A New Theory of the Tensile Behaviour of Paper

Abstract

Following considerations of previous work, the authors’ investigations indicate that the first interfibre bonds to rupture under tensile strain do so by a peeling action with shear deformation of the paper in locally weakened regions. Progressive breakdown occurs along specific narrow bands within which strain is largely concentrated. The direction of these `strain lines’ has been predicted. Only for weak papers does final fracture occur along a single strain line, when considerable shear also results. For strong papers, only short lengths of strain lines form in a widely scattered cross-cross formation. In all cases, ultimate failure depends on the relationship between the tensile strength of fibres and the shear strength of bonds.

The mechanism of strain line formation results in paper thickness increases. Permanent deformation, frozen-in stresses and the effects of drying stresses are largely associated with strain line formation and frictional forces between fibre ‘mats’. Changes in moisture content modify the frictional effects and stress distribution and some aspects of dimensional stability can be explained. The finer details of fibre orientation distribution in machine-made papers can be attributed to shear in strain lines.