Total Focusing Method with Laser-Generated Ultrasonic Waves for Defect Detection in Finite Plates

Abstract

Total Focusing Method (TFM) was employed using laser-generated ultrasonic plate waves. The goal was to assess the feasibility of using this technique for applications where testing constraints necessitate couplant-free, remote, guided-wave conditions. The application under consideration is using laser-generated TFM to assess ultrasonically welded battery tab-to-electrode foil stack joints. It was determined that laser-generated guided wave TFM can be used to remotely assess defects in a finite plate when the defects are strong reflectors in the plane of propagation. The finite dimensions of the tab necessitate a strong understanding of the edge reflection effects on the TFM image. The guided wave modes used in this study were strongly affected by scattering due to a complicated weld surface. Future work will investigate methods to compensate for the strong scattering, the use of other guided wave geometries, out of plane TFM reconstruction for other weld defect types, as well as apodization effects.