Fracture data from five series of four-point bend tests of beams and spin tests of flat annular disks were reanalyzed. Silicon nitride and graphite were the test materials. The experimental fracture strengths of the disks were compared with the predicted strengths based on both volume flaw and surface flaw analyses of four-point bend data. Surface flaw analyses resulted in good correlation with experimental results in those test series where all tested specimens were obtained from the same material batch. The Weibull slopes (moduli) and characteristic gage strengths for the disks and beams were also compared. Differences in the experimental Weibull slopes were not statistically significant. It was shown that results from the beam tests can predict the fracture strength of rotating disks under well controlled conditions.

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