where p is the upstream pressure. The S.I. units of permeance are [mol/(m2.s-Pa)]

 According to the standard test method, the permeability P is defined by the product

of permeance P and the specimen thickness t and "the permeability is meaningful only

for homogeneous materials [18]." In this study, although the laminated composites are

considered as orthotropic materials, its permeability P is calculated by following the

corresponding definition for isotropic materials [22].

 Calibration

 The position of capillary indicator is very sensitively to even small variations of

testing conditions such as ambient pressure and temperatures caused by closing doors or

air-conditioning system in the laboratory. For example, during one test, the variation of

the ambient pressure was approximately 0.3% for a 13 hour period (Figure 4-5). For the

permeability calculation, the ambient pressure is assumed to be constant. However, the

variation is large enough to cause error in measuring the rate of rise of the capillary

indicator. The moving distance is needed to be calibrated to compensate for error due to

the variation of ambient pressure.


Time (hour)