Stochastic simulations of square aluminium tubes subjected to axial loading

Stochastic simulations of square aluminium tubes of 6060 T6 aluminium alloy subjected to axial crushing have been performed and compared to an experimental program carried out previously at SIMLab. The main variables during testing were the extrusion length, the wall thickness of the extrusions and the impact velocity of the impactor. Three different buckling modes were observed: progressive buckling, transition from progressive to global buckling and global buckling. Progressive buckling was primarily observed in the short specimens, while increasing the length a transition mode took place. However, for the thick-walled tubes a direct global buckling mode was found. In the present study, it has been investigated if geometric imperfections modelled by assumed Gaussian random fields could explain the experimentally observed behaviour. Variation of the random field parameters by use of a factorial design resulted in variations in especially the buckling modes and consequently the average force, and the same buckling modes found in the experiments were obtained in the simulations. For the chosen model, the shape of the geometric imperfections seemed to be more important than the amplitude. Further, simulations of profiles with three different lengths subjected to impacts at two different velocities were performed. The estimated probability for progressive buckling to appear decreased as the length increased, while the change in velocity had minor effects for the chosen parameter range.