Compression strength mechanisms of low-density fibrous materials

Research output: Contribution to journalArticleResearchpeer-review

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.

LanguageEnglish
Article number384
JournalMaterials
Volume12
Issue number3
DOIs
Publication statusPublished - 26 Jan 2019
MoE publication typeNot Eligible

Fingerprint

Compaction
Fibers
Imaging techniques
Mechanical testing
Cellulose
Buckling
Foams

Keywords

  • Compression test
  • Fiber buckling
  • Foam forming
  • Image analysis
  • Nanocellulose
  • Regenerated fibers
  • Strain
  • Stress
  • Wood fibers

Cite this

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title = "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.",
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Compression strength mechanisms of low-density fibrous materials. / Ketoja, Jukka A. (Corresponding Author); Paunonen, Sara; Jetsu, Petri; Pääkkönen, Elina.

In: Materials, Vol. 12, No. 3, 384, 26.01.2019.

Research output: Contribution to journalArticleResearchpeer-review

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