Numerical study on the influence of the Portevin-Le Chatelier effect on necking in an aluminium alloy

The constitutive relation proposed by McCormick (1988 Acta Metall. 36 3061 - 7) for materials exhibiting negative steady-state strain-rate sensitivity and the Portevin-Le Chatelier (PLC) effect is incorporated into an elastic viscoplastic model for metals with plastic anisotropy. The constitutive model is implemented in LS-DYNA for corotational shell elements. Plastic anisotropy is taken into account by use of the yield criterion Yld2000/Yld2003 proposed by Barlat et al (2003 J. Plast. 19 1297 - 319) and Aretz (2004 Modelling Simul. Mater. Sci. Eng. 12 491 - 509). The parameters of the constitutive equations are determined for a rolled aluminium alloy (AA5083-H116) exhibiting negative steady-state strain-rate sensitivity and serrated yielding. The parameter identification is based on existing experimental data. A numerical investigation is conducted to determine the influence of the PLC effect on the onset of necking in uniaxial and biaxial tension for different overall strain rates. The numerical simulations show that the PLC effect leads to significant reductions in the strain to necking for both uniaxial and biaxial stress states. Increased surface roughness with plastic deformation is predicted for strain rates giving serrated yielding in uniaxial tension. It is likely that this is an important reason for the reduced critical strains. The characteristics of the deformation bands ( orientation, width, velocity and strain rate) are also studied.