Self-healing FRCs: A New Approach to Damage Tolerant Cryotanks

Composite cryotanks, or Composite Overwrapped Pressure Vessels (COPVs), offer advantages over currently used aluminum-lithium cryotanks, particularly with respect to weight savings. Future NASA missions are expected to use COPVs in spaceflight propellant tanks to store fuels, oxidizers, and other liquids for launch and space exploration vehicles. However, reliability and reusability of the COPVs are of concern, especially in cryogenic temperature applications; this limits adoption of COPVs in future reusable vehicle designs. The major problem with composites is the inherent brittleness of the epoxy matrix, which is prone to microcrack formation, either from exposure to cryogenic conditions or from impact from different sources. If not prevented, the microcracks can grow into larger cracks, leading to catastrophic failure and loss of function of the composite. Accordingly, materials innovations are needed to mitigate, as well as self-heal, microcrack damage in composite cryotanks. In Phase I we propose to demonstrate microcrack prevention and mitigation in composite test panels through the use of a novel nanocomposite matrix containing engineered nanoscale materials which will also enable self-healing of microcracks. Phase II will build upon the Phase I program in order to optimize the material design and to characterize the long-term durability of the scaled-up composite test panels.

Future NASA missions will rely on the use of composite structures as main structural members of space vehicles and composite overwrapped pressure vessels (COPVs) for spaceflight propellant tanks to store fuels, oxidizers, and other liquids for launch and space exploration vehicles. These COPVs must be able to operate at the cryogenic conditions imposed by typical propellants, liquid oxygen (90?K) and liquid methane (110?K). NASA applications for the research proposed herein include: earth-based and space-based cryogenic storage vessels (e.g. cryogenic fuel storage for first stage and upper stage launch vehicles including Multi-Purpose Crew Vehicles); long system life cryogenic storage that is both reliable and safe and would perform well beyond the current vessel design life (e.g. orbiting space fuel depots); and space-based habitat structures that are manufactured using fiber-reinforced composite materials.

The aerospace and the commercial communities have shown significant interest in using COPVs for cryogenic and non-cryogenic applications. Non-NASA commercial applications for the research proposed include the following: Liquid hydrogen fuel cells in terms of increased safety and reliability; vehicular cryo-compressed gas storage of hydrogen and natural gas which dramatically increases the fuel storage density thus increasing the amount of fuel that can be stored in a vehicle; environmentally-friendly and safer earth-based cryogenic fluid storage where the composite structures will not need painting, stripping, and repainting in order to prevent corrosion as does current metal/steel construction and are also easier to transport due to their light-weight nature; and interest in the marine transport of propane via tanker ships where very large (5300 m3) COPVs will be needed.

This is early/mid-stage (TRL 3) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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