J. Martinez.Fernandez, G N Morscher Journal of the European Ceramic Society 20(2000)2627-2636 vo=5c 000 言 9876 □ ChnC 700C CNic(1 TTTTmTTTTTTTTmmF 0.010.101.0010.0 00100000 00.00100000 Time(hrs Fig 3. Minicomposite stress-rupture data: (a)compared with previous data on Nicalon minicomposites: (b) compared with previous data on BN- HiNic minicomposites. 2. and 78%(111 N) of the average strength, respectively. MPa, the stress on the fibers where fully loaded would Since the fraction of the average strength using the be 500 MPa). For the tests run at 700 and 950C, failure lower precrack load is closer to the previous ones, the always occurred in the hot zone of the furnace For all results with the samples precracked at 280 MPa were he tests run at 1200C. the failure occurred outside the the ones used for comparison hot zone region, about 2 cm from the center of the fur The results from the fatigue experiments are plotted in nace. In these regions, the temperature is approximately Fig. 5 together with the stress-rupture results from 900oC, based on the temperature profile of the furnace samples precracked at 280 MPa(same precrack load). The data from these tests were very similar to the data The time taken for the fatigue experiments is the total from the tests run at 950 C. time under cyclic loading conditions. At 700oC, the Some of the minicomposites did not fail after very behavior is essentially the same as the constant load long rupture times(e.g. 1000, 500, and 400 MPa for 700 conditions. The minicomposite resistance to fatigue 950, and 1200C, respectively). These tests as well as rapidly decreased at 950C. At this temperature, the some tests at shorter times were stopped before rupture samples tested at the highest peak stress failed in the and the retained strengths of the minicomposites were first or second fatigue cycle (for peak stresses over 75 determined at room temperature. The general trend was 700c:119N 00950c:119N▲ 950c.126N 00c:119N 5 Stress-nuoture 1200 C r10 TTTT TTTTT 1000100.001000.00 0010.1010010.00100.001000.00 Time(hrs sS-rupture data for two differe Fig. 5. Peak stress for fatigue experiments vs the survival time andand 78% (111 N) of the average strength, respectively. Since the fraction of the average strength using the lower precrack load is closer to the previous ones, the results with the samples precracked at 280 MPa were the ones used for comparison. The results from the fatigue experiments are plotted in Fig. 5 together with the stress-rupture results from samples precracked at 280 MPa (same precrack load). The time taken for the fatigue experiments is the total time under cyclic loading conditions. At 700C, the behavior is essentially the same as the constant load conditions. The minicomposite resistance to fatigue rapidly decreased at 950C. At this temperature, the samples tested at the highest peak stress failed in the ®rst or second fatigue cycle (for peak stresses over 75 MPa, the stress on the ®bers where fully loaded would be 500 MPa). For the tests run at 700 and 950C, failure always occurred in the hot zone of the furnace. For all the tests run at 1200C, the failure occurred outside the hot zone region, about 2 cm from the center of the fur￾nace. In these regions, the temperature is approximately 900C, based on the temperature pro®le of the furnace. The data from these tests were very similar to the data from the tests run at 950C. Some of the minicomposites did not fail after very long rupture times (e.g. 1000, 500, and 400 MPa for 700, 950, and 1200C, respectively). These tests as well as some tests at shorter times were stopped before rupture and the retained strengths of the minicomposites were determined at room temperature. The general trend was Fig. 3. Minicomposite stress±rupture data: (a) compared with previous data on Nicalon minicomposites;1 (b) compared with previous data on BN± HiNic minicomposites.2 . Fig. 4. Minicomposite stress±rupture data for two di€erent precrack loads. Fig. 5. Peak stress for fatigue experiments vs the survival time and comparison with stress±rupture data. 2630 J. Marti nez-FernaÂndez, G.N. Morscher / Journal of the European Ceramic Society 20 (2000) 2627±2636