Reliability Prediction Model for Large, Reusable Propellant Tanks

NASA has defined goals for development of future reusable launch vehicles (RLV). Systems must be reliable with less than 1 flight failure in 10,000 missions with mission cost of 1000 dollars per pound per payload (or less). X-33 propellant tank incidents indicate need for improving state-of-the-art design and/or manufacture of composite storage tanks. Bond integrity has been an issue during development of X-33 prototype tanks and the associated reliability issues could become even more of a concern during fabrication of full-scale RLV tanks. This project will assess the variability influencing factors associated with manufacture of composite sandwich bonds and evaluate the feasibility for development of a prediction tool for assessing manufacturing bond reliability for full-scale configurations. The proposed research will develop a probabilistic analysis framework incorporating composite sandwich design methodologies to predict the reliability of the bonds between the face sheet and the core. Models will be developed that relate overall stress, strain, loading and displacement to bond strength integrity. These models will account for such microstructural parameters as adhesive strength, bondline thickness, and face sheet core interaction.