A Novel Approach to Subsurface Defect Analysis with Lock-In Thermography Using Unified Formulation

Abstract This work examines the sensitivity of Lock-In Thermography (LIT) for subsurface defect detection using an advanced Finite Element Model based on the Carrera Unified Formulation (CUF). The model significantly reduces computing costs while accurately simulating heat transfer in composite laminates with simulated defects using a 2D in-plane mesh with a through-thickness approximation. This computation method has a significant advantage over traditional numerical approaches because it enables defect position variation without requiring mesh modifications. As expected, simulation results show that larger defects are simpler to detect, but deeper defects require optimal excitation frequencies to enhance detection. To verify the sensitivity of the adopted model to defect size and depth, statistical analysis was performed changing the excitation frequency. Furthermore, the developed numerical model is a robust tool for predicting thermographic responses under varying conditions. It enables the refinement of inspection parameters for both industrial applications and academic research, reducing experimental costs and enhancing the understanding of Lock-In Thermography (LIT) methodologies.