Strain Rate Effect on Edge Formability of Complex-Phased Advanced High-Strength Steels in the Hole Expansion Test

This study aims to investigate the influence and mechanism of strain rate variation on the hole expansion ratio of complex phase advanced high-strength steels. Two different speeds of hole expansion tests were conducted within the quasi-static range, accompanied by a uniaxial tension test with a deformation mode similar to hole expansion for supplementary analysis. Finite element simulation was utilized to analyze the detailed deformation behavior within the material, particularly at the hole edge where cracks occur during hole expansion. The mechanical and fracture properties obtained from the uniaxial tension test were incorporated into the simulation, taking into account the anisotropy of the material to predict the precise location of crack initiation within the hole edge. To account for the strain rate effect on the experimentally determined hole expansion ratio, a ductile fracture model was introduced and its necessity was validated by considering the occurrence of material fracture before and after crack initiation. By utilizing 3D solid elements, considering material anisotropy, and applying the ductile fracture model, the simulation provided reasonable predictions for the hole expansion ratio, which exhibited variation with strain rate.