Fracture of Functionally Graded Materials - Modeling, Synthesis and Experiments

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9713798 Paulino Physically based models which can be used to predict and optimize FGM mechanical performance are developed under this project. Discrete and continuous FGMs are analyzed using the boundary integral equations and the finite element methods, respectively. Optimization of the compositional gradient by means of numerical simulations provides relevant input for material synthesis. A novel technique known as Field- Activated Combustion Synthesis (FACS), is used in the synthesis process. Brittle FGM system, MOSi2/SiC, consisting of two layers joined by a compositionally graded interface sandwiched between the layers is used. With different applied electrical fields, different compositional profiles are obtained for this system. The spatial distribution of the phase concentrations of Mo and Si are determined from electron microprobe analysis. The distinct samples, with various compositional profiles at the graded interface, are tested by carefully placing a crack inside the compositionally graded.layer. The fracture behavior of FGMs with crack faces parallel and perpendicular to the property gradient are investigated both experimentally and numerically. The numerical models are calibrated by fracture mechanics experiments. The influence of compositional distribution functions on the structural behavior and the mechanics of crack initiation and propagation in FGMs under mechanical and/or thermal loads is studied. The study contributes to the understanding of mechanical behavior and optimal (or near optimal) compositional distribution functions of MoSi,)/SiC and Ti3SiC2/SiC FGMs, in particular, and to the actual design of FGMS, in general. ***