Compression Strength Mechanisms of Low-Density Fibrous Materials

Abstract

In this work we challenge some earlier theoretical ideas on the strength of lightweight fiber materials by analyzing an extensive set of foam-formed fiber networks. The experimental samples included various different material densities and different types of natural and regenerated cellulose fibers. Characterization of the samples was performed by macroscopic mechanical testing, supported by simultaneous high-speed imaging of local deformations inside a fiber network. The imaging showed extremely heterogeneous deformation behavior inside a sample, with both rapidly proceeding deformation fronts and comparatively still regions. Moreover, image correlation analysis revealed frequent local fiber dislocations throughout the compression cycle, not only for low or moderate compressive strains. A new buckling theory including a statistical distribution of free-span lengths is proposed and tested against the experimental data. The theory predicts universal ratios between stresses at different compression levels for low-density random fiber networks. The mean ratio of stresses at 50% and 10% compression levels measured over 57 different trial points, 5.42 ± 0.43, agrees very well with the theoretical value of 5.374. Moreover, the model predicts well the effect of material density, and can be used in developing the properties of lightweight materials in novel applications.

Analysis of the foam-forming of non-woven lightweight fibrous materials using X-ray tomography

“…12 ). According to Ketoja et al [ 16 ], when a random fibre network is compressed, the buckling continues throughout the compression cycle, up to the densification regime. This results from an exponential distribution of fibre-segment lengths, valid also for flocculated networks.…”

“…Gibson and Ashby considered the compression of cellular structures and found that the individual columns buckle when the applied force, , reaches a critical level [ 17 ] given by Euler’s formula Here E is the elastic modulus, I is the cross-sectional moment of inertia, a is the free-span length of the column and is a pre-factor which depends on the boundary conditions at the column ends. Effectively, this is the same formula as for fibre buckling [ 16 ], but the distribution of column lengths for the more correlated cellular structure probably differs from the exponential distribution of the fibre segments. Kim et.al.…”

Foam forming of fiber products: a review

“…The vertical fiber orientation is caused by the direction of foam flow in filling the mold. (b) A small part of a thick plate-like sample [126] with natural wood fibers (density 60 kg/m 3 ). (c) Sheet with CTMP fibers (density 111 kg/m 3 ).…”

A Review of Recent Trends and Challenges in Computational Modeling of Paper and Paperboard at Different Scales

“…For example, in [72], a theory has been developed, that describes the statistical properties of rod packings, while taking into account that the deposited rods cannot overlap and thus induce steric hindrances. Further, a new buckling theory including a statistical distribution of free-span lengths has been proposed in [130] and tested against experimental data.…”