MEASUREMENT OF CRACK-TIP TOUGHNESS IN ALUMINA AS A FUNCTION OF GRAIN-SIZE

Crack profile measurements near the crack tip in the SEM were used to measure crack tip toughness of alumina as a function of grain size (av erage grain size 0.9-16 mu m). For comparative tests, two crack config urations were included in the present study: straight cracks (CT speci men) loaded with an in situ device; and radial indentation cracks, The measured crack tip toughness values were independent of crack geometr y, and no grain size dependence could be discerned. A mean crack tip t oughness of 2.3 MPa . m(1/2) was evaluated. The crack tip toughness de termined from crack profile measurements is significantly lower than t he toughness evaluated with conventional indentation techniques (e.g., indentation strength bending).