Design and 3D Printing of Graded Bionic Metamaterial Inspired by Pomelo Peel for High Energy Absorption

Light-weight, high-strength metamaterials with excellent specific energy absorption (SEA) capabilities are significant for aerospace and automobile. The SEA of metamaterials largely depends on the material and structural design. Herein, inspired by the superior impact resistance of pomelo peel for protecting the pulp and the elevated SEA ability of a functionally graded structure, a graded bionic polyhedron metamaterial (GBPM) was designed and realized by 3D printing using a soft material (photosensitive resin) and a hard material (Ti-6Al-4V). Guided by compression tests and numerical simulations, the elevated SEA ability was independent of the materials. The fluctuation region appeared in hard-material-fabricated bionic polyhedron metamaterial (BPMs) and was absent in soft-material-fabricated BPMs in the stress–strain curves, resulting in the growth rate of the SEA value of the soft-material-fabricated GBPM being enhanced by 5.9 times compared with that of the hard-material-fabricated GBPM. The SEA values of soft- and hard-material-fabricated GBPM were 1.89 and 44.16 J/g, which exceed those of most soft- and hard-material-fabricated metamaterials reported in previous studies. These findings can guide the design of metamaterials with high energy absorption to resist external impacts.