In Situ Observations of Toughening Processes in Alumina Reinforced with Silicon Carbide Whiskers

An in situ study is made of crack interfaces in composites of alumina reinforced with silicon carbide whiskers. Both qualitative observations of the whisker-bridging micro-mechanisms and quantitative measurements of the crack profile are made to assess the specific role of the whiskers on the toughness curve (T-curve or R-curve). At small crackwall separations the whiskers act as elastic restraints to the point of rupture. In some cases the whiskers remain in frictional contact with the alumina matrix over large pullout distances (more than 1 μm) corresponding to a bridging zone approaching 1 mm. The results are discussed in relation to existing models of whisker reinforcement and published long-crack T-curve data