Statistical Analysis of the Ultimate Strength of Filaments, Tows and Minicomposites

The present paper investigates the failure of SiC and alumina-fiber-reinforced minicomposites in relation to the strength distributions of filaments, and the failure behavior of the reinforcing dry tows. The strength data are measured on single-filament, dry-tow and minicomposite specimens using tensile tests under commonly used test condition of strain-controlled loading. Pertinence of the normal distribution of strengths at different length scales is assessed using the construction of p-quantile diagrams, and the pertinence of the Weibull distribution was assessed by comparing to the normal distribution function. SiC and alumina minicomposites exhibited significantly different failure behaviors. Comparison with filament strength distributions and the behavior of the underlying tow in relation to the loading condition (stress- or strain-controlled conditions) allows for the interpretation of the results. The sensitivity of the results to loading conditions is highlighted. Various scenarios of minicomposite failure are discussed as alternatives to the stress concentration induced by clusters of broken fibers. It appears that the failure of alumina-fiber-reinforced minicomposites is stable and dictated by the highest-strength filaments, whereas the SiC-fiber-reinforced minicomposites exhibited premature failure that is attributed to the microstructural imperfections that induced overstressing by the fiber or fiber/matrix interactions.