Anisotropic Deformation and Damage in Aluminium 2198 T8 Sheets


The deformation and damage mechanisms of sheets aluminium alloy 2198 are investigated experimentally and numerically. Mechanical tests in three different orientations are carried out on smooth and U-notched flat specimens. The material's microstructure is characterized to obtain the second phase area content, the morphology of particles and the void volume fraction. The fracture surfaces of the different specimens are examined using scanning electron microscopy. Smooth specimens loaded in the longitudinal and transversal orientation exhibit a slanted fracture surface, which has an angle of about 45° with respect to the loading direction. Samples loaded in 45°-orientation fail in a flat manner. Notched specimens show a V-shaped fracture surface. Failure initiates here at the notch root. It is shown that primary voids are first initiated at intermetallic particles. Void growth is promoted and rupture is caused by shear failure between regions of cavities. Finite element calculations are performed to simulate the orientation-dependent deformation and damage behavior. A phenomenological yield criterion combined with a porosity-based isotropic damage model allows for the quantitative prediction of specimen's failure for different triaxialities. An interaction of deformation and damage evolution can be demonstrated. The deficit of the von Mises yield criterion for this kind of metallic materials becomes evident.
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