Influence of forming effects on the axial crush response of hydroformed aluminum alloy tubes

The impact behaviour of tubular hydroformed axial crush tubes is examined. The results of dynamic axial crush tests performed with both non-hydroformed and hydroformed AA5754 aluminum alloy tubes were compared to predictions from finite element models. Explicit dynamic finite element simulations of the hydroforming and crash events were carried out with particular attention to the transfer of forming history from the hydroforming simulations to the crash models. The values of tube thickness, work hardening, and residual stresses at the end of the hydroforming simulations were used as the initial state for the crash models. In general, simulations performed using the von Mises yield criterion with isotropic material behaviour gave reasonable predictions when compared to experimental data. It was found that it was important to account for the forming history of the hydroforming operation in the axial crush models. The results showed that work hardening resulting from hydroforming is beneficial to increasing the energy absorption during crash, whereas thickness reduction decreased the energy absorption. Residual stresses had little effect on the energy absorption characteristics. It was also shown that the energy absorption characteristics of tubes with the same mass could vary greatly by adjusting the geometry of the tube and the amount of work hardening experienced by the tube during hydroforming.