Out-of-Furnace Brazing Technology for Assembly of Large Carbon-Carbon Space Structures

Foster-Miller has previously developed an attachment scheme for 2-D carbon-carbon (C/C) composites which, compared to a conventinal braze or mechanical joint, would enhance the thermal and mechanical efficiency of space structures. Developed for NASP applications, the design is comprised of a metal brazed joint that is integrally reinforced by transverse (Z-direction) pins. Preliminary results reveal a threefold increase in joing strength and up to 50% increase in through-thickness thermal conductivity. Unfortunately, as in the case for most C/C brazing research being conducted in the US, Foster-Miller's process has been developed for a vacuum furnace. Real military space structures, such as the Space Based Radar or Survivable Power Subsystem, involve complex truss structures that may exceed 350 ft in length. The space structure manufacturing community would certainly benefit from the development of an out-of-furnace on-line joining for sequential assembly of large structures. Foster-Miller proposes to demonstrate that RF induction heating is the key to implementing the Z-direction reinforced brazed joint on the shop floor. Induction heating is rapid, highly localized and involves inexpensive, easy-to-use equipment. By using high strength electrically conductive fibers as reinforcement, the Z-fibers will not only provide performance advantages, but may overcome some of the heating uniformity problems associated with RF heating of anisotropic composites. Based on materials and applications inputs from Rockwell-Space Systems and Lockheed Missile and Space Company and induction equipment expertise from Ameritherm Inc., the Phase I program will focus on understanding the interaction of the C/C adherends, Z-direction fibers, and brzae with the induction coil and machine parameters. Brazed joints will be subjected to mechanical and thermal conductivity tests. Phase II would involve process optimization and development of a prototype fabrication line.