Out-of-plane compressive response of aluminum honeycomb sandwich panels: Adhesive geometry and bonding effects

Lightweight aluminum honeycomb sandwich panels are widely used in industrial engineering, particularly in aircraft applications. Due to their thin-walled nature, the honeycomb cell walls are especially susceptible to buckling under out-of-plane compressive loading, while the adhesive fillet that secures the honeycomb to the face-sheet remains intact. This paper investigates the effect of the adhesive geometry and bonding constraints on the out-of-plane compressive response through experimental, Finite Element (FE), and mathematical methods. A hybrid method accounting for adhesive bonding between the face-sheet and the cell walls, and different adhesive fillet geometries was proposed to predict strain onset and stress-strain relationships during densification. The resulting stress-strain curves predicted the energy absorbed by the panels to within 3.5% of the experimental results. The widely used material model for honeycomb core does not account for densification and underpredicted the absorbed energy by 15.6%. These findings emphasize the need for detailed adhesive analysis in the design of lightweight, thin-walled sandwich structures.