Gauge Length and Surface Damage Effects on the Strength Distributions of Silicon Carbide and Sapphire Filaments

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Abstract
The assumption of the constancy of the Weibull distribution parameters with variations in gauge length was tested for SiC-on-carbon and sapphire filaments. Surface damage was superimposed on the gauge length variations to investigate the effect of the additional flaw spectrum on the gauge length conclusions. The results have demonstrated that, even when failure is due to a single flaw spectrum, the Weibull m parameter is not constant over a gauge length range of 40 times the shortest length. When failure is due to overlapping flaw distributions the possibility of extrapolations assuming constant Weibull parameters is even more remote. The constant gauge length data was used in a modified form of the Poisson distribution proposed by Phoenix to compare to the extrapolative ability of the Weibull distribution. Very little difference in accuracy was found with the former approach being marginally better.