用中心管限位的椭球壳无模液压成形试验研究

理论与实践均证明,长短轴比大于2的椭球壳体在自由胀形时会在赤道附近起皱,其原因是由于存在纬向压应力。首次提出采用带中心管约束法整体无模胀形技术,对长短轴比为2的椭球壳体进行液压胀形试验研究,得到了椭球壳体胀形时应变分布及尺寸变化规律。试验结果表明：在中心管约束下的椭球壳体胀形可以较好地控制椭球轴长比。椭球状壳体在胀形过程中经历焊缝起皱凸起,后又在更高内压的作用下逐渐消皱的过程。塑性变形首先发生在赤道焊缝处,随后球瓣靠近南北极的部位也发生塑性变形,并由赤道和极板向温带区域扩展。用此方法所获得的壳体可以直接用于椭球形水塔。

Research on Dieless Hydrobulge Forming of Ellipsoidal Shells with Central Tube Constraint

It is proved by theory and practice that the wrinkles appear at equator during hydrobulge forming ellipsoidal shell if the length ratio of long axis to short axis is over 2,due to the latitudinal compression stress existing at the equator.The integral dieless hydrobulge forming experiment using ellipsoidal shells with central tube constraint is suggested first.The length ratio of long axis to short axis reached 2（λ=2）.The strain distribution of the outer surfaces of the shells during bulging and size variation before and after bulging were measured and analyzed.The experiment results show that with central tube constraint,the λ value of ellipsoidal shell could be controlled varying in a small range.The shells experienced winkling at equator near the weld seam and flattening of wrinkles due to the expansion of shells at higher pressure.Plastic deformation took place first at equator near the weld seam,followed by the areas nearby the pole,and expanded to temperate zone.The bulged ellipsoidal shells obtained by this method can be directly used as water tower.