Thermal nondestructive testing of corrosion in aviation aluminum panels and data processing algorithms

Rear-surface corrosion on aviation aluminum panels is evaluated by infrared thermal nondestructive testing (TNDT). The corrosion detection capability of the experiment setup is analyzed. The validity of theoretical analysis and some available data processing algorithms are verified. In the inspection of a reference sample with flat-bottomed hole surrogates of corrosion, the highest signal-to-noise ratio (SNR) is ensured by Fourier transformation in time domain; the corrosion detection limit has been estimated as about 10% in defect areas with diameter larger than 10 mm on 1.8 mm-thick aluminum panels. The inspection of a naturally-corroded aircraft panel shows that high SNR values can be provided by original thermal images or simple processing algorithms, such as averaging, however the validity of some advanced algorithms, such as pulsed phase thermography (PPT), principle component analysis (PCA), polynomial fitting and correlation analysis, is doubtful in detecting naturally-corroded aircraft panels. The thermal NDT of the aircraft aluminum sample is analyzed by numerical solution to the corresponding 3D heat conduction problem, the theoretical temperature distribution and evolution are similar to the measured values. A well known 1D corrosion characterization approach is verified on aviation aluminum plates, and is proven to be valid.