Inverse identification of CDM model parameters for DP1000 steel sheets using a hybrid experimental-numerical methodology spanning various stress triaxiality ratios

A hybrid experimental-numerical methodology is presented for the identification of the model parameters regarding a mixed hardening anisotropic finite plasticity fully coupled with isotropic ductile damage in which the micro-crack closure effect is accounted for, for DP1000 steel sheets. The experimental tests involve tensile tests with smooth and pre-notched specimens and shear tests using recently proposed specimen [16]. These tests cover stress triaxiality ratios lying between 0 (pure shear) and 1 / 3 (plane strain). To neutralize machine stiffness effects, displacements of the chosen material surface pixels are kept track of using the digital image correlation system ARAMIS, where recorded inputs are synchronized with force measurements. Advanced constitutive equations fully coupled with ductile damage implemented into ABQUS/Explicit using a user defined material subroutine VUMAT are used. 3D hexahedral elements (rather than thin shells elements) are used to model the tests and the identification methodology combines the FEM using the VUMAT together with experimental results using an appropriate inverse method in framework of MATLAB. The validity of the material model and transferability of its parameters are checked using tests involving complex strain paths.