Flexible CMC Structures for Propulsion Efficiency

Physical Sciences Inc (PSI) will fabricate high temperature spring preloaders for turbomachinery seals from our flexible Carbon fiber-reinforced Silicon Carbide (C/SiC) Ceramic Matrix Composite (CMC) system. The team will fabricate springs of different lengths, thicknesses, and stiffnesses with an accordion fold geometry and variable lengths. PSI will evaluate the springs’ mechanical performance at both ambient and elevated temperatures to model their mechanical response based on the different fabrication variables to meet NASA’s performance requirements for spring preloaders in turbomachinery sealing systems. Seals have historically been a major area of concern with propulsion systems, both turbines and hypersonics, to prevent leaks and uncontrolled changes in pressure of the flight system. Existing sealing systems for these applications have an upper use temperature of ~2000 °F. Combustors can reach temperatures upwards of 3000 °F in J-class turbine engines, well beyond the upper use temperature of metallic alloys. The High Mach Gas Turbine (HMGT) and Turbine Based Combined Cycle (TBCC) propulsion systems, currently being explored by NASA and AFRL for use in DARPA’s NextRS systems, will also require innovative higher temperature materials systems than metallic alloys can provide to reach the desired speeds. PSI’s flexible C/SiC CMCs are the most flexible CMCs available with active bend radii as small as 3.5” and tailorable stiffness. The flexible CMCs can be fabricated in complex geometries with bend radii as small as 1/16” for complex structures such as accordion fold spring preloaders. PSI’s Flexible CMC material has resilience in extended bend fatigue testing to a 3.5” radius in ambient environments for thousands of cycles. There is no measurable loss in the flexure of the material after the initial few cycles. PSI’s flexible CMCs have been tested under continuous actuation in highly aggressive oxidating environments at temperatures up to 5000 °F

NASA GRC has been investigating high temperature spring preloaders to provide spring back/resiliency for seals and structures anticipated in future vehicle systems. The purpose of preloaders is to always ensure the seals/structures are engaged with their mating surfaces while not exerting excessive loads that may damage the seals or adjacent walls. It is important that the preloaders do not take on excessive compression set or lose preload at operating temperature. Maintaining preload over the system’s lifetime is essential. New materials systems such as flexible ceramic matrix composites (CMCs) are required for the increased operating temperatures in these propulsion systems. Morphing and flexible structures are of great interest in the fields of propulsion and hypersonics to improve efficiency in these systems. Future propulsion systems such as the High Mach Gas Turbine (HMGT) and Turbine Based Combined Cycle (TBCC) propulsion systems, currently being explored by NASA and AFRL for use in DARPA’s NextRS systems, will require innovative higher temperature materials systems than metallic alloys can provide in order to operate at higher efficiencies and temperatures. Springs built using PSI’s flexible ceramic matrix composite technology are for use in extreme ultrahigh (> 1000 C) temperature and chemically corrosive environments. Springs for ultrahigh temperature include those used to support spring seal applications as well as vibration isolation in scramjet and rocket motor propulsion systems. PSI’s flexible CMC technology can be in direct contract with hot structures to provide a simplified solution compared to thermally insulated metallic springs. Simplified design is particularly important to reduce weight in scramjet propulsion and rocket systems to enable maximum vehicle performance. High temperature applications also exist in DoD artillery, rocket/missile recoil and naval vibration isolation systems where the high stiffness and chemically inert flexible CMC material can reduce maintenance costs. Commercial applications for the CMC springs include J-class turbines for power generations as well as scramjet propulsion. Additionally, the flexible CMC materials system has garnered interest for TPS materials, morphing control structures such as leading edges and flaps, and even for morphing hypersonic ducts. Morphing and flexible structures are of great interest in both propulsions and hypersonics to improve efficiency in these systems. PSI has already succeeded in providing the most flexible CMC systems available in the market through work done on MDA SBIR Phase 1 and 2 programs and becoming the top supplier of flexible CMCs for the DoD’s multi-department SMASH program.

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