Investigation of failure mechanisms in dual-phase steels through cohesive zone modeling and crystal plasticity frameworks

Dual -phase (DP) steels are characterized by their good formability and interesting material properties, which primarily originate from their unique composition, combining the ductile ferrite phase with the hard martensite phase. At the microscale, DP steels exhibit various fracture mechanisms that need to be investigated through proper plasticity and failure models. These mechanisms include interface decohesion between ferrite-martensite and ferrite-ferrite phases, as well as martensite cracking, depending on the steel's microstructure. In this study, crystal plasticity and cohesive zone frameworks are employed together with a ductile failure model in 3D polycrystalline Representative Volume Element simulations to address the multiscale characteristics of the fracture mechanisms in DP steels. The analysis requires an extensive parameter identification procedure, which is presented in detail. The obtained results demonstrate the framework's capability to effectively identify the primary failure mechanisms correlated with crucial microstructural features, including crystallographic orientation, morphology, volume fraction, and stress triaxiality. Findings indicate that an increase in the connectivity of the martensitic phase induces a shift from ferrite-ferrite decohesion to ferrite- martensite decohesion and martensite cracking. Similarly, as the volume fraction of martensite increases, decohesions become constrained, making martensite cracking the main failure mode. The numerical observations regarding triaxiality highlight that as stress triaxiality increases, the predominant failure mechanism is changed from martensite cracking and ferrite-martensite decohesion to ferrite-ferrite decohesion.