Development and application of a microstructure-based approach to characterize and model failure initiation in DP steels using XFEM

We develop a microstructure-based model to characterize and model failure initiation in DP steels using an extended finite element method (XFEM) to simulate martensite cracking on the mesoscale combined with representative volume element (RVE) modeling. A mini tensile test with digital image correlation (DIC) analysis is linked to local SEM analysis to identify the local strain at which failure is initiated. In-situ bending tests in SEM with electron backscatter diffraction (EBSD) measurements before and after the test are carried out to validate that the crack initiates in the martensite islands. Empirical equations for XFEM parameters as functions of local carbon content in martensite are fit to experimental results for laboratory-annealed DP600 steels with varying martensite content. The equations are then shown to predict successfully failure initiation in industrially produced DP steels with various chemistries, strengths and martensite fractions.