0.002 Energy, Advanced Research and Technology Development, Fossil Energy Material Program, and Office of Industrial g0.0015 Technology, Energy Efficiency and Renewable Energy, AXIAL W-31-109-Eng-38. The authors thank R. A. Lowden(Oak Ridge National Laboratory) for pro- ber-reinforced SiC matrix composit 0.0005 Ramakrishna T Bhatt (U.S. Army Propulsion Directorate NASA Lewis Research Center) for providing SIC/RBSN RANSVERSE composites, and grant Pollard for providing experimental -0.00 References Fiber Content, V,(vol % f Sic/rBSN composites as a function of fiber mic matrix composites. J Am Ceramic Soc 1985: 68(5): 225-231 tron diffraction in the intense pulsed neutron [2] Evans AG, Marshall DB. The mechanical behavior of ceramic matrix source at Argo onal Laboratory and analytically predicted by opposites, Overview No 85. Acta Metall 1989, 37(10): 2567-2583 Majumdar et al. [1 B Thouless MD, Sbaizero O, Sigl LS, Evans AG. Effect of interface mechanical properties on pullout in a Sic-fiber-reinforced lithium 4. Summary aluminum silicate glass ceramic. J Am Ceramic Soc 1989: 72(4) 25-532 1. Processing-induced damage of Nicalon fibers can be [4] Mah T, Mendiratta MG, Katz AP, Ruh R, Mazdiyasni ks Room minimized by the application of a carbon coating, mperature mechanical behavior of fiber-reinforced ceramic matri composites. J Am Ceramic Soc 1985: 68(1): C27-C30 which leads to a corresponding increase in the retained 5 Lowden RA Fiber coatings and the mechanical properties of a fiber in-situ strength of the fibers during composite processing inforced ceramic composite. Adv Composite Mater, Ceramic Trans 2. Ultimate strength and work of fracture(wOF)of comp 1991;19:619-630 sites were found to increase with increasing coating [6]Stinton DP, Caputo AJ, Lowden RA. Synthesis of fiber-reinforced SiC mposites by chemical vapor infiltration. Am Ceramic Soc Bull thickness up to = 0.3 um. Further increase in coating 98665(2):347-350 thickness did not significantly affect mechanical prop. [7 Stinton DP, Bessman TM, Lowden RA. Advanced ceramics erties, indicating an optimum coating thickness for deposition techniques. Am Ceramic Soc Bu processIng 867(2:350-355 3. A similarity between the dependence of in-situ fiber 8]Bhatt RT. Method of preparing fiber-reinforced ceramic materials. US atent No, 4689188 strength, ultimate strength and WoF on fiber coating [9] Bright JD, Shetty DK, Griffin CW, Limaye SY. Interfaci thickness suggests a direct correlation between retained and friction in silicon carbide (filament)-reinforced cera in-situ fiber strength and resulting mechanical properties lass-matrix composites. J Am Ceramic Soc 1989, 72(10) 4. The increase in ultimate strength and WoF with increas- [10] Kirchner HP, Gruver RM. Fracture mirror in alumina ceramics. Phil ing fiber coating thickness may also be partly caused by Mag1973:27:1433-1446 improved fiber/matrix interfacial characteristics [11] Mecholsky JJ, Freiman Sw, Rice RW. Fracture surface analysis of ceramics. J Mater Sci 1976: 11:- 1310-1319 5. For SiC-fiber-reinforced reaction-bonded SizNa matrix [12] Curtin WA. Theory of mechanical properties of ceramic-matrix composites, both debonding and frictional shear stresses composites. J Am Ceramic Soc 1991; 74(11): 2831-2845 generally decreased with increasing fiber content. These [13] Goettler RW, Faber KT Interfacial shear stresses in Sic and AL,O ariations are consistent with the variations in residual fiber-reinforced glasses. Ceramic Engng Sci Proc 1988; 9(7-8): 701 radial stress of fibers measured by neutron diffraction, the [14] Saigal A, Kupperman DS, Singh JP, Singh D, Ri J. Bhatt rt latter decreased with increasing fiber content. Thermal residual strains and stresses in silico forced silicon nitride composites. Composite 075-1086 Acknowledgements [15] Majumdar S, Singh D, Singh JP. Analysis of pushout tests on a SiC- fiber-reinforced reaction-bonded Si, N4 composite Composites Engng 1993;3(4)287-312 This work was supported by the Us Department of4. Summary 1. Processing-induced damage of Nicalon fibers can be minimized by the application of a carbon coating, which leads to a corresponding increase in the retained in-situ strength of the fibers during composite processing. 