Binarization Mechanism Evaluation for Water Ingress Detectability in Honeycomb Sandwich Structure Using Lock-In...

Area of Science:

• Materials Science
• Non-Destructive Testing
• Aerospace Engineering

Background:

• Composite honeycomb structures are increasingly used in aircraft, necessitating advanced non-destructive evaluation (NDE) methods.
• Active thermography offers advantages for NDE of composites, but challenges like non-uniform heating and noise persist.
• Water ingress in honeycomb structures can compromise integrity, requiring reliable detection techniques.

Purpose of the Study:

• To investigate the efficacy of lock-in thermography (LIT) for detecting water ingress in aircraft composite honeycomb sandwich structures.
• To analyze the influence of modulation frequency on defect detection performance.
• To evaluate the binarization of phase signals using the Otsu algorithm for quantitative defect assessment.

Main Methods:

• Lock-in thermography (LIT) was applied to a composite honeycomb sample with simulated water ingress defects.
• Defects were created by filling cells with water at varying percentages (25%, 50%, 75%, 100%).
• The sample was excited at multiple modulation frequencies (0.01 Hz to 1 Hz), and phase signals were binarized using the Otsu algorithm.

Main Results:

• Lock-in thermography successfully detected water ingress across different defect sizes and water fill levels.
• Phase contrast and CNR varied with modulation frequency, indicating optimal frequency ranges for detection.
• Binarized images allowed for quantitative analysis of water ingress by comparing detected pixels to theoretical values.

Conclusions:

• Lock-in thermography, combined with Otsu-based binarization, provides an effective NDE method for identifying water ingress in composite honeycomb structures.
• Modulation frequency plays a critical role in optimizing detection sensitivity and characterization accuracy.
• This technique holds promise for ensuring the structural integrity and safety of aircraft components.