초록
R-curve, of three kinds of silicon nitride-based ceramics were measured, using single edge notched beam (SENB) method at room and at elevated temperatures, up to $1200^{\circ}C$. Stable fraacture was seen on ceramic materials with SENB specimens if the machined notch is deep enough, even though the crack resistance did not increase with crack length. Hot pressed silicon nitride did not show the rising R-curve behavior at room temperature, but it showed some rising at $1000^{\circ}C$ and above. Si3N4 reinforced with SiC whiskers showed no rising behavior at room and elevated temperatures, as it has smaller grain size, compare to the monolithic specimen. Gas pressure sintered silicon nitride had very large and elongated grains, and it showed rising R-curve even at room temperature. However, it showed some creep behavior at $1200^{\circ}C$ and the calculated R-curve on this condition did not show a good result. We cannot apply this technique on this condition for obtaining the R-curve.