Crack Initiation and Propagation in Dual-phase Steels Through Crystal Plasticity and Cohesive Zone Frameworks

Ferrite-martensite dual-phase (DP) steels have become popular in weight-reduced automotive components due to their straightforward thermomechanical processing and excellent mechanical properties. Even though it has been a popular and productive area of research, there are still many open questions related to their interesting microstructure. Being composed of brittle martensitic clusters dispersed in a ductile ferrite matrix, DP steels benefit from the properties of both phases, which induce interesting failure mechanisms at the same time. The microstructural parameters such as martensite volume fraction, grain size, carbon content, martensite/ferrite morphology, ferrite grain size, and texture, as well as micro and mesoscale segregation, make them difficult to analyze. However these aspects have to be studied in order to link the underlying microstructural influence to macroscopic behaviour. Therefore, the modelling techniques at the microstructure scale should be utilized for physical understanding. In this work, a multi scale modeling strategy is followed for the analysis of plastic deformation and failure in DP steels. A rate-dependent crystal plasticity framework and the isotropic J2 plasticity model are employed for the simulation of the plastic deformation in ductile ferrite phase and in the hard martensite phase respectively at the RVE scale. Moreover, the intergranular cracking is studied by the incorporation of a cohesive zone model at the ferrite-martensite grain boundaries and the failure in martensite phase is addressed through a ductile failure model. The effect of microstructural parameters on both plastic and fracture behaviour is analyzed under axial loading conditions.