Competing Failure Mechanisms in Metal Matrix Composites and Their Effects on Fracture Toughness

Abstract Development of high performance Metal Matrix Composites (MMCs) requires careful microstructure design which can improve material's fracture toughness while maintaining high strength. Microstructure and constituent properties combine to determine the overall fracture toughness of MMCs through the activation of different deformation and failure mechanisms. Although the effects of key microstructural attributes on the fracture toughness of MMCs have been discussed in previous studies, their effects on the interplay between plastic deformation and crack formation, as well as their effects on the competing failure mechanisms have not been systematically studied. In this paper, an integrated experimental and analytical framework is presented to evaluate the fracture toughness of MMCs through an assessment of energy contributions in terms of plastic deformation and crack surface formation in the matrix, reinforcement particles and interface. J-integral is calculated through displacement field measurement using Digital Image Correlation method. The competition of different failure mechanisms and their relations with material deformation are quantified through an analytical model by considering the effects of reinforcement volume fraction, interfacial property and yield stress of the matrix. Calculations carried out concern 6092Al/SiCp, but the overall approach applies to other MMCs as well. Results from this work indicate that interface debonding is a beneficial failure mechanism for fracture toughness enhancement of MMCs. It not only increases the surface energy dissipation by creating tortuous crack paths, but also promotes plastic deformation in the ductile matrix which largely contributes to the toughening of MMCs. The activation of interface debonding primarily depends on the volume fraction of SiCp, the yield stress of Al and the interface bonding energy.