Research on hydro-forming of combined prolate ellipsoidal shell with double generating lines

In order to resolve the problem that the polar zone is not deformed during hydro-forming of prolate ellipsoidal shell, a combined prolate ellipsoidal shell with double generating lines has been designed as the pre-form shell before hydro-forming. The distribution of the stress and variation of shell shape were analyzed by numerical simulation for hydro-forming of the combined prolate ellipsoidal shell, and the effect of structural design before hydro-forming was mainly discussed on the plastic deformation of the polar zone. It is shown that the polar zone is completely deformed towards to the design shape. The dividing line disappears with the increasing of internal pressure, and finally, every position along the longitudinal and latitudinal direction is a smooth arc. An experiment was conducted on hydro-forming of the new combined prolate ellipsoidal shell. The plastic deformation of the polar zone was deeply observed, and the variation of axis lengths and thickness was mainly measured in the experiment. It is shown that the polar zone is successfully deformed and the long axis has reached the design dimension during hydro-forming. Meanwhile, a sound prolate ellipsoidal shell has been obtained. It is proved that the needed prolate ellipsoidal shell can be formed by designing a reasonable pre-form shell.