Energy absorption and mechanical response of Graded face-centered cubic structures

Enhancing the energy absorption capability of lightweight structures, through the use of functionally-graded materials, has recently attracted attention. The thickness grading method of plate lattices in the literature is limited to a discrete layer-by-layer grading, as the thickness in any single layer is uniform but different from the thickness of the other layers. The sudden changes between the layers result in a stress concentration. A continuous thickness grading is achieved in this study, and the effect of employing distinct grading schemes applied to FCC structures has been investigated. Axial continuous thickness grading, lateral continuous thickness grading, and an axial-lateral hybrid continuous thickness grading are examined, alongside discrete layer-by-layer unit cell size grading. Manufactured from Nylon using the material extrusion additive manufacturing method, the samples were benchmarked against uniform structures. To further understand the behavior of these structures, a numerical study, via Abaqus models of the quasi-static compression test, was undertaken and the resulting predictions offered good agreement with the experimental data. The axial thickness grading exhibits significant potential, resulting in a substantial increase of up to 39 % in specific energy absorption due to the layer-by-layer deformation, compared to their uniform counterparts. In contrast, unit cell size grading compromises the energy absorption efficiency, while improving the crushing force efficiency by 35 %. A higher mean crushing force up to 8 % was achieved by the lateral grading method. This investigation highlights the effect of adopting distinct grading approaches on both energy absorption and mechanical response, yielding useful information for the design of advanced protective systems.