Experimental determination of Lamb wave dispersion diagrams over large frequency ranges in fiber metal laminates

Fiber metal laminates (FML) are of high interest for lightweight structures as they combine the advantageous material properties of metals and fiber-reinforced polymers. However, low-velocity impacts can lead to complex internal damage. Therefore, structural health monitoring (SHM) with guided ultrasonic waves, in this case, referred to as Lamb waves, is an approach to identify such damage. Numerical simulations form the basis for corresponding investigations, but experimental validation of propagation diagrams over a wide frequency range is hardly found in the literature. In this work the dispersive relation of Lamb waves is experimentally determined for an FML made of carbon fiber-reinforced polymer and steel. For this purpose, a multi-frequency excitation is used to generate Lamb waves and the resulting wave field is measured via laser scanning vibrometry. The data are processed by means of a non-uniform discrete 2d Fourier transform and analyzed in the frequency-wavenumber domain. The experimental data are in good agreement with data from a numerical solution of the analytical framework. In conclusion, this work presents a highly automatable method to experimentally determine dispersion diagrams of Lamb waves in FML over large frequency ranges with high accuracy and reproducibility.