Energy absorption in the axial crushing of hierarchical circular tubes

In this numerical study by means of finite element modeling, the concept of hierarchy is incorporated into thin-walled circular tubes for a configuration with optimum energy absorption. Hierarchical circular tubes (HCTs) are constructed by replacing the wall of an initially single-cell circular tube (SCT) with a series of small tubes placed next to each other (Fully packed, HCT-F) or at a distance apart (partially packed, HCT-P); the total net cross-sectional area and hence the mass is kept the same. The behavior of these new classes of hierarchical tubes under axial crushing is investigated in terms of deformation modes, crushing forces and energy absorption. Two deformation modes are identified and they have different crushing behavior of the HCTs. The initial peak force (PF) remains almost constant after micro-cell tubes are hierarchically introduced, but the mean crushing force (MCF) and hence the specific energy absorption (SEA) can be significantly improved by choosing suitable configurations. It is also demonstrated that partial hierarchy performs better in enhancing the crushing performance of the tubes compared with the full hierarchy.