Quantitative Depth Estimation in Lock-In Thermography: Modeling and Correction of Lateral Heat Conduction Effects.

Area of Science:

• Materials Science
• Non-destructive Testing
• Heat Transfer

Background:

• Lock-in thermography is crucial for detecting subsurface defects.
• Accurate defect depth estimation is vital for material integrity assessment.
• Lateral heat conduction can introduce significant errors in depth measurements.

Purpose of the Study:

• To investigate the influence of lateral heat conduction on quantitative depth estimation in titanium alloys.
• To compare the effectiveness of the blind frequency method and the phase difference method.
• To develop a correction strategy for improving depth estimation accuracy.

Main Methods:

• Combined one-dimensional analytical modeling and three-dimensional finite element simulations.
• Conducted parametric analyses for various defect radius-to-depth ratios and excitation frequencies.
• Developed an exponential correction model to compensate for lateral conduction effects.

Main Results:

• The blind frequency method showed significant underestimation (up to 20.7%) at small radius-to-depth ratios (0.5).
• The developed correction model reduced errors to within ±5% for the blind frequency method.
• The phase difference method's accuracy depends on defect depth, frequency, and radius-to-diffusion length ratio, with negligible errors when the ratio exceeds 3.

Conclusions:

• Lateral heat conduction is a primary source of bias in quantitative thermography depth inversion.
• The proposed exponential correction model effectively mitigates depth estimation errors.
• This work enhances the accuracy of nondestructive testing for engineering applications.