Investigation of ductility limits based on bifurcation theory coupled with continuum damage mechanics

Abstract

The ductility limits of an St14 steel are investigated using an elastic‒plastic‒damage model and bifurcation theory. An associative J2-flow theory of plasticity is coupled with damage within the framework of continuum damage mechanics. For strain localization prediction, the bifurcation analysis is adopted. Both the constitutive equations and the localization bifurcation criterion are implemented into the finite element code ABAQUS, within the framework of large strains and a fully three-dimensional formulation. The material parameters associated with the fully coupled elastic‒plastic‒damage model are calibrated based on experimental tensile tests together with an inverse identification procedure. The above-described approach allows the forming limit diagrams of the studied material to be determined, which are then compared with experimental measurements. A main conclusion of the current study is that the proposed approach is able to provide predictions that are in good agreement with experiments under the condition of accurate material parameter calibration. The latter requires a careful identification strategy based on both calibrated finite element simulations of tensile tests at large strains and appropriately selected necking measurements. The resulting approach represents a useful basis for setting up reliable ductility limit prediction tools as well as effective parameter identification strategies.