Fiber push-out testing of sapphire fiber alumina matrix composites

Abstract: A current area of international research and development concerns composite materials consisting of oxides reinforced with continuous oxide fibers. These materials have an inherent resistance to oxidation and therefore have potential as structural materials for applications at extremely high temperatures. The mechanical behavior of such composites is critically dependent on the achievement of a correct balance of the properties of the fiber/matrix interface. More specifically, both the strength of the interfacial bond and the frictional sliding resistance of the interface after debonding must be optimized. For this reason, several methods have been developed to measure these properties. In this study these methods have been critically reviewed and one of the methods has been applied experimentally to composite consisting of monocrystalline sapphire fibers in a polycrystalline aluminum oxide matrix. The method consists of pushing fibers out of a suitably thin layer of the composite. Composites with a number of different interface structures - prepared by coating the fiber with zirconium oxide with various degrees of porosity - have been examined extensively with this method. In one case, it has been possible to compare the results of the push-out test with the macroscopic mechanical behavior of the composite tested in bending and tension. The measured interfacial sliding stress was in excellent agreement with that derived from the composite behavior.