Typical stress states of tube hydroforming and their distribution on the yield ellipse

In this paper the authors try to extend the stress mechanics of tube hydroforming by combining the typical characteristics of stress states and yield equations of tube hydroforming with practical results. By determining how the stress state moves on the yield ellipse during the process, the characteristics of tube hydroforming are presented for the first time. The authors also discuss how the stress state effects the process and reach the conclusion that the control of tube hydroforming parameters is in fact the control of the stress state.