Issues and progress in determination of the basis for failure evaluation of advanced SiC/SiC composites in BA activities; Crack propagation behavior and fracture resistance

Nozawa, Takashi; Tanigawa, Hiroyasu

Due to the cumulative accumulation of micro cracks, fracture behavior of SiC/SiC composites is generally quasi-ductile with irreversible damages. Therefore the design basis for this class of material is quite different from that for ductile metals. Accordingly, BA activity aims to develop the design basis for SiC/SiC composites with three pragmatic phases: (1) definition of design parameter, (2) standardization of test methods, and (3) data-basing. This study aims to evaluate fracture resistance of SiC/SiC composites. Importantly, crack propagation behavior was investigated by the single-edge notched-bend technique. Test results identified failure process as: (1) micro-crack formation, (2) macro-crack extension and (3) interfacial friction and fiber breaks. Failure energy in each stage was successfully measured by hysteresis analysis, eventually giving a fracture resistance. Besides, with the fact of notch instability of composites, a stress criterion in composite failure was concluded.