A comparative study on mechanical behavior and damage scenario of DP600 and DP980 steels.

• The influence on the stress state on the mechanical behavior was analyzed by ARAMIS approach which is based on DIC. • The MMC damage model could be used for the prediction of the damage behavior under different stress states for DP steel material. • Three different types of damage initiation mechanisms were observed in DP600 and DP980 steels. • The most important damage initiation mechanisms in DP600 and DP980 were in the middle of large ferrite phase and at the interface of ferrite and martensite phase, respectively. • Two effective micro-crack initiation mechanisms were observed during in-situ test and DP600 and DP980 steels have the same behavior in the micro-crack initiation stage. In this study, the mechanical behavior of two cold rolled commercial dual phase steels (DP) were analyzed on micro and macro scales. First, the anisotropic behavior of these steels were investigated by standard tensile tests in three directions. The results showed that the anisotropy behavior of the fracture strain of DP980 is more pronounced than of DP600. Then, in order to assess the influence on the stress state on the mechanical behavior, four specimens with different stress states were analyzed by ARAMIS approach which is based on digital image correlation (DIC). The ARAMIS results were compared with 3D numerical simulations using the Abaqus/Explicit solver. In this part, the effect of stress state on flow curve and strain distribution in the specimens (i.e. tensile, notched-tensile, shear and bulge specimens) were investigated. To predict the fracture behavior of DP600 and DP980 steels under various loading conditions, the Modified Mohr-Coulomb (MMC) damage model was utilized. A VUMAT subroutine was developed to include a MMC damage model in the 3D models, and good agreement between the numerical and experimental results was observed. Finally, the microstructure failure mechanisms at three different stages (i.e. strain localization, micro-crack initiation and micro-crack coalescence) during uniaxial tensile loading were investigated inside the microstructure of DP600 and DP980 steels using an interrupted in-situ setup. In the results three different damage localizations were observed in both materials, and strain localization in the center of large ferrite phases and at the boundary of ferrite and martensite phases were dominant in DP600 and DP980, respectively. Two different micro-crack initiation mechanisms were observed that were similar in both materials. [ABSTRACT FROM AUTHOR]