Effective elastic properties of sandwich-structured hierarchical honeycombs: An analytical solution

Sandwich-structured honeycombs (SSHCs) are hierarchical structures comprising sandwiched cell walls and are known to exhibit enhanced mass-specific properties. Here, we present an analytical model capable of predicting the effective elastic properties of hexagonal SSHCs, employing a sandwich beam theory that accounts for the effect of thick faces and regards the core as structurally weak. The analytical solutions of the nine elastic constants are compared with the numerical predictions obtained from a finite element-based homogenization technique, and an excellent agreement is reported for a wide range of architectural parameters such as the beam size, core thickness, and angle. Overall, it is found that SSHCs outperform conventional (monolithic) honeycombs in terms of their in-plane elastic and shear moduli, reporting values up to 20 times the monolithic counterparts of identical mass. In contrast, the out-of-plane shear moduli of the SSHCs showed reductions of at least 10% as compared to the traditional monolithic honeycomb structures.