CHARACTERIZATION OF NICALON FIBERS WITH VARYING DIAMETERS - PART II -MODIFIED WEIBULL DISTRIBUTION

Diameters vary significantly in a tow of commercial Nicalon(TM) fibres , which is one of the most attractive ceramic reinforcements for struc tural composites. It was found that the strength distribution of Nical on fibres could not be adequately characterized using either single- o r bi-modal Weibull distribution. A recently proposed modified Weibull distribution can account for the effect of varying diameter in the cha racterization of fibre strength. To verify the validity of the modifie d Weibull distribution, comprehensive mechanical testing and fractogra phic studies have been conducted on Nicalon SiC fibres with diameters varying from 8 to 22 mu m. The experimental results have been reported in Part I. Part II of this paper further modifies the derivation of t he modified Weibull distribution to yield a relationship which is simi lar in form, but soundly based on experimental findings. Factors consi dered in the modified Weibull distribution include the dependence of f racture toughness and flaw density on fibre diameter, both of which ma y vary with fibre diameter, as reported in Part I. Comparison with exp erimental data shows that the current modified Weibull distribution wo rks very well, while both single-modal and bi-modal Weibull distributi ons are inadequate for describing Nicalon fibres with varying diameter s. (C) 1998 Chapman & Hall.