An Experimental-numerical Study on the Plastic Flow Localization Based on a Generalized Micromorphic Formulatio

Abstract

An experimental-numerical study based on simple plane strain tensile tests of a high strength metallic sheet is presented. The development of an 'advanced' modelling of multiphysic thermomechanical coupling in the framework of the generalized continuum mechanics (micromorphic theory) is already proposed in published works in order to introduce the concept of internal lengths that are representative of the material’s microstructure while accounting for the various initial and induced anisotropies under large plastic strains. These internal lengths have to be experimentally determined from accurate measurements of highly localized displacement/strain (or velocity/strain rate) fields by using advanced methods to measure the kinematic fields at the relevant scales. We seek to locally measure the displacement and velocity fields in order to access to the local strain/strain rate fields inside the localized zones. Attention is paid to the prediction of the plastic flow and damage localization into narrow shear bands (localized necking) which follows the diffuse necking stage. The effect of the micromorphic material properties which define the intrinsic characteristic internal length on the evolution of these highly localized shear bands regarding the mesh size is deeply investigated. The numerical work is based on an advanced numerical methodology developed for metal forming simulations including thermodynamically-consistent nonlocal constitutive equations accounting for various fully coupled mechanical phenomena under finite strains in the framework of the micromorphic continua. The numerical implementation into ABAQUS/Explicit software is made thanks to VUMAT user’s subroutine for the implementation of the micromorphic constitutive equations and the VUEL user’s subroutine for 2D quadrilateral assumed strain elements with an additional micromorphic degree of freedom related to the micromophic damage.