properties near a crack tip, but not global properties of the laminate system. At cryogenic

temperature the fracture load decreases 15% with increase of mid-ply thickness. The

fracture load significantly decreases due to the material degradation at cryogenic

temperature. The thermal stresses cause microcrack propagation in the vicinity of the

crack. Although the fracture loads decreases by 15% from Specimen 1 to Specimen 3,

fracture toughness increases by only 5%. For both cases at room and cryogenic

temperature, fracture toughness was estimated approximately as 58 MPa-m0.29. The result

indicates fracture toughness is a characteristic property not governed by temperature

changes. The analysis is useful to predict the transverse crack propagation of composite

laminates under cryogenic conditions.

 Permeability Testing for Laminated Composites for a Liquid Hydrogen Storage
 System

 The experimental analysis was performed to measure the gas permeability various

composite material systems for the liquid hydrogen composite tank and the effect of

cryogenic cycling of composite laminates on the permeability was investigated. The

permeability test facility was constructed following the standard test method documented

in ASTM D1434-82 (Re-approved 1997). The permeability test was conducted at room

temperature. The sensitivity of permeability measurement can be improved by increasing

the gas transmission area of a specimen. Since hydrogen is flammable and explosive

when it mixed with air, the helium gas is substitute for hydrogen. The calibration is

performed to compensate the ambient pressure differences during the test. The correction

factor is found as 0.21 mm/Pa. The actual moving distance of the liquid indicator is

calibrated by the correction factor.