A novel 3D printed self-similar hierarchical re-entrant honeycomb with enhanced energy absorption and shape recoverability

This paper introduces a self-similar hierarchical design and lattice filling density process for regular re-entrant (R-Re) honeycombs. Two categories of honeycomb are considered, one with a low lattice filling density (L-Re) and the other with a high one (H-Re). Here, the stress response and energy absorption responses of re-entrant honeycombs are obtained by conducting a series of quasi-static compression tests. The mechanical behavior is subsequently predicted by the finite element simulations. The results show that the stress, specific energy absorption and mean crushing force values of the H-Re honeycombs are two to six times higher than those of their L-Re and R-Re counterparts. In particular, the H-Re honeycomb exhibits pronounced structural recoverability after testing. Following unloading, the H-Re structure can rapidly recover up to 75 % of its original height, and its original height after 6 hours under room temperature conditions. In addition, parametric analyses have been developed to study the effect of lattice filling density on energy absorption, as well as the influence of the representative volume element distribution and relative density on the crashworthiness and failure modes. The results of this study can be used to identify the factors that affect the energy-absorbing characteristics of re-entrant honeycombs and facilitate the design of the next generation of complex hierarchical structures.