Characterization of anisotropy of sheet metals employing inhomogeneous strain fields for Yld2000-2D yield function

A method to include the distribution of strains in the identification of the planar anisotropy of sheet metals is proposed. The method includes the optical measurement of strains on a flat specimen with a varying cross-section and an inverse parameter identification scheme which minimizes the differences between the numerical simulation results and the experimental measurements by using Levenberg-Marquardt algorithm. The main advantage is the reduction of the needed number of material tests especially for complex material models, under the assumption of negligible kinematic hardening. The utilized specimen geometry covers a deformation state between uniaxial tension and plane strain tension cases. In order to supply additional information to the inverse scheme, the equi-biaxial stress state obtained from layer compression test is also included in the definition of the objective function. The anisotropy of the sheet is modeled with the Yld2000-2D model which is implemented as a VUMAT subroutine for ABAQUS-Explicit. Numerical tests point out that the orientation of the specimen defines the quality of the found yield loci. The proposed method is applied to characterize the commercial aluminum alloy AA6016-T4 and the obtained material parameters are used to analyze a deep drawn car hood geometry. The results show that the use of the strain distribution is a crucial point in identification of the planar anisotropy. The yield loci obtained with the proposed method are in accordance with the conventionally obtained yield stresses and r-values. (C) 2012 Elsevier Ltd. All rights reserved.