ICF100915OR DUCTILE RUPTURE OF ALUMINUM SHEETS W. Brocks 1, J. Besson 2, O. Chabanet 3, D. Steglich 1 1 Institute of Materials Research, GKSS Research Centre, D-21502 Geesthacht, Germany 2 Centre des Materiaux, Ecole des Mines de Paris, France 3 Pechiney CRV, Parc Economique Centr'Alp, F-38341 Voreppe, France ABSTRACT Crack growth resistance of thin aluminium sheets under monotonic loading is studied and numerically simulated. A phenomenological cohesive zone model and the micromechanically based damage model of Gurson are applied. The yield curve is determined from tensile tests on smooth flat specimens, the model parameters describing separation and damage, respectively, are fitted for a Kahn specimen. Both models guarantee transferability of the respective parameters from the small Kahn specimen to a large M(T) specimen. The respective contributions of elastic, plastic and separation energy to the total external work differ significantly for the two specimens. Crack growth is predicted as normal fracture if the common assumptions of symmetry are applied to the FE mesh, whereas the tests show a transition from normal to slant fracture. The general ability of damage models to simulate slant fracture is demonstrated on a Hill specimen. KEYWORDS aluminium sheets, fracture resistance, damage models, cohesive zone model, parameter identification, numerical simulation, slant fracture INTRODUCTION A realistic assessment of the residual strength of sheet materials, e.g. aluminum panels and shells in aircraft structures, with defects requires methods to experimentally characterize crack growth resistance as well as numerical simulation tools capable of predicting crack initiation and propagation. The global approach to failure uses macroscopic parameters like J-integral, CTOD, CTOA, energy disspation etc. [1]. These quantities suffer from a general lack of transferability of fracture resistance data obtained from specimens to large scale structures. The damage mechanics approach, on the other hand, provides a solution for the transferability problem by describing the degradation of the material by additional internal state variables, such as void volume fraction, porosity, micro-crack density, etc. [2]. These models have been applied successfully to predict crack growth in thick-walled structures [3] where a high stress triaxiality triggers the growth of voids. Their application to thin-walled high strength aluminum alloys, however, faces some specific problems: • the stress triaxiality is much lower than required for the applicability of the respective models, • the fracture plane often shifts from a normal to a 45° inclined orientation to the applied load,
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