Damage imaging using 2D teager-kaiser operator for early-time ultrasonic guided wavefields

Abstract

Ultrasonic wavefield imaging using wavefield measurement systems, such as scanning laser Doppler vibrometer systems, has proven to be a powerful non-destructive testing (NDT) technique. Yet, conventional energy-based imaging methods require bypassing the incident wave and reflection from borders to isolate trapped waves, which makes these approaches less effective in scenarios where excitation occurs within the inspection area and boundaries are closely situated, like an adhesive lap joint. This study introduces a damage imaging approach using the 2D Teager-Kaiser energy operator (TKO) applied to the wavefield and its square waveform. The proposed method exploits early wavefield propagation for direct damage imaging. This is particularly advantageous for disbond imaging, where the S0 mode is converted to A0 in the disbond region. In such cases, it enhances effectiveness in systems where measurements are more sensitive to the out-of-plane vibrations (A0) while the in-plane vibrations (S0) are weak. It is found that applying TKO to the wavefield achieves high contrast imaging compared to root-mean-square (RMS) calculations. The proposed method, applied to the square waveform of the wavefield, indirectly exploits its phase sensitivity to the disbond region and directly provides high contrast imaging, which provides an effective solution for high contrast disbond imaging using early wave propagation. Numerical simulation and experimental validation on different adhesive joints with a variety of disbond sizes demonstrate that the proposed technique effectively amplifies weak defect-induced interactions while reducing masking effects from direct wave propagation.