Chapter 66. Thermomechanical Fatigue of Crossply SiCf/Si3N4 Ceramic Composites under Impinged Kerosene-Based Flame
- John B. Wachtman Jr.
Published Online: 28 MAR 2008
Copyright © 1993 The American Ceramic Society
Proceedings of the 17th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 14, Issue 7/8
How to Cite
St. Hilaire, G. M. and Ertürk, T. (1993) Thermomechanical Fatigue of Crossply SiCf/Si3N4 Ceramic Composites under Impinged Kerosene-Based Flame, in Proceedings of the 17th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 14, Issue 7/8 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470314180.ch66
- Published Online: 28 MAR 2008
- Published Print: 1 JAN 1993
Print ISBN: 9780470375266
Online ISBN: 9780470314180
The thermomechanical fatigue behavior of crossply SiC fiber-reinforced Si3N4 matrix ceramic composites was investigated under impinged kerosene-based flame in cycles between 500-1350°C. Hot pressed [(0/90)3/0]S SCS-6 and [(0/90)5/0]S SCS-9 SiC fiber reinforced crossply composite panels were 3.175 mm thick and contained 30 vol % fibers. Thermomechanical fatigue testing consisted of one minute direct flame impingement followed by one minute ambient temperature cooling under a constant applied tensile stress. Nine SCS-9 and four SCS-6 fiber-reinforced specimens were tested using the NASA Lewis burner rig facility. Specimens reinforced with SCS-6 fibers failed in 20-40 cycles at prestresses as low as 110 MPa. Specimens containing SCS-9 fibers, on the other hand, showed runout conditions (1000 cycles) up to 125 MPa. The number of cycles-to-failure in the SCS-9 specimens declined abruptly at 140 MPa; at 168 MPa prestress the number of cycles-to-failure was 5-42. SEM fractographs of control and failed specimens in both type composites showed minor fiber pullout. Room temperature strength and modulus degraded approximately 10% in the SCS-9 runout specimens.
The TMF behavior of 13-ply SCS-6 and 21-ply SCS-9 0/90 crossply SiCf/Si3N4 ceramic matrix composites under impinged flame conditions in cycles between 500-1350°C has been studied. Specimens reinforced with SCS-9 SiC fibers showed superior TMF resistance compared to SCS-6 SiC fiber-reinforced Si3N4 at any preapplied stress. The SCS-6 reinforced specimens were more susceptible to the thermal gradients imposed during testing. Strength and modulus degraded approximately 10% in SCS-9 TMF runout specimens. Minor fiber pullout was observed in room temperature tension tests in both control and TMF runout samples prestressed up to 105 MPa. An abrupt decline in TMF resistance in SCS-9 SiC fiber-reinforced Si3N4 matrix composite specimens in the preapplied stress range 140-168 MPa implies fiber creep-controlled failure. SCS-9 SiC fiber-reinforced crossply Si3N4 matrix composite exhibited TMF runout conditions (1000 cycles) at prestresses better than 70% of the room temperature proportional limit.