Theory is presented for the fractional contact area of fibres in random networks. The theory considers first the statistical geometry of two-dimensional networks of mean grammage determined by the sheet porosity. To allow application to real sheets, the theory is developed to account for the additional contacts arising from the interaction of fibres between the layers of mul-tiplanar structures. The expressions derived allow the fractional contact area to be calculated with a knowledge of the sheet porosity only for thick sheets. For thin sheets of a given gram-mage, the fractional contact area depends on sheet porosity and fibre grammage. The model is compared with data from the literature and the agreement is excellent.
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