Analytical predictions and experimental measurements of hydrogen permeability in a microcrack damaged composite
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Future launch vehicles will require significant reductions in empty weight to reduce the cost of space access. Cryogenic fuel tanks typically constitute a large fraction of a launch vehicle's empty weight. Polymer matrix composite materials have high strength and low density, which makes them attractive candidates for use as cryo-tank materials. Under the conditions prevalent inside the fuel tank, these composites develop micro cracks that become leak paths for cryogen. In this study, experiments were conducted to estimate the leak rate of gaseous hydrogen through a micro crack-damaged graphite-epoxy composite specimen. The variation of hydrogen leak rates with applied mechanical load was recorded at 23C and at 190C. Analytical predictions of hydrogen leak rate were performed, using a simple model, which was based on the effective conductance of idealized crack junctions. Crack density and crack opening values obtained through X-rays and edge optical inspection techniques respectively were utilized in the model predictions. Experimental measurements and analytical predictions of hydrogen leak rate were eventually compared. Copyright 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