2. Ultimate strength and work of fracture (WOF) of compo￾sites were found to increase with increasing coating thickness up to <0.3 mm. Further increase in coating thickness did not significantly affect mechanical prop￾erties, indicating an optimum coating thickness for processing. 3. A similarity between the dependence of in-situ fiber strength, ultimate strength and WOF on fiber coating thickness suggests a direct correlation between retained in-situ fiber strength and resulting mechanical properties. 4. The increase in ultimate strength and WOF with increas￾ing fiber coating thickness may also be partly caused by improved fiber/matrix interfacial characteristics. 5. For SiC-fiber-reinforced reaction-bonded Si3N4 matrix composites, both debonding and frictional shear stresses generally decreased with increasing fiber content. These variations are consistent with the variations in residual radial stress of fibers measured by neutron diffraction, the latter decreased with increasing fiber content. Acknowledgements This work was supported by the US Department of Energy, Advanced Research and Technology Development, Fossil Energy Material Program, and Office of Industrial Technology, Energy Efficiency and Renewable Energy, under Contract W-31-109-Eng-38. The authors thank R. A. Lowden (Oak Ridge National Laboratory) for pro￾viding Nicalon-fiber-reinforced SiC matrix composites, Ramakrishna T. Bhatt (U.S. Army Propulsion Directorate, NASA Lewis Research Center) for providing SiC/RBSN composites, and Grant Pollard for providing experimental assistance. References [1] Marshall DB, Evans AG. Failure mechanisms in ceramic-fiber/cera￾mic matrix composites. J Am Ceramic Soc 1985;68(5):225–231. [2] Evans AG, Marshall DB. The mechanical behavior of ceramic matrix composites, Overview No 85. Acta Metall 1989;37(10):2567–2583. [3] Thouless MD, Sbaizero O, Sigl LS, Evans AG. Effect of interface mechanical properties on pullout in a SiC-fiber-reinforced lithium aluminum silicate glass ceramic. J Am Ceramic Soc 1989;72(4): 525–532. [4] Mah T, Mendiratta MG, Katz AP, Ruh R, Mazdiyasni KS. Room temperature mechanical behavior of fiber-reinforced ceramic matrix composites. J Am Ceramic Soc 1985;68(1):C27–C30. [5] Lowden RA. Fiber coatings and the mechanical properties of a fiber￾reinforced ceramic composite. Adv Composite Mater, Ceramic Trans 1991;19:619–630. [6] Stinton DP, Caputo AJ, Lowden RA. Synthesis of fiber-reinforced SiC composites by chemical vapor infiltration. Am Ceramic Soc Bull 1986;65(2):347–350. [7] Stinton DP, Bessman TM, Lowden RA. Advanced ceramics by chemical vapor deposition techniques. Am Ceramic Soc Bull 1988;67(2):350–355. [8] Bhatt RT. Method of preparing fiber-reinforced ceramic materials. US Patent No. 4689188. [9] Bright JD, Shetty DK, Griffin CW, Limaye SY. Interfacial bonding and friction in silicon carbide (filament)-reinforced ceramic- and glass-matrix composites. J Am Ceramic Soc 1989;72(10):1891–1898. [10] Kirchner HP, Gruver RM. Fracture mirror in alumina ceramics. Phil Mag 1973;27:1433–1446. [11] Mecholsky JJ, Freiman SW, Rice RW. Fracture surface analysis of ceramics. J Mater Sci 1976;11:1310–1319. [12] Curtin WA. Theory of mechanical properties of ceramic-matrix composites. J Am Ceramic Soc 1991;74(11):2831–2845. [13] Goettler RW, Faber KT. Interfacial shear stresses in SiC and Al2O3 fiber-reinforced glasses. Ceramic Engng Sci Proc 1988;9(7–8):701– 861. [14] Saigal A, Kupperman DS, Singh JP, Singh D, Richardson J, Bhatt RT. Thermal residual strains and stresses in silicon-carbide-fiber-rein￾forced silicon nitride composites. Composites Engng 1993;3(11): 1075–1086. [15] Majumdar S, Singh D, Singh JP. Analysis of pushout tests on a SiC- fiber-reinforced reaction-bonded Si3N4 composite. Composites Engng 1993;3(4):287–312. 450 J.P. Singh et al. / Composites: Part A 30 (1999) 445–450 Fig. 10. Residual strain of SiC/RBSN composites as a function of fiber content, measured by neutron diffraction in the intense pulsed neutron source at Argonne National Laboratory and analytically predicted by Majumdar et al. [15] (solid lines)