Ductile fracture initiated by interface nucleation in two-phase elastoplastic systems

• Interface cracks can arrest due to blunting, limiting the initial nucleated porosity.
• Minimum ductility at intermediate phase fractions is explained by high local triaxiality.
• High overall triaxiality favours all steps from nucleation to coalescence.
• Ductility is primarily dominated by strength mismatch.

Dual-phase materials often show damage nucleation along the interface between the two phases followed by void growth and coalescence. This failure mechanism is investigated using a microstructure model with both phases deforming plastically according to a physics-based hardening law. The interface is modeled as a cohesive zone whose constitutive behavior is described by a bi-linear traction–separation law. The interface is specified with a weak site where damage first initiates representing the presence of a small particle sitting along the interface. A parametric study is conducted through finite element unit cell calculations to examine the effect of the morphological and rheological factors on the complete ductile damage process. The mismatch of phase properties influences the local stress triaxiality evolution, which, in turn, significantly affects damage nucleation and interface decohesion involving possible crack arrest. The strength contrast appears to be more critical than the phase morphology in defining the ductility of typical two-phase metallic systems. The nucleation strain decreases by a factor of 10 when the imposed overall stress triaxiality increases from 0.67 to 2.0.