Journal of the American Ceramic Society-Morscher et aL. 3w× 80SE(M 11/e2 11bm号2aw1 nox SE1an Fiber BN Fiber BN sav 113mmx20c4 0401110620v14 Fig. 4. FESEM images of fracture surfaces of SYL- iBn composites showing outside debonding(a, b)and inside debonding(c, d) higher than the stresses for matrix cracks to penetrate the load- contact, the thinner areas of BN earing fibers (determined from the onset of hyste op fusion occurred for rupture times activity, 175 MPa for f=0. 2 composites used in this study ) In several regions of significant fib other words, the SYL-iBN composites are significantly cracked at section of the fracture surface the stress-rupture conditions of this study, even for specimens that A few specimens(SYL and SYL-iBN)were precracked at room did not fail after long periods of time. temperature and compared with the rupture behavior of pristine Examination of the rupture specimen fracture surfaces con- from the same panel(Fig. 8). It was evident that firmed the survival of most of the bn around the fibers in the onding SYL composites with nominally good rupture matrix crack even though significant oxidation had occurred in the were significantly poorer in rupture behavior with matrix crack( Fig. 7). However, at regions of near fiber-to-fiber ng as has been observed in another study. On the other 600 f=0.18 f。=0.2 f。=017 200 Change in slope at-70 MPa not associated with occurrence of ae 0203040.50.6 Strain. Fig. 5. Room-temperature tensile stress-strain curves for a number of outside-debonding composites with different fiber volume fractions.108 Journal of the American Ceramic Society-Morscher et al. Vol. 87, No. 1 Fig. 4. FESEM images of fracture surfaces of SYL-iBN composites showing outside debonding (a,b) and inside debonding (c,d). higher than the stresses for matrix cracks to penetrate the load￾bearing fibers (determined from the onset of hysteresis loop activity, - 175 MPa for f = 0.2 composites used in this study). In other words, the SYL-iBN composites are significantly cracked at the stress-rupture conditions of this study, even for specimens that did not fail after long periods of time. Examination of the rupture specimen fracture surfaces con￾firmed the survival of most of the BN around the fibers in the matrix crack even though significant oxidation had occurred in the matrix crack (Fig. 7). However, at regions of near fiber-to-fiber 600 500 6 300 b a 200 12 100 200 -I contact, the thinner areas of BN were oxidized and fiber-to-fiber fusion occurred for rupture times greater than 80 h. There were several regions of significant fiber pullout throughout the cross section of the fracture surface. A few specimens (SYL and SYL-iBN) were precracked at room temperature and compared with the rupture behavior of pristine specimens from the same panel (Fig. 8). It was evident that inside-debonding SYL composites with nominally good rupture properties were significantly poorer in rupture behavior with precracking as has been observed in another study." On the other 1& Change in slope at - 70 MPa not associated with occurrence of AE 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Strain, % , = 0.18 Fig. 5. Room-temperature tensile stress-strain curves for a number of outside-debonding composites with different fiber volume fractions