A FIBER DAMAGE MODEL FOR EARLY-STAGE CONSOLIDATION OF METAL-COATED FIBERS

Recent studies of the high temperature consolidation of titanium alloy coated a-alumina fiber lows and SiC monofilaments have both revealed the widespread occurrence of fiber bending and fracture during early s tage consolidation. This damage was shown to arise from the bending of unaligned fibers during consolidation and was found to be affected by the mechanical behavior of the metal-metal contacts al fiber crossove rs. To predict the incidence of fiber fracture during early stage high temperature consolidation, a time-temperature dependent micromechanic al model incorporating the evolving contact geometry and mechanical be havior of both the metal matrix and the ceramic fibers has been combin ed with a statistical representation of crossovers in the pre-consolid ated layup. The damage predictions are found to compare Favorably with experimental results. The model has subsequently been used to explore the effects of fiber strength, matrix constitutive properties and the processing conditions upon the incidence of fiber Fracture. It reveal s the existence of a temperature dependent pressurization rate below w hich fracture is relatively unlikely. This critical pressure rate can be significantly increased by the 'enhanced' superplasticity of the in itially nanocrystalline coating. Copyright (C) 1997 Acta Metallurgica Inc.