A Study of Statistical Variability in the Strength of Single Aramid Filaments

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Abstract
Variability in the failure load, tenacity, and linear density of single aramid filaments is studied experimentally. Data indicate that both the failure load and the tenacity of filaments, for a given gauge length and yarn cross section, can be fitted to a two parameter Weibull distribution; however the fit is better for tenacity than for failure load, and the Weibull shape parameter for the former is typically smaller. Within a yam cross section filaments vary significantly in linear density (and diameter), and this variability contributes a component to the variability in failure load, but not to the tenacity. Also, the mean tenacity and the variability in linear density and in failure load may differ greatly from spool to spool. The implications of the variability are discussed in light of the work of Bunsell. The effect of gauge length on the strength distribution of filaments is examined. Weibull statistics are used to separate out this effect. As previously shown for other brittle filaments, the Weibull shape parameter for aramid filaments depends on the gauge length; however values for the shape parameter calculated at a fixed gauge length are substantially lower than those obtained by a procedure based on varying the gauge length. This suggests short range correlations in flaw strengths along a filament.