Analytic modeling and experimental validation of intumescent behavior of charring heatshield materials

Intumescing heatshield materials have been shown to provide significant thermal protection for missile system environments. The design and use of these materials requires the analytic understanding of a considerable level of thermodynamic phenomena occurring on the surface as well as in-depth. These phenomena can include in-depth thermochemical decomposition, pyrolysis gas generation and mass transfer, thermophysical property change, thermochemical and mechanical ablation, intumescence or conduction path growth, and boundary layer modification due to pyrolysis gas injection or surface reactions. Existing numerical design codes do not specifically address the thermodynamic effects of intumescent behavior.; The purpose of this research was to significantly enhance the current state of the art for modeling thermochemically decomposing heatshield materials through the addition of intumescent behavior effects to the Charring Material Thermal Response and Ablation Program (CMA). Additional efforts were devoted to the design of experiments to specifically quantify the intumescence phenomena. The intumescence material properties were primarily developed utilizing the low shear thermal testing performed at the Wright-Patterson Laser Hardened Materials Evaluation Laboratory. Transient radiography of in-depth thermochemical decomposition and intumescence as well as embedded thermocouples were utilized quantifying properties of the various reacting regions within the material. The resulting intumescence model was applied and validated for a low shear hypersonic high altitude environment generated at the National Aeronautics and Space Administration Marshall Space Flight Center Hot Gas Test. The validated analytic model was then applied to the high shear convective heating environments generated at the Holloman High Speed Test Track at Holloman Air Force. This test environment provided an evaluation of the analytic model applicability for high shear environments.; These results of this research clearly show that through the use of a variety of aerothermal test environments, embedded thermocouples, transient radiography, and collection of detailed ablation measurements the in-depth thermodynamic behavior of intumescing heatshield materials can be accurately modeled and used for any variety of aerodynamic boundary conditions. These results further provide an indication of mechanical shear sensitivity along with justification for future enhancement through development and implementation of erosion effects modeling.