Implementation of YLD-96 Plasticity Theory in Formability Analysis of Bi-axial Pre-strained Steel Sheets

Abstract

In the present work, 15% bi-axial pre-strain with 0.98 strain ratio was induced in extra deep drawing (EDD) steel sheets using an in-plane stretch forming set-up. Subsequently the quasi-static uni-axial tensile responses were evaluated experimentally, and the YLD-96 plasticity theory was implemented to estimate the anisotropic coefficients of both as-received and pre-strained materials. The strain based forming limit diagrams (ɛ-FLD) were evaluated by deforming sheet materials under six different strain paths ranging from 0.94 to -0.31 in a limiting dome height (LDH) test set-up. It was found that the failure strains of the pre-strained material decreased significantly with a shift towards tension-tension region, and hence, the polar effective plastic strain-FLD (PEPS-FLD) was estimated using the formulated YLD-96 plasticity theory to restrict the dynamic shift of failure strains. The FE models of LDH testing of both as-received and pre-strained materials were developed, and the formability was predicted successfully by incorporating PEPS-FLD as a damage model within an error of approximately 6%.