Lock-In Thermography with Cooling for the Inspection of Composite Materials

Area of Science:

• Materials Science
• Non-Destructive Testing
• Thermal Analysis

Background:

• Lock-in thermography is a valuable non-destructive testing technique.
• Detecting flaws in composite materials like glass fiber-reinforced polymers (GFRP) is crucial.
• Optimizing thermography parameters can enhance defect detection capabilities.

Purpose of the Study:

• To develop and evaluate a lock-in thermography system with an integrated cooling system.
• To investigate the impact of heating modes and excitation periods on defect detectability in GFRP.
• To quantitatively assess the improvements in signal-to-noise ratio (SNR) for flaw detection.

Main Methods:

• Development of a lock-in thermography system incorporating a cooling mechanism.
• Testing system feasibility on a square-shaped GFRP sample with artificial outer flaws.
• Conducting experiments in two modes: solely heating and simultaneous heating-cooling.
• Varying sinusoidal excitation signal periods (shorter and longer) in each mode.
• Quantifying defect detection using the signal-to-noise ratio (SNR).

Main Results:

• The mixed heating-cooling mode demonstrated improved SNR compared to conventional heating alone.
• Extending the excitation signal period further enhanced the SNR.
• The optimal configuration, combining simultaneous heating-cooling with longer excitation periods, yielded the highest SNR for most detected defects.

Conclusions:

• The addition of a cooling system to lock-in thermography significantly enhances defect detection in GFRP.
• Optimizing excitation signal periods in conjunction with the cooling system provides superior flaw characterization.
• This advanced thermographic approach offers improved non-destructive evaluation capabilities for composite materials.