Cavity caused by oxidation (Credit: N. Jacobson/NASA Glenn).

Damage caused by oxidation of the carbon component of Reinforced Carbon-Carbon (RCC) is a key safety concern for the Space Shuttle Program. Oxidation typically occurs via a crack or fissure in the protective coating, which allows the entrance of oxygen and the escape of the carbon oxidation products.

Like many composites, RCC contains extensive porosity from fabrication. Thus, the first step is to establish the difference between as-fabricated porosity and porosity due to oxidation. NASA Glenn Research Center’s current efforts are focused on determining the appearance of oxidation damage under a wide range of conditions and developing mathematical models to predict oxidation. At Glenn, the work is being performed by the Structures and Materials Division and the Instrumentation and Controls Division.

Cavity created in processing (Credit: N. Jacobson/NASA Glenn).

Machinists create well-defined holes or slots in the SiC/glass coating system in RCC samples. Then, the samples undergo oxidation treatments for varying conditions. Post-exposure examination of the samples reveals the patterns of oxidation damage and guides model development.

Current studies are focused on oxidation over a wide range of temperatures and pressures, similar to what the orbiter would experience during re-entry. Typical oxidation damage patterns in carbon/carbon are quite dependent on temperature. Models are being refined to accurately describe the observations. Such studies assist in NASA’s understanding of mission-exposed flight hardware and allow accurate prediction of expected oxidation damage.