Determination of the forming limit of impact hydroforming by frictionless full zone hydraulic forming test

It is impossible to obtain the forming limit curve (FLC) by full zone hydraulic forming test under quasi-static (QS) condition since the liquid will leak from the notches of the specimen once the pressure increases. In this study, a novel method is proposed to investigate the frictionless full zone hydraulic FLC of AA5A06 under high strain rate (HSR) condition based on the impact hydroforming technology (IHF). It is found that the FLC is increased significantly by IHF compared with the quasi-static rigid punch (QS-R) forming and the quasi-static hydraulic (QS-H) forming. Differentiating with the QS-H, the increase amounts of FLC at the biaxial tension zone and the tension-compression zone are notably different for IHF. Additionally, the theoretical calculations of FLC is conducted by using M-K model combining with Hill48 anisotropic yield criterion under QS and HSR conditions. The results calculated by the M-K model reasonably agree with the ones obtained from experimentation under QS and HSR condition, and a higher initial thickness ratio is assigned for HSR considering the neck postponing effect of inertia.