FRACTURE-RESISTANCE BEHAVIOR OF SILICON-CARBIDE WHISKER-REINFORCED ALUMINA COMPOSITES WITH DIFFERENT POROSITIES

Fracture resistance behavior was characterized for SiC‐whisker‐reinforced alumina composites with porosities ranging from 0.6% to 11.5% The composites were hot‐pressed from an Al2O3 powder with 25 wt% SiC whiskers. Strengths of individual specimens were measured in four‐point flexure either for natural flaws or for Vickers‐indentation flaws as a function of radial crack size. Indentation crack sizes were controlled with indentation loads which varied between 2 and 200 N. A novel method of analysis of these measurements indicates that the fracture resistance of these composites increases as a function of crack extension, a rising R curve. This behavior is interpreted in terms of tractions from both crack‐bridging whiskers and interlocking grains, which develop in the wake of the crack tip as it extends. A decrease in porosity raises the level of fracture resistance, but has a negligible effect on the relative steepness of the R curve. The sizes of natural flaws which causes failure in flexure testing were also estimated from analysis of the data. Copyright © 1990, Wiley Blackwell. All rights reserved