Development of Plane Strain Fracture Toughness Test for Ceramics Using Chevron Notched Specimens
The chevron-notch specimen is especially useful for measuring the plane strain fracture toughness, KIc, of ceramics. During test, a crack initiates at the tip of the chevron notch and extends stably as load is increased. For materials with flat crack growth resistance curves, maximum load for a given specimen configuration will always occur at the same relative crack length independent of the material. KIc is calculated from maximum load and the corresponding (minimum) value of the dimensionless stress intensity factor coefficient (Y m * ), with no need for crack length measurement.
Y(Y m * ) values have been determined for the short bar and four-point-bend specimens and have been used in fracture toughness measurements on hot pressed silicon nitride and sintered aluminum oxide. KIc for Si3N4 was essentially independent of specimen size and chevron notch configuration, with values ranging only from 4.6 to 4.9 MNm−3/2. jn contrast, significant specimen size and notch geometry effects were observed for Al2O3, with KIc values ranging from 3.1 to 4.7 MNm−3/2. These effects are believed due to a rising crack growth resistance curve for the A12O3 tested.
KeywordsFracture Toughness Crack Growth Resistance Curve Toughness Test Fracture Toughness Test Plane Strain Fracture Toughness
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