Fracture Mechanics Based Simulation for Microstructural Control in Metal Matrix Composites

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Effects of locally-inhomogeneous microstructures, such as PFZ layrs around reinforcements, coarse interfacial equilibrium precipitates, solute atom segregation, on deformation and fracture characteristics of the MMCs are analyzed by means of the elastic-plastic finite element analysis.Due to the ductile nature of the PFZ layrs, concentrated plastic flow within the PFZ layrs promotes increase of effective plastic strain in the whole matrix, thereby reducing stregth of the MMCs. On the other hand, the interfacial precipitates effectively retard the concentrated plastic flow within the PFZ layrs and consequently they suppress reduction of the strength due to the formation of the PFZ.The initiation rate of the void is remarkably affected by the morphologies and density of the precipitates.Taking above-mentioned microstructural features into account, we constructed a simulation program which simulates crack propagation through the discontinuously-reinforced. Micro-cracking, crack deflection, interaction between the main crack and the microcracks, and transition of stationary to non-stationary crack-tip singularities are taken into consideration in the simulation. Effects of the various microstructural parameters on the crack propagation resistance are evaluated. The most interesting information of this study is that the properly inhomogeneous distribution of the reinforcement improves the crack propagation resistance. We also evaluated static strength of such composites having reinforcement segregation by means of numerical simulation. The optimum microstructural configuration was proposed by the simulation.