Aluminum hexagonal honeycomb panels are commonly used in the aerospace industry to reduce weight due to their high stiffness to mass ratio. The panels are commonly involved in incidents where they are dented in the out-of-plane direction which causes plastic deformation in the face-sheet and buckling collapse of the thin repeating cell-walls in the core. This thesis investigates the responses to barely-visible-impact-damage (BVID) in aluminum honeycomb sandwich panels in the out-of-plane direction with particular attention to the structural adhesive. The structural adhesive forms a fillet shape between the face-sheet and the aluminum core during the 120oC curing process and can coat over 50% of the honeycomb core thickness in some cases. Because BVID is common in honeycomb panels, this study looks to improve the understanding of how various factors affect the panel’s response to denting, starting with the adhesive at the interface between the face-sheets and core.

To simplify the problem, the out-of-plane direction was isolated by compressing a panel uniformly. This provided results showing how the adhesive geometry affects the stiffness in a key loading direction with respect to denting. The adhesive was found to cause a higher critical buckling stress and a lower percent compaction before densification. Buckling location was more random when compared to the honeycomb core with no adhesive due to fixed constraints at the top and bottom of the core, where damage would usually initiate. A new mathematical prediction of the stress-strain response was developed, which will be referenced as a material model, to account for adhesive effects. The proposed mathematical material model for the stress-strain curve resulted in R-squared values above 0.82 when compared to experimental data.

Force-displacement data collected from quasi-static experiments with a spherical contact showed that the amount of adhesive was positively correlated to the damage resistance, energy absorbed and the depth of interior buckling damage in the core. This study provides researchers and engineers with experimental results that present a relationship between the structural adhesive and the response to BVID in honeycomb panels.