Applications of a new plane stress yield function to orthotropic steel and aluminium sheet metals

Many metallic sheets exhibit a certain initially plastic anisotropy that influences considerably the mechanical behaviour of the sheet material in forming operations. Nowadays, computer modelling based on the finite element method (FEM) in conjunction with the concept of anisotropic yield functions is successfully utilized to design sheet forming processes. The yield function applied in the FEM analysis affects very strongly the computed results such as material flow, springback, wrinkling and limiting strains. Consequently, in order to increase the accuracy of the FEM simulations the yield function used should be as accurate as possible in order to capture all the important anisotropy effects. In this paper, the new plane stress yield function for orthotropic sheet metals recently introduced by the author (Aretz H 2003 J. Mater Process. Technol. submitted) is applied to orthotropic steel and aluminium sheet metals. The yield function contains eight anisotropy parameters that may be fitted by means of a Newton solver or a least square solver to selected experimental input data. The main attractiveness of the new yield function lies in its very simple mathematical form, which makes it very effective and thus quite interesting for implementation in finite element codes. The capabilities of the new yield function are demonstrated by applications to selected orthotropic sheet materials.