Numerical evaluation of interfibre joint strength measurements in terms of three-dimensional resultant forces and moments

Abstract

The interfibre joint is one of the key elements in creating the strength of self-binding fibrous materials such as paper and board. In order to tailor the properties of such materials by chemical and/or mechanical treatments of the fibres, and to learn how such modifications influence the properties at the microscopic level, a greater understanding of how to evaluate the mechanical properties of interfibre joints is desirable. The methods reported in the literature for determining of the interfibre joint strength do not in general distinguish between the contributions of normal and shear stresses in the bonded region. This paper presents a numerical analysis procedure, based on the finite element method, for evaluating interfibre joint strength measurements in terms of the normal, shear, and moment loading components during testing. The method is applied to investigate the strength of Kraft pulp interfibre joints under two principally different modes of loading. The results show that for a typical interfibre joint test of an isolated fibre-fibre cross with long free fibre segments, modes of loading other than pure shear cannot, in general, be neglected, and are strongly dependent on the structural geometry of the fibre-fibre crosses. In addition, the resultant forces and moments were scaled in terms of the interface area and the twisting and bending resistance of the interface approximated as an ellipse to account for differences in interface area between the measurements. These scaled resultants were used to quantify how the mode of loading influences the relation between the amount of normal stress and the amount of shear stress that develop in the interfibre joint.

Effect of Silica Bodies on the Mechanical Behaviour of Oil Palm Empty Fruit Bunch Fibres

“…The three modes of failure in the CZM are usually referred to as opening Mode I (normal tension mode), Mode II (shear mode), or Mode III (out of plane shear mode) (Camanho and Davila 2002;Magnusson and Ostlund 2013). In this work, only Mode I (normal tension mode) was considered to simplify the model, since only tensile tests of OPEFB were available.…”

A Proposed Failure Mechanism for Pulp Fiber-Fiber Joints

“…The applied loading caused resultant reaction forces and moments in the bonding region compared with the similar treatment in Magnusson and Östlund (2013). These were described in a local coordinate system, the origin of which was defined at the centroid of the interface region.…”

“…The fiber's cell wall is made of up to 80-85% of the S2 layer (Page 1969a), and it is commonly assumed in literature that this layer has the highest influence on the fiber's mechanical behavior (e.g. Magnusson and Östlund 2013). Therefore, the pulp fiber will be modeled by the S2 layer only.…”

“…The modulus of elasticity E1=30GPa was chosen as an average of the data given by Magnusson and Östlund (2013). It has to be mentioned that the material properties of the S2 layer are subject to wide variations (Page et al 1977;Groom et al 1995;Neagu et al 2004).…”

“…Still, no conclusive failure mechanism has been worked out for this material, although several different failure mechanisms have been discussed (Wang et al 1997;Gasser 2011). Recently, a comprehensive finite element method (FEM) framework to model the behavior of fiber-fiber joints during mechanical testing was presented by Magnusson et al (2013). The work focused on resultant forces and moments in the bonding regions and did not consider local stress concentrations.…”