Experimental study on the detection of flat-bottomed hole defects in metals using eddy current pulsed thermography

The detection of internal defects in metallic materials plays a crucial role in ensuring the structural integrity and safety of industrial components. Among various non-destructive testing (NDT) techniques, active thermography has gained significant attention due to its ability to detect subsurface defects without damaging the material. This paper focuses on the detection of flat-bottomed hole (FBH) defects in metals using eddy current pulsed thermography (ECPT), a transient thermographic method that leverages localised induction heating for rapid thermal excitation. Furthermore, the study evaluates the effectiveness of traditional image enhancement techniques, such as principal component analysis (PCA), pulsed phase transform (PPT) and thermographic signal reconstruction (TSR), for improving the signal-to-noise ratio (SNR) of ECPT thermal images. Experimental results demonstrate that ECPT exhibits high sensitivity to subsurface defects in aluminium, a metal with high thermal diffusivity. Among the image processing methods tested, PCA provides the most significant SNR improvement for ECPT data, outperforming both PPT and TSR. These findings highlight the potential of integrating ECPT with PCA-based image enhancement as a robust and reliable approach for non-destructive evaluation of internal defects in metals, contributing to the advancement of non-destructive evaluation methods in industrial applications.