Phase-Based Thermal Wave Analysis for Lateral Characterization of Subsurface Defects in Solid Materials via Modeling...

Area of Science:

• Materials Science
• Non-Destructive Testing
• Infrared Thermography

Background:

• Lock-in thermography is a key infrared non-destructive testing (NDT) method.
• Quantitative characterization of subsurface defects at various depths is challenging.
• Optimizing defect detection requires understanding thermal wave behavior.

Purpose of the Study:

• To investigate the lateral resolution of subsurface defect detection using phase-based lock-in thermography.
• To analyze the influence of excitation frequency on defect visibility and boundary definition.
• To establish guidelines for selecting optimal excitation frequencies in thermal-wave NDT.

Main Methods:

• Integration of analytical modeling and finite element simulation.
• Phase-based analysis of surface temperature variations.
• Phase difference analysis to assess defect characteristics.

Main Results:

• Excitation frequency significantly affects defect visibility and boundary definition.
• Thermal diffusion length, dependent on frequency, controls penetration depth and lateral spread.
• Higher frequencies improve lateral resolution; lower frequencies enhance detectability of deeper defects.
• A radius-to-depth ratio threshold of 2 is critical for reliable boundary delineation.

Conclusions:

• Excitation frequency is a crucial parameter for balancing depth sensitivity and lateral resolution in lock-in thermography.
• Practical guidance is provided for optimizing frequency selection in thermal-wave NDT.
• Defect size and depth ratio critically influence detection reliability.