摘要：

Dynamic fracture behavior of silicon nitride ceramics is directly observed using a dynamic fracture testing apparatus of caustics combined with an ultrahigh-speed camera, Imacon 790, at room and elevated temperatures over 1000°C. Consequently, it is confirmed that dynamic fracture toughness KId is almost the same as the value of static fracture toughness KIc in this temperature range. These values of KId and KIc are slightly increased from room temperature (R. T.) to 800°C and they are decreased at temperatures above this. Crack-propagation fracture toughness KID at R. T. is nearly constant at KID=6.0 MN/m3/2 in the crack velocity range up to 3800 m/s, and this is the same tendency at 1000°C. The effect of the notch root radius ρ on the values of KIc and KId is also studied in the ρ range from 0 to 1.0 mm under R. T. condition. Moreover, the visualized AE-wave which is emitted from the notch tip at the initiation of fracture is shown.

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