Plate Tearing Under Mixed Mode Loading

Cohesive-zone finite element modeling is often the technique of choice when dealing with extensive crack growth in large-scale ductile sheet metal structures. Shell elements with in-plane dimensions much larger than the plate thickness are typically employed to discretize the structure, and thus the mesh cannot accurately capture the localization process that precedes ductile failure. To fertilize accurate predictions of such sheet tearing, the energy dissipated during localization must, therefore, be accounted for in the cohesive traction-separation law. The fact is that the local thinning that takes place in front of an advancing crack can significantly enhance the crack growth resistanceas the energy going into thinning the sheet typically dominates the total fracture energy.This has been investigated in great details for the case of pure Mode I tearing and both the energy dissipation, peak stress, and shape of the cohesive traction-separation law have been laid out. In a similar fashion, the present study resolves the sequence of failure details related to steady-state sheet tearing under mixed mode loading by employing the micro-mechanics based Gurson model. But, the fracture process in front of an advancing crack is here approximated by a 2D plane strain finite element model to facilitate a comprehensive parameter study to evaluate the mixed Mode I-Mode III load case.