Mechanical analysis of toughness degradation due to premature fracture of course inclusions in wrought aluminium alloys

The present work is aimed at numerical analyses of toughness degradation due to damage evolution at coarse inclusions, with particular interests on microstructural control for toughness enhancement by controlling the damage initiation. The investigation employs a combination of crack-tip singularity and Eshelby internal stress analysis within each inclusion. The essential feature of the model is to predict crack initiation toughness and crack path morphology using a mixed-mode fracture criterion. The procedure accounts a criterion for the damage evolution, effects of a deflected crack-tip, and shielding/antishielding effects due to the damaged inclusions. The toughness is found to be degraded by increasing the grain size of the matrix and the volume fraction of the inclusion, and also by decreasing the fracture strength of the inclusion and hence its coarsening. The effects are remarkably pronounced when the inclusions are agglomerated. Especially, weak inclusions agglomerated on grain boundary act to deflect the crack along the grain boundary even when inferior crack propagation resistance within grain boundary PFZ is not considered. The in-situ fracture strengths of several inclusions are also estimated in the lights of the numerical results.