Practical microstructure-informed dual-scale simulation for predicting hole expansion failure of hyper-burring steel

A practical dual-scale finite element model is developed to enable the formability prediction in the hole expansion of a hyper-burring steel sheet. This numerical approach resorts to the isotropic macroscale hole expansion simulation for calculating the deformation histories near the hole edge, since they are known to be the potential fracture initiation site. The deformation histories are used as boundary conditions in the lower microscale model for calculating the local fracture of the steel sheet. The microscale simulation utilizes the dislocation density based constitutive model and a microstructure-based representative volume element (RVE), with realistic grain morphology taken from experimental microscopy. The fracture initiation at the hole edge region is evaluated from the microscale simulation using four frequently employed uncoupled ductile fracture models, which enable the definition of the critical fracture strain. The proposed dual-scale model can better predict the failure initiation and location near the hole edge when the modeling parameters are calibrated taking into account not only the deformation histories of the hole edge, but also the local stress triaxiality. Moreover, the proposed dual-scale model is applied to analyze the microstructure effect on the hole expansion ratio by providing the insights into the effect of grain size and grain boundary characteristics.