Investigation and prediction of tearing failure during extrusion based on a modified shear damage model

In this study, a recent modified shear GTN model suitable for various triaxialities was implemented and validated, which combines the porous plasticity model with a damage mechanics concept. The original Gurson model was modified by coupling the shear damage and void volume fraction parameters into the yield surface. The stress update algorithm was developed via a user-material subroutine. With the help of representative volume elements (RVEs), a connection between the formation of macroscopic cracks and the microstructure was established. The modified GTN model was applied to predict the damage and tearing fracture. Additionally, the cohesive zone model was applied to the RVE to simulate the de-bonding of the grain interfaces from a microscopic perspective. Metallurgical inspection by means of optical and scanning electron microscopy was performed to explore the failure mechanism and validate the numerical computation results. Furthermore, the deformation of the shear band and the damage propagation mechanism during the extrusion process were discussed.