Y Li et al/ Materials Science and Engineering A 507(2009)6-12 mm x500 SE 5.0V 12 9mm x500 SE(M (a)10-1/s 150v129mmx500sE 15012m×8sEM loum 1.1×1031/ 3.0×1031/s Fig. 7. SEM micrographs of the 3D needling-punched C/SiC composites ruptured surface under static and dynamic compression. Table 1 lists shear fracture angles of both kinds of 2D composite SEM images of the ruptured surface of both kinds of 2D-C/Si and 3D needle-punched C/SiC composite. It can be seen that the composite loaded under quasi-static and dynamic loading condi 3D composite shows larger shear fracture angle under quasi-static tions are shown in Fig 9 respectively. For LD 2D-C/SiC composite, loading than that of LD 2D-C/SiC composite but smaller than that of in Fig 9, pull out fibers can be observed while bundles of fibers were HD 2D-C/SiC composite. As mentioned above, higher compression cut off for HD 2D-C/SiC composite. The smoother fracture surface of strength will lead to larger shear fracture angle. Thus, larger shear HD composites under both quasi-static and dynamic compression fracture angle also indicates excellent compression behavior of the indicates more small cracked fibers. Matrix fragments generated 3D composite which is consistent with above conclusion derived under dynamic compression for both Ld and HD composites. while directly from Fig. 8. for 3D needle-punched C/Sic composite, the fracture surfaces are relative rough and more fibers were pulled out under both quasi static and dynamic loading(see in Fig. 7). This phenomenon can be LD-2D C/SiC(00001 1/s) attributed to needle-punched carbon fibers in thickness direction. b - LD-2D C/SiC(2300 1/s) As proposed in Section 3. 2, the Weibull modulus of the 3D HD2Dc/Sic(0.00011/s) needle-punched C/sic composite is 8.19 while those of the LD and HD-2D C/SiC(850 1/5) HD 2D-C/SiC composites are 8.36 and 5.27 respectively. It is obvious 3 D C/SiC(0.00011/s) that the Weibull modulus of the 3D needle-punched C/Sic compos- 3D C/SiC(000 1/s) ite is comparable with that of Ld 2D-C/Sic composite and higher than that of HD 2D-C/SiC composite As a result, low dispersity is expected for the compression strength of the 3D needle-punched Table hear fracture angles of 2D-CSic composites and 3D needle-punched C/Sic composit Quasi-static loading Dynamic loading True strain 36°(=23001/s) 知应 55°(E=850110 Y. Li et al. / Materials Science and Engineering A 507 (2009) 6–12 Fig. 7. SEM micrographs of the 3D needling-punched C/SiC composites ruptured surface under static and dynamic compression. Table 1 lists shear fracture angles of both kinds of 2D composite and 3D needle-punched C/SiC composite. It can be seen that the 3D composite shows larger shear fracture angle under quasi-static loading than that of LD 2D-C/SiC composite but smaller than that of HD 2D-C/SiC composite. As mentioned above, higher compression strength will lead to larger shear fracture angle. Thus, larger shear fracture angle also indicates excellent compression behavior of the 3D composite which is consistent with above conclusion derived directly from Fig. 8. Fig. 8. Comparison of the 3D needling-punched C/SiC composites with low density and high density 2D-C/SiC composites under static and dynamic compression. SEM images of the ruptured surface of both kinds of 2D-C/SiC composite loaded under quasi-static and dynamic loading condi￾tions are shown in Fig. 9 respectively. For LD 2D-C/SiC composite, in Fig. 9, pull out fibers can be observed while bundles of fibers were cut off for HD 2D-C/SiC composite. The smoother fracture surface of HD composites under both quasi-static and dynamic compression indicates more small cracked fibers. Matrix fragments generated under dynamic compression for both LD and HD composites. While for 3D needle-punched C/SiC composite, the fracture surfaces are relative rough and more fibers were pulled out under both quasi￾static and dynamic loading (see in Fig. 7). This phenomenon can be attributed to needle-punched carbon fibers in thickness direction. As proposed in Section 3.2, the Weibull modulus of the 3D needle-punched C/SiC composite is 8.19 while those of the LD and HD 2D-C/SiC composites are 8.36 and 5.27 respectively. It is obvious that the Weibull modulus of the 3D needle-punched C/SiC compos￾ite is comparable with that of LD 2D-C/SiC composite and higher than that of HD 2D-C/SiC composite. As a result, low dispersity is expected for the compression strength of the 3D needle-punched C/SiC composite. Table 1 Shear fracture angles of 2D-C/SiC composites and 3D needle-punched C/SiC composite. Material Shear fracture angles Quasi-static loading Dynamic loading LD-2D composite 30◦ (ε˙ = 10−4 l/s) 36◦ (ε˙ = 2300 l/s) HD-2D composite 50◦ (ε˙ = 10−4 l/s) 55◦ (ε˙ = 850 l/s) 3D composite 30◦ (ε˙ = 10−4 l/s), 45◦ (ε˙ = 10−2 l/s) –