Strength variability in alumina fiber-reinforced aluminum matrix composites

Abstract

The strength variability of an Al-2% Cu alloy matrix reinforced with 65 vol.% Nextel -610 Al₂O₃ fibers has been investigated, with the aim of identifying and separating the contributions associated with the variabilities in both the fiber bundle strength and the fiber volume fraction. Strength distributions have been measured using three test geometries, including three- and four-point flexure and uniaxial tension. The measured distributions are rationalized on the basis of a fiber strength distribution that follows Weibull statistics and a fiber volume fraction distribution characterized by a Gaussian. The fiber bundle strength distribution is found to be extremely narrow, with a Weibull modulus in the range of ~50-60. In addition, the coefficient of variation in the fiber volume fraction distribution is inferred to be ~6%; by comparison, measurements made on relatively large specimens yield a coefficient of variation of ~3%. The differences in these values are attributed to local volume fraction variations which are not detectable by the global measurements. The measured strengths are compared with the predicted values based on the theoretical work of Curtin and co-workers, incorporating the effects of local load sharing between broken fibers and their neighbors. Good correlations are obtained between the experimental data and the model predictions.