Quasi-static biaxial plastic buckling of tubular structures used as an energy absorber

The aim of this experimental study is to improve the energy absorption capacity of tubular metallic structures during their plastic buckling by increasing the strength properties of materials. Based on a novel idea, a change in the plastic strength of materials could be predictable through the loading pathcomplexity concept. An original experimental device, which represents a patent issue, is developed. From a uniaxial loading, a biaxial (combined compression-torsion) loading path is generated by means of this device. Tests are carried out to investigate the biaxial plastic buckling behavior of several tubular structures made from copper, aluminum, and mild steel. The effects of the loading path complexity, the geometrical parameters of the structures, and loading rates (notably the tangential one) on the plastic flow mechanism, the mean collapse load, and the energy absorbed are carefully analyzed. The results related to the copper and aluminum metals show that the plastic strength properties of the tubes crushed biaxially change with the torsional component rate. This emphasizes that the energy absorption improves with increasing the applied loading complexity. However, the energy absorbed data for the mild steel tubular structures do not demonstrate the same sensitivity to the quasi-static loading path complexity.