A Continuum Approach to Permeation With Interfacial Leakage: A Space Seal Approach

Prior analyses in elastomer space-seals thrived on the assumption that mass flow over/through a seal was due to permeation. In fact, the state-of-the-art space-seal leakage prediction method relies on this assumption. Well-documented efforts have shown that the aforementioned prediction method is versatile in its ability to predict leak rates in nominal operational conditions. Its merits, however, fall short in the application of low seal contact loading and in applications with substantial space environmental exposure (e.g., ultraviolet radiation, atomic oxygen). In response to this shortfall, a unique method and analysis was recently developed to parse total leakage into interfacial leakage and permeation, with the intent of capturing the effects of surficial degradation; results highlighted that while permeation dominated interfacial leakage for high contact seal loading, the interfacial component was not negligible. Furthermore, the interfacial component was shown to dominate permeation for low contact pressure, as would be the case with a faulty docking mechanism. Presented herein is a novel continuum approach to seal leakage that retains the compressible permeation approach previously developed and enhances the overall fidelity by incorporating interfacial leakage with entrainment terms which describe the movement of mass orthogonal to the seal-counter face boundary (i.e., mass transfer from the elastomer to the interfacial zone). Integral to the proposed model, the interfacial leakage component is a function of seal contact pressure, pressure gradient, and, ultimately, space environmental exposure. Also presented is an application of the model to a candidate, elastomer space seal. Results showed an improved prediction and provide a measure of verification and validation to the proposed seal leakage model.