Design and processing of perspirable skin through numerical analysis.

摘要

An autonomous and reusable self-cooling thermal protection system (TPS) was designed for externally heated surfaces such as the surface of the space shuttle. This material system, named 'Perspirable Skin,' contains cores shrink-fitted into the holes on the Reinforced Carbon-Carbon (RCC) composite skin. The cores are made of either pure ZrW2O8 (zirconium tungstate) or ZrW2O8-ZrO2 (zirconia) Functionally Graded Material (FGM). The choice of ZrW2O8 is due to its highly negative coefficient of thermal expansion in a wide range of temperatures. When the temperature increases, a gap is formed between the core and the RCC skin due to the difference in thermal expansions. The compressed coolant gas onboard is passed through this gap onto the surface. The coolant gas is expected to mix with the surface air to eliminate the frictional heating. The geometry and gradient of the cores as well as the fiber arrangement for RCC skin were designed by Finite Element Analysis (FEA). Optimal core design was successfully fabricated using powder metallurgy methods. Influences of powder metallurgy steps on the final properties of ceramic powders were also investigated, both experimentally and numerically. The effects of powder mixing on the compaction capabilities of ceramic powders, as well as dimension and density variations in the green bodies after compaction are discussed.