Experiments and FE simulation of edge cracking considering prehardening after blanking process

Edge cracking is a significant problem in the stamping of advanced high-strength steels (AHSS) and is very sensitive to the local material properties at the sheared edge after the blanking process. Edge cracking can be predicted with the finite element (FE) method with satisfactory accuracy due to the complex hardening condition along the sheared edge and the microstructure. In this research, hole-punching experiments and tension tests with central-hole specimens for two kinds of AHSS, namely, dual-phase steel and martensitic steel, are carried out to study the edge cracking failure after the blanking process. The prehardening of the sheared edge is investigated by measuring the hardness distribution. A method for characterizing the maximum hardness of the sheared edge of high-strength steel is proposed based on the yield strength σ_s, hardening index n-value and shear clearance c. A FE simulation method considering the prehardening of the sheared edge is proposed to predict the edge cracking initiation. The experiments and simulation results show that the prehardening of the sheared edge is a critical factor for predicting the early edge fracture phenomenon after the blanking process, and the proposed FE simulation method can predict this problem with reasonable accuracy.