Stress triaxiality effect on void nucleation in ductile metals

The stress triaxiality effect on the strain required for void nucleation by particle-matrix debonding has been investigated by means of micromechanical modelling. A unit-cell model considering an elastic spherical particle embedded in an elastic-plastic matrix was developed to the purpose. Particle-matrix decohesion was simulated through the progressive failure of a cohesive interface. It has been shown that the parameters of matrix-particle cohesive interface are correlated with macroscopic material properties. Here, a simple relationship for the maximum cohesive opening at interface failure as a function of material fracture toughness and yield stress has been derived. Results seem to confirm that, increasing stress triaxiality, the strain at which void nucleation is predicted to occur decreases exponentially in a similar way as for fracture strain. This result has substantial implications in modelling of ductile damage because it indicates that if the stress triaxiality is high enough, ductile fracture can occur at plastic strain lower than that necessary to nucleate damage for moderate or low stress triaxiality regime.