A PARAMETRIC DESCRIPTION OF ORTHOTROPIC PLASTICITY IN METAL SHEETS

A polar-coordinate representation of the yield surface in principal st ress space is utilized to formulate constitutive equations for plane-s tress plasticity of orthotropic sheets. The yield function and the ass ociated flow rule are analysed by taking account of the orientation of the principal stress axes, and conditions for internal consistency of the model are derived. An orthotropic yield criterion is proposed, wh ich is devised as an extension of a previous isotropic yield function involving the second and third invariants of the deviatoric stress ten sor. Comparisons with micro-macro computations and experimental measur ements of yield surfaces are discussed.