Quantitative evaluation of crack orientation in aluminium plates based on Lamb waves

The forward- and back-scattering of Lamb waves by through-thickness cracks of varying length and orientation was studied by numerical simulation and experimental validation. Surface-bonded piezoelectric discs were arrayed as actuators and sensors to generate and collect Lamb waves, respectively, and the effect of crack orientation on Lamb wave propagation was evaluated. Lamb waves reflected and transmitted by cracks of finite size were assessed to obtain the reflection and transmission coefficients subject to crack orientation, with the aid of a Hilbert transform. Using this relationship, crack orientation was quantitatively determined by evaluating the different amplitudes of energy peaks in the Hilbert spectra. The distribution of scattered waves around a crack was further studied for the circumstance of normal wave incidence. The limitation of the proposed technique for effective damage identification based on forward analysis of wave scattering was also discussed.