CHAPTER 4
 PERMEABILITY TESTING OF COMPOSITE MATERIALS FOR A LIQUID
 HYDROGEN STORAGE SYSTEM

 The permeability is defined by the amount of gas that passes through a given

material of unit area and unit thickness under a unit pressure gradient in unit time. The SI

unit of the permeability is mol/sec/m/Pa. Experiments were performed to investigate the

effect of cryogenic cycling on permeability of laminated composites and to provide

useful comparison of permeabilities of various composite material systems.

 Standard Test Method for Determining Gas Permeability

 The standard test method for determining gas permeability is documented in

ASTM D1434-82 (Re-approved in 1997) "Standard Test Method for Determining Gas

Permeability Characteristic of Plastic Film and Sheeting [18]." The permeability can be

measured by two methods, manometric determination method and volumetric

determination methods. The permeability experiment using the monometric

determination method is shown in Figure 4-1. The lower pressure chamber is initially

vacuumed and the transmission of the gas through the test specimen is indicated by an

increase in pressure.

 The permeability is measured using volumetric determination as shown in Figure

4-2. The lower pressure chamber is exposed to atmospheric pressure and the

transmission of the gas through the test specimen is indicated by a change in volume. The

gas volume-flow rate is measured by recording the rise of liquid indicator in a capillary

tube per unit time. The gas transmission rate (GTR) is calculated using the ideal gas law.