Sammendrag
The influence of crystallographic texture and homogenization scheme on the yield surface for aluminium sheets has been studied numerically. A rate-dependent single crystal plasticity model was adopted to describe the behaviour of the grains, whereas the behaviour of the polycrystal was obtained either by the crystal plasticity finite element method (CP-FEM) or by the full-constraint Taylor approach. A representative volume element (RVE) of the material including 800 grains was considered. The grain orientations were defined according to typical rolling and recrystallization textures exhibited in rolled aluminium sheets. With CP-FEM, the RVE was discretized with finite elements, using in average 30 cubical solid elements per grain, whereas in the full-constraint Taylor approach, all grains are assumed to be subjected to the same deformation. Stress states located on the yield surface were determined by subjecting the RVE to proportional deformation in different directions, assuming yielding to occur at a given plastic work per unit volume. The yield surface was then described analytically by fitting the Yld2004-18p yield function to the obtained stress states at yield, and further employed to calculate stress ratios and Lankford coefficients in uniaxial tension. The resulting yield surfaces for aluminium with rolling and recrystallization textures are markedly different. The influence of homogenization scheme is moderate, but significant effects are found on the predicted Lankford coefficients.