Correlative characterization and plasticity modeling of microscopic strain localizations in a dual phase steel

Microscopic strain localizations were explored with correlative characterization and J2 plasticity modeling. The former involved electron backscattered diffraction (EBSD), nano-indentation mapping and microscopic digital image correlation. These 'mapped' the evolution of strain localizations during controlled tensile deformation of dual phase (DP) steel microstructures. Though the initial multi-phase microstructures were similar, they had different hardness differentials (AH) between ferrite and martensite. It was shown both experimentally and from the numerical model that AH controlled the strain partitioning between the phases, which triggered the microscopic strain localizations and determined the macro-tensile behavior. For example, highest AH provided most severe strain localizations in the ferrite phase, ultimately leading to micro-cracking in the martensite. Further, the experimental microstructures were used in our plasticity modeling, and the state of stress and strain were simulated. In the regions of interest in the present study, both interface decohesion and cracking inside martensite was observed, although the martensite interior experienced negative stress triaxiality. This was possibly triggered by severe strain localizations at the interface. This study thus provided a niche combination of correlative characterization with plasticity modeling, which were adopted to explore the mechanical behavior of complex multi-phase microstructure(s).