Numerical study of the thickness transition in bi-dimensional specimen cracks

Concerning bi-dimensional crack configurations, classical linear elastic fracture mechanic theory ignores the three-dimensional effects of crack propagation. Issues as the influence of the specimen thickness are not considered. Nevertheless, real cracks show some effects difficult to explain. It is the case of the load effect on fatigue crack closure. The yielded zone size close to the crack front is an important factor in fracture and fatigue of metallic materials. They are related to the two extreme stress states: plane stress or plane strain, but no clear information about out-of-plane plastic zone development or stress state has been provided. In the present work, a CT aluminium specimen has been modelled three-dimensionally and several calculations have been made considering a huge combination of different single load levels and specimen thickness. Due to the abrupt transition from plane strain to plane stress, an ultrafine mesh along the thickness has been applied. The analysis of the evolution of the plastic zone and the stress state along the thickness provides information about the combined influence of these parameters on fracture mechanics.