Inversion technique for an all-optical inspection of materials' elastic properties

In this paper we present a complete non-contact, all-optical inspection tool, for the extraction of the principal mechanical characteristics of plate-like structural materials (effective stiffness, Poisson ratio and plate's thickness). Broadband ultrasonic guided waves - Lamb waves - are optically generated and detected for incremental source detector distances. A two dimensional Fourier transform is applied to these measured time signals in order to extract dispersion information, which is highly affected by elastic properties as well as by sample geometry. The elastic properties and thickness of the structure under test are obtained from this experimentally extracted dispersion information, by an inversion technique which is presented and analysed in the paper. These values are verified with a complementary experiment. Monitoring changes in the estimated material properties could be used to indicate changes in the structural condition.