A new technique for precracking ceramic specimens in fatigue and fracture

This paper highlights the design and performance of an articulated bridge fixture to precrack ceramic specimens with 100% success. The precracked specimens were subsequently used to determine and study the fatigue crack growth rate and fracture toughness of a 25 wt% SiC whisker reinforced Al2O3 composite. Precracking was initially done by using Vickers indentation as a cracker starter. However one can argue that the residual stress introduced due to the indentation might influence the fracture toughness and fatigue crack growth rate values determined subsequently. The success achieved in precracking by using this fixture led us to substitute the Vickers indentation with a 0.1 mm deep groove as a crack starter. The fracture toughness values obtained from V notched and precracked specimens were about 7.2% lower than those obtained from indentation as a crack starter in indented and precracked specimens, However, fatigue crack growth rates using both these crack starters were not widely different.