Micromechanics of ductile fracture in multiphase alloys - Application to cast aluminium alloy with penny shape voids

The use of many multiphase metal alloys reaching superior strength is impeded by a poor resistance to damage and fracture. In order to relate the fracture properties to the elastic and plastic behaviour and distribution of phases, it is essential to develop micromechanical models that properly capture the elementary damage mechanisms occurring in the different phases at the various length scales as well as the stress and strain partitioning among the phases. For the sake of illustrating the importance of modelling the stress transfer and accounting for the initial crack-like shape of voids, the ductility of a quasi cast aluminium alloy has been investigated experimentally and modelled. In contrast with classical void growth based analysis of ductile fracture, three key aspects of the particular mechanisms of fracture in cast Al alloys have received special attention: (i) a void nucleation condition that takes into account the stress partitioning among the elastic inclusions and the plastically deforming matrix, (ii) a proper description of the initial penny shape of the crack, (iii) a coalescence criterion incorporating the effect of the current void shape and void spacing.