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An interlaboratory round robin study was conducted on the tensile strength of SiC‐SiC ceramic matrix composite (CMC) tubular test specimens at room temperature with the objective of expanding the database of mechanical properties of nuclear grade SiC‐SiC and establishing the precision and bias statement for standard test method ASTM C1773. The mechanical properties statistics from the round robin study and the precision statistics and precision statement are presented herein. The data show reasonable consistency across the laboratories, indicating that the current C1773‐13 ASTM standard is adequate for testing ceramic fiber reinforced ceramic matrix composite tubular test specimen. It was found that the distribution of ultimate tensile strength data was best described with a two‐parameter Weibull distribution, while a lognormal distribution provided a good description of the distribution of proportional limit stress data.

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The fracture properties of two nuclear-grade graphites, the Japanese IG11 graphite and Chinese NG-CT-01 graphite, were evaluated under flexural conditions. Three-point bend tests were performed on centre-notched beams to determine the tension softening curve (TSC), Mode-I fracture toughness K IC and the fracture energy G F. The TSC of the nuclear graphites was originally determined by a newly developed incremental displacement collocation method, and was shown to be able to predict the post-peak behaviour accurately. The TSC was simplified to the bilinear, tri-linear and exponential curves. The tri-linear curve was found to be the best approximation for modelling the tension softening of these nuclear graphites. Furthermore, scanning electron microscope images of their microstructures showed that the difference in brittleness and fracture behavior between the two graphites was probably caused by a difference in grain size and the degree of binder infiltration.

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