Design and fabrication issues of high temperature PMCS for aerospace propulsion applications

A Second generation PMR (in situ polymerization of monomer reactants) polyimide resin, PMR-II-50, has been considered for high temperature and high stiffness space propulsion composites applications, such as a facesheet of various sandwich structures with high stiffness carbon fibers. Various fiber reinforcement architectures including 4 & 8 harness satin (HS) fabrics, uni-tape, stitched fabrics, tri-axial braided fabric and their hybrid structures have been investigated for optimum stiffness-thickness-weight-hygrothermal performance design criteria. This paper discusses the overall program plan, primary design and fabrication efforts, and initial composite property and performance data of certain architectures. As part of composite processing optimization, two commercial prepregging methods, solution vs. hot-melt processes, were investigated for graphite fiber/PMR-II-50 composites. A systematic chemical, physical, thermal and mechanical characterization of these composites indicated that poor resin-fiber interfacial wetting at the molecular level, especially in hot-melt process, resulted in poor composite quality. Effects of the wetting on composite mechanical properties and high temperature durability will be discussed.