Study on the splitting and expansion–splitting modes of thin-walled circular tubes under axial compression

In this paper, the deformation and energy absorption of thin-walled circular tubes in splitting and expansion–splitting modes are investigated by experiments and theory modeling. First, axial compression experiments of both steel and aluminum alloy tubes were conducted. The results show that the initial peak force in splitting mode could be reduced by increasing the number of initial cracks, and the steady force and the stroke efficiency of tubes could be greatly improved by introducing splitting deformation to the expansion mode in series. Afterwards, theoretical models for these two modes are developed by considering the stress coupling and stress equilibrium, which can well predict the experimental results. Based on the theoretical models, it is found that the initial peak force increases with the decrease of the number and the length of the initial cracks. However, when these two parameters are smaller enough, the initial peak force will not increase. In expansion–splitting mode, the splitting effect can weak the force induced by the expansion deformation, and there is a critical expansion die angle to make the steady force minimum. Moreover, the plastic dissipation is always larger than the tearing dissipation, while the friction dissipation can account for the largest proportion when the expansion die angle is small.