Crushing Behavior of Hierarchical Hexagonal Thin-Walled Steel Tubes Under Oblique Impact

In this paper, oblique crushing behaviors of the hierarchical hexagonal steel tubes were investigated. In the oblique impact, the crushing mode transfers from axial crushing dominated mode to bending dominated mode with the increase of the impact angle. In normal impact, the hierarchical steel tubes have progressive folding and global folding, depending on the cell number and the thickness of the sandwich wall. There are two hybrid crushing modes at oblique impact, progressive-folding-bending (hybrid mode II) and global-folding-bending (hybrid mode III). Before the hybrid crushing mode appears, the peak force is reduced but the energy absorbing performance changes little compared with the normal impact. When the impact angle is 10°, the hierarchical steel tube still has excellent energy absorption. It is also found that when the cell number in the sandwich wall changes from 4 to 6, the crushing mode at the impact angle of 10° transfers from progressive folding, hybrid folding II to hybrid folding III, while the crushing mode at normal impact transforms from progressive folding, hybrid folding I to global folding. It is found that adopting hierarchical topology can greatly improve the energy absorption at oblique impact, even better than that of the normally impacted single-cell tubes.