Carbon-fiber-reinforced YMAS glass- ceramic-matrix composites--IV 2. from 1050 or 1 150 to 20oc for the stresses induced In cases 2 and 3, it was supposed that the CTEs of in composites cquivalent to the composite P5 or both the fibers and the matrix could be extrapolated at T3[ Figs 6 and(b)Fig. 7(b)]; and high temperatures 3. from 1250 to 20c for the stresses induced in For this, the transverse Young' s modulus of the P25 composites equivalent to the composite Pll fiber was chosen as 15GPa26 and that of the T400H IFig. 6(c) fiber as 10 GPa.26 The Poisson's ratios vf, are approxi mately equal to 0-4 for both fibers. 18, 20,22 Taking into and unt the texture, the differences between Et and E between vf, and vl are in that order of magnitude The modulus of the glass measured by the ultrasonic technique was equal to 118 GPa For the P25 composites, the interface is always in Lension, equal at least to 150 MPa at 20"C. If the composite is heated up to 1250C, this stress becomes even higher and reaches 250 MPa. These tensile stresses should lead to the debonding of the interface, particu 020040060080010001200 emperature(C) larly in the last case. Not only the longitudinal stress in 150+. 020040060080010001200 020040060080010001200 R25 E200 020040060080010001200 0204006008001120 Temperature(C) Fig. 6. Thermal residual stresses in P25/YMAS com Fig. 7. Thermal residual stresses in T400H/YMAS composites s(a)and when composite when the matrix is still vitreous(a) and when the composite been hot-pressed up to 1050oC(b)and up to 1250c has been hot-pressed up to 1150 C(b) Table 3. Longitudinal and transverse coefficients of thermal expansion of the P25 and T400H carbon fibers P25 fiber △T(°C) 50-200 350-500 700-1000 a{(10-6°C 58 (10-6° 10.5 14·7 65 T400H fiber 200-400 600-800 800-1000 (10-6 5.7 125Carbon-fiber-reinforced YMAS glass-ceramic-matrix composites-IV 415 2. from 1050 or 1150 to 20°C for the stresses induced in composites equivalent to the composite P5 or T3 [Figs 6 and (b)Fig. 7(b)]; and 3. from 1250 to 20°C for the stresses induced in composites equivalent to the composite Pll [Fig- 6(c)]. 350 - 300 -’ 250 .. 200 400 600 800 1000 1200 Temperature (“C) (a) 0 200 400 600 800 1000 1200 Temperature (“C) (b) (a) 350 300 250 200 150 100 50 0 0 200 400 600 800 1000 1200 Temperature (“C) (cl Fig. 6. Thermal residual stresses in P25/YMAS composites Fig. 7. Thermal residual stresses in T400H/YMAS composites when the matrix is still vitreous (a) and when composites have when the matrix is still vitreous (a) and when the composite been hot-pressed up to 1050°C (b) and up to 1250°C (c). has been hot-pressed up to 1150°C (b). In cases 2 and 3, it was supposed that the CTEs of both the fibers and the matrix could be extrapolated at high temperatures. For this, the transverse Young’s modulus of the P25 fiber was chosen as 15 GPa26 and that of the T400H fiber as 10GPa.26 The Poisson’s ratios 4, are approxi￾mately equal to 0.4 for both fibers.‘8,20,22 Taking into account the texture, the differences between J!$ and g and between uf, and uf, are in that order of magnitude. The modulus of the glass measured by the ultrasonic technique was equal to 118 GPa. For the P25 composites, the interface is always in tension, equal at least to 150 MPa at 20°C. If the composite is heated up to 1250°C this stress becomes even higher and reaches 250 MPa. These tensile stresses should lead to the debonding of the interface, particu￾larly in the last case. Not only the longitudinal stress in 350 7 300 .. 3 250 .. 1 0 200 400 600 800 1000 1200 Temperature (“C) 400 600 800 Temperature (“C) (b) Table 3. Longitudinal and transverse coefiicients of thermal expansion of the P25 and T4OOH carbon fibers P25 fiber AT(C) 50-200 200-350 350-500 500-700 700-1000 of (lo-6”C-‘) oi (lo-6”C-1) 2,7 3.8 4.6 5.3 5.8 10.5 14.7 16.5 T4OOH fiber AT(C) 50-200 200-400 400-600 600-800 800-1000 (2: or (lOW”C-‘) (lo-6°C’) 2.6 579.9 3612.5 4.5 12.9 5.1 11.1 5.6