The Location Monitoring of Fatigue Crack Damage by Using the Spectral Area Extracted from FBG Spectra

Area of Science:

• Structural Health Monitoring
• Optical Fiber Sensing
• Materials Science

Background:

• Fiber Bragg Gratings (FBGs) are widely used for structural health monitoring.
• Detecting crack locations accurately is crucial for infrastructure safety.
• Existing methods may be sensitive to environmental factors and noise.

Purpose of the Study:

• To introduce and validate a new damage feature, spectral area, for crack detection using FBGs.
• To assess the robustness and reliability of the spectral area method.
• To compare the performance of different FBG sensor lengths for crack detection.

Main Methods:

• Simulated FBG reflection spectra using the Transmission Matrix Method (TMM) based on strain data from Extended Finite Element Method (XFEM) simulations of fatigue crack propagation.
• Conducted fatigue crack growth monitoring experiments using FBG sensors.
• Employed Digital Image Correlation (DIC) to measure strain at FBG sensor locations.
• Performed temperature characteristic tests on FBGs.

Main Results:

• The spectral area was found to be insensitive to temperature variations and experimental noise.
• The spectral area demonstrated high sensitivity to the non-uniform strain field induced by crack damage.
• A 10 mm FBG sensor provided a larger critical detection range for crack damage compared to a 5 mm sensor.
• Quantitative crack location detection was achieved using the spectral area feature.

Conclusions:

• The spectral area is a reliable damage feature for quantitative crack location detection.
• FBG sensors, particularly longer ones, can effectively monitor fatigue crack propagation.
• The proposed method offers a robust approach for structural health monitoring applications.