Strain-dependence of thermal conductivity in flexible fibrous insulation materials

Inflatable aeroshells are an upcoming Entry, Descent, and Landing (EDL) technology currently in development through projects such as the Hypersonic Inflatable Aerodynamic Decelerator (HIAD). These aeroshells use flexible thermal protection systems (F-TPS) that stretch across the inflatable structure to protect the aeroshell and payload from aerodynamic heating. These multi-layer F-TPS are often comprised of fibrous materials whose conductivity is highly dependent upon the internal geometry of the material. As these materials deform through inflation of the structure or through aerodynamic loading, the material’s internal structure will change and subsequently so will the conductivity. There is little data available on how the conductivity of these fibrous insulation materials change as a function of mechanical loading and strain. Thus a thermal conductivity measurement system was developed that will strain these materials to quantify their dependence on mechanical loading. Results showed a decrease in effective conductivity as strain increased for Alumina Paper at 15%, 25%, 50%, and 65% strain. This is possibly due to a decrease in the radiative contributions to heat transfer within the material.