A GENERAL ANISOTROPIC YIELD CRITERION USING BOUNDS AND A TRANSFORMATION WEIGHTING TENSOR

A GENERAL EXPRESSION for the yield surface of polycrystalline material s is developed. The proposed yield surface can describe both isotropic and anisotropic materials. The isotropic surface can be reduced to ei ther the Tresca or von Mises surface if appropriate, or can be used to capture the yield behavior of materials (e.g. aluminum) which do not fall into either category. Anisotropy can be described by introducing a set of irreducible tensorial state variables. The introduced linear transformation is capable of describing different anisotropic slates, including the most general anisotropy (triclinic) as opposed to existi ng criteria which describe only orthotropic materials. Also, it can su ccessfully describe the variation of the plastic strain ratio (R-ratio ), where polycrystalline plasticity models usually fail. A method for obtaining the material constants using only uniaxial test data is desc ribed and utilized for the special case of orthotropic anisotropy. Fin ally, the use of tensorial state variables together with the introduce d mathematical for mulation make the proposed yield function a very co nvenient tool for numerical implementation in finite element analysis.