Distorted yield surfaces - modelling by higher order anisotropic hardeningtensors

Most of the constitutive models for metallic materials assume yield functio ns of von Mises or generalized Tsai-Wu type. Isotropic and/or kinematic evo lutions are developed for hardening, which correspond to affin expansions o r simple shifting of original yield surfaces, whereas experimental results show a distinctive change of the shape of yield surfaces (rotated or dented ) depending on loading conditions and load path. To cover the material beha viour with distorted yield surfaces a hierarchical expansion of yield funct ions to hardening tensors of the fourth and the sixth order is proposed. Pa rameters of corresponding evolutionary equations are determined by model pa rameter optimization. The extended model is investigated comparing numerica l results to cyclic experimental data in biaxial sigma-tau space. (C) 1999 Elsevier Science B.V. All rights reserved.