Orientation of the Permeability Principal Axes in Bi-Directional Textile Fabrics

For various commercial woven glass fiber fabrics, the orientation of the permeability principal axes has been experimentally determined as function of the fiber angle, carrying out two-dimensional flow experiments with radial liquid injection. The investigated fabrics have in general been found to significantly show anisotropic properties even for the unsheared material. The orientation of the permeability principal axes of sheared fabrics is related to the degree of anisotropy, characterized by the ratio of the permeability principal values for the unsheared fabrics. The orientation of the permeability principal axes as a function of the fiber angle is described by an empirical formula, with the ratio of the permeability principal values of the unsheared fabric as parameter. Comparison of experimental and theoretical results in general indicates correspondence. Exceptions can be explained by uncertainties in the experimentally determined permeability principal values of the unsheared fabric.