Hydroforming and buckling of a longan-shaped pressure vessel with longitudinal tension rods

The hydroforming process of a longan-shaped multi-segmented preform with longitudinal tension rods and the buckling behaviour of a hydroformed longan-shaped pressure vessel were numerically and experimentally investigated. The shape of the longan followed the Cassini oval equation, with a shape index of 0.1. A preform with a nominal size of 400 mm for the major axis, 396 mm for the minor axis and a wall thickness of 1 mm was fabricated. Two longitudinal tension rods with a radius of 3 mm and a length of 420 mm were employed in the multi-segmented preform, which was the first to use longitudinal tension rods in the preform. The numerical analysis and experimental results showed that the excessive deformation of the polar plates was significantly reduced. Simultaneously, the overall geometric accuracy of the hydroformed pressure vessel was significantly improved. The results of the analytical, experimental and numerical approaches are in good agreement with one another.