Journal of the American Ceramic SocieryRebillat et al. Vol 81. No 9 M F 1 gm Fig 8. SEM micrographs on protruding fibers after a push-back test on composite b((a) protruding fiber and(b) sliding fiber surfaces). surfaces are not apparent. Deep grooves can also be observed significantly larger than Plateau (Table Ill). Moreover, T data parallel to the direction of sliding. These reflect fiber- for the multilayered interphases(composites A and K)are sim- ilar to those estimated for carbon interphases thinner than 0.5 IV. Results The highest axial and radial residual stresses were also ob- tained for the composites with multilayered interphases(Fig A 30% scatter was obtained for all the interfacial 11). However, these residual stresses, derived from Hsueh ments(Tables III-V). The influence of the number of ( C-SiC) model, are too high when compared to those generally de- ayers(n) can be observed in comparison of these characteris- rmined for SiC/C/SiC composites that possess a carbon tics with previous results terphase 28-30 The magnitude of the residual radial stres at the fiber surface estimated using a coaxial cylinder-based pendent on the interphase thickness; it de- ()Composites Reinforced with As-Received Fibers creases from 100 MPa to -200 MPa as the carbon thickness Higher resistances to fiber debonding and to frictional slid decreases from I um to 0 um. 9 Magnitudes of 40 MPa and g seem to be observed for composites that possess multilay 50 MPa have been obtained for typical thicknesses of 0.5 and ered interphases, as indicated by the plots of debonding stress 0.2 um, The overestimation of the clamping stress highlights a (Fig. 9)and frictional shear stress(Fig. 10)and by the fric limit of hsueh's model in that it does not consider the effect of tion coefficients(Table III). The frictional shear stress(t) de- surface roughness during sliding. This shortcoming was over- rived from the nonlinear domain of the push-out curves are come by introducing a radial compressive stress at the inter-surfaces are not apparent. Deep grooves can also be observed parallel to the direction of sliding. These grooves reflect fiber￾surface roughness and confirm that fiber sliding was restricted. IV. Results A 30% scatter was obtained for all the interfacial measure￾ments (Tables III–V). The influence of the number of (C–SiC) layers (n) can be observed in comparison of these characteris￾tics with previous results on composites with a single carbon interphase.14 (1) Composites Reinforced with As-Received Fibers Higher resistances to fiber debonding and to frictional slid￾ing seem to be observed for composites that possess multilay￾ered interphases, as indicated by the plots of debonding stress (Fig. 9) and frictional shear stress (Fig. 10) and by the fric￾tion coefficients (Table III). The frictional shear stress (t) de￾rived from the nonlinear domain of the push-out curves are significantly larger than tplateau (Table III). Moreover, t data for the multilayered interphases (composites A and K) are sim￾ilar to those estimated for carbon interphases thinner than 0.5 mm.15,26,27 The highest axial and radial residual stresses were also ob￾tained for the composites with multilayered interphases (Fig. 11). However, these residual stresses, derived from Hsueh’s model,16 are too high when compared to those generally de￾termined for SiC/C/SiC composites that possess a carbon interphase.28–30 The magnitude of the residual radial stress at the fiber surface estimated using a coaxial cylinder-based model28–30 is dependent on the interphase thickness; it de￾creases from 100 MPa to −200 MPa, as the carbon thickness decreases from 1 mm to 0 mm.29 Magnitudes of 40 MPa and −50 MPa have been obtained for typical thicknesses of 0.5 and 0.2 mm. The overestimation of the clamping stress highlights a limit of Hsueh’s model in that it does not consider the effect of surface roughness during sliding. This shortcoming was over￾come by introducing a radial compressive stress at the inter￾Fig. 8. SEM micrographs on protruding fibers after a push-back test on composite B ((a) protruding fiber and (b) sliding fiber surfaces). 2320 Journal of the American Ceramic Society—Rebillat et al. Vol. 81, No. 9