(FT/P2-17) Evaluation on Failure Resistance to Develop Design Basis for Quasi-Ductile Silicon Carbide Composites for Fusion Application
1) Japan Atomic Energy Agency, Tokai, Ibaraki, Japan
2) Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto,Japan
Abstract. Silicon carbide composites (SiC/SiC) are promising candidate materials for fusion blanket with advanced features such as high thermal efficiency. Of many composite types, a nano-infiltration and transient-eutectic-phase sintered (NITE) SiC/SiC composites, as well as chemical-vapor-infiltration (CVI) SiC/SiC composites, is believed to be viable because of excellent baseline mechanical properties and proven radiation stability of microstructure and strength under certain irradiation conditions. With a completion of the “proof-of-principle” phase, the R&D on SiC/SiC composites is now shifting to the more pragmatic phase of material data-basing and development of design basis. This paper will provide a present status in development of design basis for SiC/SiC composites as a structural application. Composites exhibit “quasi-ductility” in fracture, which is totally different from the ductility of metals since this “quasi-ductility” occurs as a result of cumulative accumulation of irreversible permanent damages such as interface debonding, fiber pullouts with friction at the fiber/matrix interface, and fiber breaks. From this aspect, the damage accumulation behavior of SiC/SiC composites was first evaluated in this paper with a final goal to develop the design basis for generation of practical database with a direction to use this class of composites for structural application. Recent fatigue test result demonstrated that the latest NITE-SiC/SiC composites are more crack resistant compared with the conventional low-stiffness, porous SiC/SiC composites. The improved crack resistance of NITE-SiC/SiC composites thus results in better helium gas tightness. In contrast, detailed crack extension behavior of NITE-SiC/SiC composites was evaluated by the single-edge notched-bend technique. A developmental analytical model based on the non-linear fracture mechanics, which can separately discuss the effect of irreversible energies such as interfacial friction, thermal-residual strain energy and fiber breaks, provides a non-linear fracture toughness for NITE-SiC/SiC composites of ∼ 4 kJ/m2, which is an actual energy consumed during macro-crack extension. Besides it is worth noting that, with a fact of the notch-insensitivity and very minor size effect on the failure behavior, a stress criterion is suggested in failure of SiC/SiC composites.
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