In-Situ microstructure characterization and micromechanical modelling of damage initiation and propagation in DP1000 dual phase steel

Dual Phase (DP) steels are widely used in the automotive industry due to their excellent strength-ductility balance. Advancing next-generation steels requires a deeper understanding of deformation and damage mechanisms at the microstructural level. The present study investigates damage initiation and propagation in DP1000 steel through in-situ tensile and bending tests inside a scanning electron microscope (SEM), combined with digital image correlation (DIC) for strain mapping. Results show that plastic deformation localizes in ferrite, while damage initiates at ferrite-martensite interfaces and propagates within martensite islands during early plastic deformation. Finite element (FE) simulations reveal a correlation between local stress and martensite damage initiation, whereas ferrite damage events remain limited. Bending tests further highlight crack formation along strain localization paths in ferrite. These findings provide valuable insights for predictive multi-scale modelling of DP steels. Finally, the Gurson-Tvergaard-Needleman (GTN) damage modelling approach was adopted to predict the load–displacement curve of the tensile sample by calibrating damage parameters.