Parameter calibration for a shear modified GTN model and its application to forming limit prediction

Abstract

Damage evolution is an unavoidable problem in the forming process of sheet metal, and an improper forming technology may cause ductile fracture of the final parts. The damage mechanics theory can give great insight to the failure mechanism and the numerical simulation using damage model can provide a new way to predict the fracture behaviour for sheet metal. The shear modified GTN model by Nahshon and Hutchinson with a piecewise interpolation function was applied, which can capture the damage evolution under both low and high stress triaxiality. Then, a method combined numerical simulation and optimization algorithm was adopted to calibrate the damage-related parameters. Furthermore, the shear modified model was used to predict the forming limit of a high strength steel 22MnB5.With the help of digital image correlation technique (DIC), both the strain field and forming limit curve obtained by the numerical simulation were compared with the experimental ones, and satisfactory results are obtained.