Characterization and modelling of failure initiation in DP steel

This work aims to study the failure initiation in dual-phase (DP) steel. A microstructure based approach using representative volume elements (RVEs) is utilized to evaluate the microstructure deformation and the failure initiation on the mesoscale. In situ analysis of bending test in large-chamber SEM (LC-SEM) combined with electron backscatter diffraction (EBSD) measurements in a conventional field-emission gun SEM (FEG-SEM) before and after the test showed that on the deflection side under plain stress condition crack initiation occurs in martensite islands. Mini tensile test with DIC analysis was carried out and linked to local SEM analysis to identify macroscopic failure initiation strain values. RVE modelling combined with extended finite element method (XFEM) was applied to simulate martensite cracking on mesoscale. XFEM failure parameters have been identified based on local and macroscopic mini tensile evaluation applying classical J-Integral theory. Validation of this approach has been performed using the in situ EBSD results of bending test in LC-SEM by comparing martensite failure initiation points experimentally versus RVE numerically.