Validation of multi-concentric cylinder model for sapphire/Mo/NiAl composites

Fiber coatings have been extensively modeled and proposed as a means to mit igate the thermal residual stresses in advanced composites, including the s apphire-fiber reinforced NiAl (sapphire:NiAl) system. While the finite elem ent models have been useful for screening candidate coating materials, few, if any, experimental studies have been performed to validate the results o f the models. The residual stress distribution in sapphire/NiAl composites with three thickness' of Mo fiber coatings was modeled using the multiple c oncentric cylinder model (MCCM) from NASA-LeRC. The modeling results were c ompared to experimental measurements made using both continuous indentation and neutron diffraction. In this study, good agreement between the measure d and calculated residual stress distributions in all samples was obtained. The results demonstrated the potential for continuous indentation to measu re the local stress variations in composites both in the matrix and in the fiber coatings, and validated the calculations of the models for both local and average residual stresses. (C) 1999 Elsevier Science S.A. All rights r eserved.