Research on hydro-forming of combined ellipsoidal shells with two axis length ratios

Abstract

In order to avoid the wrinkling occurrence in the equatorial zone during hydro-forming of ellipsoidal shells with the axis length ratio exceeding 2, a combined ellipsoidal shell with two axis length ratios has been designed as the pre-form shell before hydro-forming. The distribution of the latitudinal stress was analyzed by numerical simulation for hydro-forming of the combined ellipsoidal shells and the influence of the effective axis length ratio was discussed on the deformation. It is shown that there is latitudinal compressive stress in the equatorial zone at an early stage of deformation and then it becomes tensile stress with the internal pressure increasing, so that the wrinkling does not occur. An experiment was conducted on hydro-forming of the new combined ellipsoidal shells with the effective axis length ratio 1.47 and 1.65, respectively. The deformation of the shell shape, the variation of axis length, the roundness of the equatorial zone and thickness distributions were measured in the experiment. The wrinkling can be successfully avoided during hydro-forming and the sound ellipsoidal shells have been obtained. It is proved that hydro-forming of the combined ellipsoidal shell with two axis length ratios is reasonable and this new structure shell is suitable for manufacturing of the large-size ellipsoidal shells.