Physics-guided ultrasonic measurement strategy for robust debonding detection in thermal protection tiles under damage-geometry variations

Reliable inspection of thermal protection tiles requires measurement techniques capable of maintaining diagnostic accuracy under variations in sensor coupling and damage configurations. However, ultrasonic guided-wave measurements obtained using mobile contact scanning often suffer from arrival-time fluctuation, waveform distortion, and distribution shifts caused by changes in defect geometry. This work presents a physics-guided measurement framework for robust debonding detection in multilayer thermal protection structures. A deployable pitch-catch scanning strategy using a removable transducer pair is developed, followed by a physics-guided signal standardization procedure to reduce coupling-induced temporal variability and isolate damage-sensitive wave packets. A domain-adaptive learning model is subsequently introduced to compensate for residual distribution differences associated with damage-geometry variations. Experimental measurements from thermal protection tile specimens demonstrate that the proposed method achieves 95.68% accuracy and a Macro-F1 score of 0.952 on physically held-out target specimens, outperforming the source-only CNN and the compared domain-adaptation methods. The proposed methodology provides a robust ultrasonic measurement solution for reliable inspection of reusable aerospace thermal protection structures under practical scanning conditions.