Comparative analysis of out-of-plane performance in 3D-printed graded lattice structures

Graded lattice structures have garnered significant attention for their ability to combine lightweight properties with superior mechanical performance. Their tailored structures/properties under in-plane loading make them ideal for impact resistance and energy absorption (EA) applications in aerospace, automotive, and biomedical engineering. Despite the research advances in this field, research into out-of-plane of graded lattice structures is relatively limited. This study investigates the out-of-plane EA performance of three common lattice structures, namely, hexagonal honeycomb (HEX), auxetic re-entrant (REE), and double arrowhead (DAH). Unique grade patterns including bottom thick (BOT), mid thick (MID), and ends thick (EDG), were introduced in the lattices' out-of-plane direction and their mechanical behavior was examined under quasi-static compression conditions using both experimental and finite element analysis. Parametric investigations were conducted to examine the effects of grade ratio, cell wall thickness, and grade patterns, aiming to optimize mechanical EA and crashworthiness of each structure. Results show that the specific energy absorption (SEA) of all structures follows the trend MID > EDGE > BOT > UNI and HEX_MID demonstrated the highest SEA value amongst all designs. On the other hand, all graded lattice structures demonstrated significantly enhanced crash force efficiency, with HEX_BOT, REE_EDGE, and DAH_EDGE approaching similar to 90% of the maximum performance, showcasing their potential for efficient EA.