Lamb waves evaluation in CFRP plates with laser shock wave technique

Abstract

Lamb waves, which are guided waves propagating along the surface of a thin plate structure, have been investigated to remotely perform nondestructive testing for aircraft or infrastructures made of carbon fiber reinforced plastic (CFRP) plates. CFRP plates are prone to internal damage such as delamination, which does not occur in metallic materials. Although nondestructive methods such as X-ray, flash thermography, etc. have been investigated in several studies, they may have some disadvantages such as risks of radiation exposure or limitation in terms of size of the structures to be tested for the former, and heat diffusion for the latter. Laser thermoelasticity can generate Lamb waves remotely and nondestructively. However, the generated Lamb waves have a small amplitude; therefore, hundreds of measurements must be averaged to achieve a sufficient signal-to-noise ratio. For these reasons, it has not yet been demonstrated as possible to detect damage in large CFRP structures within a short time using nondestructive, remote-controlled methods. As a first step towards performing nondestructive tests in CFRP plates, this paper demonstrates the generation of A0 mode Lamb waves in the experimental plate samples using laser-induced plasma (LIP) shock waves. The validity of the proposed system is verified by comparing the phase velocities of Lamb waves in the CFRP plates with three different layups obtained with the proposed system, with the theoretical values obtained analytically. This system can generate vibrations in CFRP plates in frequency ranges of a few hundred kHz and allow to determine the phase velocity of the experimental Lamb waves up to approximately 100 kHz.