Hydroforming and buckling of toroids with polyhedral sections

The hydroforming and buckling of toroids with polyhedral sections were examined. The cross section of a polyhedral preform had the form of an irregular octagon with a uniform thickness of 1.1 mm. This octagon was inscribed on the circular section of a target toroid with a rotation radius of 150 mm and a cross-sectional radius of 75 mm. Two nominally identical preforms were fabricated, internally hydroformed, and externally collapsed. The internally and externally applied pressures were recorded, and the geometric shapes and thicknesses were measured before and after the hydroforming process. The nonlinear finite-element method was used to investigate the hydroforming and buckling properties. The experimental results and numerical estimations were compared, and the results indicate that the hydroformed toroid can be employed in underwater vehicles. Jordan’s equation can provide a conservative prediction of the ultimate allowable outer pressure of hydroformed toroids when the hydroforming pressure exceeds a certain threshold.