Experimental study of energy absorption capability in the lattice structures based on the octagonal bipyramid unit cell

This study has developed and suggested novel lattice structures fabricated by 3D-printing method applicable to energy absorbers. Lattice structures have been designed in two different configurations of bipyramid octagonal microstructure with equal density. They are produced by additive manufacturing technology with two different polymer materials called polylactic acid and polyamide as functionally graded and uniform layers with fused filament fabrication. Quasi-static compression testing has been conducted to analyze the energy absorption ability of such structures. Also, foam injection in structures porosity space has been used to prevent sudden failure of lattice structures in compression experiments. Investigating ten different lattice structure states that lattice structures produced with foam-injected polylactic bipyramid double microstructure with graded layers enjoy higher energy absorption capability and more smooth and stable plateau stress behavior. Furthermore, by injecting foam in this configuration, the specific energy absorption capability has increased by 492%. Therefore, it is possible to improve the mechanical behavior of the structure in equal weights without endangering bearing capacity with the architectural order of the unit cell and promote the energy absorption capability of the structure. Finally, analytical relations and numerical modeling were extracted to calculate the stiffness of both structures in the foam injection state, and the results were compared with the experimental ones.