Resolution study of laser-ultrasound technique for disbonds detection in multilayered metallic structures

Multilayered metallic structures, such as adhesively bonded aluminum plates, are increasingly used as construction elements for their reduced weight and strong mechanical properties. However, non-destructive inspection of these components is challenging due to multiple reflections and mode conversions in traditional ultrasonic scans. Laser ultrasound (LU), a fully optical, non-contact technique, offers fast and efficient inspection with high-resolution performance. LU generates a broad range of frequencies, and shear modes can be efficiently produced in the thermoelastic regime using low laser energies. This paper analyses the resolution of a laser-generated shear wave technique for inspecting adhesively bonded aluminum plates. Multiphysics finite-difference simulations are performed on a two-layer aluminum plate model bonded with an epoxy film, incorporating a defect simulating delamination. Various defect depths are examined to evaluate the technique’s resolution, and the simulation results are validated through experiments on a structure composed of three aluminum plates bonded with an epoxy film.