314 International Jourmal of Applied Ceramic Technolog-Nozawa and Tanigawa Vol 7, No 3, 2010 formations. This issue is then discussed by considering an Eventually, by substituting releasing energy for energy release rate by microcrack accumulations until rocrack formation from the total crack surface forma- macrocrack causes. Figure 12 also shows a schematic il- tion energy, the actual fra cture resistance lustration for the determination of an energy release rate consumption of macrocracking of x2.4 kJ/m would during microcrack formation from the load-displacement be roughly estimated for the NITE-Thick-Coat curve. Figure 14 shows crack surface formation energy with respect to the initial notch depth to width ratio, Conclusions W, using various specimens. From this figure, microcrack surface formation energy(T m) was empirically expressed as Silicon carbide composites are promising candidate materials for fusion reactors and other high-temperatur ImW、C (5) applications. This paper aims to evaluate fracture resis- ance of a new class of SiC/SiC composites, that is, NITE-SiC/SiC composites, using the SENB test and where Ci (i=1, 2,., n)are constants. Then, an energy the dnt test. Both senb and dnt test results identi release rate(GJ) when microcracks form can be defined as fied the notch insensitivity of NITE-SiC/SiC composite With the fact of notch insensitivity, unique PLS and frac- Gc≡t△a (6) ture strength were identified regardless of the presence of artificial notches. Based on the nonlinear fracture me- Simply applying the power law fit in Fig. 14,w chanics, this study provided a rigorous solution to distin- ntributions obtained an energy release rate of -1 4k]/m fo microcracking from macrocrack NITE-Thick-Coat. This value is quite lower than that extension energy. By applying the technique, micro-and of PIP-Coat, 4.8 kJ/m*. As this energy release rate cally, lower microcrack formation energy was identified represents the magnitude of crack density induced in the damage process, this implies that NITE-Thick-Coat are tem. From these facts, the superior crack resistance of NITE-SiC/SiC composites was finally demonstrated. are more s abject to the damage until macrocracking References NITE- Thick-Coat I. A. Kohyama, S M. Dong, and Y Katoh, "Development of SiC/SiC Com- of Advanced Material Systems for Reactor Core Com- PIP. Coat 3. T. Hinoki and A. Kohyama, Current Status of SiC/SiC Composites for 4. Y. Katoh, er al., "Current Starus and Critical Issues for Devel omposites for Fusion Applications, J. Nud. Mater, 367-370 659-671 G=48±15kJm2 5. T. Hino, E. Hayashishita, Y. Yamauchi, M. Hashiba, Y. Hirohata, and A. Kohyama, "Helium Gas Permeability of SiC/SiC Composite Used for In- 8 6. C. P C Wong, et al. An Overview of Dual Coolant Pb-17Li Breeder First c=1 sion Eng. De, 81 461-467(2006) 7. P. Norajitra, L. Buhler, U. Fischer, S. Gordeev, S. Malang, and G. Reimann, 0 ower Plant Conceptual Study, Fusion Eng. Des, 69 669-673(2003) 0.2 04 0.6 0.8 Plant, Fusion Eng. Des., 82 217-236(2007). 9. J. R. Rice, " A Path Independent Integral and th gy release rate by king with a finction Concentration by Notches and Cracks, "/. Appl Mech., 35 379-386(1968) 10. J. R. Rice, P. C. Paris, and J. G. Merkle, "Progress in Flaw Growth and notch depth to width ratioformations. This issue is then discussed by considering an energy release rate by microcrack accumulations until macrocrack causes. Figure 12 also shows a schematic il￾lustration for the determination of an energy release rate during microcrack formation from the load–displacement curve. Figure 14 shows crack surface formation energy with respect to the initial notch depth to width ratio, a0/ W, using various specimens. From this figure, microcrack surface formation energy (Gm) was empirically expressed as Gm ffi Wt Xn i¼1 Ci 1  a0 W i ð5Þ where Ci (i 5 1, 2,y, n) are constants. Then, an energy release rate (Gc) when microcracks form can be defined as Gc   DGm tDa ffi Xn i¼1 iCi 1  a0 W i1 ð6Þ Simply applying the power law fit in Fig. 14, we obtained an energy release rate of B1.4 kJ/m2 for NITE-Thick-Coat. This value is quite lower than that of PIP-Coat, B4.8 kJ/m2 . As this energy release rate represents the magnitude of crack density induced in the damage process, this implies that NITE-Thick-Coat are more crack resistant, while, PIP–SiC/SiC composites are more subject to the damage until macrocracking. Eventually, by substituting releasing energy for mi￾crocrack formation from the total crack surface forma￾tion energy, the actual fracture resistance for consumption of macrocracking of B2.4 kJ/m2 would be roughly estimated for the NITE-Thick-Coat. Conclusions Silicon carbide composites are promising candidate materials for fusion reactors and other high-temperature applications. This paper aims to evaluate fracture resis￾tance of a new class of SiC/SiC composites, that is, NITE–SiC/SiC composites, using the SENB test and the DNT test. Both SENB and DNT test results identi- fied the notch insensitivity of NITE–SiC/SiC composites. With the fact of notch insensitivity, unique PLS and frac￾ture strength were identified regardless of the presence of artificial notches. Based on the nonlinear fracture me￾chanics, this study provided a rigorous solution to distin￾guish contributions of microcracking from macrocrack extension energy. By applying the technique, micro- and macrocracking energies were separately estimated. Specifi- cally, lower microcrack formation energy was identified compared with conventional low-stiffness composite sys￾tem. From these facts, the superior crack resistance of NITE–SiC/SiC composites was finally demonstrated. References 1. A. Kohyama, S. M. Dong, and Y. Katoh, ‘‘Development of SiC/SiC Com￾posites by Nano-Infiltration Transient Eutectoid (NITE) Process,’’ Ceram. Eng. Sci. Proc., A23 311–318 (2002). 2. A. Kohyama, ‘‘R&D of Advanced Material Systems for Reactor Core Com￾ponent of Gas Cooled Fast Reactor,’’ Proceedings ICAPP’05, Seoul, Korea, 2005 (CD-ROM). 3. T. Hinoki and A. Kohyama, ‘‘Current Status of SiC/SiC Composites for Nuclear Applications,’’ A., Ann. Chim. Sci. Mater., 30 659–671 (2005). 4. Y. Katoh, et al., ‘‘Current Status and Critical Issues for Development of SiC Composites for Fusion Applications,’’ J. Nucl. Mater., 367–370 659–671 (2007). 5. T. Hino, E. Hayashishita, Y. Yamauchi, M. Hashiba, Y. Hirohata, and A. Kohyama, ‘‘Helium Gas Permeability of SiC/SiC Composite Used for In￾Vessel Components of Nuclear Fusion Reactor,’’ Fusion Eng. Des., 73 51–56 (2004). 6. C. P. C. Wong, et al., ‘‘An Overview of Dual Coolant Pb-17Li Breeder First Wall and Blanket Concept Development for the US ITER-TBM Design,’’ Fusion Eng. Des., 81 461–467 (2006). 7. P. Norajitra, L. Bu¨hler, U. Fischer, S. Gordeev, S. Malang, and G. Reimann, ‘‘Conceptual Design of the Dual-Coolant Blanket in the Frame of the EU Power Plant Conceptual Study,’’ Fusion Eng. Des., 69 669–673 (2003). 8. The ARIES Team, et al., ‘‘Advanced Power Core System for the ARIES-AT Power Plant,’’ Fusion Eng. Des., 82 217–236 (2007). 9. J. R. Rice, ‘‘A Path Independent Integral and the Approximate Analysis of Strain Concentration by Notches and Cracks,’’ J. Appl. Mech., 35 379–386 (1968). 10. J. R. Rice, P. C. Paris, and J. G. Merkle, ‘‘Progress in Flaw Growth and Fracture Toughness Testing,’’ ASTM STP, 536 231–245 (1973). Fig. 14. Energy release rate by microcracking with a function of notch depth to width ratio. 314 International Journal of Applied Ceramic Technology—Nozawa and Tanigawa Vol. 7, No. 3, 2010