Large Form-Factor Ox/Ox Window for Hypersonic Seekers

Antenna aperture materials are critical for successful flights of hypersonic vehicles.  Antenna window materials for hypersonic vehicles experience high heat loads and, depending on their position on the vehicle and the manner in which they are attached to the vehicle structure, they may also experience significant stresses. These materials must also be transparent and have low dielectric constants over a range of electromagnetic frequencies; ideally these dielectric constants will also have little temperature-dependence. The MR&D proposal will seek to mature window technologies for use in RF seekers for extreme hypersonic environments.  Specifically, we are proposing to continue to mature the material development work that MR&D, COI Ceramics, and Textile Engineering and Manufacturing (TEAM) performed together under the AFRL Contract FA8650-17-C-5239 for the AFRL BAA AFRL-RQKM-2016-0012.  In the AFRL Contract FA8650-17-C-5239 effort, we utilized 3D woven preforms with N720 yarns with a nominal filament count of 400 (1500 denier).  For the 3D woven reinforced alumina silicate (AS) matrix composites, we obtained our best and most repeatable results by weaving near net shape articles requiring limited compaction during the manufacturing of the 3D woven parts.  Angle interlock preforms incorporating horizontal warp weaver yarns proved to be most effective at enhancing interlaminar properties while retaining good in-plane strengths.  For the oxide-oxide manufacturing, the biggest challenges were uniform infiltration of the oxide slurry into the tows and between the tows.  This was ultimately accomplished using sonication with limited compaction and two additional slurry infiltrations.  Reasonable levels of success were also achieved using a pseudo-VARTM approach with limited compaction; that processing approach may also be considered within this maturation effort. The work performed in AFRL Contract FA8650-17-C-5239 effort did not investigate weather particulate impact assessment, nor did it address RF performance testing of the 3D oxide-oxide subcomponent window after it had been subjected to a shock/vibration environment.  Both of these evaluations will be conducted as part of the MR&D proposed program.