Experiment and numerical simulation of hydro-forming toroidal shells with different initial structure

In this paper, the effect of the initial structure on formation of toroidal shells is investigated for avoiding wrinkling in the hydro-forming process for manufacturing large elbows. The experimental results show that no wrinkling occurs on a toroidal shell with an octagonal cross-section. However, there are some tiny wrinkles on a toroidal shell with a hexagonal cross-section. The deformation process was simulated using an explicit dynamic finite element code LS-DYNA. The simulation results are basically in agreement with the experimental results. The reason for wrinkling is discussed. Research results show that wrinkling can be prevented by selecting an appropriate initial structure.