Mode-I and mixed-mode I/II fracture behaviour of sintered alumina at ambient and elevated temperatures

The mode-I and mixed-mode I/II fracture toughness of sintered alumina has been evaluated using SENB (Single edge notched bend) specimens under three point bend loading at both ambient and elevated temperatures. The specimens were subjected to asymmetrical loading conditions to determine the mixed-mode I/II fracture toughness. The fracture resistance of the ceramic, in terms of plane-strain fracture toughness (K-lo) and total fracture toughness (K) parameters, has been found to decrease with increasing test temperature. However the nature of fracture is found to be similar (quasi-cleavage) at both ambient and elevated temperatures. The imposition of mode-II components on mode-l loading has resulted in only a marginal decrease in the total fracture toughness (K-t) value. The crack path profiles of the mixed-mode tested specimens reveal that the crack front rotates towards mode-I fracture direction. Thus, designing of the components and structures made of such materials can be done based on mode-l fracture toughness, K-lc. The results obtained in the study are discussed in the light of microstructure, crack path profiles and fracture mechanisms.