外文翻譯--在碳纖維復(fù)合材料的沖擊損傷檢測使用布拉格光纖光柵(英文）

1、This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 138.253.100.121This content was downloaded on 11/12/2014 at 20:32Please note that terms and condition

2、s apply.Impact damage detection in CFRP using fiber Bragg gratingsView the table of contents for this issue, or go to the journal homepage for more2004 Smart Mater. Struct. 13 719(http://iopscience.iop.org/0964-1726/13/4

3、/009)Home Search Collections Journals About Contact us My IOPscienceH Tsuda et allight transmitted through FBG broadband light sourceoptical circulatorFBGintensitywavelengthλ Blight reflected from FBGλ Bcompression te

4、nsionlonger wavelength shorter wavelength1 23wavelengthintensityintensitycompression tensionFigure 1. Intensity distribution of light reflected from and transmitted through a FBG.active sensing system with a FBG sensor i

5、s investigated. A cross-ply CFRP with visible impact damage was used as the specimen to be monitored. An ultrasonic wave generated with a PZT pulser was propagated in the specimen and the resultant FBG sensor response wa

6、s recorded. The influence of damage on response signal behavior was investigated. Furthermore, ultrasonic wave detection with a PZT sensor was performed to compare with the FBG sensor response.2. Fiber Bragg gratings2.1.

7、 Operation principle of FBGs [12, 13]FBGs are a periodic perturbation of the refractive index along the fiber which is formed by exposure of the core to an intense optical interference pattern. When broadband light is tr

8、ansmitted to a FBG, a narrowband spectrum is reflected with a central wavelength called the Bragg wavelength, while other wavelengths are transmitted onward through the fiber. Figure 1 illustrates an optical system with

9、a FBG and the light intensity distribution of the system. The optical circulator depicted in figure 1 is an optical device that transmits light only in one direction through a series of ports. In the case of figure 1, li

10、ght can go from port 1 to port 2 and port 2 to port 3, but not from port 2 to port 1. The Bragg wavelength, λB is given by equation (1): λB = 2n? (1)where n and ? are the effective refractive index of the fiber core and

11、the grating period, respectively. Both the refractive index and the grating period of a FBG vary with strain and temperature the FBG is subjected to. The relative shift in the Bragg wavelength, ?λB, for an applied strain

12、 along the fiber axis by ε under a constant temperature condition is given by equation (2):?λB = 0.787λBε. (2)From the above equation an imposed strain of 1% would lead to a 12.2 nm shift in the Bragg wavelength of a FBG

13、 whose Bragg wavelength at strain free is 1550 nm. The shift in the Bragg wavelength is positive when the FBG is elongated. Conversely, when the FBG is being compressed, the Bragg wavelength shifts to negative. The optic

14、al power versus wavelength can be measured with the optical spectrum analyzer (OSA). Accordingly, strain can be evaluated by connecting light reflected from the FBG, port 3 in the example shown in figure 1, to the input

15、of the OSA.2.2. Principle of ultrasonic detection using FBGsThe propagationofanultrasonic wave inmaterials causes high- speedstrainchange inthe microstrainrange. The samplingrate of the OSA is a few hertz at the maximum.

16、 Owing to the low sampling rate, the OSA cannot detect high-speed strain change caused by an ultrasonic wave whose frequency ranges from 100 kHz to a few megahertz. Such high-speed strain change can be detected with FBG

17、sensors from a wavelength–intensity conversion technique. Consider light reflected from a FBG conducted into an optical filter whose transmissivity changes with wavelength. Then, the intensity of light transmitted throug

18、h the filter depends on the Bragg wavelength of the FBG. In other words, the intensity of light transmitted through the filter depends on the strain applied to the FBG. Light intensity can be measured with photodetectors

19、. The response frequency of photodetectors is usually over 10 MHz. Hence, high-speed strain change can be detected by measuring the intensity of lighttransmittedthroughthe opticalfilterusingphotodetectors. In order to de

20、tect subtle strain change in the microstrain range, the optical filter must meet stringent optical character- istics whose transmissivity varies within a narrow wavelength range that includes the Bragg wavelength of the