Three‐Point Bending Behavior of Foam‐Filled Conventional and Auxetic 3D‐Printed Honeycombs

Cellular hexagonal (conventional) and re‐entrant (auxetic) honeycombs are applicable in automotive, construction, and protective engineering. Auxetic structures own excellent energy absorption and flexural behavior due to their special deformation under loading. This work explores the performance of additively manufactured polylactic acid (PLA)‐ and thermoplastic polyurethane (TPU)‐based hexagonal and re‐entrant honeycombs under flexural loading via experimental three‐point bending (TPB) tests and finite‐element analysis (FEA). 3D‐printed conventional and auxetic cellular structures are filled with polyurethane (PU) foam and their energy absorption capacity and flexural modulus are compared with hollow structures. The results reveal that TPU‐based structures’ energy absorption capacity and flexural modulus improve significantly, whereas the PLA‐based structures’ performance deteriorates when filled with PU foam. Moreover, re‐entrant honeycombs are better reinforced with foam in comparison to the hexagonal honeycombs, as the re‐entrant's unit cell is more spacious than the hexagonal unit cell. Finally, parametric studies are performed via FEA to investigate the influence of geometric parameters of structures and flexural loading setup on the performance of the honeycombs, showing that structures with thicker struts and higher cell angle can act stiffer under TPB. The outcomes of this research indicate the promising performance of foam‐filled TPU‐based auxetic structures.