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 Nicalon/C/SiC composites indicate behavior that is distinctly different from other composites. These composites have been analyzed using a model that explicitly includes two sets of debond‐crack‐surface topographies that correspond to two stages of crack propagation. The model successfully duplicates the observed unusual push‐out load‐deflection behavior by adjusting interfacial toughness and topographical parameters to fit the experimental data. Although the topographical parameters of the debonding cracks are largely unconfirmed, the fitted values are consistent with observations and expectations. This analysis has determined interfacial fracture energies that are unusually high for composites with acceptable mechanical behavior but are consistent with measurements on bulk pyrocarbons. The analysis provides a unifying rationalization of the apparent inconsistencies in results reported for such materials.