Journal of the American Ceramic Society-Levi et al. Vol 8l. No 8 f=3 All-Oxide CFCC 芝苏 s Imu 心2 SICC CFCC adoum (b) behavior of the oxide composites in this study: (a) at of SiC/carbon composites of similar fiber content and(b) 36 Strains at maximum load for the +45 specimens are-0.49 and-0.8% in(b) arent pull-out"of the fibers within the tows evolves erent mechanism than is typical of more conventional CFCCs, as there are no matrix sockets apparent on the fracture surface. Instead, the intervening matrix fragments in the region of strain localization. A fraction of particles remains attached to the fiber surfaces(e. g, Fig. 7(c), indicative of the sites where the matrix bonds to the fibers by alumina bridges(cf Fg.1) In the +45 orientation, the elastic modulus is much lower (E4s= 35 GPa), and inelastic deformation commences at mod- erately low stresses, <25 MPa, consistent with domination by velop at an essentially constant flow stress, oo =50 MPa, as (C) Fig. 7. Fracture surfaces of N610 composites in the 0/90 orienta material exhibits pronounced hysteresis with appreciable per- tion. Note the fibrous fracture with extensive pull-out in(a)and the manent strains, as illustrated in Fig. 8(a), that is remarkably similar to the behavior observed in carbon/carbon composites, residue of matrix attached to the fibers in(b) and (c) Fig. 8(b). 5, 36 The inelastic deformation is accompanied by a modest reduction in modulus(E4s 30 GPa upon unloading creases. For example, the +45 specimen in Fig. 6(a) has a after 0.65% strain) width of 6 mm and a strain of -0.4% at the maximum load The conditions for failure in the +45 orientation and the whereas the 12 mm sample in Fig 8(a) achieves a strain of associated mechanisms are sensitive to specimen width and -0.9% prior to the onset of softening. Even in the latter case lateral constraints. Specifically, in straight te most of the tows pull out from the edge of the specimen, Fig ith small widths, the fibers detach from the edges and with 9(a). Matrix fragmentation also occurs, enabling the tows to draw into the specimen, causing failure to occur at relatively rotate as they withdraw, thereby enhancing graceful failure small strains controlled primarily by the matrix. As the width beyond the onset of strain localization. This additional dis- increases, fiber withdrawal is delayed and failure strain placement is manifested in rather large apparent failure strainsapparent ‘‘pull-out’’ of the fibers within the tows evolves by a different mechanism than is typical of more conventional CFCCs, as there are no matrix sockets apparent on the fracture surface. Instead, the intervening matrix fragments in the region of strain localization. A fraction of particles remains attached to the fiber surfaces (e.g., Fig. 7(c)), indicative of the sites where the matrix bonds to the fibers by alumina bridges (cf. Fig. 1). In the ±45° orientation, the elastic modulus is much lower (E45 ≈ 35 GPa), and inelastic deformation commences at mod￾erately low stresses, <25 MPa, consistent with domination by the porous matrix. Thereafter, appreciable inelastic strains de￾velop at an essentially constant flow stress, so ≈ 50 MPa, as evident in Fig. 6(a). Upon periodic unloading–reloading, the material exhibits pronounced hysteresis with appreciable per￾manent strains, as illustrated in Fig. 8(a), that is remarkably similar to the behavior observed in carbon/carbon composites, Fig. 8(b).5,36 The inelastic deformation is accompanied by a modest reduction in modulus (E45 ≈ 30 GPa upon unloading after 0.65% strain). The conditions for failure in the ±45° orientation and the associated mechanisms are sensitive to specimen width and lateral constraints. Specifically, in straight tensile specimens with small widths, the fibers detach from the edges and with￾draw into the specimen, causing failure to occur at relatively small strains controlled primarily by the matrix. As the width increases, fiber withdrawal is delayed and failure strain in￾creases. For example, the ±45° specimen in Fig. 6(a) has a width of 6 mm and a strain of ∼0.4% at the maximum load, whereas the 12 mm sample in Fig. 8(a) achieves a strain of ∼0.9% prior to the onset of softening. Even in the latter case, most of the tows pull out from the edge of the specimen, Fig. 9(a). Matrix fragmentation also occurs, enabling the tows to rotate as they withdraw, thereby enhancing graceful failure beyond the onset of strain localization. This additional dis￾placement is manifested in rather large apparent failure strains; Fig. 6. Tensile behavior of the oxide composites in this study: (a) compared with that of SiC/carbon composites of similar fiber content and (b) from Ref. 36. Strains at maximum load for the ±45° specimens are ∼0.4% in (a) and ∼0.8% in (b). Fig. 7. Fracture surfaces of N610 composites in the 0°/90° orienta￾tion. Note the fibrous fracture with extensive pull-out in (a) and the residue of matrix attached to the fibers in (b) and (c). 2082 Journal of the American Ceramic Society—Levi et al. Vol. 81, No. 8