Abstract
Fracture toughness (KIC) of structural ceramics such as alumina, silicon nitride, silicon carbide was evaluated using a single edge precracked beam (SEPB) technique. An indentation crack or a sawed notch was introduced into the specimen as an origin for sharp precrack, followed by developing an atomically sharp pop-in crack from the crack or notch. The sharply precracked specimens were fractured by 3-point bending under a cross-head speed of 0.5mm/min at room temperature. The KIC values obtained from each measurement showed a good repoducibility for alumina and silicon carbide. For silicon nitride, however, the values scattered a little, especially when a sharp pop-in crack was introduced from the indentation crack. The causes of the scattering were discussed on based the observation of inclined precrack front and deflected fracture surface.
