Numerical modeling of ductile fracture of hot stamped 22MnB5 boron steel parts in three-point bending

With the increasing demand in car safety and energy consumption reduction, the driving force in developing components made of UHSS steels has risen during the last decade, increasing the use of hot stamping process. While several research studies have focused on the modeling of the fracture occurrence during hot stamping, very few analyze the ductility and failure behavior of hot stamped components during static loading as well as crashworthiness events. In this framework, the paper intends to study the failure behavior of hot-stamped boron steel 22MnB5 under different loading conditions. Three-point bending tests are conducted on hot stamped U-shaped beam assemblies to evaluate the effect of complex loading on the damage evolution. Through SEM-based microscopic analyses, the material failure mechanisms, such as the mode of void coalescence, are explored, as well as the relation between the direction of the maximum shear stress and fracture surface. A FE-based model of the three-point bending tests incorporating a ductile fracture criterion is calibrated and implemented in ABAQUS/Explicit software using VUMAT subroutines. It is proved that the numerical model is capable to properly reproduce the deformation sequence and predict two symmetric macro-cracks under a circular punch. The load-stroke curve of FE simulation is finally compared with that of simulation to show its reliability.