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Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography
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Lateral heat flux reduction using a lock-in thermography compensation method
Johannes Rittmann1, Marc Kreutzbruck2
1Institute for Plastics Technology, University of Stuttgart, Pfaffenwaldring 32, 70569, Stuttgart, Germany.
Scientific Reports
|October 10, 2023
Summary
Active thermography (AT) uses thermal waves for non-destructive testing. This study introduces structured heating to improve image clarity and feature detection in optical lock-in thermography (LT).
Area of Science:
- Physics
- Materials Science
- Non-Destructive Testing
Background:
- Active thermography (AT) utilizes surface temperature differences to analyze material properties, but interpretation is challenging due to thermal wave lossiness.
- Current AT evaluation methods often simplify 3D heat flux to 1D, blurring edges and small features.
- Lateral heat flux and temperature gradients complicate analysis in optical lock-in thermography (LT).
Purpose of the Study:
- To present a novel method for reducing lateral heat flux and local temperature gradients in LT measurements.
- To enhance the interpretation of 2D temperature fields in active thermography.
- To improve feature detection efficiency and image quality in LT.
Main Methods:
- Implementation of spatial- and temporal-structured heating in optical lock-in thermography.
- Minimizing lateral heat flux by reducing local temperature gradients at feature areas.
- Converting the 3D heat flux problem into a solvable 1D problem.
Main Results:
- The proposed method effectively reduces lateral gradients, simplifying the problem to a 1D heat diffusion scenario.
- The technique bypasses the 'blind frequency' limitation of LT, making inspections less dependent on excitation frequency.
- Significant improvements in edge sharpness and feature separability were observed, enhancing detection efficiency.
Conclusions:
- Structured heating offers a robust solution for overcoming limitations in optical lock-in thermography.
- This approach enhances the accuracy and efficiency of non-destructive evaluation of materials and components.
- The method promises improved defect detection and characterization in various technical and biological applications.
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