Study of curvature and pre-damage effects on the edge stretchability of advanced high strength steel based on a new simulation model

Edge cracking is one of the common failures during the stamping of Advanced High Strength Steel(AHSS). The limit strains of the edge are hard to predict by traditional methods because edge formability is influenced by many factors such as edge quality, process parameters, material properties and so on. Hole expansion tests are conducted with DP780 under three hole diameters and two punching clearances to investigate the effects of curvature and pre-damage caused by punching on edge stretchability. The corresponding simulations are carried out meanwhile with a new model based on Marciniak and Kuczynski (M-K) model and Hill's localized necking theory to predict the edge limit strain. This new model is proposed for the hole edge with pre-damage and improves the predictability of edge cracking in hole-expansion simulation. The problem that the traditional ideal model fails to predict the hole expansion ratio (HER) of pre-damage edge is also successfully solved by the new model with the use of the Damage Zone and Effective Failure Strain Ratio (EFSR). The comparison between the experiments and simulations reveals that this new model can be used in edge forming failure prediction of AHSS.