Journal of the American Ceramic Society-Lee et al. Vol 87. No. 7 Table L. Summary of Bending Strength and Fatigue Limit of Heat-Treated Smooth Specimens and Crack-Healed Specime Test temperature(°C Gn(MPa)t σn(MPa)2 p/oB (% Gn (Mpa) cd/aB(% Heat-treated smooth specimen 1000 800 Crack-healed specimen 75 750 8897 1100 500 h.Static fatigue limit. Cyclic fatigue limit. Room temperature he bending strengths of the specimens that survived static fatigue (4 Cyclic Fatigue Strength at High Temperature tests were also investigated at each testing temperature, ie, 900% and The cyclic fatigue strengths of heat-treated smooth specimens 1100.C. The bending strengths are shown on the right-hand side of and crack-healed specimen have also been investigated at 900 and Fig. 5. The crack-healed specimens that survived the static fatigue test 1 100C. The experimental results are shown in Fig. 6. The values showed bending strengths similar to monotonically tested specimens, of the cyclic fatigue limit(op) of the heat-treated smooth indicating that significant crack growth from the crack-healed zone or specimen and the crack-healed specimen at 900C are about 800 mal defects did not occur and 700 MPa, respectively. These values are more than 90% Slow crack growth Pre-crack A B Sic whisker Oxide 200um SXkax500 5 e.aky×s.ae5u Fig. 4. SEM micrographs of fracture surface of the test specimens fractured during static fatigue test at mperature(slow crack growth occurred during the fatigue test, applied stress =800 MPa, tr=110 s):(a) crack profile, (b) detail of crack-healed zone shown by A in(a),(c)detail of slow crack owth zone shown by B in(a),(d) detail of area outside the slow crack growth zone shown by C in(a)The bending strengths of the specimens that survived static fatigue tests were also investigated at each testing temperature, i.e., 900° and 1100°C. The bending strengths are shown on the right-hand side of Fig. 5. The crack-healed specimens that survived the static fatigue test showed bending strengths similar to monotonically tested specimens, indicating that significant crack growth from the crack-healed zone or internal defects did not occur. (4) Cyclic Fatigue Strength at High Temperature The cyclic fatigue strengths of heat-treated smooth specimens and crack-healed specimen have also been investigated at 900° and 1100°C. The experimental results are shown in Fig. 6. The values of the cyclic fatigue limit (f0) of the heat-treated smooth specimen and the crack-healed specimen at 900°C are about 800 and 700 MPa, respectively. These values are more than 90% Fig. 4. SEM micrographs of fracture surface of the test specimens fractured during static fatigue test at room temperature (slow crack growth occurred during the fatigue test, applied stress  800 MPa, tf  110 s): (a) crack profile, (b) detail of crack-healed zone shown by A in (a), (c) detail of slow crack growth zone shown by B in (a), (d) detail of area outside the slow crack growth zone shown by C in (a). Table I. Summary of Bending Strength and Fatigue Limit of Heat-Treated Smooth Specimens and Crack-Healed Specimens Test temperature (°C) B (MPa)† t0 (MPa)‡ t0/B (%) f0 (MPa)§ f0/B (%) Heat-treated smooth specimen RT¶ 1000 800 80 800 80 900 850 800 94 1100 850 700 82 Crack-healed specimen RT¶ 1000 750 75 850 85 900 750 550 73 700 93 1100 650 450 69 500 77 † Average bending strength. ‡ Static fatigue limit. § Cyclic fatigue limit. ¶ Room temperature. 1262 Journal of the American Ceramic Society—Lee et al. Vol. 87, No. 7