Impact damage visualization in a honeycomb composite panel through laser inspection using zero-lag cross-correlation...

Area of Science:

• Materials Science
• Nondestructive Testing
• Composite Materials

Background:

• Composite materials are crucial in aerospace and automotive industries.
• Detecting barely visible impact damage (BVID) is vital for structural integrity.
• Existing inspection methods may have limitations in sensitivity and non-contact capabilities.

Purpose of the Study:

• To develop and validate a fully non-contact laser-based nondestructive inspection (NDI) system.
• To characterize and quantify barely visible impact damage (BVID) in a honeycomb composite panel.
• To demonstrate the effectiveness of a zero-lag cross correlation (ZLCC) imaging condition for damage visualization.

Main Methods:

• Utilized a Q-switched Nd:YAG pulse laser to generate guided waves via thermo-elastic expansion.
• Employed a laser Doppler vibrometer (LDV) to measure out-of-plane velocities.
• Applied wavenumber filtering and zero-lag cross correlation (ZLCC) in the space-frequency domain for imaging.

Main Results:

• Successfully imaged two delamination regions in the composite panel.
• The main delamination was characterized as skewed elliptic (17mm x 10mm), and a secondary region (6mm x 4mm) was observed at higher frequencies.
• ZLCC imaging revealed resonance modes within the delaminated area.

Conclusions:

• The developed laser-based NDI system effectively detects and visualizes impact damage in composite structures.
• ZLCC imaging provides accurate damage characterization, comparable to ultrasonic C-scan and X-ray CT.
• The system's ability to reveal resonance modes offers further insights into damage mechanisms.