In-plane elastic wave propagation in aluminum honeycomb cores fabricated by bonding corrugated sheets

Aluminum honeycomb cores are widely used in sandwich structures due to their high stiffness-to-weight ratios and very low densities. However, owing to their porous architecture, honeycomb cores are inherently week and are susceptible to damage due to inadvertent or improper loadings on their encompassing sandwich structure. This damage can potentially lead to the failure of the sandwich structure, and therefore it should be detected and evaluated, preferably using nondestructive methods. Common nondestructive techniques have limited effectiveness in inspecting aluminum honeycombs due to their porous structure and dispersive properties. Since honeycombs are less dispersive at sub-ultrasound frequencies, inspecting them using low and sub-ultrasound frequencies has been introduced lately as a promising alternative to ultrasound inspection. However, this approach requires a priori knowledge of the wave propagation characteristics in the inspected material, which is not readily available for most commercially available aluminum honeycombs, especially the ones manufactured by joining thin corrugated sheets. Thus, this work utilizes finite element computations to assess the low frequency wave propagation characteristics (i.e. phase velocity and dispersive properties) in commercially available aluminum honeycombs made by bonding thin corrugated sheets. Results illustrate that the dispersive behavior and acoustic anisotropy of the studied honeycombs are more significant at higher porosities and high frequencies as well as identify the frequencies below which honeycombs exhibit their least dispersive acoustic behavior.