Mechanical properties and energy absorption of 3D printed square hierarchical honeycombs under in-plane axial compression

Hierarchical structural design was considered as a promising approach to improve the performance of regular cellular materials. In this study, square hierarchical honeycombs (SHHs) were fabricated by employing a commercial 3D printer, and their in-plane mechanical properties and energy absorption were investigated. The SHHs were constructed by replacing each solid cell wall of a regular square honeycomb (RSH) with different numbers of smaller square substructures. In-plane quasi-static compressive tests were conducted on SHHs, and the effect of substructure number on the deformation mode, mechanical properties and energy absorption performance were studied. The results revealed that the cells of SHHs and RSH collapsed layer-by-layer along the loading direction, while more localized bands and damage were found for SHHs. Enhanced compressive strength, specific energy absorption and crush force efficiency were found for SHHs when compared with RSH of equal mass. Moreover, the reason for the enhancement and the effect of substructure number on the enhancement were also explored. In addition, analytical expressions for the Young's modulus and compressive strength of SHHs were developed, and the results from experiments and simulations were employed to verify the analytical results. This study elucidates the effect of structural hierarchy on the mechanical properties and energy absorption performance of regular cellular materials.