Load transfer from broken fibers in continuous fiber Al 2O 3-Al composites and dependence on local volume fraction

Abstract

The load transfer characteristics of a continuous, high volume fraction alumina (Al 2O 3)fiber reinforced aluminum matrix composite are determined by combining high spatial resolution stress measurements and computational micromechanical modeling. The residual stresses in individual fibers and the redistribution of applied load due to fiber failure have been measured using photostimulated Cr 3+ luminescence based piezospectroscopy. From these measurements, the load transfer profiles along broken fibers and the induced stress concentration profiles on their adjacent neighbors have been determined. They are found to depend on the local inter-fiber spacing. They are compared with fiber stress profiles predicted by a shear-lag stress analysis which accounts for the influences of matrix yielding, called the quadratic influence superpositon (QIS) technique, as well as other shear-lag based multifiber composite models. The current study indicates that fiber breaks are accompanied by matrix yielding extending on the order of fiber diameters and which induce significant stress concentrations on neighboring fibers, dependent on the local fiber spacing and extent of plastic yielding. Additionally, the matrix yield strength is dependent on the local fiber spacing and increases with decreasing local fiber spacing. The implications of the micromechanical load sharing characteristics and composite processing on ultimate tensile strength are discussed.