2468 Joumal of the American Ceramic Sociery-Bertrand et al. Vol. 82. No 9 100nm Fibe Interphase Matrix Fibe C3 Sicl 1 Fiber Fig. 3. TEM micrographs of a multilayered interphase(batch(3/30)o)(a)cross section of the minicomposite and( b) interfacial zone):a high-resolution TEM micrograph of the interfacial bond between the fiber and the interphase is shown in Fig. 3(c) quantity ErV(Er is the fiber Young's modulus, and Vr is the scribed by Droillard and Lamon. They are much larger than fiber volume fraction), which indicates that the applied load is that observed in the 2D woven Nincalon/SiC composites with borne only by the fibers. Therefore, the debonding of fibers multilayered interphases and strong fiber/interphase bonding complete at this stage. The minimum is reached at deforma-(-20 um) tions of-0.4%, which correspond to the deformations at matrix The longitudinal cracks were not detected before the tests cracking saturation that are indicated by the force-deformation They cannot be attributed to thermally induced stresses that are curves(Fig. 5). For certain minicomposites, the minimum generated while cooling from the processing temperature. Fur- seems to be smaller than Er Ve This discrepancy may be at thermore. the fiber and the matrix exhibit identical coefficients tributed to the presence of broken or bent fibers and/or uncer- of thermal expansion(CTEs)(Table II). As discussed in a later tainty in the data, including the modulus measurements, Ep section, their presence may be related to the initial twisting of and I the fiber tows (B) SEM Analysis: The matrix cracks that are detected at The pull-out lengths(100 um, Fig. 2)are similar to those the surface of the minicomposites after ultimate failure includ neasured in Nicalon/SiC minicomposites' and 2D woven transverse cracks as well as a few longitudinal cracks. The Nicalon/SiC composites with multilayered interphases and average spacing distance at saturation for the transverse cracks weak fiber/interphase bonding. Figure 8 shows the double (s)is 90-185 um(Table I). These values are similar to those deflection of a matrix crack, first in the interphase/matrix in- measured on the 2D woven Nicalon/SiC composites with mul- terface and then in the fiber/interphase interface. Figure 2 tilayered interphases and weak fiber/interphase bonding, de shows that the surface of the pulled-out fibers is smooth, whichquantity Ef ?Vf (Ef is the fiber Young’s modulus, and Vf is the fiber volume fraction), which indicates that the applied load is borne only by the fibers. Therefore, the debonding of fibers is complete at this stage. The minimum is reached at deforma￾tions of ∼0.4%, which correspond to the deformations at matrix cracking saturation that are indicated by the force–deformation curves (Fig. 5). For certain minicomposites, the minimum seems to be smaller than Ef ?Vf . This discrepancy may be at￾tributed to the presence of broken or bent fibers and/or uncer￾tainty in the data, including the modulus measurements, Ef , and Vf . (B) SEM Analysis: The matrix cracks that are detected at the surface of the minicomposites after ultimate failure include transverse cracks as well as a few longitudinal cracks. The average spacing distance at saturation for the transverse cracks (lS) is 90–185 mm (Table I). These values are similar to those measured on the 2D woven Nicalon/SiC composites with mul￾tilayered interphases and weak fiber/interphase bonding, de￾scribed by Droillard and Lamon.4 They are much larger than that observed in the 2D woven Nincalon/SiC composites with multilayered interphases and strong fiber/interphase bonding4 (∼20 mm). The longitudinal cracks were not detected before the tests. They cannot be attributed to thermally induced stresses that are generated while cooling from the processing temperature. Fur￾thermore, the fiber and the matrix exhibit identical coefficients of thermal expansion (CTEs) (Table II). As discussed in a later section, their presence may be related to the initial twisting of the fiber tows. The pull-out lengths (∼100 mm, Fig. 2) are similar to those measured in Nicalon/SiC minicomposites3 and 2D woven Nicalon/SiC composites with multilayered interphases and weak fiber/interphase bonding.4 Figure 8 shows the double deflection of a matrix crack, first in the interphase/matrix in￾terface and then in the fiber/interphase interface. Figure 2 shows that the surface of the pulled-out fibers is smooth, which Fig. 3. TEM micrographs of a multilayered interphase (batch (3/30)10) ((a) cross section of the minicomposite and (b) interfacial zone); a high-resolution TEM micrograph of the interfacial bond between the fiber and the interphase is shown in Fig. 3(c). 2468 Journal of the American Ceramic Society—Bertrand et al. Vol. 82, No. 9