  This study addresses the issue of whether or not a normal distribution
appropriately represents permeability variations. To do so, (i) the
distribution of local fibre volume fraction for each tow is experimentaly
determined by estimation of each pair of local areal density and thickness,
(ii) the Kozeny-Carmen equation together with the change of variable technique
are used to compute the PDF of permeability, (iii) using the local values of
fibre volume fraction, the distribution of local average permeability is
computed and subsequently the goodness of fit of the computed PDF is compared
with the distribution of the permeability at microscale level. Finally
variability of local permeability at the microscale level is determined. The
first set of results reveals that (1) the relationship between the local areal
density and local thickness in a woven carbon-epoxy composite is modelled by a
bivariate normal distribution, (2) while fibre volume fraction follows a normal
distribution, permeability follows a gamma distribution, (3) this work also
shows that there is significant agreement between the analytical approach and
the simulation results. The second set of results shows that the coefficient of
variation of permeability is one order of magnitude larger than that of fibre
volume fraction. Future work will consider other variables, such as type of
fabrics, the degree of fibre preform compaction to determine whether or not the
bivariate normal model is applicable for a broad range of fabrics.

Soft Condensed Matter;Materials Science;Fluid Dynamics