Validation of the dual-phase steel failure model at the microscale

Dual-phase (DP) steel sheets are subjected to large plastic strains during forming of the body and structures of automotive components. These steels primarily contain hard martensite and soft ferrite phases in their microstructure and involve brittle and ductile fracture mechanisms for the ferrite and martensite phases, respectively. An uncoupled, multiscale finite-element model consisting of continuum (or macro) and microstructural (or micro) scales for large uniaxial tensile plastic deformation and failure of DP steel is developed. This model, based on a digital material representation (DMR) approach, is presented and validated with experimental results. The micromodel incorporates the above phase-specific fracture mechanisms, utilizes experimentally measured DP steel microstructures obtained as scanning electron microscopy (SEM) images, stress-strain (or flow curves) of individual ferrite and martensite phases as inputs, and deformation boundary conditions from two-scale macromodels of the uniaxial tensile test. The response of the micromodel in terms of local fracture behavior of the individual phases at large strains is compared with an experimental in situ SEM uniaxial tensile deformation study of the DP steel microstructure in the literature and good agreement is observed.