Nondestructive evaluation of bilayer metal-composite structures using finite element simulation of guided Lamb wave propagation

Nondestructive evaluation (NDE) of the mechanical properties and thickness loss of bilayer structures is of great importance for health monitoring purposes. This study aimed to propose an NDE method based on the Lamb wave propagation for the inspection of bilayer metal-composite structures. The finite element model of a steel substrate coated with a layered composite material was developed, where the composite coating constituted by chopped strand glass fiber mat and woven roving glass fiber cloth layers. The fundamental antisymmetric Lamb wave mode (A0) with different excitation frequencies were generated and propagated on the modeled bilayer specimens. The dispersion curves for the A0 Lamb wave mode were obtained for the simulated specimens, considering different thicknesses and a range of material properties decay for the metal substrate and composite coating. The obtained results showed that the effect of the thickness and decay in the mechanical properties of the substrate on the A0 Lamb wave mode velocity was more than the effect of the thickness and decay in the mechanical properties of the composite coating. Besides, the estimation of coating thickness was performed more accurately at low frequencies, while the decay in the mechanical properties of the coating and substrate was better evaluated at higher frequencies. It was concluded that the simulated Lamb wave propagation method can be used as a virtual lab for the development of methods for nondestructive evaluation of bilayer metal-composite structures with different material properties and thicknesses.