Abstract
This study investigated the reflected spectral deformation mechanism of fiber Bragg grating (FBG) sensors with crack propagation. This analysis was performed based on the simulated FBG response by applying modified-transfer matrix modeling (TMM) with the strain states, which were extracted by the finite element method (FEM) analysis. Experimental data were obtained from FBG sensors bonded in an aluminum alloy structure and subjected to multiple crack lengths, and the strain values were obtained by digital image correlation (DIC) technology. Based on the simulations and the experimental full spectral response, we compared the performance of two damage features: The full width at half maximum (FWHM) and the spectral difference. In addition, results showed that the two features were insensitive to experimental noise and were highly sensitive to the complex strain field caused by crack propagation. Moreover, the damage features changes in the crack propagation process also provided a way for crack position measurement. Ultimately, the 10 mm grating lengths sensors showed better performance to the crack detection with longer sensitivity distance. According to the research in this paper, the crack position was quantitatively determined by evaluating different damage features of the reflected spectrum.
Highlights
Crack damage usually occurs in aircraft structures
The Strain Detected by digital image correlation (DIC) with fiber Bragg grating (FBG) Spectra Variation
The DIC experimental measurements of the strain fields in the FBG sensor location were focused on
Summary
Crack damage usually occurs in aircraft structures. it only can be detected by global sensors due to the changing of significant structural properties when the damage is at a high level [1]. The spectral difference algorithm based on the dynamic time warping (DWT) method overcame the limitations of traditional cross-correlation coefficient definition It considers the phenomenon of reflected spectrum shifting during crack propagation [12] and ignores the requirement of same comparative signal lengths in traditional definition [13]. Each feature was tested for two cases: First, simulated FBG reflected spectra under a strain state which were extracted by FEM analysis for different crack lengths. These simulation signals were used to evaluate the theoretical sensitivity of each feature to different damage stages. Sensors constant during spectral data acquisition, and a setting of 70–90% of the maximum force may be perfect considering the effects of crack retardation or crack arrest caused by high holding loads [18]
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