Abstract: The stress distribution and deformation pattern of the corner are analyzed by mechanical analysis and numerical simulation, and then the mechanism of thinning and cracking at the transition region is disclosed. It is presented that the material at the transition region is the easiest region to satisfy plastic yielding conditions and produce thickness compressive strain. Therefore severe thinning deformation is easy to occur at the transition region and when the ratio of wall thickness to corner radius is bigger than 0.5, the difference of yielding conditions between straight side and corner is more significant so that the deformation nonuniformity is increased, and is easier to induce the excessive thinning and cracking. The result is useful for lightweight part design and process design of tube hydroform-ing (internal high pressure forming) to improve product quality.

Key words: Local thinning Fracture, Transition corner forming Lightweight component, Tube hydroforming