Compression failure in dense non-woven fiber networks

Abstract

Investigating the compression properties of randomly ordered fiber networks experimentally is difficult which has resulted in ongoing disputes as to the mechanisms controlling the compression strength in such materials. In this work, we investigated compression properties of randomly oriented fiber networks with a special emphasis on cellulose products such as paperboard. We numerically reconstructed the conditions of the short span compression test widely used to quantify the compression strength of paperboard. We found that the phenomenological failure mode of such networks is elasto-plastic buckling. The x-shaped failure mode observed in physical experiments appears when test specimen restraints are included in the model. The most significant improvements to sheet strength can be obtained by improving the elastic properties while the strain to failure is increased most by an improvement of the plastic yield and hardening properties of individual fibers. Bond breaks were confirmed to have a smaller influence on the overall response. Fiber level microscopic buckling was investigated in depth, providing quantitative estimates of the fraction of mass likely to buckle at the microscopic level. The analysis indicated that only a low to moderate number of load carrying fibers can be expected to buckle. The inherent strength reserve in non-ordered fiber networks was investigated by introducing hinge mechanisms throughout the network, and the effect was shown to be small for a small to moderate number of hinges.

The Effect of Ply Properties in Paperboard Converting Operations: A Way To Increase Formability

“…The absolute values of the strain levels in the bottom plies are high, about 10% in the CD and 3% in MD for Board A, and 8 % in CD and 3% in MD for Board B. Even though locally, much higher strains can exist than what is observed in a standard tensile test (Brandberg and Kulachenko 2020;Hagman and Nygårds 2012), these values are high. A possible contribution to that is not including the delamination in the model which can potentially decrease the strain in the critical area.…”

Experimental and finite element simulated box compression tests on paperboard packages at different moisture levels

“…Noteworthy from Figure 14 is the elements with compressive stresses. In the material model, strengths in tension and compression were assumed equal owing to the complexity of measuring the in‐plane compression strength 20–22 . In order to evaluate the impact of this assumption on the BCT model, the result from Figure 13 were compared with data from short‐span compression tests (SCTs) for MD (20 MPa) and CD (14 MPa).…”

“…The thickness of the board was assumed to remain constant. Owing to the documented complexity of measuring the in‐plane compression strength, 20–22 the strength values in tension and compression were assumed to be equal at 50% RH. However, the relation to moisture ratio was different for the different properties according to Table 1.…”

Phenomenological analysis of constrained in-plane compression of paperboard using micro-computed tomography Imaging

“…Failure of multi-ply sheets in the SCT is initiated by shearing of the interfaces and delamination Hagman et al 2013. This is, however, pre-determined by the clamps that compress the sample and induce out-of-plane shear damage before the start of the in-plane compression Brandberg and Kulachenko 2019. The different modes of deformation and the pre-determination of the deformation by the measurement device itself make it difficult to distinguish between the influence of fibers, fiber-fiber joints and the behavior of the network structure Fellers and Donner 2002.…”