Cross scale numerical simulation and experimental study on hydroforming of double-layer Y-shaped tube

Abstract During the hydroforming process of the double-layer Y-shaped tube, defects such as wrinkling and rupture severely affect the forming quality. In this study, for the first time, hydroforming of multi-pass pipes is combined with crystal plasticity finite element modeling (CPFEM). A cross-scale simulation approach is proposed, where the displacement boundary conditions of the macroscopic finite element model are applied to the Representative Volume Element (RVE) through the submodel function in ABAQUS. A macroscopic-microscopic finite element model for hydroforming of double-layer Y-shaped tube is established, and the deformation behavior in the representative region is systematically studied. The effects of non-uniform deformation on stress and strain are analyzed from the perspective of crystal plasticity finite element modeling, and the results are validated by hydroforming experiments. The results show that both macroscopic and microscopic finite element model exhibit good consistency with the experimental results. Considering the microstructure, initial stress concentrates on specific grains due to grain orientation differences. As work hardening occurs, slip systems in other grains are gradually activated, ultimately leading to a uniform stress distribution. The effect of stress state on the slip mode is also discussed. The stress state and slip mode in the same regions of the inner and outer tubes are identical. Moreover, the cross-scale simulation can accurately predict the macroscopic deformation in the critical regions of the hydroforming tube, thus compensating for the limitations of traditional finite element simulations. This cross-scale numerical simulation method also lays the foundation for further research on hydroforming of multi-pass pipes.