Honeycomb cores with enhanced buckling strength

Honeycombs, as cores in sandwich panels, are in wider use in transport applications where density-specific performance is critical. The ability of honeycombs to withstand through-thickness compression, and in particular resist buckling, is a key performance factor in many applications. However reports of the systematic study of buckling limits in such materials are scant. Honeycomb unit cells with a range of geometries, including conventional hexagonal, re-entrant hexagonal geometries, and modifications of both thereof, were tested mechanically and simulated via finite element modelling. The primary figure of merit was the density-specific peak compressive stress immediately prior to onset of buckling collapse. The conventional hexagonal honeycomb unit cell, as examined here, is not well optimised for density-specific peak stress; in comparison the re-entrant unit cell examined here had approximately 13% higher density-specific peak stress. Modifications to these geometries, such as face stiffeners and fillets, increased absolute values of peak stress but in most cases were deleterious or at best neutral to density-specific peak stress due to the subsequent increase mass of the honeycombs.