Micromechanical studies of crack growth in a ceramic matrix composite.

摘要

This research explored the interrelationships between the fracture mechanisms of short fiber-reinforced slip-cast fused silica matrix composites and the properties of the fiber and of the fiber to matrix interface. The approach taken combined experimental mechanical property determinations and fracture surface analyses with finite element microstructural modeling.; Composites were formed by incorporating short, randomly oriented aluminoborosilicate fibers in a silica/water suspension, slip-casting, and sintering. The ambient and 1000{dollar}spcirc{dollar}C flexural strengths, plane strain fracture toughness, fracture surface energy and crack resistance curves were determined for each material. Quantitative fractography and scanning electron microscopy were employed to determine the fracture origins and paths. Interface strengths were evaluated by fiber micro-indentation testing. The results indicated that fiber reinforcements which were weakly bonded to the matrix improved the fracture resistance of the slip cast fused silica matrix, with a slight loss in the material stiffness and strength. These composites exhibited rising crack growth resistance curves, and up to a two-fold increase in the fracture surface energy.; In the second part of this research, a two-dimensional finite element model for crack growth was developed, in which individual microstructural parameters are varied. This permitted the isolation of the effects of each feature on the composite's fracture behavior. Fracture paths were predicted for isolated fibers at discrete orientations with respect to the crack plane. Increases in material toughness were determined by calculating the strain energy release rate after each increment of crack growth. Results indicated that the fracture process is strongly influenced by the fiber orientation, the residual stress state, and the strength of the fiber to matrix interface bond.