STRENGTH VARIABILITY IN ALUMINA FIBER-REINFORCED ALUMINUM-MATRIX COMPOSITES

The strength variability of an Al-2% Cu alloy matrix reinforced with 6 5 vol.% Nextel-610 Al2O3 fibers has been investigated, with the aim of identifying and separating the contributions associated with the vari abilities in both the fiber bundle strength and the fiber volume fract ion. Strength distributions have been measured using three test geomet ries, including three-and four-point flexure and uniaxial tension. The measured distributions are rationalized on the basis of a fiber stren gth distribution that follows Weibull statistics and a fiber volume fr action distribution characterized by a Gaussian. The fiber bundle stre ngth distribution is found to be extremely narrow: with a Weibull modu lus in the range of similar to 50-60. In addition, the coefficient of variation in the fiber volume fraction distribution is inferred to be similar to 6%; by comparison, measurements made on relatively large sp ecimens yield a coefficient of variation of similar to 3%. The differe nces in these values are attributed to local volume fraction variation s which are not detectable by the global measurements. The measured st rengths are compared with the predicted values based on the theoretica l work of Curtin and co-workers, incorporating the effects of local lo ad sharing between broken fibers and their neighbors. Good correlation s are obtained between the experimental data and the model predictions . (C) 1997 Acta Metallurgica Inc.