Numerical and experimental studies of plate boards using air-borne ultrasound

The paper presents the results of the comparative numerical and experimental studies of the propagation of low-frequency ultrasonic Lamb waves in flat polyethene boards. A non-contact ultrasonic technique was applied in the experiments. At the same time, numerical simulations were performed using the k- Wave MATLAB toolbox to simulate acoustic wave fields in the time domain. The studies focused on analysing the amplitudes of an antisymmetric (A0) Lamb wave mode. The subjects of the studies were homogeneous, isotropic polyethene boards in undamaged and damaged states. The three damaged states are delamination, a crack at the board's edge, and rupture in the middle part of the board. In the experiments, even minor defects of a few millimetres in size lead to 20% changes in the A0 Lamb wave amplitude. A qualitative agreement was observed between numerical simulations and experimental ultrasonic results. It was shown that the sensitivity of the experimentally measured Lamb-wave amplitudes was higher than that of the simulated amplitudes.