INTERFACE PROPERTIES IN HIGH-STRENGTH NICALON C/SIC COMPOSITES, AS DETERMINED BY ROUGH-SURFACE ANALYSIS OF FIBER PUSH-OUT TESTS/

Fiber push-out curves generated on high-strength, treated-fiber Nicalo n/C/SiC composites indicate behavior that is distinctly different from other composites. These composites have been analyzed using a model t hat explicitly includes two sets of debond-crack-surface topographies that correspond to two stages of crack propagation. The model successf ully duplicates the observed unusual push-out load-deflection behavior by adjusting interfacial toughness and topographical parameters to fi t the experimental data. Although the topographical parameters of the debonding cracks are largely unconfirmed, the fitted values are consis tent with observations and expectations. This analysis has determined interfacial fracture energies that are unusually high for composites w ith acceptable mechanical behavior but are consistent with measurement s on bulk pyrocarbons. The analysis provides a unifying rationalizatio n of the apparent inconsistencies in results reported for such materia ls.