Elastic wave based Non-Destructive Evaluation for joint characterization in thin section welded structures

Ensuring safety and reliability in aerospace, automotive, civil, and mechanical industries require efficient evaluation of weld integrity. This involves assessing mechanical, metallurgical, and morphological properties of the bonded zone. Elastic wave-based Non-Destructive Evaluation provides a cost-effective and efficient alternative for long-range, through-thickness, and in-situ inspection. For this investigation, two 2mm-thick plates of Al5052-Al6083, measuring 250mm x 180mm, were friction stir welded in a lap arrangement. Out-of-plane displacement was generated by a Piezoelectric Transducer and measured using a Laser Doppler Vibrometer. To generate pulses of 60V and 120V at frequencies of 60kHz and 80kHz, a high-voltage amplifier was utilized. Additionally, visco-elastic bands were employed at the structure boundary for damping purposes. This study used both fundamental modes to analyze various weld discontinuities such as voids, tunnels, microcracks, hooking bonds etc. Frequency-wavelength filtering techniques were applied for advanced signal processing. Also, the results were cross validated using X-ray, SEM, EDS, and CT scans. This investigation found a direct correlation between lamb wave propagation and weld performance, as the defect size increased, wave transmission decreased from 13.50dB to 6.34dB at 120V and 60kHz. Abruptly lower transmission behavior at 80 kHz of D2 defect is due to S0 mode conversion. Keywords: Lamb wave, Non-Destructive Evaluation, Weld integrity, Friction stir welding, Thin section lap joint