Prediction of permeability of cryogenic composites
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abstract
Damage in cryogenic composite fuel tanks induced during manufacturing and advanced by thermomechanical cycling can accelerate leakage of the propellant. Whether the leakage exceeds tolerable levels depends on many factors, including pressure gradients, microcrack density, other damage such as delamination, connectivity of the cracks, residual stresses from manufacture, service-induced stresses from thermal and mechanical loads, and composite lay-up. Although it is critical to experimentally characterize permeability during various thermal and mechanical load histories, optimal design depends on having analytical models that can predict the effect of various parameters on performance. The broad goal is to develop such models. Efforts will focus on three areas. The first is determining the effect of laminate design on opening of transverse matrix cracks and delaminations. The second area is experimental characterization and development of predictive models for initiation and evolution of damage during thermomechanical cycling. The third area is three-dimensional description of the damage state for laminates with known permeability. This last area has required the evaluation and development of destructive and non-destructive techniques for detecting the damage. The studies in these areas will be integrated to build analytical models that predict the effect of various parameters on permeability.
