Mechanical properties and durability of a composite material at cryogenic temperatures.

摘要

Several issues relevant to the use of a high-performance graphite-epoxy material in hydrogen storage tank applications have been examined. The tensile properties of IM7/977-2 were evaluated as a function of test temperature and thermal-mechanical load history. The temperature dependent coefficient of thermal expansion (CTE) of unidirectional specimens of the same material was measured between -200°C and 0°C. The effects of test temperature, mechanical loading, and damage state on the leak rate of hydrogen gas through IM7/977-2 laminates were evaluated using a novel test system. Finally, the mechanical properties of several commercially available polymer films, which might prove useful as leak-resistant liners for composite cryogenic fuel tanks, were evaluated at elevated and cryogenic temperatures.; The mechanical property study of IM7/977-2 showed that the effects of exposure to a cryogenic fuel tank environment varied significantly with test temperature and laminate schedule. Matrix dominated properties were found to be the most strongly affected by cryogenic test temperature exposure. Fiber-dominated properties were found to be comparatively insensitive to cryogenic test temperature.; The CTE measurements showed that the cryogenic conditioning did not have marked effects on the thermal expansion behavior of IM7/977-2. Transverse CTE was Coefficient of thermal expansion was calculated strongly temperature-dependent.; The leak rate study revealed that both mechanical loading and decreasing test temperatures increase the leak rate of gaseous hydrogen through the microcrack network within a damaged composite laminate. The effect of temperature on permeability was shown to be stronger than that of tensile loading. At low damage levels, proportionality was demonstrated between the number of crack junctions present within the laminate and the hydrogen gas leak rate. At higher damage levels this proportionality was not as clear, perhaps due to the greater role played by delaminations in gas leakage.; In the polymer film study, large differences were observed in tensile modulus and tensile strength at 23°C and 65°C. At -150°C, the differences were far smaller and the behavior of all of the films was uniformly brittle in nature.