Manufacturing Process Maturation for Propulsion Technology: Structural Insulators

MDA missile systems employ solid rocket motors and divert and attitude control systems (DACS) to propel and guide kinetic energy weapons. These systems create hot, high pressure gases that impose high heat loads on surrounding metal structures and electronic controls. Exist-ing designs use ablative insulators (e.g. EPDM) and monolithic ceramics (e.g. NZP) to limit the temperatures in surrounding components. While these materials offer attractive low thermal dif-fusivities, they also exhibit poor high temperature strengths and toughness that have resulted in unanticipated failures during ground testing. Clearly these insulators must be improved if MDA systems are to improve their reliability. Several possibilities exist for improved high temperature structural insulators including ceramic matrix composites (CMCs) and high strength ceramic foams. CMC solutions include various combinations of rayon-based carbon, Nicalon, and Nextel fibers with matrix materials that include CVI SiC, PIP SiC, and sol-gel oxides. The CMCs can employ needled or conti-nuous fiber preforms. High strength ceramic insulators include ceramic micro-balloons imbedded in a ceramic matrix. In addition to improved materials it may be possible to modify existing designs to limit the operational stresses. Design modifications may include layered materials tailored to the thermal environment, segmented insulators to limit thermal stresses, and the ex-ploitation of contact resistance and tortuous heat paths. The Materials Research & Design (MR&D) Phase I design and analysis results indicated that a C/SiC composite that uses a low density SiC matrix can reduce the temperature at the pin-tle attachment from about 600°F to less than 300°F. Based on this MR&D procured needled Lyocell performs that are presently being processed as low density C/SiC composites. Addition-ally, MR&D supported Powdermet’s Phase I SBIR program that examined several of their ce-ramic-based Synfoams as potential structural insulators. MR&D’s analysis of TDACS insulator made with Powdermet materials showed thermal performance that was nearly equivalent to NZP coupled with comfortably positive structural margins. Based on these results, MR&D is propos-ing an integrated Phase II program that will continue the development of low density C/SiC and ceramic-based Synfoam insulators for TDACS components. The Phase II program will be un-dertaken by a working group that includes MR&D, American Structural Needling (ASNC), All-comp, and Powdermet. In the Phase II program, MR&D will perform the design and analysis tasks, coordinate the fabrication and characterization effort, down select the materials and de-signs, manage the program, and prepare the reports. Allcomp, ASNC, and Powdermet will fa-bricate insulators that include needled C/SiC composites and ceramic-based foams. Additionally the Phase II program will be closely coordinated with other TDACS material development pro-grams underway at Ultramet and Matech; and with complimentary material characterization ef-forts at Southern Research Institute.