wwceramics. org/ACT Cracking Resistance of Silicon Carbide Composites served up to the maximum applied load(ig. 6b). How- NITE- Thick-Coat apparent energy consumpton in 031wmmW12) displacement curve in Fig. 5 implies probable accumula- tion of microcracks in the matrix. At the maximum load SENB-1b(W=4mm, t=lmm, a/=0.5) rapid crack propagation in a direction perpendicular to the longitudinal fiber direction occurred coupled with load drop(Fig. 6c). By applying, further loading many 10.2030405060.70 macrocracks, which have branched parallel to the longi Crack Opening Displacement (mm tudinal fiber direction, were observed with fber sliding at the F/M interface and fiber breaks(Fig. 6d and e). Figure 6f shows the surface image of the specimen after the test, SENB-2a (w=4mm, t=2mm, a/w=0. 25) indicating no breakage into pieces due to the huge con- SENB-2b(=4mm, t=2mm, ao /w=0.5) tribution of the strong frictional shear at the F/m inter face. In summary, three apparent damage accumulation stages in fracture behavior in the SENB test were identi fied as follows(1)initial elastic segment followed by a nonlinear stage due to microcrack formation,(2)macro- 0.10.20.3040.50.60.708 crack extension with considerable microcrack formation Crack Opening Displacement (mm and (3)load transferring by friction at the F/M interface, progressive crack brand Figure 7 plots the crack extension (Aa) measured using the replica film method for NITE-Thick-Coat. Of SENB-3a(w84mm, tamm, a/w-D. 25) particular emphasis is that unique trend was obtained by sSENB-3b(W-4mm, tamm, a /w-0. 5) normalizing specimen width(W), clearly indicating no specimen geometry effect on the crack extension behavior From Fig. 7, no crack extension was obtained in the first stage. In the second stage, it is apparent that the macro- 00.10.2030.40.5060.708 Crack Opening Displacement (mm] crack length rapidly increased with increasing displace ment. Of particular emphasis is that the crack propagation rate was almost a constant(A(a/W)/Ax= 3. 13). Con SENB-4 (W=Bmm, t=4mm, a /w=0.5) pared with the rapid crack extension in the second stage,a mild increase of the crack length was obtained in the third stage,that is, in the mixed failure accumulation process. From Fig. 5, two characteristic parameters namely: PLS as an initiation load of microcracking and ultimate flexural strength(UFS)as an initiation load of macro- cra obtained. figure 8 shows the Crack Opening Displacement [mm] rameters normalized as a Aexural stress form as: Fig. 5. Load us crack opening displacement curves in single-edge 3PL notched bend (sENB) tests for NITE-Thick-Coat where the applied load was(P), support span(L), specimen artaine linearity was obtained prior the maximum load was width(W), and specimen thickness (o). Although there ined. From Fig. 6, it is clearly identified that there were limited data sets, an important finding is that both were no a cracks initiated at the initial linear normalized PLS and fexural strength were nearly propor- ment and microcracks were initiated in the hber bundles tional to(1-do/W), indicating probable notch insensitivity parallel to the longitudinal fiber direction at the turning Regarding the notch insensitivity of NITE-SiC/SiC point from linear to nonlinear fracture behavior(Fig 6a). posites, the slope of these trends can produce a unique Beyond this load level, no further visible cracks were ob- proportional limit of flexural stress of 244 MPa,andnonlinearity was obtained prior the maximum load was attained. From Fig. 6, it is clearly identified that there were no apparent cracks initiated at the initial linear seg￾ment and microcracks were initiated in the fiber bundles parallel to the longitudinal fiber direction at the turning point from linear to nonlinear fracture behavior (Fig. 6a). Beyond this load level, no further visible cracks were ob￾served up to the maximum applied load (Fig. 6b). How￾ever, apparent energy consumption in the load– displacement curve in Fig. 5 implies probable accumula￾tion of microcracks in the matrix. At the maximum load, rapid crack propagation in a direction perpendicular to the longitudinal fiber direction occurred coupled with load drop (Fig. 6c). By applying, further loading many macrocracks, which have branched parallel to the longi￾tudinal fiber direction, were observed with fiber sliding at the F/M interface and fiber breaks (Fig. 6d and e). Figure 6f shows the surface image of the specimen after the test, indicating no breakage into pieces due to the huge con￾tribution of the strong frictional shear at the F/M inter￾face. In summary, three apparent damage accumulation stages in fracture behavior in the SENB test were identi- fied as follows (1) initial elastic segment followed by a nonlinear stage due to microcrack formation, (2) macro￾crack extension with considerable microcrack formation, and (3) load transferring by friction at the F/M interface, coupled with progressive crack branching and fiber breaks. Figure 7 plots the crack extension (Da) measured using the replica film method for NITE-Thick-Coat. Of particular emphasis is that unique trend was obtained by normalizing specimen width (W), clearly indicating no specimen geometry effect on the crack extension behavior. From Fig. 7, no crack extension was obtained in the first stage. In the second stage, it is apparent that the macro￾crack length rapidly increased with increasing displace￾ment. Of particular emphasis is that the crack propagation rate was almost a constant (D(a/W)/Dx 5B3.13). Com￾pared with the rapid crack extension in the second stage, a mild increase of the crack length was obtained in the third stage, that is, in the mixed failure accumulation process. From Fig. 5, two characteristic parameters namely: PLS as an initiation load of microcracking and ultimate flexural strength (UFS) as an initiation load of macro￾cracking were obtained. Figure 8 shows these two pa￾rameters normalized as a flexural stress form as: s0 ¼ 3PL 2tW 2 ð1Þ where the applied load was (P), support span (L), specimen width (W), and specimen thickness (t). Although there were limited data sets, an important finding is that both normalized PLS and flexural strength were nearly propor￾tional to (1-a0/W) 2 , indicating probable notch insensitivity. Regarding the notch insensitivity of NITE–SiC/SiC com￾posites, the slope of these trends can produce a unique proportional limit of flexural stress of B244MPa, and an Fig. 5. Load vs. crack opening displacement curves in single-edge notched bend (SENB) tests for NITE-Thick-Coat. www.ceramics.org/ACT Cracking Resistance of Silicon Carbide Composites 309