M.B. Ruggles-Wrenn et al. Composites Science and Technology 66(2006)2089-2099 previously subjected to 100 h at 75 MPa at 1000C. Tensile in the 0o plies break over a wide range of axial locations, stress-strain curves obtained for the N610/M/A specimens in general spanning the entire width of the specimen. In a subjected to prior creep are presented in Fig.& together given specimen, slightly different pullout lengths are pro- with the tensile stress-strain curve for the as-processed duced in different 0o plies. It is noteworthy that the average material. It is seen that prior creep had no qualitative effect fiber pullout length increases with increasing creep stress on tensile stress-strain behavior The fracture surfaces produced in monotonic tension tests at 1100C display similar"brushy'-type failure with exten 4.3. Composite microstructure sive pullout of individual fibers Fracture surfaces of the N610/M/A ns tested in Fracture surfaces of the N610/M/A specimens tested in creep at 900 C are shown in Figs. 10(ahe)for creep stress creep at 1100C are shown in Figs. 9(aHd), for creep levels of 80, 120, 130, 140 and 150 MPa, respectively. As stress levels of 40, 80, 100 and 120 MPa, respectively. The was the case at 1100C, the fracture planes obtained at fracture planes are not well defined; the fibers in the 0o plies 900C show randomly distributed fiber failure and pullout exhibit random failure producing fiber pullout. The fibers of both individual fibers and fiber tows. However, the aver age length of fiber pullout produced at 900C appears to be independent of creep stress level. Extensive fiber pullout of approximately the same average length is seen in all As-Processed 900C fracture surfaces, except in the fracture surface obtained at 150 MPa, which shows a shorter average length. Recall that this specimen also exhibited the shortest creep life, failing after 805 s. The fast fracture failure sur- faces produced at 900C also have a"brushy"appearance exhibiting significant amount of fiber pull-out Fracture surfaces of the N610/A specimens tested reep at 900C are shown in Figs. ll(a) and(b), for creep stress levels of 73 and 80 MPa, respectively. The contrast between the 80 MPa fracture surfaces of the two compos- ites(Figs. 10(a)and ll(b)is striking. The fracture surface of the N610/M/A is"brushy", showing extensive pullout Fig8. Effects of prior creep at 900C on tensile stress-strain behavior of with pullout lengths reaching al0 mm. Conversely, the the N610/M/A ceramic compo N610/A exhibits no fiber pullout, with a brittle-type 10 mm 10 mm 10 mm 10 mn e surfaces of imens tested at 1100C at creep stress levels of:(a)40. (b)80. (c)100 and (d)120 MPa. Fiber pullout with increasing creep stres 10 101 10m mI 10m Fig. 10. Fracture surfaces of the N610/M/A specimens tested at 900C at creep stress levels of: (a)80, (b)120, (c)130. (d)140 and(e)150 MPa.previously subjected to 100 h at 75 MPa at 1000 C. Tensile stress–strain curves obtained for the N610/M/A specimens subjected to prior creep are presented in Fig. 8 together with the tensile stress–strain curve for the as-processed material. It is seen that prior creep had no qualitative effect on tensile stress–strain behavior. 4.3. Composite microstructure Fracture surfaces of the N610/M/A specimens tested in creep at 1100 C are shown in Figs. 9(a)–(d), for creep stress levels of 40, 80, 100 and 120 MPa, respectively. The fracture planes are not well defined; the fibers in the 0 plies exhibit random failure producing fiber pullout. The fibers in the 0 plies break over a wide range of axial locations, in general spanning the entire width of the specimen. In a given specimen, slightly different pullout lengths are pro￾duced in different 0 plies. It is noteworthy that the average fiber pullout length increases with increasing creep stress. The fracture surfaces produced in monotonic tension tests at 1100 C display similar ‘‘brushy’’-type failure with exten￾sive pullout of individual fibers. Fracture surfaces of the N610/M/A specimens tested in creep at 900 C are shown in Figs. 10(a)–(e) for creep stress levels of 80, 120, 130, 140 and 150 MPa, respectively. As was the case at 1100 C, the fracture planes obtained at 900 C show randomly distributed fiber failure and pullout of both individual fibers and fiber tows. However, the aver￾age length of fiber pullout produced at 900 C appears to be independent of creep stress level. Extensive fiber pullout of approximately the same average length is seen in all 900 C fracture surfaces, except in the fracture surface obtained at 150 MPa, which shows a shorter average length. Recall that this specimen also exhibited the shortest creep life, failing after 805 s. The fast fracture failure sur￾faces produced at 900 C also have a ‘‘brushy’’ appearance, exhibiting significant amount of fiber pull-out. Fracture surfaces of the N610/A specimens tested in creep at 900 C are shown in Figs. 11(a) and (b), for creep stress levels of 73 and 80 MPa, respectively. The contrast between the 80 MPa fracture surfaces of the two compos￾ites (Figs. 10(a) and 11(b)) is striking. The fracture surface of the N610/M/A is ‘‘brushy’’, showing extensive pullout with pullout lengths reaching 10 mm. Conversely, the N610/A exhibits no fiber pullout, with a brittle-type 0 50 100 150 200 0.0 0.1 0.2 0.3 0.4 Strain (%) Stress (MPa) 900˚C As-Processed 145 h at 80 MPa 120 h at 120 MPa Fig. 8. Effects of prior creep at 900 C on tensile stress–strain behavior of the N610/M/A ceramic composite. Fig. 9. Fracture surfaces of the N610/M/A specimens tested at 1100 C at creep stress levels of: (a) 40, (b) 80, (c) 100 and (d) 120 MPa. Fiber pullout length increases with increasing creep stress. Fig. 10. Fracture surfaces of the N610/M/A specimens tested at 900 C at creep stress levels of: (a) 80, (b) 120, (c) 130, (d) 140 and (e) 150 MPa. M.B. Ruggles-Wrenn et al. / Composites Science and Technology 66 (2006) 2089–2099 2095