Load transfer from broken fibers in continuous fiber Al2O3-A1 composites and dependence on local volume fraction

The load transfer characteristics of a continuous, high volume fraction alu mina (Al2O3) fiber reinforced aluminum matrix composite are determined by c ombining high spatial resolution stress measurements and computational micr omechanical modeling. The residual stresses in individual fibers and the re distribution of applied load due to fiber failure have been measured using photostimulated Cr3+ luminescence based piezospectroscopy. From these measu rements, the load transfer profiles along broken fibers and the induced str ess concentration profiles on their adjacent neighbors have been determined . They are found to depend on the local interfiber spacing. They are compar ed with fiber stress profiles predicted by a shear-lag stress analysis whic h accounts for the influences of matrix yielding, called the quadratic infl uence superpositon (QIS) technique, as well as other shear-lag based multif iber composite models. The current study indicates that fiber breaks are ac companied by matrix yielding extending on the order of fiber diameters and which induce significant stress concentrations on neighboring fibers, depen dent on the local fiber spacing and extent of plastic yielding. Additionall y, the matrix yield strength is dependent on the local fiber spacing and in creases with decreasing local fiber spacing. The implications of the microm echanical load sharing characteristics and composite processing on ultimate tensile strength are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.