Energy absorption of an axially crushed square tube with a buckling initiator

Axially crushed thin-walled square tubes have been widely used as energy absorbers because of their high specific energy absorption capacity and long stroke. However, they render extremely high initial peak forces which may cause serious injury or damage to the people or structures being protected. This paper proposes a novel idea that by installing a buckling initiator near the impact end which is composed of a pre-hit column and pulling strips, the initial peak force of the square tube could be greatly reduced while its deformation mode and excellent energy absorption are retained. Both experimental and numerical investigations are conducted on aluminum alloy square tubes. The peak force, mean force and half-length of a fold of the tested specimens are examined. The results show that the mean crushing force and deformation mode are not affected by the buckling initiator, while the reduction of the peak force strongly depends on the pre-hit height. It is also found that the buckling initiator can ensure the deformation more stable and uniform. Finally, a simplified analytical model is developed to study the relationship between the reduction of the peak force and the geometric imperfections; and the model can successfully predict the effectiveness of the buckling initiator.