center wavelength of the reflected light and a center wavelength of the other of the passbands is fixed to a lower area with respect to the vibration center of the center wavelength of the reflected light.