Springback Evaluation of Porous Sheets Under Draw Bending Procedures

In the present study, springback behaviors of high strength steel sheets under draw bending procedures are investigated by using a finite element analysis. A modified Gurson yield criterion is adopted to account for macroscopic behavior of sheet metal with porosity. Plastic responses of the matrix surrounding voids are assumed to follow the planar anisotropic yield function YLD2000-2D. Various void evolution mechanisms including nucleation, growth, and coalescence are implemented into the numerical simulations. Both user subroutines, VUMAT and UMAT, are employed in the commercial package ABAQUS to account for the characteristics of the porous sheet. Parameters of the chosen combined hardening rule with softening phenomena are evaluated from measurements of uniaxial tension-compression-tension tests reported in the literature. Calculated results show that the presence of a void as well as the pre-stretching prescribed on the sheet might play a role in the springback behavior.