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

Fiber coatings have been extensively modeled and proposed as a means to mitigate the thermal residual stresses in advanced composites, including the sapphire-fiber reinforced NiAl (sapphire/NiAl) system. While the finite element models have been useful for screening candidate coating materials, few, if any, experimental studies have been performed to validate the results of the models. The residual stress distribution in sapphire/NiAl composites with three thickness’ of Mo fiber coatings was modeled using the multiple concentric cylinder model (MCCM) from NASA-LeRC. The modeling results were compared to experimental measurements made using both continuous indentation and neutron diffraction. In this study, good agreement between the measured and calculated residual stress distributions in all samples was obtained. The results demonstrated the potential for continuous indentation to measure 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.