A numerical study of dynamic buckling of thin-walled hollow square columns subjected to axial impact

Crush of square hollow columns subjected to dynamic axial loading is numerically studied. The column is thin-walled, and various cross-sectional shapes from a right square to an exact circle are treated, changing the corner radius. For calculation, the public domain version of the dynamic explicit finite element code DYNA3D is utilized. Two modes of buckling take place, i.e., an in-phase bilateral cyclic folding mode like an accordion and an out-of-phase bilateral cyclic folding mode. In the former mode, the crush strength attains a large value and is more advantageous in order to obtain a large capacity of energy absorption. The crush strength becomes greater for a larger corner radius. Hence, surprisingly enough, the circular hollow column (which is lighter than a right square one by 21.5%) attains the greatest crush strength among other cross-sectional shapes (50% or more than the right square column does). It is greater also for a faster impact speed and a thicker column wall. The buckling takes place more easily in the in-phase bilateral cyclic mode when the cross-section is closer to a circle. All circular hollow cylinders analyzed here have buckled in this mode. The impact speed higher than a certain value also leads the in-phase bilateral cyclic mode of buckling. Typical experiments are also carried out to confirm the calculation reliability.