A fully coupled void damage and Mohr-Coulomb based ductile fracture model in the framework of a Reduced Texture Methodology
Résumé
This paper deals with the modeling of ductile fracture in the whole range of stress triaxiality. At high stress triaxiality, a classical void damage based model is used. At low stress triaxiality, the Mohr-Coulomb model at the slip system scale combines the resolved normal and shear stresses for each slip plane and direction. These two models are fully coupled in the framework of classical polycrystalline plasticity. A Reduced Texture Methodology (RTM) is used to provide the computational efficiency needed for numerical applications. The RTM approach involves a significant reduction of the number of representative crystallographic orientations. The model is applied to a 6260 thin-walled aluminum extrusion. With RTM, a special hybrid experimental-numerical procedure is used to identify all plasticity parameters (including texture) from mechanical experiments. The fracture parameters are calibrated with fracture experiments on a flat notched tensile specimen and the so-called butterfly shear specimen. Fractographic examinations show a combination of dimples and large smooth areas in the notched specimens (mixed fracture) and flat smooth areas only in the shear specimens. It highlights the need of combined fracture models. With the embedded new fracture model, finite element analyses of the notched specimen can model the through-the-thickness slant fracture propagating from the center towards the edges. Because of the very large strains in the shear specimen tests/analyses, small edge cracks first appear in the tensile areas before main shear cracks initiate and propagate along the width of the specimen. The experimental and numerical results are in good agreement with regard to fracture strains and locations, macroscopic and microscopic features.