Paper tube-guided blast response of sandwich panels with auxetic re-entrant and regular hexagonal honeycomb cores - An experimental study

Auxetic honeycomb structures have drawn increasing attention for impact/blast protection purposes owing to their superior indentation resistance and energy absorption capability. However, few comparative study on the blast performance among sandwich structures with different auxetic and non-auxetic cores has been performed to date. In this paper, the dynamic behaviors of metallic sandwich panels with auxetic re-entrant and regular hexagonal honeycomb cores (i.e. RHSPs and HHSPs) under the paper tube-guided explosions were investigated by a series of blast tests. The failure modes and underlying mechanisms of the target panels with different core relative densities under different impulse levels were classified and analyzed in detail. The panel blast resistance was evaluated by means of the back-face maximum permanent deflections, introducing the testing results of double arrowhead honeycomb sandwich panels (DAHSPs) in a separate paper. It indicates that the introduction of the paper tube achieved the concentration of shock energy, thus aggravating the panel central damage levels remarkably. For the RHSPs with NPR effect, the predominated failure modes of front faces transitioned essentially from the complete petal-like tearing to a local inner dome as the blast impulse decreased. The ones for the back faces ranged from partial tearing to pure global bending deformation, while the core failure modes tuned from central crushing and peripheral buckling to global compression deformation with central shrinkage and boundary adduction. Relative to the RHSPs, the equivalent HHSPs with a higher compressive strength were less insensitive to the blast intensity. Within the scope of present study, the DAHSPs could experience lower back face deflections than those of RHSPs regardless of core relative density. The auxetic honeycomb sandwich panels not always exhibited better over the non-auxetic HHSPs, which depended greatly on the blast impulse and core density level. This comparative research provides a useful reference for the auxetic sandwich honeycomb core design in protection applications.