Furthermore, because of the porous nature of the fibrous materials, the conventional mechanical definitions such as stress and strain may not be entirely appropriate to be applied to the materials. For instance, when a pressure is exerted onto a textile surface, the effective surface area that provides resistance to the load is not the total area on which the pressure is on, because the area consists of fiber and voids, and the latter should be eliminated in normal situations. Also, when this material is deformed, the total deformation again includes those of both fiber and voids. In other words, the genuine stress and strain for fibrous structures are the ones that preclude the effect of the voids, or at least deal with the voids and fiber separately and differently. This is not a simple matter of changing the definitions, and it might have profound implications on our understanding of the behavior of fibrous systems.
Fiber Packing Fibers are not isotropic materials, having distincproperties between the axial and transverse directions. They are best performed when dealing with axial tension, but behave not as well in all other loading situations such as compression and shearing. Also, various loads have to be transfered through the fiber–fiber contact points. Therefore, the format in which the fibers are arranged in a structure becomes a critical issue; it will determine virtually all the properties of the system.