Y. Gowayed et aL/Composites Science and Technology 70(2010)435-441 (15pmx15 (a)Sic-Cvi between three SiC fibers (b) Longitudinal cross section of the fiber and the bn taken at an extreme oblique angle. The reader is reminded that the average thickness 4. Scanning probe microscopy of SiC-CVl and BN near SiC fiber. Properties of constituent material at room temperature(GPa) Property Sic-CVI SiC/si SiC-SC Si 3949 2027 4388 649 1875173.3 0.36 0.230.1770.1350026 Nano-indentation. Murthy et al. (1999). Strain Comparing the two curves, a decrease in modulus, strength and strain to failure with the increase in temperature is evident. The value of the elastic modulus was 274.8+ 10.34 GPa for samples tested at room temperature and 233.7+ 19.51 GPa for samples 9 140 tested at 1204 oC. the value of the shear modulus also decreased ····, 1204C. The value of the Poisson's ratio, measured only at room 220 om 72.4+6.21 GPa at room temperature to 60.47+0.69 GPa at temperature, was 0.127+0.003 The compressive stress-strain curve at room temperature of the ure, the slope of the stress-strain curve (ie, the through-thickness i 60 modulus)changed with the level of comFig. 5b. The modulus va- e stress until it reached an almost steady slope, as shown in lue was taken as the average value of that slope as 130 4. Numerical model Stress(MPa) any models used to calculate the elastic properties of textile composite materials from properties of their constituents are avail- Fig. 5. (a)Through-thickness compressive stress-strain curve and (b)the effect of able in literature, for example [7-9], varying from closed-form to compressive stress on the elastic modulus.Comparing the two curves, a decrease in modulus, strength and strain to failure with the increase in temperature is evident. The value of the elastic modulus was 274.8 ± 10.34 GPa for samples tested at room temperature and 233.7 ± 19.51 GPa for samples tested at 1204 C. The value of the shear modulus also decreased from 72.4 ± 6.21 GPa at room temperature to 60.47 ± 0.69 GPa at 1204 C. The value of the Poisson’s ratio, measured only at room temperature, was 0.127 ± 0.003. The compressive stress–strain curve at room temperature of the MI SiC/SiC composite is shown in Fig. 5a. As can be seen from this fig￾ure, the slope of the stress–strain curve (i.e., the through-thickness modulus) changed with the level of compressive stress until it reached an almost steady slope, as shown in Fig. 5b. The modulus va￾lue was taken as the average value of that slope as 130 ± 3.39 GPa. 4. Numerical model Many models used to calculate the elastic properties of textile composite materials from properties of their constituents are avail￾able in literature, for example [7–9], varying from closed-form to Fig. 4. Scanning probe microscopy of SiC-CVI and BN near SiC fiber. Table 1 Properties of constituent material at room temperature (GPa). Property iBN￾Sylramic fiber (b-SiC) BN coating (Si-doped BN) SiC-CVI (b-SiC) SiC/Si Porosity SiC-SC b-SiC) Si Ea 394.9 20.27 438.8 405.6 164.9 Gc 168.8 8.27 187.5 173.3 67.57 mb 0.17 0.22 0.17 0.17 0.22 Vf 0.36 0.072 0.23 0.177 0.135 0.026 a Nano-indentation. b Murthy et al. (1999). c Calculated. 0 100 200 300 400 500 600 0.000 0.002 0.004 0.006 Stress (MPa) Strain (a) 0 20 40 60 80 100 120 140 160 0 100 200 300 400 500 Through thickness compressive modulus (GPa) Stress (MPa) (b) Fig. 5. (a) Through-thickness compressive stress–strain curve and (b) the effect of compressive stress on the elastic modulus. 438 Y. Gowayed et al. / Composites Science and Technology 70 (2010) 435–441