FE simulation of edge fracture considering pre-damage from blanking process

Edge fracture has been a well-known challenge in the forming processes of Advanced High Strength Steels (AHSS). The difficulty of the problem mainly lies in the complex loading path of out-of-plane shearing followed by in-plane stretching. Existing Finite Element models can not predict edge fracture with good accuracy. In the current study, two methods were implemented to tackle the problem for the DP780 steel sheet. The first method was a one-stroke FE simulation methodology making use of very fine solid elements of size of 0.01 mm in the critical region. After simulating the hole blanking process, a subsequent hole expansion simulation was continued with the same FE model. In other words, all material parameters were inherited from the sheet blanking process when performing the hole expansion simulation. Encouraged by the one-stroke simulation, a two-step phenomenological Pre-Damage Mapping Model (PDMM), was proposed and used in edge fracture prediction. This model performed the hole blanking simulation using a 2D axisymmetric model in step I. The mesh size used in step I was of order of 0.01 mm in the critical region. Then the model mapped/prescribed pre-damage and equivalent plastic strain (PEEQ) information obtained in step I in the vicinity of the hole edge to a solid element or shell element model with regular mesh size of order of 0.1 mm in step II. The results showed that both methods accurately predict edge fracture in terms of HER. The one-stroke simulation requires enormous computational power due to the very fine 3D solid element mesh, but it provides an accurate prediction of the detail distribution and orientation of cracks. The more simplified PDMM model gives a much quicker prediction of edge fracture and can be used in both solid element and shell element models, but loses some details captured by one-stroke simulation.