Numerical prediction of sheared edge profiles in sheet metal trimming using ductile fracture modeling

In this study, experimental and numerical analyses are conducted to investigate sheared edges after trimming three automotive sheet metals including TRIP steel, hot-stamped (HS) steel, and aluminum alloy (AA) 5182. The Hosford-Coulomb (HC) ductile fracture model is used to predict the fracture initiation accurately, and a hybrid experimental-numerical technique is adopted to calibrate the HC model parameters. Further, the calibrated HC fracture loci are incorporated into the finite element (FE) simulations to predict the quality of trimmed surfaces and burr formations. It is observed that the experimental shear surface quality and the load progression curves are estimated successfully within an error margin of 10% from the FE simulations. It is interesting to observe a second load peak at the end of trimming, which can be explained by the striking of the moving punch with the curvilinear trimmed part of the sheet, and this is referred to as the second shearing phenomenon. Additionally, a correlation between the shear surface quality and mechanical properties of the three sheets is investigated based on the proposed numerical modeling. A reduction in the shear zone height and burr height for the HS sheet is observed compared to that of the TRIP steel and the highest burr is predicted for AA5182. It is also found the burr formation of the aluminum is more sensitive to the cutting clearance compared to the TRIP and HS materials. Furthermore, the burr height is less influenced by the material ductility at the very small clearance value, whereas comparatively at a larger clearance value (beyond 5% clearance), the ductility of the material primarily influences the formation of the burr.