Advancing Numerical Simulation Tools for Ductile Fracture in Thin Metal Plates

This thesis investigates the micro-mechanical material behavior leading to ductile fracture of thin metal plates. The main focus has been on how the micro-mechanical mechanisms that control ductile fracture can be linked to the phenomenological simulation tools. Tools that allow engineers, in a cost-efficient manner, to conduct accurate predictions of crack growth in large-scale plate structures subject to extreme loading conditions. The work demonstrates that tuning the key parameters defining the cohesive zone is required to represent accurately the failure predicted by micromechanics based Gurson simulations. For instance, when extensive crack growth takes place in a thin metal plate or when the damage-related microstructure (number, size, and distribution of voids) diverges from a homogeneous configuration. Throughout the thesis, mode I tearing is considered the primary loading condition, but the work also considers an additional shearing fracture mode. The effects from mixed mode loading conditions on the crack initiation and the interaction between microscopic voids are investigated as well as on the key parameters for the cohesive tractionseparation relations for a steadily growing crack. Finally, attention is drawn to the steady-state mode I tearing setup in comparison to the plane strain bending test, which are two typical loading scenarios encountered in the deformation of plate structures at the engineering scale. Despite both loading conditions experience the same nominal stress state, two significantly different fracture strains have been reported experimentally. The micro-mechanical Gurson model constitutes an indepth analysis to search for the mechanisms leading to the fracture strain difference and reveals two significantly different localization phenomena. Additionally, a new parameter based on the through-thickness stress variation to distinguish the mode I tearing loading condition from plane strain bending test is defined.