Bionic Inner-Tapered Energy Absorption Tube Featuring Progressively Enhanced Fold Deformation Mode.

Slender tubes are in high demand owing to their lightweight and outstanding energy absorption. However, conventional slender tubes are prone to catastrophic failures such as Euler's buckling under axial load. Interestingly, growing bamboos overcome this similar dilemma via a unique tapered intine in the internodes, which endows them with excellent energy absorption. Inspired by this finding, a bionic inner-tapered tube (BITT) was designed to enhance the energy absorption of slender tubes under axial load. The special energy absorption (SEA) was evaluated via a quasi-static axial compression test. Then, theoretical calculation and finite element analysis were carried out to analyze the energy absorption mechanisms. The results reveal that the tapered inner wall induces a progressively enhanced fold deformation mode for BITT, which not only prevents buckling failure and decreases initial peak crushing load but also improves the energy absorption efficiency by increasing plastic deformation. The influences of taper and length-diameter ratio on the axial energy absorption of BITT are explored. Finally, the bionic square array (BSA) and bionic hexagon array (BHA) are fabricated by taking BITT as the basic structural unit, which significantly improves the main energy absorption performance indicators under axial load.