(FT/P2-17) Evaluation on Failure Resistance to Develop Design Basis for Quasi-Ductile Silicon Carbide Composites for Fusion Application

T. Nozawa1), T. Hinoki2), A. Kohyama2), H. Tanigawa1)
 
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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