Static Fatigue Strength and Fracture Mechanism of Ceramic/Metal Joints

The static fatigue strength and fracture mechanism of ceramic/metal (Si3N4/Cu/SUS304) joints were investigated under a four point bending loading. The results clearly showed characteristic of static fatigue. The static fatigue strength at 30 days was about 65% of the static bending strength. Fracture surfaces were examined by SEM and EPMA after the static fatigue test. On the basis of these results, it was determined that the fracture mechanism of the static fatigue test is the same as that of the static bending test. The crack initiates and grows at the ceramic/brazing metal interface and finally kinks to the ceramic side. The crack initiation stress was successfully detected using the AE technique. It is shown that the crack initiates during loading and the time-dependent crack growth occurs under sustained constant load.