A SEM procedure for quantifying the percentage area of transgranular fracture and surface roughness was developed to study the fracture morphologies of stable and rapid crack growths in ceramics and ceramic matrix composites. The procedure utilizes software which interprets the SEM line scanning profiles. Results obtained through this procedure were correlated with the visual observation and profilometer measurements of AI2O3 and SiC,/AI2O3 fracture specimens. [Key words: scanning electron microscopy, fracture, brittle materials, crack growth.]

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The feasibility of using a previously developed crack-kinking criterion to predict crack arrest at a tear strap in a pressurized fuselage was studied with instrumented axial rupture tests of 21 models of an idealized fuselage. A rapidly propagating axial crack, which was initiated from a precrack, kinked immediately upon extension and propagated diagonally until it turned circumferentially and propagated along the tear straps. An elastodynamic finite element analysis of the rupturing model fuselage yielded the mixed-mode stress intensity factors, K1 and EH, and the remote stress component, ~o=. This numerical procedure was also used to predict the crack trajectories in full-scale fuselage rupture tests. All numerical results agreed well with their measured counterparts regardless of size.

The determination of bridging stresses by evaluation of crack opening profiles is outlined for a whisker-reinforced alumina. The application of the fracture mechanics weight function procedure results in an integral equation between bridging stresses and crack opening displacements. Its solution provides the bridging stress relation.

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