How does bio-inspired graded honeycomb filler affect energy absorption characteristics?

Functionally graded structures are widely observed in nature and have been considered to have excellent mechanical properties. In this paper, a novel bio-inspired graded honeycomb-filled circular tube (BGHCT) is proposed to enhance structural energy absorption characteristics under lateral load. The graded honeycomb fillers are constructed using 3D printing techniques. To systematically explore the crashworthiness of BGHCT, the nonlinear finite element models are first developed in Abaqus (explicit) and validated against the experiments. Then graded honeycomb-filled circular tubes with axial and radial graded directions are compared with uniform honeycomb-filled counterparts (UHT). Parametric studies find that BGHCT exhibits superior capacity of energy absorption. Furthermore, various parameters, like effective filling length, thickness and yield stress of column wall, have a considerable effect on the crashworthiness of this novel structure. Lastly, multi-objective optimizations of BGHCT and UHT are carried out with the aim of simultaneously improving specific energy absorption (SEA) and reducing peak crushing force (PCF), based upon the Kriging modeling technique and non-dominated sorting genetic algorithm II (NSGA-II). The optimal design parameters are obtained for these honeycomb-filled structures. By comparison we find that energy absorption characteristics can be increased by up to 89.73%, and effective length filled structure has the best crashworthiness, followed by full graded honeycomb-filled structure. The study provides new insights into the transformation of natural biological inspiration into engineering applications for crashworthiness.